Motors
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-41-1291). 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:
Stall Torque is measured when the motors RPM is zero and the motor is drawing its full Stall Current. This value is the maximum torque the motor is ever capable of outputting. Keep in mind the motor is not capable of outputting this torque for an indefinite period of time. Waste energy will be released into the motor as heat. When the motor is producing more waste heat than the motor body is capable of dissipating the motor will eventually overheat and fail.
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.
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