15mm Extrusion Basics

The 15mm profile of the Extrusion has slots on on all four sides that accept standard M3 hardware. Rather than using a T-nut, which is more expensive, slide a M3 hex head screw along the slot and adjust brackets and other build materials as needed. As illustrated in the image above, the ends of the Extrusion also have a 5mm hole pitch that can be M3 tappped.

Product Specs

• Material: 6063-T5 aluminum, clear anodized

• Height: 15mm

• Width: 15mm

• Length: Various options

  • Extrusion can be cut to shorter lengths as needed

When to Use?

The flexibility of the 15mm Extrusion makes it a great option for arms, lifts, and other robot manipulators and mechanisms. This is one of the most compact structure pieces and allows for compact designs. Depending on the design and use case, you may wish to add additional supports to avoid twisting under high loads, also known as torsion.

How to Use?

The point of the extrusion system is to offer more flexibility in design than would come in a fixed pitch system. The slots in the extrusion allow brackets and other components to be slid along the 15mm Extrusion to an infinite number of positions

The illustration above shows how easy it is to swap, adjust and iterate designs. This works for gear mating, chain tensioning, and bracket adjustments as you are iterating.

The REV DUO line of parts work together for a dual purpose: to create competition-grade robots geared towards participating in the FIRST Tech Challenge or to be used in the classroom for STEM Education.

REV Robotics is committed to designing high-quality products that make robotics accessible for any skill level. Since 2014, we have continued to iterate and adapt to the educational robotics community's needs by developing new products and refining our current product selection.

What is REV DUO?

REV DUO is a new brand that now includes all of our existing products and is the new home for many new products coming soon. Look for the REV DUO flag and logo on our website, and shop with confidence knowing all products are compatible and designed to work together seamlessly.

If there is a question that is not answered by this documentation, send our support team an email; support@revrobotics.com. We are happy to help point you in the right direction.

15mm x 45mm C Channel Basics

The C Channel uses a combination of a fixed pitch system and an extrusion system to make it easy to iterate robot designs. The Channel system overall is compatible with standard M3 hardware , and is designed to work seamlessly with existing 15mm Extrusion and 15mm x 30mm Extrusion. The extrusion system has slots that allows flexible bracket positions for easy Channel to Extrusion connection.

The 45mm wide side of the channel features the Extended Motion Pattern which uses M3 hardware for attaching brackets, extrusion, and channel together. Locations for mounting bearings, shafts, motors, and servos are available every 16mm. Slots on the 15mm sections of the channel accept standard M3 hex-head bolts or nuts, rather than expensive t-nuts.

Product Specifications

• Material: 6063 aluminum

• Height: 45mm

• Width: 15mm

• Length: Various lengths

  • Channel can be cut to length if necessary, but care should be taken to ensure cuts preserve the necessary portions of the motion pattern for the overall robot design

When to Use?

The C Channels are great for creating a sturdy robot drivetrain or for use in areas where additional torsional strength is needed.

How to Use?

The combination of the pitch and extrusion systems featured on the C channel allows flexibility in design and iterations. The extended motion pattern featured on the 15mm x 45mm C Channel allows for easy placement of moving parts, for addition constraint and support of motion. The extended motion pattern can also allow easier replacement or swapping of parts on interior portions of the robot than the 15mm Extrusion, depending on robot design.

45mm x 45mm U Channel Basics

REV 45mm U Channel has a 45mm x 45mm square profile, and is designed to work seamlessly with existing REV 15mm Extrusion. It can be used in locations where additional torsional strength is required. On the sides of the channel is the Extended Motion Pattern which uses M3 hardware for attaching brackets, extrusion, and channel together. Locations for mounting bearings, shafts, motors, and servos are available every 16mm. Slots on the top of the channel accept standard M3 hex-head bolts or nuts, rather than expensive t-nuts. The top of the channel also has the Motion Pattern with M3 holes on a 16mm diameter circle pattern repeating down the channel.

Product Specs

• Material: 6063-T6 aluminum

• Height: 45mm

• Width: 45mm

• Length: Various Lengths

  • Channel can be cut to length if necessary, but care should be taken to ensure cuts preserve the necessary portions of the motion pattern for the overall robot design

When to use?

Similar to the C Channel, the U Channel is great for applications that need additional torsional strength. The advantage of the U channel over the C Channel is that the shape, combined with the Extended Motion Pattern, allows for two points of shaft support. This reduces the need for additional support brackets in different applications, such as drivetrains and arms.

Use the U channel in places where you need a high level of torsional strength.

How to Use?

The combination of the pitch and extrusion systems featured on the U channel allows flexibility in design and iterations. The extended motion pattern featured allows for easy placement of moving parts, for additional constraint and support of motion.

The major use applications are that Core Hex Motors (REV-41-1300) and Servos (REV-41-1097) can fit completely within the U Channel and be mounted flush against the channel without the need for brackets. Simply attach build components with M3 hardware.

Structure Basics

The REV DUO Build System has two major structural components, Extrusion and Channel. REV Extrusion is a rectangular structure rail with slots for M3 hardware on all four sides. The slots in the Extrusion allow for brackets and other items to be adjusted to any position along the rail. REV Channel is a larger structural member featuring a pattern for actuators, brackets, and other elements to be placed at set intervals. Channels have a combination of a fixed pitch based system (known as the Extended Motion Pattern) and an extrusion system for design flexibility.

All REV DUO structural components are M3 hardware compatible.

Extrusion System Versus Pitch System

The 15mm extrusion system allows for a more flexible, iterative process than fixed pitch systems. Fixed pitch based systems have a set pattern of holes to use for mounting; everything that is mounted is spaced on a multiple or a set fraction of the standard pitch. In contrast, the 15mm extrusion system allows for flexible mounting positions along the slots. Simply slide any brackets that need to be mounted into the appropriate slot and adjust to the desired position.

We believe that the easier it is to adjust your design, the easier it is to iterate and improve that design.

See any of the pages linked below to learn more about how to use the extrusion system.

Extended Motion Pattern

While the 15mm Extrusion does not have a fixed pitch other components in the REV DUO Build System do. Structural brackets have M3 holes on an 8mm pitch. While Motion Brackets have the Motion Pattern, a circular M3 hole pattern on a 16mm diameter is used to mount to REV Robotics shaft accessories.

C Channel, U Channel, and Flat Plate feature the Extended Motion Pattern, a modified circular M3 hole Motion Pattern on a 32mm diameter. This repeats down the length of channel to mount bearings, shafts, brackets, and more.

The Extended Motion Pattern starts with M3 holes on an 8mm pitch down the center of the Channel. Each of the holes on the center line pitch forms the "base" for an equilateral triangle with 8mm sides that extends outward towards the edges of the Channel. Every 16mm a center hole is opened up to become a 9mm bearing seat to attach shafts and bearings.

Corrugated Plastic Sheets Basics

Corrugated plastic sheets are intended for use as a consumable flat stock to make wedges, panels, and more. This plastic is sturdy, lightweight, and easy to cut with hand tools.

Corrugated plastic sheets are a great substitute for other types of flat stock. Compared to the alternatives, this plastic is cheaper and can easily be cut to size using a box cutter when larger scale tools are unavailable. These plastic sheets come in the FTC Starter Kit V3 (REV-45-1883) and FIRST Global Kits.

When to use?

In general, corrugated plastic can be used as a substitution for other flat stock elements. There are many applications for the corrugated plastic sheets depending on need. Below are images from FIRST Global to give you some ideas of the different creative ways you can utilize the sheets from your kits

In this picture, the corrugated plastic is being used as protective panels. One wedged panel is being used to protect the Control Hub (REV-31-1595). Another set of panels is encasing the pulley intake system on the back of the robot.

Here the corrugated plastic has been cut into strips and combined with Extrusion and string to make a basket. Also seen in this picture, the plastic is attached to the Extrusions with a combination of M3 hardware and zipties.

One robot in this picture is using the plastic sheets as bumper panels. The other robot has a basket system, similar to the previous picture, but with a completely different design approach

This last team's robot is utilizing the corrugated plastic as a hopper for game object storage.

Some other general uses include:

• Team Number Plates

• Alliance Markers

How to use?

One of the benefits of corrugated plastic is how easy it is to manipulate. Once a design is plotted out, score the plastic with a straight edge and box cutter or cut it with a powered saw (band saw, jig saw, etc).

As exhibited in the example pictures, the plastic can be attached to the robot with zip ties or M3 hardware.

M3 Hardware Basics

The REV DUO build system uses M3 hardware to connect, or fasten, brackets and structure together on a robot. Different applications require different length screws. When attaching a bracket to extrusion, shorter screws are generally required. Use longer screws to connect Control System components and other thicker materials.

