EDIT: Found issue, see post after photos.
Thanks for your suggestions.
I think I have now proved that the issue is my 48V PSU but I am confused as to why.
I have 2 different models and the issue happens with both but they are both Meanwell so I guess the insides are very similar.
I don’t have a 48V battery but do have 2x 12V AGM, series output 25V.
Using those to power oDrive (with 0V connected to Jetson 0V, which is still powered from mains) then the issue disappeared.
I was not happy that this definitely proved it with only being 25V. I happened to have a very cheap and noisy 70W boost PSU. It’s output is quite rough, at 48V out (and powered from batteries) it has 6v pk-pk ripple at 6Hz.
Despite this noise, the issue was not present.
I just checked the ripple frequency on the problematic 48V PSU and I had remembered it wrong. Is actually only @ 100Hz, 100mV and it stays the same when I enter AXIS_STATE_CLOSED_LOOP_CONTROL.
So now I am confused how this can be the issue - if this noise is constant (and not as bad as the cheap PSU) then why is the USB stable in IDLE but not when holding position?
I thought the purpose of the resistor on the AUX pins was to dump power there, instead of into the power supply?
I am using the supplied 50W 2Ohm resistor. Is this suffice for using the oDrive with a 440W and eventually a 500W motor simultaneously? From my initial tests I will not be using even 300W total most of the time.
Answers to other questions:
I tried different USB cables, one was shielded, no difference.
Am pretty sure the oDrive is not rebooting in this process. I only say this because if it reboots then it reverts back to IDLE and in that state the USB behaves. I have had to cut the power to oDrive between each test to force it back into IDLE ready for the next test.
Also swapped out the oDrive for another (again) - just as sanity check but issue persists.