we lose control of the robot for a moment when the intake and drivetrain both run hard

When your intake and drivetrain run hard, they can draw excessive current, which causes control issues. Even if you do not reach the 20-amp limit of the FTC battery to blow the fuse, drawing too much current can cause other motors to feel sluggish or unresponsive .

Additionally, motors pull "transient current"—a large amount of current for extremely brief periods—when they start moving or experience a momentary load . While these transients generally do not pop the fuse, they can cause sluggish control when pulled by a motor .

To prevent this, care should be taken to ensure that more than two motors are never stalled at the same time . The stall current of FTC motors can be up to 11 amps per motor, which can easily exceed the battery's 20-amp output limit and cause sluggishness or a blown fuse .

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Motor Power > Note on Current Consumption

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You may see while looking at motor curves that the stall current of FTC motors can be as high as 11 amps per motor. FTC batteries can only provide 20 amps of current output before blowing the fuse is likely. However, even if the 20 amp limit isn't reached, drawing too much current can cause other motors to feel sluggish or unresponsive. Care should be taken to ensure that more than two motors are never stalled at the same time.

Note: You may be able to ignore this when dealing with mecanum drivetrains, as they will generally slip before the motors actually reach their stall current. However, placing very low gear ratios or more than 4 motors on traction drivetrains can exceed the current limit of an FTC battery.

Motors can pull "transient current" where they pull a large amount of current for extremely brief amounts of time. This often happens when the motor starts moving or when a momentary load is placed on it. While transients generally cannot cause a fuse to pop, they can cause other issues, such as sluggish control if pulled by a motor, or low voltage if the transient is pulled by a servo (goBILDA Super Speed servos have been observed to do this occasionally).

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Control Systems > REV Control Hub + REV Expansion Hub

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Warning: It is of vital importance to update the firmware on REV Expansion hubs to at least version 1.8.2. It includes better protection against disconnects and improves program performance. See the REV Expansion Hub firmware update docs.

This is the standard control system for teams starting out in FTC.

The Control Hub connects to the Expansion Hub through either a RS-485 connection, or a USB-A (Control Hub side) to mini-USB (Expansion Hub-side) connection. In either case, proper strain relief and cable management should be used.

For more information on setting up the Control Hub and configuring the robot, head to REV Robotics' Technical Resources Control Hub Guide (https://docs.revrobotics.com/duo-control/control-hub-gs).

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Control Systems > RC Phone + REV Expansion Hub(s)

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The Expansion Hub connects to the Robot Controller phone through its mini USB port. The REV Expansion Hub is reliable, as long as proper strain relief and wiring is carried out. This includes the USB Retention Mount, as well as 3D printing XT30 stress relief mounts.

For more information on setting up the Expansion Hub and configuring the robot, head to REV Robotics' Technical Resources Expansion Hub Guide (https://docs.revrobotics.com/duo-control/legacy/expansion-hub-gs).

USB Retention Mount (https://www.revrobotics.com/rev-41-1214/)
XT30 Stress Relief (https://www.thingiverse.com/thing:2887045)

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Control System Electronics

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This page contains a breakdown of known electronics in the REV Robotics control system, as well as notes regarding them.

Warning: Don't take apart a Control or Expansion Hub unless you really know what you are doing. They can be damaged in the process, especially if one does not know how to properly reassemble it.

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SDK Motors

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The SDK offers several methods of controlling and communicating with motors, as well as a couple of hidden methods that can be easily accessed.

All motor ports are controlled with what is called an H-bridge motor controller, a circuit that can be used to vary the output voltage as well as signage (negative or positive) of the voltage. Negative voltage through a DC Motor reverses a motor, whereas positive motor will make the motor go forward. SDK Motor power (from -1 to 1), represents a multiplier of the input voltage that is output through the motor port. The different voltages are created via PWM, where the port is turned on and off rapidly to create a lower average voltage.

In addition, the zero power behavior of the motor, that is the behavior of the motor when no power is applied, can be configured. In FLOAT mode, the motor controller simply turns off, providing minimal additional resistance. In BRAKE mode, the two motor leads are shorted together internally. Due to the inherent property that all DC brushed motors generate electricity when the shaft spins, shorting the leads causes a reverse power that stops the motor quickly and is resistant to external forces.

Note: The motor controller uses the input voltage, this means on a 13 volt battery, setting the power to 1 will create an output voltage of 13 volts. Similarly, on an 11 volt battery, a power of 1 will create an output voltage of 11 volts.

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Connectors and Wires

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XT30 — The XT30 connector is commonly used by batteries (such as the goBILDA Nested Battery and the REV Slim Battery), the robot power switch, the REV Control Hub and Expansion Hub, the REV Grounding Strap, and others. XT30 connectors are soldered onto wires.

Warning: The pins in the XT30 connectors on the Control Hub and Expansion Hub often compress over time, causing loose power connectivity. See XT30 Pins are Compressed - Expansion Hub Troubleshooting (https://docs.revrobotics.com/duo-control/troubleshooting-the-control-system/expansion-hub-troubleshooting#xt30-pins-are-compressed) for details on the issue and how to fix it.

JST VH — JST VH is a type of connector used by FTC motors to interface with the REV Control Hub and Expansion Hub. It is keyed and locks into place for excellent reliability. JST VH connectors are crimped onto wires.

JST PH — JST PH is a type of connector used by the REV Control/Expansion Hubs and various electronics, such as sensors. On the REV Control/Expansion Hubs, the 4-pin connector is used for encoder, I2C, analog, and digital connections. The 3-pin connector is used for the RS-485 connection between the Control Hub and Expansion Hub. JST PH connectors are crimped onto wires.

JST XH — JST XH connectors are used for the encoder connections on goBILDA (MATRIX) and AndyMark NeveRest motors. Both vendors sell adapters from JST XH to the JST PH encoder ports on the REV Control/Expansion Hubs. These connectors are also occasionally found on some third party sensors. JST XH connectors are crimped onto wires.

Tamiya — Used on some batteries, such as the Modern Robotics battery that was sold by goBILDA prior to goBILDA's own battery design being allowed by the competition manual.

Attention: Do not use these connectors! The metal connectors are fragile and will lead to random disconnects. It is highly recommended to replace any of these connectors with a reliable type of connector, such as the Anderson PowerPole connectors.

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