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Battlebot Weapon : Trouble spinning up

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Joined: 2018-06-03 05:47
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Battlebot Weapon : Trouble spinning up

This is well outside the typical skateboard question.  I've used VESCs of varying flavors successfully for various combat robots in the past.  However, with our 250 pound robot, we're continuing to have spin up issues for the weapon. This is a large 80mm sensorless motor, spinning about 60 pounds of steel in BLDC mode, using PPM/Duty Cycle No Reverse.  We get cogging at startup, and if we really feather the throttle, we can get it to spin up most of the time, but it's still very spotty.

The typical settings that help with large inertial loads that I've used in the past don't seem to be working as well in this case.  I'm used to playing around with Minimum ERPM and BEMF Coupling settings.  In this case, I'm using Min ERPM = 100, and BEMF Coupling = 2000.  Are there other settings that I should be looking at that may help?  Would FOC mode work better for inertial loads like this?

I don't want to use "Current" control type, as it's not well suited for this application.  PID Speed control also fails to spin up the weapon, we couldn't get that to work after playing around with it a bit, although I've used it successfully in other cases.

Another oddity that I've noticed in newer VESC firmwares:  If using PPM/Duty Cycle app mode, if I try to disable braking by setting the Motor Current Max Brake and Battery Current Max Regen to 0, the motor will not actually turn off as expected most of the time.  I've tried small non-zero values here too, but experience the same problem.

Here's some example video of the problem, along with a successful spinup.


Any ideas?