what wire gauge should I use for motor power

You should use stranded wire between 16 AWG and 12 AWG for your primary motor power cabling, though 18 AWG is acceptable for standard motor connections and extensions. According to Game Manual 0, motor power cabling is recommended to be within the 16 AWG to 12 AWG range, and it must always be stranded rather than solid wire. Game Manual 0 also notes that standard motor wires are generally 18 AWG, and specifies that any custom extensions or shortened cables must use 18 AWG or thicker wire to remain legal .

This recommendation changes if you are wiring main module power instead of individual motors, in which case Game Manual 0 advises using even thicker wire of at least 14 AWG, or ideally 12 AWG, to handle the higher electrical loads safely .

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Wiring Guide > Specific Recommendations > Motor Power

Game Manual 0·CC BY-NC 4.0

Cabling for motor power should be between 16awg and 12awg. Again, stranded, not solid, wire.

Some motors (like the REV HD Hex and Core Hex) will have removable power connectors on the back, while other motors (like the Andymark NeveRests) will have a cable permanently soldered on the back. It is much more convenient to have a connector on the back, or failing that, have a very short plug on the back of the motor. Once your wires are run and secured, taking them out won't be fun.

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Electronics and Motion Components

Game Manual 0·CC BY-NC 4.0

This chapter contains information on electric power and electronics of the robot, including information on wiring, batteries, motors, and control system.

Gauge — Wire gauge refers to the diameter of wire. AWG stands for American Wire Gauge, the general system used in the US. The larger the gauge number, the smaller the wire diameter. Generally, servo wires are 22 AWG and motor wires are 18 AWG.

Grounding Strap — The REV Grounding Strap is used to ground the metal frame of the robot to the XT30 port of the Expansion Hub. It is currently the only legal way to ground your robot.

USB Retention Mount — The USB Retention Mount, sold by REV, is a plastic part affixed to the Expansion Hub that relieves stress on the USB Mini port. This is especially important because if the USB cable is loose or disconnected, the robot phone cannot communicate with the Expansion Hub, causing a disconnect.

Note: For teams using an expansion hub, it is highly recommended for teams to purchase the USB retention mount.

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Wiring Guide > Specific Recommendations

Game Manual 0·CC BY-NC 4.0

Be aware, XT30 connectors can wear out significantly faster than PowerPole connectors. Additionally, because XT30 connectors are soldered, they can break much easier than PowerPole connections.

Cabling for module power should be at least 14awg, if not 12awg. Keep in mind that it must be stranded, not solid, wire.

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Robot Wiring Guide > Best Practices > 12V Power Distribution

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To enable full functionality of the robot's electronics, it is important to have stable 12V power and sufficient current capacity for all 12V wiring. FTC-approved 12V power components are designed with appropriate connectors and wire gauges to support a typical robot. A simple REV power system would supply 12V from the fused battery, through a power switch, into a REV Expansion Hub. Power would be daisy chained out of the parent hub into an optional child hub.

However, for robots that have high current loads (from many motors) or have a larger number of 12V components (like Servo Power Modules or SPARK Mini motor controllers), it may be desirable to utilize a 12V power distribution bus. A power bus takes a single input power feed and splits it into several 12V outputs, each of which can power a dedicated device instead of daisy chaining the power from one component to the next.

A power bus can be created by building a custom wiring harness or by purchasing a commercial power distribution block.

- .. figure:: images/power-dist-block-1.png

:alt: A REV XT30 power distribution block with multiple output ports.

Power distribution blocks - .. figure:: images/power-dist-block-2.png :alt: An Anderson Powerpole power distribution block with four output pairs.

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Robot Wiring Guide > Best Practices > Wires on Moving Parts

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Most robots have one or more components that move relative to the main drive chassis. This could be things like a pivoting arm, an extending collector, or a shooter turntable. When these components have motors and sensors attached, it is important to ensure that the connecting wires can accommodate the movement. There are several precautions that can be taken to ensure that wires do not get pinched, twisted, or entangled.

Constraining wires is the first line of defense. An unconstrained wire is likely to get caught and pulled as one component moves past another. However, moving parts often need "extra" wire when they are fully extended or rotated, so it is important to plan this extra wire when the part is retracted. The extra wire should be formed into a "service loop," which keeps wires bundled together and provides predictable movement. These bundled wires can be further protected by an expandable, spiral, or split sheathing. This sheathing serves as a flexible outer protector for the wire bundle as it moves near potential pinch/entanglement points.

