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document different control modes

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Oskar Weigl
2018-11-28 22:44:58 -08:00
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@@ -16,6 +16,7 @@ permalink: /
- [Start `odrivetool`](#start-odrivetool)
- [Configure M0](#configure-m0)
- [Position control of M0](#position-control-of-m0)
- [Other control modes](#other-control-modes)
- [What's next?](#whats-next)
<!-- /TOC -->
@@ -165,7 +166,7 @@ For instance, to set the current limit of M0 to 10A you would type: `odrv0.axis0
**Current limit**<br>
`odrv0.axis0.motor.config.current_lim` [A].
The default current limit, for safety reasons, is set to 10A. This is quite weak, but good for making sure the drive is stable. Once you have tuned the oDrive, you can increase this to 75A to increase performance. Note that above 75A, you must change the current amplifier gains. You do this by requesting a different current range. i.e. for 90A on M0: `odrv0.axis0.motor.config.requested_current_range = 90` [A], then save the configuration and reboot as the gains are written out to the DRV (MOSFET driver) only during startup.
The default current limit, for safety reasons, is set to 10A. This is quite weak, but good for making sure the drive is stable. Once you have tuned the oDrive, you can increase this to 60A to increase performance. Note that above 60A, you must change the current amplifier gains. You do this by requesting a different current range. i.e. for 90A on M0: `odrv0.axis0.motor.config.requested_current_range = 90` [A], then save the configuration and reboot as the gains are written out to the DRV (MOSFET driver) only during startup.
*Note: The motor current and the current drawn from the power supply is not the same in general. You should not look at the power supply current to see what is going on with the motor current.*
<details><summary markdown="span">Ok, so tell me how it actually works then...</summary><div markdown="block">
@@ -241,16 +242,73 @@ Let's get motor 0 up and running. The procedure for motor 1 is exactly the same,
2. Type `odrv0.axis0.requested_state = AXIS_STATE_CLOSED_LOOP_CONTROL` <kbd>Enter</kbd>. From now on the ODrive will try to hold the motor's position. If you try to turn it by hand, it will fight you gently. That is unless you bump up `odrv0.axis0.motor.config.current_lim`, in which case it will fight you more fiercely.
3. Send the motor a new position setpoint. `odrv0.axis0.controller.pos_setpoint = 10000` <kbd>Enter</kbd>. The units are in encoder counts.
### Other control modes
The ODrive also supports velocity control and current (torque) control.
## Other control modes
The default control mode is unfiltered position control in the absolute encoder reference frame. You may wish to use a controlled trajectory instead. Or you may wish to control position in a circular frame to allow continous rotation forever without growing the numeric value of the setpoint too large.
You may also wish to control velocity (directly or with a ramping filter).
You can also directly control the current of the motor, which is proportional to torque.
**Velocity control**<br>
Set `odrv0.axis0.controller.config.control_mode = CTRL_MODE_VELOCITY_CONTROL`.
You can now control the velocity with `odrv0.axis0.controller.vel_setpoint = 5000` [count/s].
- [Trajectory control](#trajectory-control)
- [Circular position control](#circular-position-control)
- [Velocity control](#velocity-control)
- [Ramped velocity control](#ramped-velocity-control)
- [Current control](#current-control)
**Current control**<br>
Set `odrv0.axis0.controller.config.control_mode = CTRL_MODE_CURRENT_CONTROL`.
You can now control the current with `odrv0.axis0.controller.current_setpoint = 3` [A].
### Trajectory control
This mode lets you smoothly accelerate, coast, and decelerate the axis from one position to another. With raw position control, the controller simply tries to go to the setpoint as quickly as possible. Using a trajectory lets you tune the feedback gains more aggressively to reject disturbance, while keeping smooth motion.
![Taptraj](TrapTrajPosVel.PNG)<br>
In the above image blue is position and orange is velocity.
#### Parameters
```
<odrv>.<axis>.trap_traj.config.vel_limit = <Float>
<odrv>.<axis>.trap_traj.config.accel_limit = <Float>
<odrv>.<axis>.trap_traj.config.decel_limit = <Float>
<odrv>.<axis>.trap_traj.config.A_per_css = <Float>
```
`vel_limit` is the maximum planned trajectory speed. This sets your coasting speed.<br>
`accel_limit` is the maximum acceleration in counts / sec^2<br>
`decel_limit` is the maximum deceleration in counts / sec^2<br>
`A_per_css` is a value which correlates acceleration (in counts / sec^2) and motor current. It is 0 by default. It is optional, but can improve response of your system if correctly tuned. Keep in mind this will need to change with the load / mass of your system.
All values should be strictly positive (>= 0).
Keep in mind that you must still set your safety limits as before. I recommend you set these a little higher ( > 10%) than the planner values, to give the controller enough control authority.
```
<odrv>.<axis>.motor.config.current_lim = <Float>
<odrv>.<axis>.controller.config.vel_limit = <Float>
```
#### Usage
Use the `move_to_pos` function to move to an absolute position:
```
<odrv>.<axis>.controller.move_to_pos(<Float>)
```
### Circular position control
This mode is useful for continuos incremental position movement. For example a robot rolling indefinitely, or an extruder motor or conveyor belt moving with controlled increments indefinitely.
In the regular position mode, the `pos_setpoint` would grow to a very large value and would lose precision due to floating point rounding.
In this mode, the controller will try to track the position within only one turn of the motor. Specifically, `pos_setpoint` is expected in the range `[0, cpr-1]`, where `cpr` is the number of encoder counts in one revolution. If the `pos_setpoint` is incremented to outside this range (say via step/dir input), it is automatically wrapped around into the correct value.
Note that in this mode `encoder.pos_cpr` is used for feedback in stead of `encoder.pos_estimate`.
If you try to increment the axis with a large step in one go that exceeds `cpr/2` steps, the motor will go to the same angle around the wrong way. This is also the case if there is a large disturbance. If you have an application where you would like to handle larger steps, you can use a virtual CPR that is an integer times larger than your encoder's actual CPR. Set `encoder.config.cpr = N * your_enc_cpr`, where N is some integer. Choose N to give you an appropriate circular space for your application.
### Velocity control
Set `axis.controller.config.control_mode = CTRL_MODE_VELOCITY_CONTROL`.<br>
You can now control the velocity with `axis.controller.vel_setpoint = 5000` [count/s].
### Ramped velocity control
Set `axis.controller.config.control_mode = CTRL_MODE_VELOCITY_CONTROL`.<br>
Set the velocity ramp rate (acceleration): `axis.controller.config.vel_ramp_rate = 2000` [counts/s^2]<br>
Activate the ramped velocity mode: `axis.controller.vel_ramp_enable = True`.<br>
You can now control the velocity with `axis.controller.vel_ramp_target = 5000` [count/s].
### Current control
Set `axis.controller.config.control_mode = CTRL_MODE_CURRENT_CONTROL`.<br>
You can now control the current with `axis.controller.current_setpoint = 3` [A].
*Note: There is no velocity limiting in current control mode. Make sure that you don't overrev the motor, or exceed the max speed for your encoder.*