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Voltage dropping when pushing joystick

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  • Voltage dropping when pushing joystick

    Ok, so we have our robot chassis built and completing the rest of the robot in the next week or so.

    We have wired everything up to run the chassis and have a basic program to drive the chassis.

    Issue: The motors will run as long as we do not push down the joysticks completely. Once it is pushed completely the voltage drops from 12V to something around 5V and the system shuts down. The assumption is that we are over loading the current above 40 amps but not sure.

    We are using CIM motors and Talon motor controllers.

    We tried another battery, switching the Talon with a Jaguar and checked the wiring.

    Any thoughts or help would be appreciated?


  • #2
    Re: Voltage dropping when pushing joystick

    If you are sure all of your wiring is correct and your batteries are in good condition, it sounds like your drivetrain is geared such that the CIM motors are drawing current beyond what the system is capable of supplying when attempting to accelerate at full throttle (if all the wiring is of the correct gauge and securely connected and the batteries are in good condition, you are likely drawing in excess of 100A per side to cause this condition). You have a few options on how to move forward:
    1. Implement an acceleration limit in software. This would prevent the output signal to the speed controllers from immediately going to full from a dead stop or rapidly reversing.
    2. Add more motors to your drivetrain. Depending on the current gearing and number of motors this may or may not help. The intention here would be to attempt to move the motor operation to a more efficient part of the speed-torque curve for greater periods of time.
    3. Add reduction to the drivetrain. This would involve adding gearing stages or changing the gearing (perhaps swapping chain sprockets) to provide a greater reduction between the CIM and the wheels.
    4. Reduce the wheel size. This effectively does the same thing as #3, just in a slightly different way.
    FRC Robotics Engineer


    • #3
      Re: Voltage dropping when pushing joystick

      Thanks Kevin and sorry for not giving probably some important information. I thought that we might have to much load on our motors so we just hooked up a motor to the talon and held in our hand. Same problem occurred.

      Additional thoughts?


      • #4
        Re: Voltage dropping when pushing joystick

        If this is happening even with a single, unloaded motor there is definitely an issue with your battery, wiring or a component in the wiring path common to the motor and roboRIO (such as the main breaker or PDP). I would recommend carefully checking if any of the wiring or connectors are getting warm to the touch.

        If you have a multimeter, see if you can move the joystick until the voltage drops, but not so low that it shuts off (you're trying to maintain a dropped voltage long enough to make measurements) then start measuring across parts of the system such as the main breaker or PDP.

        The likely causes would be the connection points:
        1. Connection between Andersen cable and battery lugs and connection between lugs and battery.
        2. Terminals on the Robot side of the Andersen connector
        3. Connections to the main breaker studs
        4. Connections to the PDP main power input.
        FRC Robotics Engineer