TL;DR Over current faults might be causing your motor to short. Check your motor for shorts by moving the phase wires around in different positions before riding (see video below)
Most of you have heard of my recent FOC failure and crash at 30mph~. This crash left me with a ER visit and minor concussion as well as another $260 bill for a new TSG Pass.
Initially, I believed this to be a failure in FOC made (and possibly DRV failure). However my findings today made me second guess that analysis.
Some background When I initially setup foc, I was getting overcurrent faults left and right ending up with 300~ amp current and 140~ filtered on each VESC. This happened a bunch as I was testing on the bench and while riding. I setup higher limts, and eventually found a solution via doubling the observer gain in FOC. While most of the faults in testing were over current faults, one of them did pop up as drv8302 error. This led me to believe the DRV completely failed recently due to my testing.
New findings Today one of my motors completely seized and died while riding in BLDC mode. The seizing occured at a similar time as when it would error in FOC, which was when I throttled up from any given point too fast. I was sure the DRV was toast at this point. Now, the motor doesn’t spin right when throttling and only cogs
However, when I got home and tested throttling, I only got over current errors and not DRV8302 error. I thought this was weird since I was sure it was a dead DRV chip. I then tested detection and, as expected, the detection failed. However, when I tested it on my other motor (same vesc) it ran fine! This led me to investigate if it was a short within the VESC itself. However, when I disconnected the motor completely, I noticed the motor still span like there was a short.
Motor shorts At this point I concluded there was definitely a minor motor short (not complete short like touching 2 phase wires together). Shockingly, I found that this was present on both motors if the wires were in a certain position.
I don’t know how to take the stator off the baseplate to investigate more closely, but I might’ve noticed some strands of copper that were broken. This is possibly causing the short. See the video below as evidence of the short in certain positions.
Questioned unanswered
Assuming the overcurrent faults caused some copper strands to break leading to motor shorts, why did the problem only really prevent itself when throttling quickly from any given point?
- My overcurrent failures were a result of throttling too quickly, which was remedied by doubling my observer gain
- After the OC fix, the motor would perma short until restart every so often when throttle to maximum speed
- My crash was caused by the short at maximum speed, after which I tested the throttle and motors responded normally.
- My motor shorted again in BLDC mode (previous notes were all FOC) when throttling from mid to high speed quickly
Now I’m still not 100% what may have caused the short, but I believe it’s likely either a manufacturing quality issue or a consequence of my over current faults. It’s also possible the shorted wires were causing the over current faults in the first place, but unsure why doubling the observer gain would resolve the issue in that case.
