Motor induced wobble at high speeds

While riding my board at 40 ish km/h if I go full throttle (getting close to 50 km/h) I start getting some weird wobbles on the back trucks. First I thought it had to do something with the bushings but I did some more testing and it feels like one of the wheels either speeds up or stops for a brief moment and this starts the wobbles.
I’ve found some leads about this this that might help me : duty cycle current limit start / TC off.
I have a V1 Xenith and don’t know what FW should I use on it. Any advice?

This happened to me in the past and rather than checking my system I crashed at full speed.

For me, there turned out to be a very bad P group in my pack, which would struggle to put out amps… At full speed the battery amp draw could max out and cause a sudden dip in voltage deep enough to hit cutoff for a second, and immediately jump back up. Even if it wasn’t reaching the cutoff, the voltage would dip low enough to not be able to spin the motors at their speed, thus cutting out the torque, and then piling it all back on.

TL;DR check your p group voltages

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Thanks for the reply. BMS shows everything to be OK, all P groups are balanced with a max delta of 30mV of each other. I checked the ride recording and the board was pulling up to 60Ams sometimes (hills or full stop > full throttle) and this didn’t occurred.

Run your board on the bench and test it full throttle , it could be DCCL that needs to be 85% … I had this happen on my unity and setting DCCL to 85% stopped it. But could be your firmware or solder joints… just had a similar thing happen 1st time was firmware but then strange thing at full speed and it was a solder joint on a phase wire. Good luck the answers are all here if you look enough :slight_smile:

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Full throttle on bench is all good, I guess there is no stress in the system with no rider.

Go into vesc tool and check your DCCL remember to do both sides of your vesc

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FW 5.2 and setting duty cycle current limit start to 85% or less (on both sides of the ESC) is a safe bet, and might fix the issue you’re having.

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Could it be motor temperature limits being hit?

I had higher motor/vesc temperatures on my ride and had no faults recorded. I know the spots where I got the wobbles and checked with the logs, the temps were lower than some other parts of my rides, eg hills.

I will give FW 5.2 a shot these days.

Any chance you’re running a Flipsky A/S?

Xenith v1 + bioboards 6374

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You could also directly go to FW5.3, so far works really well on Xenith.

Update: duty cycle current is not the culprit, I did more testing and found out that this wobble occured when motors get hot (70+ Celsius). Throttle limit for temp is at 80 but one of the motor acts up when hitting that temperature.
I want to try BLDC mode but vesc app ios won’t let me change from FOC, will try it on PC

It looks you were right, shouldn’t be both motors limited at the same time tho?

Nein - each motor can hit its own limit independently I think.
Not sure though, happy for someone else to weigh in on this.

Temperature cutout can start from one motor at a time but shouldn’t both motors get throttled so jitter would be avoided? On the steepest hill I get 90C on each motor, are these temps acceptable?

what are you checking motor temps with? do you have something recording telemetry so you can zoom in and look for noise. ( rapid jumps in readings)

motor temperature sensor noise, can cause this.

usually it causes faults, but not always, sometimes it just jumps into the temp throttling zone, and back out. sometimes it jumps far enough to trigger a fault.

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I am using stormcore app but it’s not good at checking for spikes. Mettr is not detecting my Xenith, ios and android.
I will record tomorrow on Yours Truly app.
From my testing the wobbles occur when hitting the throttle limit, I set it to 70C and it occured, then at 90C and same results. I don’t think it’s interference, I am pushing the motors really hard to find what’s causing them, huge hills and 35C weather gets me 90C motor temp. No faults were shown on Stormocore app.
I am running FW 5.2 on Xenith V1 with dual bioboards motors 6374 on gear drives.

I will be testing traction control ON to see if it helps.

I wouldn’t throw that variable into the mix.
it won’t cover up an issue well. and it’s not a real fix.
it has it’s own tunings (erpm difference) to get used to.