Motor crunch when braking hard

Your motor makes crunchy/cogging sounds when braking hard? None of us are motor experts so this is not an exact science, but here’s the best practices for getting the best possible motor performance:

  1. Make sure you got good motor detection values from the wizard!
    Correct Motor/FOC settings for LFOCv3 + Hypercore - Q&A - Troubleshooting - pev.dev
    If you don’t get those values, rerun the motor wizard a few more times. Worst case you can enter them by hand.
    Note: I will publish good values for the SuperFlux later, the above is only for the Hypercore!

  2. Make sure you cut your observer gain (FOC-General) in half - you should end up with 0.7-0.9

  3. Make sure your sensorless erpm (FOC-Hall Sensors) is 2000
    there’s also hall sensor interpolation erpm - that should be 200, not 500!

  4. FOC-Advanced: Zero Vector Frequency
    This defaults to 20kHz but many of us get better behavior with higher values, 24kHz works great for me, or even 30kHz seems very good too. I would advise against going too much higher because I’m worried we will starve the balance algorithm of resources because motor logic is updated too often.
    40kHz is confirmed to cause problems, but some are running 35kHz without issues (but I still wouldn’t dare doing that)

Most of you will now get good motor behavior, however some will still experience motor cogging / crunch noise when braking hard.

So here’s another thing you can try - so far it has fixed motor crunching for at least several riders (and no negative side effects reported yet)

  1. Apply the “t-dub adjustment” for Motor Resistance:
    In FOC-General increase “Motor Resistance” from the 85-90mOhms you got from the wizard to something between 100-110. 115 and up may cause negative side effects, so don’t go too high.
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I followed the first set of steps, but got some really strange noises when accelerating after raising the zero vector frequency anywhere above 23, so i brought that back down to 21. Still got the crunch but as soon as i adjusted the current (in second set of steps), the crunch is gone. Thanks dado.

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Raised Motor Resistance from 90 to 105
110 felt somehow mushy
Lowered Motor Inductance from 206 down to 198
Crunsh is gone now and feels great.

(Zerfo Vector Frequency didn’t change anything on the crunsh)

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Setting Motor Resistance to 105 seemed to do the trick!!! Cheers!!

Have you tried messing with the time constant? It affects the motor PIDs and how fast the motor reacts overall. On an EUC I can tweak the balance PIDs slightly higher with a lower time constant, but the motor makes a whining noise lol

Also on the boards I tested, motor crunching happens at a certain current, so you can eliminate it by lowering your current to below that. Once you’ve followed the other advice and gotten your setup to work as well as you can, drop the current down to below where the crunching happens (if it still happens). This will give you a nice and rideable max torque rather than a crunchy power loss nose dive.

Side note but in general I wanna advocate for lower max currents, I think they feel better. By lower I mean 80 or 100.

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The first few steps also helped my lil foc 3.1 with a motor vibration at low speeds. Thanks!

T-dub adjustment was what finally fixed it for me after trying everything else. Had my Little Focer at 18khz zero vector frequency but it got loud and nasty if I strayed from that, so ended up leaving it there.

I actually pursued all this not to cure motor crunch, which wasn’t really bothering me but some weird cutouts at the sensorless transition I was having when riding trails. This happened under a number of circumstances but most prominently when I would be tractoring up a hill under the sensorless transition, would start to crest the hill and speed up, as soon as I would cross the sensorless transition speed I’d get a huge current spike and the board would nose dive, then usually spin wildly for a couple seconds.

Anyways just sharing in case this it will help anyone else.

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@surfdado have you had a good test of the Superflux yet to post your motor detection results? i’m hoping to get mine installed and tested this weekend running a 20s2p 84V set up on the lil foc3.1
thanks

Some thoughts about motor crunch I experienced with my VXwheel 1 (funwheel + CFOC2) after updating to V6 firmware.

After changing many values, I found the motor resistance to be the one that mostly affects the crunch behavior.
Having the motor resistance above 150mΩ would actually create a motor crunch at hard acceleration!
Having the motor resistance under 120mΩ would create strange nosediving/crunching effect at acceleration!
Having the motor resistance somewhere between 120 and 150 would accelerate nicely, but still have some crunch at hard braking.
Since the motor wizard did not work well for this setup, I ended up with the below values by taking surfdado’s values for same setup as a start and changing them a bit to get better results for me.
142,0 mΩ
226,65 µH
159,30 µH
23,814 mWb
0,2267
124,63
0,88
With these values a normal ride works well, while I will still try to find the solution to get the hard braking crunch away for good.

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