PAJohnson
be2d1037e3
Fixed formatting in trapTraj.hpp Fixed how pos_setpoint is set in axis.cpp to avoid transients on startup so that it will handle circular position setpoints More unit corrections in the docs: radians -> turns
5.4 KiB
Parameters & Commands
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)
Table of contents
Per-Axis commands
For the most part, both axes on the ODrive can be controlled independently.
State Machine
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_IDLE. A description of all states can be found here.
Startup Procedure
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 True.
The ODrive will sequence all enabled startup actions selected in the order shown below.
<axis>.config.startup_motor_calibration<axis>.config.startup_encoder_index_search<axis>.config.startup_encoder_offset_calibration<axis>.config.startup_closed_loop_control<axis>.config.startup_sensorless_control
See here for a description of each state.
Control Mode
The default control mode is position control.
If you want a different mode, you can change <axis>.controller.config.control_mode.
Possible values are listed here.
Input Mode
As of version v0.5.0, ODrive now intercepts the incoming commands and can apply filters to them. The old protocol values pos_setpoint, vel_setpoint, and current_setpoint are still used internally by the closed-loop cascade control, but the user cannot write to them directly. This allows us to condense the number of ways the ODrive accepts motion commands. The new commands are:
<axis>.controller.input_pos = <turn><axis>.controller.input_vel = <turn/s><axis>.controller.input_torque = <torque in Nm>
Modes can be selected by changing <axis>.controller.config.input_mode.
The default input mode is INPUT_MODE_PASSTHROUGH.
Possible values are listed here.
System monitoring commands
Encoder position and velocity
- View encoder position with
<axis>.encoder.pos_estimate[turns] or<axis>.encoder.pos_est_counts[counts] - View rotational velocity with
<axis>.encoder.vel_estimate[turn/s] or<axis>.encoder.vel_est_counts[count/s]
Motor current and torque estimation
- View the commanded motor current with
<axis>.motor.current_control.Iq_setpoint[A] - View the measured motor current with
<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 approaching the maximum achievable rotational velocity of your motor for a given supply voltage, 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.
General system commands
Saving the configuration
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 also reboots the device.
Diagnostics
<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_major,<odrv>.fw_version_minor,<odrv>.fw_version_revision: The firmware version that is currently running.<odrv>.hw_version_major,<odrv>.hw_version_minor,<odrv>.hw_version_revision: The hardware version of your ODrive.
Setting up sensorless
The ODrive can run without encoder/hall feedback, but there is a minimum speed, usually around a few hunderd RPM.
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 input_vel to 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.input_vel = 400
odrv0.axis0.motor.config.direction = 1
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