How smooth can a motor run at low speed?

1

I just watched a tutotrial on how to control the odrive from as Raspberry Pi. I noticed that the motor doesn’t rum very smooth at low speeds, even though a 8096 steps encoder is used. Why is that the case? Is he using wrong parameters or is it just an inherent limitation of the motor?

I mean this video at this time:

2

It’s both. Cheap motors have high cogging torque. You can compensate for this by using higher position & velocity gains, or by trying out the “anticogging” feature.

3

He is using the original odrive D5065, does this fall into the “cheap motor with high cogging torque” category?

4

Yes. Pretty well all hobby grade brushless motors are like that.

5

I get much better low-speed with the ODrive 3.6 controller in position mode. In Python script:

import math
od=odrive.find_any()

Set position mode:

od.axis0.controller.config.control_mode=3 # postion_control
od.axis0.controller.config.input_mode=5 # trapezoidal InputMode (or input_mode=1)
od.axis0.trap_traj.config.accel_limit=10 # 600 rpm/s (example)
od.axis0.trap_traj.config.decel_limit=10 # 600 rpm/s (example)

Define a “speed function”:

def speed(vel):
dir = math.copysign(1,vel)
vel = min(od.axis0.controller.config.vel_limit, abs(vel))
od.axis0.trap_traj.config.vel_limit = vel
od.axis0.controller.move_incremental(dir*math.inf, False)

Set any speed:

speed(1/60) # one turn per minute (example)
speed(0) # stops the motor

Why this works is a mystery to me. But it does the job. My motor is a Cubemars GL40-KV210 with a factory installed AMS-AS5048A encoder, rated speed=2200 rpm.

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