Tools

We include all the tools needed to use the parts in the FTC Starter Kit. Take a moment to identify the tools below:

• 5.5mm Nut Driver (REV-41-1119)

• 5.5mm Combination Wrench (REV-41-1374)

• Allen Wrench Pack (1.5mm (REV-41-1376), 2mm (REV-41-1377), and 2.5mm Allen Wrenches)

• #25 Chain Tool (REV-41-1442)

As robots become more complex, there are additional tools, hardware, and fasteners available on the REV website:

• 5.5mm Ratcheting Combination Wrench (REV-49-1711)

• 5mm Hex Broach (REV-41-1367) for making hex-shaped holes

• Metric Step Drill (REV-49-1455) for drilling holes of different sizes

• Zip Ties (REV-41-1161)

• Hook and Loop Fastener (REV-41-1373)

• Variety of replacement screws, and additional screw lengths

T-Slot Screws

Another type of hardware included in the kit is the T-Slot Screw (REV-41-1167). These screws have a T-shaped head allowing them to drop in the slots of the Extrusion or C Channel. This allows for modification of an existing design by adding in brackets and structure without needing access to the end of a slot.

Product Specs

• Material: Corrosion resistant zinc plated steel

• Length: 8mm

How to Use?

Simply drop the t-slot screws into the channel where you want them to go and attach the brackets or structures you want and tighten until snug.

Transmitting Motion is the act of getting motion from one part of the robot to another using shafts, sprockets, gears, etc.

Transforming Motion is the act of changing the turning force (torque) and speed. Torque and speed are inverse to each other, meaning when one increases the other decreases.

The core to transmitting motion in the REV DUO Build System is the 5mm hex (hexagonal, six sided) shape. This hex shape is incorporated into the other main motion components, such as: sprockets, gears, wheels, and shafts. Shafts are available in a number of different lengths up to 400mm, and can be cut to length if needed.

The two primary systems used to transmit motion in the FTC Starter Kit V3 (REV-45-1883) and FIRST Global Kit are sprockets and gears.

Motion Component Features

Most REV DUO motion parts, mainly plastic sprockets and gears, all have a uniform thickness of 15mm. This helps to improve the iterative design experience. Changing from a gear reduction to a chain and sprocket, or going direct drive, will not require many frame or spacer changes.

Product material selection is noted below. Traction wheels and Grip Wheels (REV-41-1267) are co-molded with a polyurethane tread for increased traction.

Motion Components Materials

REV DUO wheels, sprockets, and gears have a M3 bolt hole mounting pattern that is on an 8mm pitch as shown below. This makes it easy to directly mount to REV Robotics brackets, extrusion, and channel. The 8mm pitch is also compatible with many other building systems.

Sometimes, it may be desirable to stack together multiples of the same gear or sprocket on a shaft. As a best practice, all components should have the alignment notch oriented the same direction on the shaft. The alignment notch can be found on the raised hub on either side of the gear or sprocket.

In many cases the number of teeth on the gear or sprocket is not divisible by six, the number of sides on the hex shaft, and therefore the relative rotation between two of the same part will result in the teeth being out of alignment with each other. If the first sprocket was put on a shaft with the alignment notch facing upwards, there would be a valley at the top of the sprocket. If the second sprocket was added to the shaft, but rotated clockwise by 60 degrees (by the turn of one flat side), there would be most of a sprocket tooth at the top of that sprocket.

15mm x 30mm Extrusion Basics

The 15mm x 30mm profile of the Extrusion has slots on on all four sides that accept standard M3 hardware. Rather than using a T-nut, which is more expensive, slide a M3 hex head screw along the slot and adjust brackets and other build materials as needed. As illustrated in the image above, the ends of the Extrusion also have a 5mm hole pitch that can be M3 tappped. The 15mm x 30mm Extrusion has one slot on each 15mm face and 3 slots on each 30mm face, allowing for some additional design flexibility when compared to the standard 15mm extrusion.

Product Specs

• Material: 6063 Aluminum, clear or black anodized

• Height: 15mm

• Width: 30mm

• Length: 1m or 420mm

  • Extrusion can be cut to shorter lengths as needed

When to Use?

The 15mm x 30mm Extrusion is great for areas where more torsional strength is needed in an application than the standard 15mm Extrusion.

How to Use?

The point of the extrusion system is to offer more flexibility in design than would come in a fixed pitch system. The slots in the extrusion allow brackets and other components to be slid along the 15mm Extrusion to an infinite number of positions.

Sprocket Basics

Sprockets are rotating parts that have teeth and can be used with a chain and another sprocket to transmit torque. Sprockets and chain can be used to change the speed, torque or direction of a motor. For sprockets and chain to be compatible with each other, they must have the same thickness and pitch.

Sprockets consist of a disk with straight teeth projecting radially. Sprockets will only work correctly with chain and other sprockets if they are on parallel shafts and the teeth are in the same plane. A chain consists of a continuous set of links that ride on the sprockets to transmit motion. The REV 15mm Build System is designed around #25 Roller Chain (REV-41-1365) using compatible #25 Sprockets.

Anatomy of a Sprocket

The most common and important features of a sprocket are called out in the figure below.

Anatomy of Chain

Roller chain is used to connect two sprockets together and transfer torque. Roller chain is made up of a series of inner and outer links connected together which forms a flexible strand.

Product Specifications

The REV DUO Build System includes both Metal and Plastic Sprockets. The table below covers some of the basic specifications for the different types of Sprockets.

REV DUO sprockets are a #25 pitch. Plastic Sprockets are designed to fit a 5mm hex shaft which eliminates the need for special hubs and setscrews. Most Metal Sprockets use a Locking Motion Hub (REV-41-1719) in order to connect to a Hex Shaft. The REV DUO Metal Sprockets are at less risk for wear than the Plastic Sprockets.

All REV DUO Plastic Sprockets have a M3 bolt hole mounting pattern that is on an 8mm pitch. This makes it easy to directly mount REV DUO Brackets and Extrusion to sprockets. The 8mm pitch is also compatible with many other building systems.

Using Sprockets and Chain as a Powertrain

Transforming the torque and speed of the motion is accomplished by changing the size of the sprockets.

A sprocket size ratio is the relationship between the number of teeth of two sprockets (input and output). In the image below, the input sprocket is a 15 tooth sprocket and the output is a 20 tooth. The sprocket size ratio for the example is 20T:15T. The ratio in size from the input (driving) sprocket to the output (driven) sprocket determines if the output is faster (less torque) or has more torque (slower).

Within a chain loop, motion follows the direction set by the input sprocket. In the example, both sprockets inside the chain loop move counter clockwise. Idlers, which sit outside of the chain loop, are pushed in the opposing direction. So, the 15 tooth idler sprocket is moving clockwise.

How to Use REV DUO Sprockets and Chain?

Like with other motion components, REV DUO Sprockets drive motion with the 5mm Hex Shaft. However, in order to use a Hex Shaft with the Metal Sprockets, a Locking Motion Hub will also need to be used. To learn more about using Hex Shafts and proper motion support and constraint visit the pages linked below:

Chain Tension

In order for sprockets to work effectively, it’s important that the center-to-center distance is correctly adjusted. The sprocket and chain example with the red 'X', in the image below, may work under very light loads, but they will certainly not work and will skip under any significant loading. The sprockets in this example are too close together so chain is loose enough that it can skip on the sprocket teeth. The sprockets, with the green check mark, are correctly spaced which will provide smooth reliable operation.

The first step to getting ideal chain tension is to manipulate, or cut the chain to the correct size. Using the center-to-center distance calculation is one of the most accurate ways to find the chain size needed. Once sizing is approximated, use the Chain Tool (REV-41-1442) or Master Link (REV-41-1366) to break and reform the chain.

When using the slots on REV DUO structural elements its is very easy to adjust and tension the chain if the sizing is off. When using the Extended Motion Pattern in conjunction with a chain drive, use Tensioning Bushings (REV-41-1702) and Standoffs (REV-41-1492).

Sprocket Alignment Mark

Sometimes in a design it may be desirable to stack together multiple of the same sprocket on a shaft. In the cases where the number of teeth on the sprocket is not divisible by six, because of how they are oriented when put onto the hex shaft, the teeth may not be aligned between the two sprockets. To ensure all of the sprockets are clocked the same way, use the alignment shaft notch to put all the gears on the shaft with the same orientation.

L Beam Basics

L Beams are a structural element for small load applications or as a supporting component on a larger load application. They’re compact and lightweight and provide more strength than a Flat Beam. Use them to create a corner between plates, attach channel to extrusion, or for fastening your own creations.

Product Specs

• Material: 6063-T6 Aluminum

• Length: Various Lengths

• Height: 11.5mm

• Width: 11.5mm

Bracket Basics

There are many classifications that brackets could fall into but in the REV DUO Build System there are two major groupings of brackets: motion and construction. The major distinguishing feature of motion brackets is a 9mm bearing seat to support Hex Shafts and Bearings. Construction brackets are essentially any bracket in the REV DUO Build System that does not have a bearing seat. Because the term construction bracket encompasses a broad range of REV products it can be further subdivided as structural brackets and actuator brackets.

