ODrive/docs/anticogging.md

Anti-cogging

ODrive supports an anti-cogging algorithm that attempts to compensate for the rather high cogging torques seen in hobby motors.

<odrv>.<axis>.controller.config.anticogging is a configuration structure that contains the following items:

Name	Type	Use
index	uint32	The current position being used for calibration
pre_calibrated	bool	If true and using index or absolute encoder, load anticogging map from NVM at startup
calib_anticogging	bool	True when calibration is ongoing
calib_pos_threshold	float32	(pos_estimate - index) must be < this value to calibrate. Larger values speed up calibration but hurt accuracy
calib_vel_threshold	float32	(vel_estimate) must be < this value to calibrate. Larger values speed up calibration but hurt accuracy.
cogging_ratio	float32	Deprecated
anticogging_enabled	bool	Enable or disable anticogging. A valid anticogging map can be ignored by setting this to false

Calibration

To calibrate anticogging, first make sure you can adequately control the motor. It should respond to position commands.

Start by putting the axis in AXIS_STATE_CLOSED_LOOP_CONTROL with CONTROL_MODE_POSITION_CONTROL and INPUT_MODE_PASSTHROUGH. Make sure you have good control of the motor in this state (it responds to position commands). Now, tune the motor to be very stiff - high pos_gain and relatively high vel_integrator_gain. This will help in calibration.

Run controller.start_anticogging_calibration(). The motor will start turning slowly, calibrating each point. If you like, you can start a liveplotter session before running this command so that you can watch the position move.

Once it's complete (it should take about 1 minute), the motor will return to 0 and the value controller.anticogging_valid should report True. If controller.config.anticogging.anticogging_enabled == True, anticogging will now be running on this axis.

Saving to NVM

As of v0.5.1, the anticogging map is saved to NVM after calibrating and calling odrv0.save_configuration()

The anticogging map can be reloaded automatically at startup by setting controller.config.anticogging.pre_calibrated = True and saving the configuration. However, this map is only valid and will only be loaded for absolute encoders, or encoders with index pins after the index search.

Example

odrv0.axis0.encoder.config.use_index = True
odrv0.axis0.requested_state = AXIS_STATE_FULL_CALIBRATION_SEQUENCE
odrv0.axis0.encoder.config.pre_calibrated = True
odrv0.axis0.motor.config.pre_calibrated = True

odrv0.axis0.controller.config.control_mode = CONTROL_MODE_POSITION_CONTROL
odrv0.axis0.controller.config.input_mode = INPUT_MODE_PASSTHROUGH
odrv0.axis0.requested_state = AXIS_STATE_CLOSED_LOOP_CONTROL

odrv0.axis0.controller.start_anticogging_calibration()

# Wait until controller.config.anticogging.calib_anticogging == False

odrv0.axis0.controller.config.anticogging.pre_calibrated = True

odrv0.save_configuration()
odrv0.reboot()