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Motors and Servos

The Antidote - FTC 14320

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Motors

In the FIRST Tech Challenge, teams are only allowed to use up to eight motors

Four on each REV Expansion Hub or Control Hub

Every motor has a set max torque and max speed.

Gearbox ratios help manipulate the max torque and max speed to best suit certain applications
A general rule of thumb is be under half of the motor’s stall torque (can usually be found in motor specifications)

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Types of Motors

Spur Gear Motors
Consists of numerous reduction (↑ torque, ↓ speed) geared stages
Output shaft is typically not centered with the gearbox

Helps with belt/chain tension

Less durable than other gearbox options

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Types of Motors

Planetary Gear Motors
Consists of numerous sun + planet reduction stages 🡪 extremely reliable/efficient
Centered shaft and compact 🡪 better radial/axial load

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Types of Motors

Through Bore Motors
Instead of having an output shaft, through bore motors have a slot so that a shaft can be inserted
REV Core Hex Motor

Spur Styled Gearbox
Any shaft length can be used
Very loud & inefficient power output
Unusual gear ratio

72:1 is not commonly used
Uses a less powerful motor than other FTC motors

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Types of Motors

Bare Motor
These motors (sold by AndyMark and REV Robotics) do not have an external gearbox, only a pinion gear
Teams use bare motors for custom gearboxes, primarily for lift mechanisms or intakes

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Motor Comparison Chart

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Type	REV HD Hex	AM Classic	Tetrix TorqueNADO
Gearbox	Spur	Spur	Spur
Ratio	20:1 / 40:1	40:1 / 60:1	20:1 / 40:1 / 60:1
Cost	$28	$29.50	$30

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Motor Comparison Chart

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Type	AndyMark Orbital	REV UltraPlanetary	REV HD Hex	goBILDA Yellow Jacket
Gearbox	Planetary	Planetary	Planetary	Planetary
Ratio	3.7:1 / 19.2:1	3:1, 4:1, 5:1 Cartridges	19.2:1	3.7:1 to 188:1
Cost	$33	$36	$32	$30 (with discount)

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Selecting a Motor

Avoid using spur gear motors (not recommended)

Spur gears are made of numerous layers of gears to create the final ratio
Spur gears wear down rapidly 🡪 leads to a free moving shaft
Can not withstand the rigors of the FTC competition

Use planetaries! (recommended)

Planetaries are the most reliable motors to use in FTC
Load is distributed equally among the gears
Very rare for a planetary motor to break down
goBILDA offers a wide range of ratios to be used in any FTC application.

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Motor Mounts

Clamping Mounts

Clamps onto the circular body of the motor
Tapped holes allow the motor to be placed on any flat surface
Different motor brands have different motor diameters

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Motor Mounts

Face Mounting

Uses the screw holes on the face of the motor to mount the motor
Can either use a physical bracket to help with the mounting process
Recommended option for FTC applications compared to clamping mounts

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Servos

In the FIRST Tech Challenge, teams are only allowed to use up to twelve servos

Six on each REV Expansion Hub or Control Hub

Every motor has a set max torque and max speed.

Gearbox ratios help manipulate the max torque and max speed to best suit certain applications
A general rule of thumb is be under half of the motor’s stall torque (can usually be found in motor specifications)

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Types of Servos

Positional (standard) Servos

Servos are primarily used for precise and repeatable moves
Can only rotate around 180 to 270 degrees

The input signal manipulates the position of the servo spline

Continuous Rotation Servos

These servos are similar to motors

The input signal manipulates the speed and direction of rotation

Continuous Rotation servos typically do not have any form of positional feedback

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Programming Servos

A Servo Programmer (like the ones in the images) can set custom end-stops for positional servos and change the mode of certain servos from Continuous Rotation to Positional and vice versa.

The programmer can change the mode of REV’s Smart Robot Servo and goBILDA’s Dual Mode Servo.

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Servo Blocks

Sold by ServoCity and goBILDA
A limiting factor of servos is the amount of radial load that the servo can handle.
ServoBlocks acts as an exoskeleton and isolates the load onto the bearing located above the servo spline.
It is recommended that teams use ServoBlocks for any intensive or high-torque application

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