Structural brackets act as connectors between structural components. For example, these are the type of brackets you will want to use when connecting Extrusion to Channel elements. Actuator brackets on the other hand are intended to mount and support motors and servos.

Another key point of bracket distinction in the REV DUO Build System is that there are both metal and plastic brackets available. Many of the brackets, like the 15mm 90 Degree Bracket (REV-41-1480)(REV-41-1305), come in a metal and a plastic version. Though there is some overlap between the metal and plastic brackets, there are also key differences between the two type of brackets.

Follow through the rest of this section to learn more about brackets.

Key Terms

Alignment Ribs: Protrusions on one side of the bracket seat into the extrusion channel to help align the bracket to the extrusion and add strength and rigidity to joints.

Extrusion Mounting Holes: M3 Mounting holes on an 8mm pitch.

Bearing Seat: Brackets with a 9mm hole can be used to mate with any of the plastic bearings to support a shaft.

Motion Interface Mounting Pattern: Circular M3 hole pattern on a 16mm diameter is used to mount to REV Robotics shaft accessories.

Plastic Brackets VS Metal Brackets

The image and definitions in the introduction above use the 15mm Motion Bracket (REV-41-1303), which is a plastic bracket, as an example. The table below outlines the basic differences between the plastic and metal brackets.

Actuator Brackets

The actuator brackets all have an 8mm pitch for mounting to Extrusion or Channel. The interface pattern changes depending on the specific use case bracket. For instance, the Metal Bent HD Hex Motor Bracket (REV-41-1487) has a different interface than the Metal Bent Planetary Motor Bracket (REV-41-1563).

Most of the actuator mounting brackets are metal brackets, with no plastic alternative. In the REV 15mm Build System there is a Plastic Servo Bracket (REV-41-1319) in addition to the metal servo brackets.

It is also important to note that the Core Hex Motor (REV-41-1300) has the Motion Interface Pattern and can be mounted to any bracket with the Motion Pattern.

Bracket Use Cases

Variable Angle Bracket

The Variable Angle Bracket (REV-41-1318) is a special kind of construction bracket which allows 2 pieces of extrusion to be mounted together at any angle from 0-180°. For additional strength, after the ideal angle has been set, miter the end of the extrusion with that angle. Attached the extrusion to the bracket through to arc and center hole. Then drill a hole along the alignment mark arc so that it lines up with the extrusion slot and add another bolt to fix the angle.

Indexable Motion Bracket

The Indexable Motion Bracket (REV-41-1313) is a specialized version of the Motion Bracket. This bracket is made up of two pieces: the smaller piece has alignment ribs and fits onto the extrusion, while the larger piece has a motion interface pattern and a bearing seat. On the inside face, where these brackets meet is a fine sawtooth pattern which mesh when they are bolted together to hold the shaft offset. To adjust the offset, loosen the screws and adjust as needed. Tighten the screws to fully engage the teeth to secure the bracket.

Sprocket and Chain Physics

Sprockets are one common way to transmit power and change the output torque or speed of a mechanical system. Understanding these basic concepts is required to make optimized design decisions. This section will briefly cover the definition of these concepts and then explain them in relationship to basic sprocket and chain designs.

Chain Drive

By selecting sprockets with different sizes relative to the input sprocket varies the output speed and the output torque. Total power is not effected through these changes.

Sprocket and chain is a very efficient way to transmit torque over long distances. Modest reductions can be accomplished using sprockets and chain, but gears typically provide a more space efficient solution for higher ratio reductions.

Sprocket Ratio

When a larger sprocket drives a smaller one, for one rotation of the larger sprocket the smaller sprocket must complete more revolutions so the output will be faster than the input. If the situation is reversed and a smaller sprocket drives a larger output sprocket, then for one rotation of the input the output will complete less than one revolution resulting in a speed decrease from the input. The ratio of the sizes of the two sprockets is proportional to the speed and torque changes between them.

The ratio in size from the input (driving) sprocket to the output (driven) sprocket determines if the output is faster (less torque) or has more torque (slower). To calculate exactly how the sprocket size ratio effects the relationship from input to output use the ratio of the number of teeth between the two sprockets.

Idlers

Now lets add a 15 tooth idler sprocket into the example on the outside of the chain loop. An idler sprocket is any sprocket meshed with the chain which does not drive any shaft or do any work. Idlers do not change the system reduction which remains 20T:15T.

All sprockets on the same side of a chain have the same rotation. The driving and driven sprocket are inside the chain and are rotating counter clockwise while the idler sprocket is outside of the chain loop and is rotating clockwise. This property is useful sometime when it is desirable to have two shafts powered from the same source, but with opposite rotations. Common examples of this on robots are intakes and dual wheeled shooters.

Idlers can be used to tension chain or increase the amount of chain wrap around a sprocket. From the figure below, all power transmission sprockets should have chain wrapped approximately 180° around the circumference of the sprocket. This amount of wrap is necessary so that there are sufficient teeth engaged with the chain to transmit the torque. Too little wrap (<120°) and the chain will skip under heavy load, while excessive wrap (>200°) can decrease system efficiency. The sprocket outside of the chain is noted with a warning because it has a chain wrap of <90°. If this sprocket is an idler, then it is unpowered and minimal chain wrap is acceptable, however if this sprocket will be driving a shaft which is doing work, this amount of wrap would be insufficient.

Sprocket and chain is an efficient way to transmit torque long distances in a robot. A common example of this is a sprocket and chain drivetrain. In this example the sprockets on the ends are linked to the drive wheels and the center sprocket would be driven by a motor (not shown). Because the driving and driven sprockets are all inside the chain, they all have the same rotation direction. The smaller sprockets on the outside of the chain loop are used to increase the amount of chain wrap on the center driving sprocket.

Compound Gearing

Some designs may require more reduction than is practical in a single stage. The ratio from the smallest sprocket available to the largest is 54:15, so if a greater reduction then 3.6x is required, multiple reduction stages can be used in the same mechanism which is called a compound gear reduction. There are multiple gear or sprocket pairs in a compound reduction with each pair linked by a shared axle. When using sprockets and chain in a multi stage reduction, it’s very common to use gears for the first stage and then use sprockets and chain for the last stage. The figure below is an example of a two-stage reduction using all gears, but one of the pairs could be replaced with sprockets and chain. The driving gear (input) of each pair is highlighted in orange.

Reduction is calculated the same for gears and sprockets based on the ratio of the number of teeth. To calculate the total reduction of a compound reduction, identify the reduction of each stage and then multiply each reduction together.

Where:

• CR is the total Compound Reduction

• Rn is the total reduction of each stage

Using the image above as an example the compound reduction is 12:1.

For any gear system there are a limited number of gear and sprocket sizes available so in addition to being able to create greater reductions using compound reductions it is also possible to create a wider range of reduction values or the same reduction of a single stage, but with smaller diameter motion components.

Spacing and Center to Center Distances

When REV Robotics Sprockets are used in conjunction with the slots on Extrusion or Channel, the center to center distance between axles is completely adjustable. Slide and retighten the shaft mounting plates anywhere along the slots to adjust chain tension. This system allows any combination of compatible REV Robotics Sprocket to be used together, allowing for a high level of flexibility. When adjusting the reduction of a system, just a single sprocket can be replaced reducing the amount of reassembly time.

When using the pitch featured on the Extended Motion Pattern a similar level of flexibility can be achieved in sprocket spacing by using Tensioning Bushings (REV-41-1702) with M3 Standoffs (REV-41-1492).

Spacing

In order for sprockets to work effectively, it’s important that the center-to-center distance is correctly adjusted. The sprocket and chain example with the red 'X;, in the image below, may work under very light loads, but they will certainly not work and will skip under any significant loading. The sprockets in this example are too close together so chain is loose enough that it can skip on the sprocket teeth. The sprockets, with the green check mark, are correctly spaced which will provide smooth reliable operation.

To correctly space REV Robotics Sprockets along slots, use the following procedure:

1. Securely fix the axle of either the input or output sprocket. In the case of a gear train with multiple idlers or a compound reduction, consider which axle makes the most sense to fix such as the very first input gear or the very last gear.

2. Starting with the fixed axle, then identify all the driving and driven sprockets for any sprockets on that axle. One by one loosen these axles, slide them until the chain is tensioned and then retighten the axle mounts.

3. Continue the procedure from Step 2 for each fixed axle until all the chains are tight and all the axles have been retightened.

Center to Center Distance

It is possible to mathematically calculate the number of links needed between two sprockets or the correct center to center distances for two sprockets for a given chain length. These methods are appropriate for robot planning purposes, but assembling your robot using these measurement is typically impractical. The details of these calculations are included for completeness, but most modern CAD packages or numerous free online calculators can also generate the correct values.

Center to center distance in inches

Chain length in pitches

Where:

• C= Center to Center Distance

• L= Chain Length in Pitches

• P= Pitch of Chain

• N= Number of Teeth on Large Sprocket

• n= Number of Teeth on Small Sprocket

Calculate center to center distance

Calculate center to center distance using the 'center to center distance in inches' formula and the chain drive example in the above image.

