V3.6 current_limit_violation

Support
1

I have an odrive v3.6 controlling two motors (T-motor MN1005, Kv = 90, 21 pole pairs) that are coupled so that one provides torque resistance to the other. Think dynamometer-ish, except coupled with spooled fishing line.
Spinning at close to 40 rps, with axis1 at a torque setpoint of 1.4 Nm pulling line off axis0, I keep getting an 0x1000 on axis0.motor.error.

https://docs.odriverobotics.com/v/0.5.4/fibre_types/com_odriverobotics_ODrive.html#ODrive.Motor.Error.CURRENT_LIMIT_VIOLATION

For each axis, motor.config.current_lim = 50, motor.config.current_lim_margin = 20, motor.config.requested_current_range = 75

This is ~350W mechanical on each motor. Supply is 48VDC, 1600W. So it seems like I should be in the current range of 7.3A / motor_efficiency to the driving axis, and getting most of that back from the resisting (velocity controlled) axis.

Alternately, with Kv = 90 → Kt = 8.3/90, so at 1.4Nm I expect 15A as the supply current.

So it doesn’t make sense to me that I’m tripping a current limit at 70A, especially on the dragging motor, which should be generating a bit less than what I’m putting into the pulling motor.

Can anybody set me straight? I appreciate the help. It seems like I might be pushing it on the top speed (600 Hz / 21pp = 28.5 rps), but is this why I am getting the Error.CURRENT_LIMIT_VIOLATION?

2

Maybe you have the gains too high? What control mode and input mode are you using?

3

The motor that is kicking out is in trap_traj position control. The other motor is in torque control.

4

make sure vel limit is higher than trap_traj.vel_limit