closed-loop torque (current) wheel control for mecanum

[Ether]

Has anyone tried using closed-loop torque (current) control for a mecanum or holonomic bot, instead of closed-loop speed or voltage control?


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[eugenebrooks]

We used closed loop current control last year to prevent wheel slip, as we did not design in wheel counters and a "free wheel" with a wheel counter from the start. You had to use the Jaguars for this, the Victor pulse rate is too slow to get a reliable average current measurement.

Eugene

[Ether]

We used closed loop current control last year to prevent wheel slip

I'm not sure I understand how closed-loop current control prevents the wheels from slipping. Could you elaborate a bit?


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[eugenebrooks]

The torque is proportional to the current, limit the torque to just below the torque that causes wheel slip, and your wheels never break traction. It was a good patch given the lack of wheel counters (including a free wheel) in that it only required current sensors and some software.

There are rubs:
As the speed of the robot runs up, some of the torque (measured current) is tied up in drive train friction and because of this you lose a portion of the torque that you would like applied to the wheels.
The best performance is obtained with just a little slip and you can best obtain this by using wheel counters (including a free wheel with a counter).

Eugene