Where:

• L = 48

• P = 0.25

• N = 20

• n = 15

After running calculations, the center to center distance for the example is 3.807 inches

Calculate chain length

In most design cases the chain length is not known ahead of time, but the two sprockets in the reduction and an approximate center-to-center distance to fit the reduction is known. For this example, a 20:15 reduction is needed, and the whole solution must fit in a space of five inches or less.

In this example the whole solutions must fit into a five-inch space, so in addition to the center to center distance, the chain clearance radius for both sprockets must be accounted for. Use Sprocket Measurement Details to look up the chain clearance diameter (A) for both the 15 tooth and 20 tooth sprocket and subtract the radius of each from the total given solution size to get the maximum center to center distance available.

Where:

Using the center to center distance of 3.371 inches as the maximum spacing for this reduction to fit into a five-inch space, solve the chain length in pitches equation.

Where:

• C= 3.35

• P= 0.25

• N= 20

• n= 15

Since it is not possible to have a fraction of a pitch length in the chain, the number obtained by solving the formula must be rounded to a whole even number. In this example because the center to center distance used was the maximum allowed, the exact pitch length should be rounded down to 44 to meet the design requirements.

Now that the maximum even pitch lengths in the chain has been calculated, this value can be plugged back into center to center distance formula to find the exact center to center distance using a 44 link chain:

Where:

• L = 44

• P = 0.25

• N = 20

• n = 15

For a 15T:20T reduction the longest chain which will fit in under 5-inches using a 44 link chain which gives a center-to-center distance is 3.307 inches and the total solution width of 4.957 inches.

Sprocket Measurements

Plastic Sprockets

The Motion Interface Pattern is a circular M3 hole pattern on a 16mm diameter that interfaces with certain REV Brackets and the UltraPlanetary 5mm Hex Output (REV-41-1604).

The 10 tooth #25 sprocket does not have a motion pattern due to size constraints. However, the 10 Tooth Sprocket shares features of the other Plastic Sprockets, like compatibility with #25 Chain. The table below provides the outer diameter and pitch diameter of the 10 Tooth Sprocket.

Metal Sprockets

Flat Beam Basics

These aluminum beams are simple and versatile. Having an 8mm width, 3mm height, and 8mm hole pattern makes them perfect as a support for an upright, or for use as a linkage.

Product Specs

• Material: 6063 Aluminum

• Length: Various Lengths

• Width: 45mm

• Height: 3mm

• Hole Pattern: 8mm, M3

Creating a loop of chain requires breaking off the correct number of links by removing a specific chain pin and joining the ends together. Chain can be broken using many methods, including a Chain Tool or various steel cutting blades, like a dremel. Once you have counted the number of links necessary for your application, the chain can be joined using a master link or by replacing the chain pin.

#25 Chain Tool Basics

This custom-designed #25 Chain Tool () also commonly referred to as a "chain break" or "chain breaker", allows teams to easily break and re-assemble #25 Chain (). The mandrel is used to push out the chain pin. If using Master Links (), the pin can be completely removed, but the depth guide screw allows the option of partially pressing out the pin and then re-assembling without master links.

Kit Contents

• 1 Chain tool block

• 2 set screw mandrels

• 1 depth guide screw

• 1 cup point set screw

• 1 4mm Allen Wrench

Manipulating Chain

In almost all applications, chain links are connected to form a loop. While chain can sometimes be purchased in specific length loops, it is more common and economical to buy chain by the foot and make custom loop lengths to fit the application. It’s recommend to use a specialized tool, a chain breaker, to cut chain into desired lengths to prevent accidental damage.

Chain breakers do not actually cut the chain, instead they are used to press out the pins from an outer link. After the pins have been removed the chain can be separated leaving inner links on both ends of the break.

Master Links

Roller chain is typically connected into a continuous loop. This can be done using a special tool to press the pins in and out of the desired outer link as described in the Custom Length Chain section, or if the chain is already the correct length a common roller chain accessory called a master link, or quick-release link, can be used to connect two ends of the chain.

Master links allow for easy chain assembly/disassembly without any special chain tools. Master links can typically be reused many times, but can become bent with multiple uses. At the point that master links become bent they should be discarded.

Steps to using a master link

1. Place the loose outer plate onto the two pins pressed into the other outer plate.

2. Ensure the outer plate is inserted onto the pins far enough that the grooves on the pins are fully exposed past the outer plate.

3. Align the widest gap near the middle of the clip with one of the pins.

4. The gap in the clip should allow the clip to slip over the pin and sit flush against the outer plate and aligned with the groove in the pins.

5. Use pliers or another tool to slide the clip towards the other pin until the clip is securely engaged with the grooves on both pins.

Using the Chain Tool

Resetting Chain Pins

Wheel Basics

REV Robotics offers four types of wheels: , , DUO Mecanum (), and . There are two different DUO traction wheels available: the standard DUO Traction Wheel and the DUO Grip Wheel (). The traction wheels resemble standard wheels, like what you might see on a car or a bike. The main focus of the traction wheels is to pull a robot (or create traction) in a forward/backwards motion.

Omni and Mecanum wheels, however, are omnidirectional wheels. Omnidirectional wheels give additional flexibility to a drive train by adding an additional vector of motion, known as strafing.

This section will walk through the different kind of wheels available through REV and best practices for utilizing them.

DUO Traction Wheels

The DUO Traction Wheel comes in three different sizes to allow flexibility in design and usage of the wheels.

Product Specs:

• Hub Material: Nylon (PA66)

• Tread Material: TPU

• Width: 15mm

• Hole Diameter: M3 clearance

• Hole Spacing: 8mm

DUO Grip Wheels

DUO Grip Wheels are wider than standard DUO Traction Wheels, offering traction while still being lightweight in specific drivetrain applications, like driving on soft foam tiles. These wheels are designed for optimal grip in situations where the material the wheel is interacting with is compliant like soft foam tiles, carpet, or foam balls.

Product Specs:

• Diameter: 90mm

• Width: 25mm

• Hub Material: Nylon (PA66)

• Hub Bore: 5mm Hex

• Tread Material: TPU

• Tread Durometer: 65A

• Hole Diameter: M3 Clearance

• Hole Spacing: 8mm

• Weight (single wheel): 88g (3.10oz)

DUO Omni Wheels

A single omni wheel is the same thickness, 15mm, as all other motion components. In some applications, it might be desirable to stack two omni wheels, with one rotated by 60° from the other, as shown below. By setting your wheels in this configuration you ensure that a roller is always in contact with the ground. This results in smoother and more consistent operation.

Product Specs:

• Hub Material: Nylon (PA66)

• Roller Material: TPU

• Thickness: 15mm

• Hole Diameter: M3 clearance

• Hole Spacing: 8mm

Mecanum Wheels

‌REV DUO Mecanum Wheels have a similar functionality to the Omni Wheel. The Mecanum Wheels have rollers around the whole circumference of the steel plate rim, set at a 45° angle. The full set of rollers present on the Mecanum Wheel remove the need to stack two wheels together like is required with the omni wheel.‌

Tested for the rigors of competition, REV DUO Mecanum Wheels are steel plates with rollers supported by ball bearings allowing for the perfect combination of wheel rigidity and roller movement. Included in the set of wheels are Universal Hex Adapter making mounting to 5mm hex shaft easy. With a 75mm diameter these wheels allow for a lower profile giving more space for building mechanisms and space for game elements.‌

Product Specs:

• Hub Material: Steel

• Roller Material: NBR

• Diameter: 75mm

• Width: 40mm

• Weight (single wheel without Universal Hex Adapter): 179 g (0.395 lbs)

DUO Compliant Wheels

The 2in Compliant Wheels are used for intakes and conveyor systems. Featuring a solid 5mm Hex Hub molded into the wheel making sure more power is driven by the wheel, combined with the “hurricane” cutouts to ensure even compliance across the rotation of the wheel. These wheels come in two different durometers, Soft - Light Gray 30A and Medium - Gray 45A. As the tread durometer increases the compliant wheel gets harder which will change traction, wear, and compliance of the wheel.

Product Specs

• Diameter: 2in (50.8mm)

• Width: 0.5in (12.7mm)

• Hub Material: Polypropylene

• Hub Bore: 5mm Hex

• Tread Material: Thermoplastic Rubber

• Weight (single wheel): 18.1g (0.64oz)

• RPM Rating: 5,500 RPM

Durometer Specs:

DUO Flap Wheels

Flap Wheels are used for intakes and conveyor systems to pick up irregular gamepieces, playing a similar role to compliant wheels. DUO Flap wheels feature cut marks every 3.2mm on the flaps for consistent cutting, allowing for versatility and adaptability for unique game pieces. The DUO Flap wheels have a solid 5mm Hex Hub molded into the wheel making sure more power is driven by the wheel. These wheels come in three different durometers, Soft - Light Gray 30A, Medium - Dark Gray 40A, and Hard - Black 60A. As the tread durometer increases the compliant flap gets harder which will change traction, wear, and compliance of the flap.

