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 in . It should respond to position commands.

Start by putting the axis in AXIS_STATE_CLOSED_LOOP 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()