Infinite rotation with circular position control

1

Hi all

Just to give a little background, I am trying to create a camera motion system where a motor pulls a camera dolly along a track:

picture_camera_motion_system
picture_camera_motion_system1919Ɨ1080 186 KB

The motor has a worm gear and thus needs to rotate a lot. The idea is also that I can add more tracks and make the hole system much longer.

Therefore it makes sense to me to control the motor in circular position mode. I read some of the info here and here

I start with the following commands in odrivetool:

calibration

In [6]: odrv0.axis0.requested_state=4

In [7]: odrv0.axis0.requested_state=6

In [8]: odrv0.axis0.requested_state=7

In [9]: odrv0.axis0.requested_state=8

set circular mode

In [10]: odrv0.axis0.controller.config.circular_setpoints = True

First thing I notice now is that pos_estimate and pos_circular are not the same. It would be nice if this was the same because after calibration I would expect the axis to be at zero, but if I now sent a new pos_input of 0 the axis will suddenly start to move. But okay I can work around thisā€¦

In [11]: odrv0.axis0.encoder.pos_estimate
Out[11]: 0.021331787109375

In [12]: odrv0.axis0.encoder.pos_circular
Out[12]: 0.7835273742675781

next I set the range and the input mode I set to input_mode_trap_traj

In [13]: odrv0.axis0.controller.config.circular_setpoint_range=1

In [14]: odrv0.axis0.controller.config.input_mode=5;

Now I try to sent some commands to keep the motor to rotate. I tried to make the input_pos higher. Sending 0.5 and next 1.5 does not create a rotation but I understand that this is normal in position mode.

In [17]: odrv0.axis0.controller.input_pos=0

In [18]: odrv0.axis0.controller.input_pos=0.5

In [19]: odrv0.axis0.controller.input_pos=1.5

In [20]: odrv0.axis0.controller.input_pos=1

Next I tried sending some incremental_move() commands, because I want to have the motor allways moving in the same direction, but the axis just moves back and forwardā€¦


In [23]: odrv0.axis0.controller.move_incremental(0.5,True)

In [24]: odrv0.axis0.controller.move_incremental(0.5,True)

In [25]: odrv0.axis0.controller.move_incremental(0.5,True)

In [26]: odrv0.axis0.controller.move_incremental(0.5,True)

So my question: what do i need to sent to allways have the same rotation in the same direction? Iā€™m a bit confused because I thought the hole idea of the circular pos mode is to keep the rotor spinning with the same amount of steps, and never have a problem with overflow (like the wheels of a robotā€¦). But I dont really understand what I have to sent to the odrive in order to keep the motor spinning in the same directionā€¦

Or does this only work with the step/direction method by sending signals to some GPIO pints?

any help appreciated

1 Like
2

No, i donā€™t think circular position is what you are after. Try using incremental moves with ordinary position mode.

minor note: itā€™s hard to see what you are doing when you use the enum values instead of names :stuck_out_tongue: , e.g. ā€˜8ā€™ instead of AXIS_STATE_CLOSED_LOOP_CONTROL. If you donā€™t want to type it out, you can use the ā€˜tabā€™ key. i.e. AX<tab>C<tab> is five keystrokes.

Really nice camera rig though! :+1: Is that for 3D scanning or what?

3

Yeah ordinary position mode works, already tried that. Just wondering (also for future projects) how this cicrular position mode works to avoid the risk of a position value becoming too bigā€¦

Great tip, I learned something!

Thank you! I still need to work on it though, the movement is a bit jittery, probably due to some stick slip. I will probably get rid of the rope and add the motor on the camera dolly itself (most professional rigs seem to work like this).

Itā€™s funny, almost everyone who sees the rig asks me if it is for 3D scanningā€¦ (perhaps that is a reason by itself to try it at some point.) But my main goal is to make some cool 3d printing time-lapses: while the printer is printing the camera will move very slowly around the print bed.

1 Like
4

Try moving in increments that is smaller than 1/2 of the circular setpoint range. If you move by the same or larger amount, it will associate it with the ā€œother sideā€ of the circle.

2 Likes
5

Just tried to do the same as before, but this time only with 0.3 increments.

In [22]: odrv0.axis0.requested_state=AXIS_STATE_ENCODER_OFFSET_CALIBRATION

In [23]: odrv0.axis0.requested_state=AXIS_STATE_CLOSED_LOOP_CONTROL

In [24]: odrv0.axis0.controller.config.circular_setpoints=True

In [25]: odrv0.axis0.controller.move_incremental(0.3,True)

In [26]: odrv0.axis0.controller.move_incremental(0.3,True)

In [27]: odrv0.axis0.controller.move_incremental(0.3,True)

In [28]: odrv0.axis0.controller.move_incremental(0.3,True)

In [29]: odrv0.axis0.controller.move_incremental(0.3,True)

In [30]: odrv0.axis0.controller.move_incremental(0.3,True)

In [31]: odrv0.axis0.controller.move_incremental(0.3,True)

In [32]: odrv0.axis0.controller.move_incremental(0.3,True)

In [33]: odrv0.axis0.controller.move_incremental(0.3,True)

The behaviour is now something like, 2 times a rotation to the right, one time a rotation to the left, 2 times a rotation to the right, one to the left and so on ā€¦

So still does not work, direction still alternates. I will move again to the simple position control mode, but I donā€™t think this circular control mode works correctly right now (that or I still donā€™t get it)

6

Ok thanks for letting us know, weā€™ll look into it.
EDIT: I think move_incremental is unlikely to be broken, but trap_traj does not support circular position mode.
So either use linear mode, or use position mode without trajectory.

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