Product Specs

• Length: 4in (101.6mm)

• Width: 0.44in (11.1mm)

• Material: Polypropylene & TPR

• Hub Bore: 5mm Hex

• Hub Width: 0.59in (15.0mm)

• Weight (single wheel): 9.07g (0.03lb)

Durometer Specs:

Timing Belt and Pulley Basics

The Timing Belt and Pulley system is a pulley-based motion transmission system. Timing Belts and Pulleys transmit motion similarly to sprockets and chains. Both the Belt and the Pulley have teeth that interlock and engage with each other to drive motion.

Timing Belts and Pulleys are lighter, more compact, and more efficient at transferring motion than chains and sprockets. Belts do not stretch over time as much as chain, making re-tensioning less of an issue. In general, a timing belt and pulley system should last a full season, if properly installed. Follow through the rest of this section to learn more about the proper installation and tensioning of the .

Product Specs:

The REV GT2 3mm Pitch Pulleys and the GT2 3mm Pitch Belt come in various sizes to fit your needs.

All pulleys, except the 12 Tooth (), come with two ends and an inset to adjust the width of the pulley as needed to drive multiple belts.

Belt Installation

All of the GT2 3mm Pitch Pulleys, with the exception of the 12 Tooth Pulley, have flanges to keep the belt on track. This is because the belts tend to thrust to the side when in motion. It is recommended that at least one pulley in the system have flanges to keep the belt from slipping. In situations where the center distance between shafts is more than 8 times the diameter of the smaller pulley or when the drive is operating on vertical shafts, both pulleys should have flanges on both sides.

When choosing what structural aspect to use to support a pulley system, it is important that the support be rigid or capable of withstanding torsion. Any significant flex or give in the supporting structure can cause the center-to-center distance between the pulleys to change. Repercussions of a change in the center distance are slack in the belt and the belt jumping teeth.

During the installation process, ensure that supporting shafts are parallel and that pulleys are aligned.

Belts require relatively little maintenance if installed correctly, but it's always advised to run the center distance calculation to account for the installation and removal of belts.

Belt Tension

The Timing Belt should be snug when installed to ensure a longer life and less wear on the mechanism. A taut belt is not going to have the same lifespan as a snug belt, and a loose belt may jump teeth in situations where torque is high.

Linear Motion Basics

The REV DUO 15mm Linear Motion kit is designed for use with the slots on . The Linear Motion Kit v2 () contains all the necessary hardware to build a single stage lift if a team already has an FTC Starter Kit. Items necessary for powering the linear motion system are sold separately or as part of a linear motion bundle. That being said, requirements are highly dependent on implementation so tools and actuators are excluded from the bundle. This guide is designed to build a three stage lift in two possible configurations (Cascading or Continuous). Additional materials are needed to finish the build and detailed in the Tools and Materials.

Linear motion can typically be defined as "straight line" or one-dimensional motion. Mechanisms like elevators and lifts are common examples of one-dimensional motion in robotics. The REV DUO Build System supports linear motion through the REV DUO Linear Motion Kit.

Product Specifications

Driving Linear Motion

Bearings Basics

The REV Robotics 15mm Extrusion Building System primarily uses plastic acetal (Delrin/POM) molded bearings. These bearings have a maximum 9mm outer diameter (OD) which fit inside the 9mm inner diameter (ID) hole in the all the motion brackets and the bearing seat of the Extended Motion Pattern.

These Delrin bearings provide stable, low friction axle support in our nylon brackets. The two materials were carefully chosen because they have a very low coefficient of friction and are also incompatible materials, meaning that they will not stick together under extreme heat. These bearings come in three varieties.

End cap bearings are closed on one end, so when these bearings are placed on both ends of a shaft and fit into motion brackets the shaft is free to rotate but is fully constrained laterally (sideways).

Short Through-bore Bearings are low profile pass-through bearings intended to seat directly into any of the motion brackets. These low-profile bearings have a 3mm contact surface which makes them flush with one side of the motion plate. Shaft collars are recommended to laterally constrain the shaft.

Long Through-bore Bearings are full depth pass-through bearings which can be used with any of the motion brackets or the bearing pillow block. Unlike the end cap bearing, because a shaft can pass though this bearing, it can be used with the bearing pillow block to have a pivot between two fixed shaft ends. Shaft collars are recommended to laterally constrain the shaft.

There are number of different bearing, shaft collar, and motion bracket combinations that are recommended. See the image below for a visual representation of some of the recommended combinations.

How to Use?

The figures in the table below show several possible combinations for bearings, motion brackets, and pillow blocks. In these figures the brackets are all depicted as facing “up” but brackets can also point “down” just as well.

Ball Bearings

Flanged Bearing

5mm Hex Bearing Block

Gear Basics

Gears have teeth that mesh with other gears in order to transmit torque. Gears can be used to change the speed, torque (turning force), or direction of a motor’s original output. For gears to be compatible with each other, the meshing teeth must have the same shape (size and pitch).

There are many different types of gears; one of the simplest and most commonly used is a spur gear, and that is the gear type used in the REV DUO Build System. Spur gears consist of a disk with straight teeth projecting radially (outward from the center) and these gears will only mesh correctly with other gears if they are on parallel shafts.

Anatomy of a Spur Gear

Common and important features of a spur gear are highlighted in the image below.

Product Specifications

Plastic Gears

Metal Gears

Using Gears as a Powertrain

Meshing two or more gears together is known as a gear train. Selecting the gears in the gear train as larger or smaller relative to the input gear can either increase the output speed, or increase the output torque but the total power is not affected.

A gear ratio is the ratio of the sizes of two gears. For instance, in the image below, the input gear is a 15 tooth gear and the output gear is a 72 tooth gear. So, the gear ratio is 72T:15T. The ratio in size from the input (driving) gear to the output (driven) gear determines if the output is faster (less torque) or has more torque (slower). The gear ratio is proportional to the speed and torque changes between them.

In the image above, the 15 tooth input gear is rotating clockwise. As the input gear rotates, it pushes down on the output gear where the teeth are meshed. This action transmits the motion to the output gear, but forces the output gear to rotate in the opposite direction of the input gear.

How to Use REV DUO Gears?

Gear Spacing

In order for gears to work effectively, and not become damaged, it’s important that the center-to-center distance is correctly adjusted. The gears in DETAIL A, of the figure below, may work under very light load, but they will certainly not work and will skip under any significant loading. The gears in that example are too far apart and so the teeth of each gear barely contact each other. The gears in DETAIL B are correctly spaced and will provide smooth and reliable operation.

Gear Alignment Mark

Sometimes in a design it may be desirable to stack together multiples of the same gear on a shaft to increase the load carrying capacity of the gears. In the case where the number of teeth on the gear is not divisible by six, because of how they are oriented when put onto the hex shaft, the teeth may not be aligned between the two gears. To ensure all of the gears are clocked the same way, use the alignment shaft notch to put all the gears on the shaft with the same orientation.

Being aware of the alignment mark will ensure all of the gear teeth are aligned on the shaft. The figure below is an example of a basic robot arm which may have to lift a heavy load. Using two gears to lift the arm doubles the material interfacing with the hex shaft and will allow the arm to perform with heavier loads.

5mm Hex Shaft

The REV DUO Build System is built around a . Using a hex shaft to transmit torque in the system removes the need for set screws, which can loosen over time and can damage shafts so that they become unusable. REV Robotics Hex Shafts are precision ground 5mm stainless steel and fit in all other REV hex drive components.

Product Specs

• Material: Stainless steel (SUS303)

• OD: 5mm hex

• Length: Four Lengths, can be cut if needed

When to Use?

Use the 5mm Hex Shaft in areas where you have moving parts or need to transmit torque.

How to Use?

Shaft Collars

When to Use?

Shaft collars are used to prevent lateral (sideways/sliding) movement of a shaft, or an item on the shaft. Since shaft collars are used to prevent lateral shaft movement they are often used in place of shaft spacers.

How to Use?

The REV Robotics shaft collar has a 6mm inside diameter and is customized with a M3 thread so a standard hex cap bolt can be used instead of the supplied set screw.

Spacers

When to Use?

• For larger sections of exposed shaft, shaft collars are preferred because installing multiple spacers is less efficient and is more difficult to manage during robot building and maintenance.

• For shorter shaft lengths, spacers are generally more efficient.

Adapters

High Strength Hex Hub

These aluminum hubs can be mounted to any of the REV robotics hex driven motion products to increase their maximum torque. When the hex hub adapter is used on a REV product, the raised part of the hub should face away from the gear. There will be a small gap between the back of the hub and the body of the gear because of the built in spacer on the gear. Insert a shaft into both parts and then using M3x20mm and nylocs, evenly tighten the hub against the gear to ensure good alignment.

In addition to the increasing the maximum torque of REV products, the High Strength Hex Hub can be used to convert almost any of the Tetrix and AndyMark gears with the 4-hole mounting pattern to accept a 5mm hex drive shaft. Hex hub adapters allow teams to use the parts they already have with the reliability and convenience of a hex drive shaft.