(Figure: Wires near moving parts

The upper motor is mounted to a movable arm, which rotates relative to the robot chassis.
The motor's power and encoder wires have been bundled (yellow and green zip ties) into a service loop.
Wires are anchored to the motors (white zip ties). This maintains control over the wires when the arm rotates and ensures that none are pinched.)

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Motor Wiring And Mounting

Game Manual 0·CC BY-NC 4.0

Depending on the vendor, the motors can come with one of the following connectors:

JST VH connector (REV motors, some AndyMark NeveRest motors)
3.5mm Bullet connector (goBILDA motors)
Anderson PowerPole (some AndyMark NeveRest motors)

Since REV hubs use JST VH connectors, to connect a motor with 3.5mm Bullet or Anderson PowerPole connectors, you need adapters which you can purchase from REV Robotics, goBILDA, and AndyMark.

You can extend or shorten motor power cables by soldering additional length of cable. This is legal as long as you use 18 gauge or thicker cables. Teams can also purchase extender cables to chain multiple pieces of cable together.

For more tips on wiring the robot, see /docs/power-and-electronics/wiring.

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Robot Wiring Guide > Best Practices > Strain Relief

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Strain relieving is the technique used to reduce the amount of stress at a wire connection. In our case, this connection is typically a two-part connector. Proper strain relief will prevent the connector from becoming unplugged, or from having the wires break loose from the connector itself. In general, all connections should be properly strain relieved.

Immobilize the wire an inch or two from the connector and leave a little slack on the connector side. This prevents unintended tension on the wire from damaging the connector and allows the connector to be unplugged, if desired, for testing or module replacement. This can easily be done with a few zip ties. It may be acceptable to mount the connector more rigidly, but only if all parts involved are also mounted solidly on a rigid panel.

(Figure: Strain relief and wire restraints

Wires are channeled with zip ties.
Wires are also bundled based on their destination, such as motors, and then neatly coiled.
The 12V battery is held in place by a metal TETRIX bracket and Velcro (under the battery), and the main power connector is also constrained to the c-channel. The power switch is mounted in an easily accessible location, protected behind a side shield with a finger hole.
The REV Expansion Hub is mounted to a plastic base, which extends 1/8" beyond the metal chassis to minimize ESD (electrostatic discharge).)

Important: Every wire connection is a possible point of failure. This applies to all electronics.

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Wiring Guide > Specific Recommendations > Servo Wires

Game Manual 0·CC BY-NC 4.0

Using heavy-duty extension wires are recommended.

Tape the connections between extension wires and servo wires with electrical tape. This is as the connections can become loose over time and are easy to pull out.

The VEX Motor Controller 29 has the wrong gender connector on the 3-pin end. You are required to either use an adapter cable, or add the right connector to the wires (recommended). Be sure to protect the MC29, as it is fragile and prone to failure if it takes impact from another object.

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Robot Wiring Guide > Best Practices > Wire Management

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The most important step towards neat wiring is the implementation of proper wire management. Wire management involves bundling and routing wires along a defined path to the various electrical parts.

(Figure: Multiple wire management types

This robot utilizes multiple actuators, requiring level converters, boosters, and wire extensions. Clutter is eliminated by organizing a logical flow through the robot, then bundling and constraining wire clusters wherever possible.
Four encoder level converters are mounted to a plastic plate which is bolted to the main chassis. Wires to and from these converters are strain relieved on either side.
Motor wires pass through Anderson Powerpole connectors and are bundled and restrained.
Servo PWM cables (and their extensions) are grouped in a flat bundle and routed to a servo booster module. Wires from the booster module are bundled and wrapped with a spiral sheath which runs all the way up the arm support to the rotating grabber. A service loop is created and attached to the arm on one side, and the grabber on the other side.)

Tips to keep in mind to ensure neat, robust wiring:

Keep the wiring stationary.
Protect the wiring.
Where possible, make sure all cables are the correct length.
Bundle cables together if they are running to a common destination.
Use right-angle USB connectors if they keep wiring more compact.
Use wire management hardware.
Self-adhesive cable tie mounts help attach wires to surfaces without holes.
Grommets protect wires from damage from sharp edges.
Wire sheaths allow teams to quickly protect at-risk wiring.

(Figure: Wire management hardware)

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Robot Wiring Guide > Adapting Power Systems

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- .. figure:: images/xt30-connector-1.jpg

:alt: A male XT30 connector on a black and red wire.

XT30 connectors (male and female) - .. figure:: images/xt30-connector-2.jpg :alt: A male XT30 connector viewed from the side.

.. figure:: images/xt30-connector-3.jpg

:alt: A female XT30 connector on a black and red wire.

