We will use the
<odrv> as a placeholder for any ODrive object. Every ODrive controller is an ODrive object. In
odrivetool this is usually
odrv0. Furthermore we use
<axis> as a placeholder for any axis, which is an attribute of an ODrive object (for example
odrv0.axis0). An axis represents where the motors are connected. (axis0 for M0 or axis1 for M1)
For the most part, both axes on the ODrive can be controlled independently.
The current state of an axis is indicated by
<axis>.current_state. The user can request a new state by assigning a new value to
<axis>.requested_state. The default state after startup is
AXIS_STATE_IDLEDisable motor PWM and do nothing.
AXIS_STATE_STARTUP_SEQUENCERun the startup procedure.
AXIS_STATE_FULL_CALIBRATION_SEQUENCERun motor calibration and then encoder offset calibration (or encoder index search if
AXIS_STATE_MOTOR_CALIBRATIONMeasure phase resistance and phase inductance of the motor.
Trueand save the configuration. After that you don’t have to run the motor calibration on the next start up.
AXIS_STATE_SENSORLESS_CONTROLRun sensorless control.
AXIS_STATE_ENCODER_INDEX_SEARCHTurn the motor in one direction until the encoder index is traversed. This state can only be entered if
AXIS_STATE_ENCODER_OFFSET_CALIBRATIONTurn the motor in one direction for a few seconds and then back to measure the offset between the encoder position and the electrical phase.
<axis>.encoder.is_readygo to true.
AXIS_STATE_CLOSED_LOOP_CONTROLRun closed loop control.
<axis>.motor.is_calibrated) and the encoder is ready (
By default the ODrive takes no action at startup and goes to idle immediately.
In order to change what startup procedures are used, set the startup procedures you want to
The ODrive will sequence all enabled startup actions selected in the order shown below.
See state machine for a description of each state.
The default control mode is position control.
If you want a different mode, you can change
Possible values are:
CTRL_MODE_VOLTAGE_CONTROL- this one is not normally used.
<axis>.controller.pos_setpoint = <encoder_counts>
<axis>.controller.current_setpoint = <current_in_A>
<axis>.controller.vel_setpoint = <encoder_counts/s>
The motion control gains are currently manually tuned:
<axis>.controller.config.pos_gain = 20.0[(counts/s) / counts]
<axis>.controller.config.vel_gain = 5.0 / 10000.0[A/(counts/s)]
<axis>.controller.config.vel_integrator_gain = 10.0 / 10000.0[A/((counts/s) * s)]
An upcoming feature will enable automatic tuning. Until then, here is a rough tuning procedure:
vel_gainby around 30% per iteration until the motor exhibits some vibration.
vel_gainto 50% of the vibrating value.
pos_gainby around 30% per iteration until you see some overshoot.
pos_gainuntil you do not have overshoot anymore.
0.5 * bandwidth * vel_gain, where
bandwidthis the overall resulting tracking bandwidth of your system. Say your tuning made it track commands with a settling time of 100ms: this means the bandwidth was 1/100ms or 10. In this case you should set the
vel_integrator_gain = 0.5 * 10 * vel_gain.
<axis>.motor.current_control.Iq_measured[A]. If you find that this returns noisy data then use the command motor current instead. The two values should be close so long as you are not approching the maximim achieveable rotational velocity of your motor for a given supply votlage, in which case the commanded current may become larger than the measured current.
Using the motor current and the known KV of your motor you can estimate the motors torque using the following relationship: Torque [N.m] = 8.27 * Current [A] / KV.
All variables that are part of a
[...].config object can be saved to non-volatile memory on the ODrive so they persist after you remove power. The relevant commands are:
<odrv>.save_configuration(): Stores the configuration to persistent memory on the ODrive.
<odrv>.erase_configuration(): Resets the configuration variables to their factory defaults. This only has an effect after a reboot. A side effect of this command is that motor control stops (in case it was running) and the USB communication breaks out temporarily. This is because erasing flash pages hangs the microcontroller for several seconds.
<odrv>.serial_number: A number that uniquely identifies your device. When printed in upper case hexadecimal (
hex(<odrv>.serial_number).upper()), this is identical to the serial number indicated by the USB descriptor.
<odrv>.fw_version_revision: The firmware version that is currently running.
<odrv>.hw_version_revision: The hardware version of your ODrive.
The ODrive can run without encoder/hall feedback, but there is a minimum speed, usually around a few hunderd RPM.
However the units of this mode is different from when using an encoder. Velocities are not measured in counts/s, instead it is electrical rad/s. This also applies to the gains. For example,
vel_gain is in units of
A / (rad/s) instead of
A / (count/s).
To give an example, suppose you have a motor with 7 pole pairs, and you want to spin it at 3000 RPM. Then you would set the
3000 * 2*pi/60 * 7 = 2199 rad/s electrical.
Below are some suggested starting parameters that you can use. Note that you must set the
pm_flux_linkage correctly for sensorless mode to work.
odrv0.axis0.controller.config.vel_gain = 0.01 odrv0.axis0.controller.config.vel_integrator_gain = 0.05 odrv0.axis0.controller.config.control_mode = 2 odrv0.axis0.controller.vel_setpoint = 400 odrv0.axis0.sensorless_estimator.config.pm_flux_linkage = 5.51328895422 / (<pole pairs> * <motor kv>)
To start the motor:
<axis>.requested_state = AXIS_STATE_SENSORLESS_CONTROL