Locking Motion Hub

Gear Physics

Gears are one common way to transmit power and change the output torque or speed of a mechanical system. Understanding these basic concepts is required to make optimized design decisions which consider the trade-off between torque and speed for a system with a given power.

Gear Train

Meshing two or more gears together is known as a gear train. Selecting the gears in the gear train as larger or smaller relative to the input gear can either increase the output speed or increase the output torque, but the total power is not affected.

Gear Ratio

When a larger gear drives a smaller one, for one rotation of the larger gear the small gear must complete more revolutions - so the output will be faster than the input. If the situation is reversed, and aa smaller gear drives a larger output gear, then for one rotation of the input the output will complete less than one revolution – so the output will be slower than the input. The ratio of the sizes of the two gears is proportional to the speed and torque changes between them.

The ratio in size from the input (driving) gear to the output (driven) gear determines if the output is faster (less torque) or has more torque (slower). To calculate exactly how the gear ratio effects the relationship from input to output, find the ratio for the number of teeth between the two gears. In the image below, the ratio of the number of teeth from the input gear to the output gear is 72T:15T which means the input needs to turn 4.8 rotations for the output to complete one rotation.

Idlers

What happens when a 45 tooth idler gear is inserted into the gear example? An idler gear is any intermediate (between input and output) gear which does not drive any output (work) shaft. Idler gears are used to transmit torque over longer distances than would be practical by using just a single pair of gears. Idler gears are also used to reverse the direction of the rotation of the final gear.

Regardless of the number or size of idler gears in the chain, only the first and last gear determine the reduction. Since idler gears do not change the gear reduction, the reduction in the example remains 72:15, but the direction of the output stage is now reversed from the previous example.

Idler gears are a good way to transmit power across distances in your robot. A common example of this is an all gear drivetrain. In this example the gears on the end are linked to the drive wheels and one of the center gears would be driven by a motor (not shown). The orange arrows indicate the relative rotation of each of the gears showing that the two wheels are mechanically linked and will always rotate in the same direction.

Because idler gears reverse the direction of rotation, it is important to pay attention to the number of gears in the drivetrain. In the picture below there is an even number of gears, and because of this the wheels will always spin in the opposite direction.

Compound Gearing

Some designs may require more reduction than is practical in a single stage. The ratio from the smallest gear available to the largest in the REV 15mm Build System is 125:15, so if a greater reduction then 8.3 is required, multiple reduction stages can be used in the same mechanism, this is called a compound gear reduction. There are multiple gear pairs in a compound reduction with each pair of gears linked by a shared axle. Below is an example of a two-stage reduction. The driving gear (input) of each pair is highlighted in orange.

To calculate the total reduction of a compound reduction, identify the reduction of each stage and then multiply each reduction together.

Where:

• CR is the total Compound Reduction

• Rn is the total reduction of each stage

Using the image above as an example the compound reduction is 12:1.

For any gear system there are a limited number of gear sizes available, so in addition to being able to create greater reductions using compound reductions it is also possible to create a wider range of reduction values, or the same reduction of a single stage, but with smaller diameter gears.

Spacing and Center to Center Distance

Spacing

In order for gears to work effectively, and not become damaged, it’s important that the center-to-center distance is correctly adjusted. The gears in DETAIL A ,of the figure below, may work under very light load, but they will certainly not work and will skip under any significant loading. The gears in that example are too far apart and so the teeth of each gear barely contact each other. The gears in DETAIL B are correctly spaced and will provide smooth and reliable operation.

To correctly space REV Robotics Gears along slots, use the following procedure:

1. Securely fix the axle of either the input or output gear. In the case of a gear train with multiple idlers or a compound reduction, consider which axle makes the most sense to fix, such as the very first input gear or the very last gear.

2. Starting with the fixed axle, identify all the driving and driven gears for any gears on that axle. One by one, loosen these axles and slide them until the teeth of both gears are fully engaged and parallel. Re-tighten the axle mounts.

3. Continue the procedure from Step 2 for each fixed axle until all the gears are tightly meshed and all the axles have been re-tightened.

Center to Center Distance

Where:

• CCD is the Center to Center Distance

• PD1 is the pitch diameter for gear one

• PD2 is the pitch diameter for gear two

Using the example in the figure with the 60 tooth and 72 tooth gears, the correct center to center distance calculation for a 72T:60T gear ratio is 49.5 mm.

Gear Measurements

Plastic Gear Measurements

The 15 tooth and 30 tooth plastic gears do not have a motion pattern due to size constraints. However, they share the same 0.75 module as the other acetal gears. The table below provides the outer diameter and pitch diameter of these gears.

Metal Gear Measurements

The 12 Tooth and 28 Tooth Metal Gears do not have a motion pattern due to size constraints. They are also made from sintered steel rather than aluminum. However, they share the same 0.8 module as the other metal gears. The table below provides the outer diameter and pitch diameter of these gears.

Flat Plate Basics

is a 45mm wide, bendable metal featuring the Extended Motion Pattern. This product comes in various lengths. The Extended Motion Pattern supports for attaching brackets, extrusion, and channel.

Product Specs

• Material: 5052 Aluminum

• Width: 45mm

When to use?

The alloy of aluminum used in the flat plate makes it more malleable than other structure pieces in the 15mm Build System. Utilize the flat plate to create curved aspects for your robot like a shooter hood, an intake, or a bumper.

How to Use?

Step 1: Approximate the diameter of the curve you want.

Step 2: Find an object, like a can, that is close to the diameter you need.

Step 3: Adjust the flat plate around the object with your hands or hand tools until you reach your desired curve.

HD Hex Pinion Pressing Guide

Needed Materials:

• HD Hex Motor (REV-41-1291)

• A Small Phillips Head Screwdriver

• Press Fit Pinion

• Arbor Press

Core Hex Motor Basics

The Core Hex Motor (REV-41-1300) is a motor that features a 90 degree orientation and a female output shaft for maximum flexibility and ease of use. Insert any of the REV standard 5mm Hex Shafts into or through the Core Hex Motor to create custom length motor output shafts. The Core Hex Motor has a built in magnetic quadrature encoder which is compatible with 5V or 3.3V logic level devices including the Control Hub (REV-31-1595) and Expansion Hub (REV-31-1153).

Pinout

The Core Hex Motor uses a 2-pin JST-VH Connector for motor power and a 4-pin JST-PH for sensor feedback from the built-in encoder. For more information on using the cables and connectors included with the Core Hex Motor, see the REV Control System - Cable and Connectors documentation. The image below has the pinout for the motor power and the encoder.

Product Specs

• Output Shaft: 5mm Female Hex

• Weight: 7 oz

• Voltage: 12V DC

• Free Speed: 125 RPM

• Stall Torque: 3.2 N-m

• Stall Current: 4.4 A

• Gear Ratio: 72:1

• Encoder Counts per Revolution

  • At the motor - 4 counts/revolution

  • At the output - 288 counts/revolution

When to Use?

The general recommendation is to use the Core Hex motor for lighter duty arms and intakes.

How to Use?

How to Mount the Core Hex Motor

The Core Hex Motor has two faces for mounting on two sides of the motor. The combination of the Motion Pattern is clocked to different angles on each face giving twelve different motor angles. The images below exhibit a basic mounting structure for two of the twelve positions that are available.

HD Hex Pinion Pressing Guide

Needed Materials:

• HD Hex Motor (REV-41-1291) With Pinion Pressed On

• A Small Flathead Screwdriver

• Hex Shaft For Leverage (or similar)

Motor Basics

Electric motors are the core power plant of most robots. There are two types of motors in the REV DUO Build System: the Core Hex Motor (REV-41-1300) and the HD Hex Motor (REV-41-1301). Both motors are brushed DC motors. The image below showcases the common elements of a bushed DC motor.

Elements of a Brushed DC Motor

Brushed DC motors without a gear box can be estimated to be ~80% efficient, meaning if a motor is drawing 60 watts of power ~48 watts will be turned into mechanical energy and ~12 watts will become heat. Once a gear box is added the overall efficiency of the system goes down.

Key Metrics

DC brushed motors can be described by some key metrics:

The prototypical performance graph of a Brushed DC motor can be used to estimate the performance of a motor. In most cases amperage, the unit of measurement for current, is the easiest value to find as it can be reported by the REV Control Hub (REV-31-1595) and Expansion Hub (REV-31-1153).

Preventing Premature Motor Failure

In order to ensure that an electric motor lasts as long as possible a few rules of thumb should be kept in mind:

• Smooth loading - large torque spikes or sudden changes in direction can cause the wear and premature failure of gear box components. This is only an issue when the torque spike exceeds the rated stall torque of the motor. When shock loading is necessary, it is best to utilize mechanical braking or a hard stop that absorbs the impact instead of the motor.

• Overheating - when a motor is loaded at near its maximum operating torque it will produce more waste heat than when operating at a lower operating torque. If this heat this allowed to build up the motor can wear out prematurely or fail spontaneously.

