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DcMotor.ZeroPowerBehavior in RUN_USING_ENCODER mode, to ease strain on NeveRest20s?

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  • DcMotor.ZeroPowerBehavior in RUN_USING_ENCODER mode, to ease strain on NeveRest20s?

    The javadoc for the DcMotor.ZeroPowerBehavior describes being able to set a motor to either BRAKE or FLOAT when zero power is applied. However, it doesn't specify if this occurs in a particular RunMode, or in all of the RunModes, etc. One team I work with would like to run their shooter in RUN_USING_ENCODER mode to set specific shooter speeds, but also let the motors FLOAT when turned off so they slowly come to a stop rather than being suddenly stopped, straining the gearbox. They fear that the motor gearboxes may break if suddenly set to zero power in BRAKE mode, and they are concerned by the new warning below for AndyMark NeveRest20 motors.

    Has anyone tried FLOAT mode in RUN_USING_ENCODER mode to see if it does float rather than brake abruptly?

    From AndyMark's NeveRest20 product page:

    Product Usage Note:
    We have received some feedback from a small number of customers regarding the durability of the gearbox on the NeveRest 20 Gearmotor. After some internal testing, as well as review of returned gearmotors, we have found that this particular gearbox is more susceptible to failure from shock loads as compared to the NeveRest 40. These sort of failures happen most commonly in high-shock applications such as flywheel shooters, as well as drive chassis. We recommend these gearmotors to be used in low shock-load applications such as intake rollers, internal conveyors, etc.

  • #2
    We've tried setting all of the drive motors to FLOAT mode with RUN_USING_ENCODER and have still destroyed the 20 gearboxes. FLOAT would probably help if you're driving along full speed and suddenly set the power to 0.0. It probably wouldn't help driving at a high speed into a wall or quickly reversing directions - you know, the kind of stuff that just happens driving robots.

    If you're talking about a flywheel shooter I suspect that the biggest shock comes when it contacts the ball, not when you cut the power. I'd still be reluctant to use the 20 gearboxes at this point.

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    • #3
      Originally posted by mlwilliams View Post
      FLOAT would probably help if you're driving along full speed and suddenly set the power to 0.0.

      If you're talking about a flywheel shooter I suspect that the biggest shock comes when it contacts the ball, not when you cut the power. I'd still be reluctant to use the 20 gearboxes at this point.
      In a flywheel shooter if you're running at full speed and then you tell the motor in RUN_USING_ENCODER mode to stop and BRAKE, that will be a HUGE shock as suddenly it is trying to instantaneously stop the wheel. To do this, it essentially has to power the motor in reverse instantaneously. In comparison, contacting the relatively light, low-mass ball doesn't come anywhere close to stopping the wheel, so the relative shock is not nearly as great.

      This team has successfully made and tested a flywheel shooter with geared up 20s, but it's been tested by plugging in the motors directly to the battery and then cutting the power when the test is over, similar to a FLOAT mode. So far, they haven't seen any failures in the 20s when they do this. But if suddenly they use the motor controllers in BRAKE mode where the motor will likely be suddenly changed to full REVERSE power to try to stop the motor, they might. That's why FLOAT mode working correctly is important for their usage case.

      I agree that using the 20s in a drivetrain is not a good choice because you HAVE to try to stop, reverse directions, etc. But a flywheel shooter can ramp power up and down more gradually. I wonder if folks are seeing flywheel failures because of the braking.

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      • #4
        I agree that trying to stop a flywheel shooter suddenly would be a problem and that FLOAT mode should help because the momentum of the flywheel will allow the motor to be spun longer. Using RUN_USING_ENCODER they might also consider gradually reducing the target velocity instead of immediately setting it to zero.

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