Custom motor/encoder setup custom calibration?

Support
1

Hi!

Apologies if this has been answered, I searched and found some similar questions but haven’t quite figured it out.

I built a custom motor connected to an optical encoder elsewhere (picture a robot joint with the encoder moving at a different rate from the motor). It doesn’t work like the typical brushless motor config (i.e. one rotation does not equate to a full rotation on the encoder with x pulses, in this setup it can’t physically do a full rotation etc…) and so I believe it requires a different type of calibration method than the out of the box setup: odrv0.axis1.requested_state = AXIS_STATE_FULL_CALIBRATION_SEQUENCE

As you might expect, calling: dump_errors(odrv0) after a stock calibration sequence results in:
axis: Error(s):
AXIS_ERROR_ENCODER_FAILED
…
Error(s):
ENCODER_ERROR_CPR_POLEPAIRS_MISMATCH

So my question is really this: If I know the shadow tick counts after manually moving the encoder to the end limits print(odrv0.axis1.encoder.shadow_count), can I somehow feed this information back in as a configuration in place of the stock calibration?

What other parameters would need to be manually set to make that work?

Am I thinking about this the wrong way?

Any help is appreciated.

2

Should be fine so long as you factor the gear ratio into the CPR config
So if your gearing is 3:1 for a 4000cpr encoder, you should set the ODrive for 12000cpr.
But make sure you DON’t use the index, because obviously that won’t work - you will have to do offset calibration on each boot.

3

Un-shelving this project and revisiting. Thanks for the reply @towen . Do you know by chance how to calibrate with end stops in place? I can remove load on the motor for calibration but not the hard stops which would otherwise allow for free movement. Thanks!

4

It depends on the gear ratio i.e. how much movement of the motor do you have between the hardstops?
You can try setting encoder.config.calib_scan_distance to a lower value, but you would lose some precision in the encoder calibration.