• Poorly supported output shaft, most motor output shafts are not designed to take large thrust forces or forces normal to the shaft. Bearings need to be used to support the axle when loads in these directions are expected.

REV Motor Specifications

REV DUO Robotics motors come in two types, HD Hex Motors and Core Hex Motors. All REV DUO Motors have a Hex Shaft or female hex coupler as the output from its gearbox. The Hex Shaft is extremely reliable at transmitting torque without being reliant on set screws that can come loose or not be tightened sufficiently. REV DUO motors also include keyed locking connectors for both the motor power and the built-in encoder.

Introduction

Choosing between actuators can be a difficult process. Without applying physics and math, you may be left wondering how to make the choice between an HD Hex Motor (REV-41-1301) and a Core Hex Motor (REV-41-1300)? This section will take you through the process and mathematics to help you make the best decision for your robot!

Before getting too far here are some general guidelines for where REV DUO actuators are best utilized.

Though these basic suggestions are here to guide you in the right direction, all robots are different. Follow through the rest of this guide to find the best fit for your mechanisms.

Core Concepts

When designing a robot, selecting the correct actuator for the application is a critical design challenge. Some tools can be used to estimate the performance of a motor in a particular application.

Understanding these basic concepts is required to make optimized design decisions which consider the trade-offs inherent to any design. This section will briefly cover the definition of these concepts and then explain them in relationship to basic powertrain concepts.

Choosing an Actuator Walkthrough

The first round of analysis to narrow down your actuator is to compare the the maximum output power of the actuator to the power required to run the mechanism.

Lets say you are building an elevator that lifts a game piece. Before you can begin your calculations you have to make some basic assumptions about your design. In this case, assume zero frictional losses and instantaneous acceleration. Consider also, the following information:

• Game piece weight: 0.5 kg

• Lifter weight: 1.5 kg

• Lifter maximum height: 1.5 meters

• Time to full extension: 5 seconds

Step 1: Calculate Work

Work is a concept used to describe changes in energy. Path Independent work is defined as force times displacement. Since Force is mass times acceleration the following formula for work can be derived:

As a standard when calculating work, calculate Net Work, or the total amount of forces displacing your mechanism. In the example, the only force to account for is the acceleration against gravity at a constant velocity, as it has been assumed there are no frictional forces at play. Therefore in the example Work is:

Where the 2(kg) = the combined mass of the elevator and the game element.

Step 2: Calculating Power

Power (P) is the rate of work over time. The difference between work and power is that it takes the same amount of work to carry a brick up a mountain whether you walk or run, but running takes more power because the work is done in done in a shorter amount of time. So, power can be represented as: $P = W/t$ ,where t = time period

In the example, work was calculated to be 29.4. It was also stated that the time period is 5 seconds. With those numbers known power can be calculated as:

When you are building a mechanism it is advisable to apply a safety factor (sf) to the power of the mechanism to ensure that your mechanism is able to withstand things like unexpected loads or degradation over time. For this example, apply a safety factor of 2.

After applying the safety factor of 2 and rounding, it is found that 12 watts of power are needed to power the mechanism. Now that the power estimate is known it is time to decide which actuator meets the criteria given.

Step 3: Choosing an Actuator

Take the known power estimate of 12 watts and compare it against the Maximum Output Power for the various actuators in the key metric table. Choose a motor that has a maximum output power greater than that of the estimated power for the mechanism. With those parameters given, the likely choices for the elevator are any of the HD Hex Motor variants.

Step 4: Estimating Performance

A motor performance graph can be used both for selecting a motor and for understanding the motors behavior once installed in the robot. The below prototypical performance graph can be used to estimate the performance of a motor.

The prototypical performance graph exhibits standard curves to help calculate where your motor falls on the performance scale.

Using the Performance Curve to Select an Actuator

When selecting a motor the expected power requirement for the motor is used. In the example estimate power was found to be 12 watts. The graphic below for finding power/torque range has a power estimate similar to that of the example (12 watts is 80% of max power). This will still be a good example of how to use the motor performance graph to estimate your metrics.

Using the Performance Curve to Understand Behavior

If you have already selected an actuator and installed it you may want to check to see what your robots performance is. This process is similar to the estimation to select a motor.

Previously the power estimate was used to find the other metrics, now amperage will be used as it can be reported by the Control Hub (REV-31-1595) and Expansion Hub (REV-31-1153). When amperage is known, draw a line horizontally at the known value using the current scale, then at the point your horizontal line intersects the current curve, draw a vertical line. The points at which the vertical line intersects the key metric curves will give you the estimated performance for each metric.

Step 5: Powertrain Design

Once a motor has been selected, a power train can be designed. The goal of the power train is getting the final torque and angular velocity to the necessary values within the possible range that can be produced by the motor. When designing the power train, the fewer elements present in the power train the more efficient the power train will be. For example, using 30:72 gear box and a 20:20 chain drive will be less efficient than directly using 20:54 chain drive.

Motor performance curves are useful at this stage of design as well because given an estimated power requirement you can estimate an angular velocity and torque range that the motor will be outputting. When designing the power train, the values used should be at the lower end of the viable rpm and torque range as the motor can be given more power to bring it into performance should the estimates be off.

HD Hex Motor Basics

The HD Hex Motor (REV-41-1301) features an integrated encoder and power that plug right into the REV Control Hub (REV-31-1595) and Expansion Hub (REV-31-1153). The gearbox options feature 5mm Hex output or coupler making it easy to connect gears, sprockets, wheels, etc. Encoder and power cables are always included with motor. The HD Hex Motor is similar in size and power to other brushed 550 class motors with more convenient output options and connectors.

The HD Hex Motor matches the design flexibility of other REV products with a series of compatible gearboxes to choose from. Gearbox options include the UltraPlanetary Gearbox (REV-41-1600), Spur Gearboxes, Planetary Gearbox, and no gearbox.

This section will focus on general HD Hex Motor information such as motor specifications and mounting techniques.

Pinout

The HD Hex Motor uses a 2-pin JST-VH Connector for motor power and a 4-pin JST-PH for sensor feedback from the built-in encoder. For more information on using the cables and connectors included with the HD Hex Motor, see the REV Control System - Cable and Connectors documentation. The image below has the pinout for the motor power and the encoder.

HD Hex Motor (No Gearbox)

Why would you get a motor without a gearbox? Lets consider a few scenarios:

• Motors Can Fail - If you have a motor that has failed but the gearbox is still in good condition, it is typically cheaper to buy the bare motor and attach the gearbox you already have.

• Customization - If you want to make your own gearbox, having the No Gearbox version of the motor will make that easier.

Product Specifications

• Weight: 234g

• Body Diameter: 37mm

• Voltage: 12V DC

• No-Load Current: 400mA

• Stall Current: 8.5A

• Free Speed: 6000 rpm

• Stall Torque: .105 Nm

• Max Output Power: 15W

• Encoder Counts per Revolution

  • At the motor - 28 counts/revolution

Planetary Gearboxes

Planetary gearboxes are designed for increased robustness when compared to Spur gearboxes, and are generally less susceptible to damaging shock loads due to more gear teeth being engaged to carry the load. There are a two planetary gearbox options from REV, the 20:1 Planetary gearbox (REV-41-1211) and the UltraPlanetary gearbox. The 20:1 Planetary gearbox has a set gear ratio where the UltraPlanetary allows for swapping out of cartridges to adjust the final gear ratio.

UltraPlanetary Gearbox

The UltraPlanetary System is a cartridge based modular gearbox designed to handle the rigors of the competition and the classroom. The UltraPlanetary System includes an input stage and pinion gear that works with the REV HD Hex Motor and other 550 class motors. Building on the ability to iterate and adjust designs easily using the REV Building System, the UltraPlanetary System consists of pre-assembled and lubricated cartridges allowing for swapping gear ratios on the fly and with ease. Users can configure a single-stage planetary using one of three different reduction cartridges, build multi-stage gearboxes through stacking individual cartridges together, and choose two different ways for transferring power: either through face mounting directly on the output stage or choosing the length of 5mm hex shaft best suited for the application.

The UltraPlanetary system has a variety of options for mounting with four different brackets available for mounting to REV 15mm Extrusion, REV C Channel, or REV U Channel.

Sample Gearbox Choices

A wide range of gear ratios are possible with the three included cartridges. When combining up to three cartridges, just multiply each cartridge gear ratio to find the overall gear ratio. For example, a combination of the 4:1 and 5:1 cartridges would make a 20:1 overall gear ratio. The table below shows the common use cases for all possible ratios that can be created with the included UltraPlanetary kit.

Below are the specifications for a small sample of the options available with the UltraPlanetary Gearbox Kit.

20:1 Planetary

The 20:1 Planetary gearbox features mounting holes on a 14mm bolt circle. The gearbox is compatible with the Planetary Gearbox Flat and Bent motor mounting brackets. To mount the 20:1 Planetary directly to the Extended Motion Pattern on REV Channel use a HD Hex Planetary Facemount Spacer.