REV Robotics: The REV system uses XT30 connectors for the power wires. These connectors are used in the RC vehicle industry and are designed to withstand repeated connect and disconnect cycles. It is not necessary to replace these connectors with Anderson Powerpoles. However, there have been credible reports of occasional disconnects between the XT30 connectors provided with the REV Robotics hardware.

If you suspect that you might have a loose XT30 connection, conduct a careful physical inspection of the connection. Check to make sure the connectors fit snugly together and there is a slight amount of retention between the connectors when you try to pull them apart. Also check to make sure that power is not disrupted when the ends of the power cables that connect through the XT30 connectors are jiggled. If you do find a loose connection, first try replacing the cable, or if the bad connector is mounted on the Hub, you can attempt a repair yourself (https://docs.revrobotics.com/duo-control/troubleshooting-the-control-system/control-hub-troubleshooting) or contact REV Robotics support.

If you prefer to use Anderson Powerpoles as your primary connectors, you can attach an XT30/Anderson Powerpole converter cable to the Hub and strain relieve it properly. Once this converter is plugged into the Hub, it can be left in place, and the battery can connect or disconnect using the Anderson Powerpole connection. This will reduce the wear experienced by the XT30 connectors.

Warning: built-in reverse polarity protection, it is still possible to damage Hubs when reverse polarity power is applied.

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Robot Wiring Guide > Common Problems and Troubleshooting > Hub and Phone Communication Issues

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The signals that pass between the Android phone and the controllers are sensitive to interference. If a motor power wire or servo wire is routed next to a USB cable, it is possible to induce a stray signal that can lead to intermittent problems.

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Wiring Guide > Specific Recommendations > Sensor Wires/Encoder Wires

Game Manual 0·CC BY-NC 4.0

Sensor wires and their connectors can be incredibly fragile. Use caution when routing, and keep slack on the connector end when adding strain relief to the cable.

The JST data connectors on the REV Expansion Hub and Control Hub have +5v, GND, and two data pins. If you are using a digital or analog sensor that does not use I2C, you can use a Y cable that gives two sensors off of one port.

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Motor Wiring And Mounting > Mounting Motors

Game Manual 0·CC BY-NC 4.0

There are two ways to mount a motor: using a clamping mount (such as 32mm goBILDA clamping mount (https://www.gobilda.com/1400-series-1-side-2-post-clamping-mount-32mm-bore/)) or face mounting, using threaded holes in the front face of the gearbox.

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Motor Wiring And Mounting > Encoders

Game Manual 0·CC BY-NC 4.0

Note: Encoder cables are very fragile. Take care to protect them from snagging and sharp impacts! It may be prudent to inspect encoder wires once in a while.

If using encoders, you need to connect them to the REV hub by a 4-wire cable. REV Hub uses 4-pin JST PH connector for encoder ports. REV motors also use JST PH encoder ports, so you can connect them to the hub by JST PH 4-wire cable, available from REV Robotics.

goBILDA and AndyMark motors use JST XH 4-pin encoder port (note the difference: XH vs PH), so to connect them, you need a JST PH to JST XH cable, available from goBILDA and AndyMark.

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Robot Wiring Guide > Adapting Power Systems > Making an Adapter

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Teams may wish to replace the connectors on their batteries and install more reliable connectors in their place. If teams choose to do this, the old connectors can be useful.

(Figure: Anderson Powerpole and XT30 connectors)

When removing the unwanted connectors from the battery, do not cut the wires flush with the end of the connector. Instead, leave a 1/2" length of wire attached to the connector.

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Robot Wiring Guide > Adapting Logic Levels

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There are two voltage levels commonly used for logic on integrated circuits (like the chips in a REV Robotics Expansion Hub): 5V and 3.3V. The REV Expansion Hub uses 3.3V logic levels, but some third-party devices work using 5V logic levels. If you would like to use a 5V I2C sensor with the REV Robotics Expansion Hub, then you will need:

Logic level converters (also known as level shifters) to convert the signals to and from the sensor.
A REV Robotics Sensor Adapter Cable (REV-31-1384) to connect the 5V sensor to the logic level converter.
A complete explanation can be found in the

REV Robotics Expansion Hub Getting Started Guide (https://docs.revrobotics.com/duo-control/adding-more-motors/adding-an-expansion-hub).

(Figure: Logic level converter)

(Figure: Level shifters)

These level shifters are being used to interface motor encoders with the Expansion Hub. Four motors require four encoders, so four shifter modules have been mounted to a plastic bracket to minimize ESD and then bolted to the chassis. Wires leading to and from the modules have been restrained to provide strain relief to the connectors, and the cables are bundled to consume minimal space.

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