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

The REV Robotics 15mm Extrusion Building System also uses metal ball bearings. These bearings come in two types, 8mm x 12mm Flanged Bearing (REV-49-1559) and the 5mm Hex Bearing Block (REV-41-1683). Ball bearings provide better performance in high load or high speed applications than the Delrin bearings.

Flanged Bearing

The 8mm x 12mm Flanged Bearing has a 12mm outer diameter (OD) which press fits into the 12mm inner diameter (ID) hole of the 15mm Metal Ball Bearing Mount V2 (REV-41-1452). The 8mm inner diameter (ID) of the bearing fits the 5mm Hex to 8mm Bearing Insert (REV-41-1528).

5mm Hex Bearing Block

The 5mm Hex Bearing Block has a pre-pressed in 5mm Hex Bearing. The block has mounting holes designed to match the Extended Motion Pattern.

5mm Hex Shaft

The REV DUO Build System is built around a 5mm hex shaft. 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 snugly 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.

For high load applications it is recommended to use the REV precision shaft, stack multiple gears or sprockets in parallel, or use the High Strength Hex Hub Adapter (REV-41-1147) to increase strength.

How to Use?

Shaft Collars

A shaft collar is a hollow cylinder with one or more set screws which tighten towards its center and an inner dimension (ID) that is just slightly larger than the shaft it is being used on. Most standard 6mm ID shaft collars can be used on the REV Robotics 5mm hex shaft, but the REV Robotics Shaft Collar (REV-41-1327) is customized with a M3 thread so a standard hex cap bolt can be used instead of the supplied set screw.

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?

To use the shaft collar, slide it onto the hex shaft and rotate it until a flat side is facing the setscrew. Adjust the collar to the desired location and use a 1.5mm Allen Wrench (REV-41-1376) to tighten the included set screw snuggly against the shaft.

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

Spacers for the 15mm building system have a 5mm hex center, are made of Delrin, and come in 3 lengths. Spacers are used between parts on a shaft to take up the extra space and prevent the parts from sliding on the shaft. If more than a few spacers are needed, it is typically better to use a shaft collar.

When to Use?

Spacers and shaft collars are used for the same purpose: to constrain components on a shaft. This keeps shafts from falling out and also keeps motion components, such as gears and sprockets, aligned.

• 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

The Locking Motion Hub (REV-41-1719) places a motion pattern on any 5mm hex shaft. Use this to connect metal sprockets to 5mm hex shaft or add strength to any REV product with the Motion Pattern. The Locking Motion Hub has a shaft collar component built-in and does not need an additional shaft collar to constrain the Hex Shaft.

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. are available in a number of different lengths up to 400mm, and can be cut to length if needed.

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.

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.