20:1 Planetary Specs

• Weight: 436g (including motor)

• Output Shaft: 5mm hex

• Output Shaft Length: 40mm

• Free Speed: 300 rpm (31.4 rad/s)

• Stall Torque: 297.4 oz-in (2.1 Nm)

Spur Gearboxes

The Spur gearboxes feature the REV Motion Pattern that is compatible with REV Motion Brackets and the Extended Motion Pattern on REV Channel. There is a second mounting pattern that is standard for most spur gearboxes. This pattern is featured on the flat and bent motor mounting brackets for Spur Gearboxes.

20:1 Spur Specs

• Product SKUs

  • Gearbox (REV-41-1064)

  • Motor with gearbox (REV-41-1298)

• Weight: 350g (including motor)

• Output Shaft: 5mm hex

• Output Shaft Length: 40mm

• Mounting Holes: 10 - M3 tapped - use a 5mm length or shorter bolt

• Free Speed: 300 rpm (31.4 rad/s)

• Stall Torque: 297.4 oz-in (2.1 Nm)

40:1 Spur Specs

• Product SKUs

  • Gearbox (REV-41-1065)

  • Motor with gearbox (REV-41-1301)

• Weight: 350g (including motor)

• Output Shaft: 5mm hex

• Output Shaft Length: 40mm

• Mounting Holes: 10 - M3 tapped - use a 5mm length or shorter bolt

• Free Speed: 150 rpm (15.7 rad/s)

• Stall Torque: 594.7 oz-in (4.2 Nm)

Why Supporting Motion is Important

Supporting the assemblies that move on the robot is very important. Without planning proper supports, may not be able to spin or actuators could be easily damaged.

How to Support Motion

Forces, or loads, that are at a right angle to the shaft are the most important forces to counteract. The floor pushing on a wheel or two gears pushing against each other are two examples of these forces.

It is best to support a shaft with two supports, one on each end. Without two supports, the shaft can pivot in the direction of the force. If, and only if, two supports are not possible, it is very important to minimize the distance between the force and the single support.

Some products that can be used to support motion assemblies are:

Constraining Motion Basics

Robots need movement to accomplish goals; arms must pivot, wheels must turn, etc. However, movement that isn’t directly related to those actions can affect the accuracy and precision of the robot mechanisms. This unintended motion must be properly restricted, or constrained.

Long and thin structures can flex and deform, making it difficult to interact with objects and operate in a repeatable manner. Make use of brackets and additional or to strengthen and constrain these structures.

How to Constrain Motion

Gears and sprockets must stay aligned or else they won’t work properly.

Keeping parts aligned on a shaft, and keeping the shaft itself from sliding out is critical for reliably working robot mechanisms. Use a combination of spacers and shaft collars to align and constrain these parts into place.

Constructing Joints

Another crucial piece to proper motion constraint is joint construction. Places where structural components, like an Extrusion and Channel, meet need to be properly supported in order to avoid structural collapse during motion.

Secure with 2 or More Brackets

Use Beveled Extrusions

When using brackets to connect extrusion, the joint will be much stronger if the end of the extrusion is beveled (cut at an angle) so that the end will sit flush with the face of the adjoining extrusion.

Different bracket angles can be combined to make structures. The joints in this example are all beveled to sit flush against the adjoining extrusion.

Ways to Create 90 Degree Joints

There are three main ways to create extrusion joints that are at 90 degrees. The most common is the 90° bracket which mates to pieces of extrusion at 90° in the same plane. The second is an inside corner bracket is functionally equivalent to the 90° bracket. The third type is called a lap joint bracket which allows two pieces of extrusion to “overlap.”

90° Bracket

Inside Corner Bracket

Servo Basics

Servo motors are a specialized kind of motor which can be controlled to move to a specific angle instead of continuously rotating like a DC motor. Instead of a hex output shaft like the DC motor, servos have an output spline. A spline is a specific groove pattern cut into the shaft which allows the rotation of the servo motor to be transmitted to the attached Aluminum Servo Horn () or . Splines are like keys, so only matched types will fit together. The REV Robotics Servos all use a 25T spline pattern. If the gears or spline of the REV Robotics Smart Robot Servo () become damaged, they are replaceable using a Replacement Gear Set ().

Common servo motors take a programmed input signal range and map that to an angular range. For example, for a servo with a 270° range, if the input range was from 0 to 1 then a signal input of 0 would cause the servo to turn to point -135°. For a signal input of 1, the servo would turn to +135°. Inputs between the minimum and maximum have corresponding angles evenly distributed between the minimum and maximum servo angle.

Servo Adapters

REV Robotics Servo Adapters fit 25T spline servos like the REV Robotics Smart Robot Servo. In addition to the variety pack of generic servo horns which come with the Smart Robot Servo, there are four other custom servo adapters which make using servos with the REV 15mm Building System easy.

Servo Gear Adapters convert a 25T servo into 15 tooth Delrin gear which is compatible with the other REV Robotics Plastic Gears.

Servo Shaft Adapters convert a 25T spline servo output shaft into a female 5mm hex socket. This adapter can be used to drive a hex shaft directly.

Aluminum Servo Horns have a tapped hole pattern that can be directly mounted to any of the REV Robotics gears, wheels, or sprockets with the Motion Pattern.

Servos with the Control Hub and Expansion Hub

Normally servos do not draw the maximum current, but teams do not know what might happen during matches. To protect against overdrawing the current on the Hub, only attach 2 servos to a Control Hub or Expansion Hub. Teams can safely use 4 servos: 2 servos on the Control Hub and 2 servos on the Expansion Hub.

Compatibility Basics

Increase the reliability of any robot system by switching from set screws to transmit motion to . Set screws can become loose and damage your shafts over time but using a hex shaft to transmit torque doesn’t require any set screws or keys, it just simply works.

Converting part of an existing design, or using already purchased parts, with hex is easy. The simplest option is to change to the HD Hex Motor () and directly drive , or use a High Strength Hex Hub () with an existing 4-hole pattern wheel. Use a shaft color to secure the wheel from sliding off the shaft.

Tetrix channels also use an 8mm hole spacing so almost all REV DUO brackets can mount directly to the channel. There are several ways to mount motion brackets and a structural bracket to the Tetrix Channel. The motion brackets accept a 9mm bearing so they can be used to add hex shaft to a Tetrix robot.

The 90 degree bracket above is one way to mount extrusion to Tetrix channel. A stronger method would be to miter the end of the extrusion as needed and then bolt it directly to the Tetrix channel as shown in below. Install M3 hex cap bolts and nylocs in the Tetrix channel with the heads on the side the extrusion will be installed on. Slide the extrusion into place with the bolt heads in the extrusion channel and tighten. This method will also work with Actobotics channel.

SRS Basics

The REV Robotics Smart Robot Servo (SRS) () is a configurable metal-geared servo that takes the guesswork out of aligning and adjusting servo based mechanisms. One SRS can be used as a standard angular servo, a custom angular servo, and a continuous rotation servo by simply changing its settings.

Documentation Links

Snug, Not Stuck!

When tightening a screw, firm will do. Do not keep tightening until the screw can no longer turn because this can damage structure, actuators, and eventually the screw itself. Simply secure the screw to the point that the pressure is firm.

Bracket Ribs Should Face the Extrusion Slot

The side with the small ribs will always face towards the extrusion when assembling, so that the ribs can help square the bracket to the extrusion.

Pre-Load Brackets With Screws

When securing a bracket to extrusion it is recommended to pre-load the bracket with screws. When the screws are loaded on the bracket before it is even brought near the extrusion, it is less likely that screws will fall out or get misaligned. The bracket can then be slid into place along the slot.

Studs Should Be Up

Building “stud up” is recommended with the REV DUO Build System. This means building with the screw head inside of the extrusion. Pay attention to the direction that screws go into the brackets, only the screw head will fit in the extrusion.

Nut Direction Matters

When using the nyloc nuts, make sure the beveled “nyloc” side is facing out.

Plan Ahead!

Modifying Length

When building different mechanisms, your design may need a specific length of extrusion or channel. Cutting structure down to the correct size is easy to do, and is recommended for these applications. Here are a few tips when cutting down structure to the right size.

• Measure twice, cut once

  • Use a straight edge, not a measuring tape, to get a proper length. Using a marker with a sharp point, like a sharpie, helps as the "inside" of the mark is where to cut.

• Use painter's tape

  • Preparing the structure before cutting by applying painter's tape can help make straight cuts. Align the edge of the tape with the mark and wrap along the cutting plane to help identify where to cut.

• Use the right tool

  • At minimum, use a handheld hacksaw with a vice or clamp.

  • If using a powered saw, REV recommends using a horizontal bandsaw with proper clamping and safety measures to prevent injury.

  • Make sure that both sides of the structure being cut are supported while cutting to ensure a straight cut.

Single Sprocket Shaft Assembly Parts Required