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VESC BASED CONTROLLERS - Brakes locking at low speed for larger wheels in FOC - possible Unity Fix


#21

I have a theory that its worse on low KV motors. I run 140kv what all you guys that had problem running?


#22

That would make sense if the full short occurs at a specific eRPM as indicated on 2.xx firmware


#23

149kv with 1:5 gearing on 8" wheels.
Edited my previous post, too


#24

This is just a workaround but doesnt address the actual problem.

Max erpm at full brake is a setting that works great in bldc, the same should be available for foc, imho.

I believe Deodand can do it with feedback from us.


#25

Similar question but is there any setting to hold the position of the board and not “creep” down a slight hill? I have the same issue listed above. 190kv 12s 8” wheels.


#26

at no speed the brakes should feel like their locked in foc with some slippage.

short of a mechanical brake the motor can’t lock the brakes 100%.


#27

Why is this so? They have sensors so shouldn’t they be able to fully lock


#28

the motor magnets aren’t nearly strong enough to have a complete attractive force.


#29

I am gonna keep really close watch on this thread, it is absolutely annoying to be riding slow along next to someone and touch the brakes and jerk.

I have 90mm wheels, 12s, 190kv. Two focboxes, never had an issue in BLDC when I had my Torqueboards controllers, but as soon as I switched, and switched to FOC, I have had the locking issue.

Also sidenote I couldn’t get BLDC to even work on my FOCBOX’s. No idea why, Sensored FOC works perfectly fine.


#30

curious, 90mm wheels shouldn’t be affected.

but, let’s see how this develops.


#31

Could you explain this further?


#32

You can try current with reverse. This is what I do to hold position on a downhill slope- come to a stop as much as possible and engage reverse and hold that slightly to keep held in one position. Don’t know if something similar is possible with current no reverse.


#33

So I’m talking about when you do motor detection. When I had the TB vescs, I only ran them in hybrid BLDC, which worked perfectly. I could run motor detection perfectly fine, and I never tried FOC.

However, as soon as I got the FOCBOX’s I tried to set them up to run BLDC and I could never get motor detection to run and detect the motors. I had nothing on the motors, and even tried looking around, all over the forum and I couldn’t figure out why. Tried increasing amps, etc. So I ended up just doing sensored FOC which detected perfectly fine on both.


#34

That’s weird. I had issues getting them to detect when I had my gear drives and pneumatics attatched but when I ran it with just the motor it worked just fine. I like FOC more anyways but something to try if you really want BLDC


#35

Do you use symmetric settings for motor regen and battery regen. Like -30A and -30A?
Some people use crazy high motor regen values but terrible low battery regen values. Like -80A and -10A. In that case your brakes at speed would be super weak and would get super aggressive when you are slow. Such a setting could lock your wheels if you don’t release the trigger fast enough. Symmetric settings give the most linear braking behavior and guarantee good brakes at speed.


#36

that’s not really true, i use -60/-15 and my brakes are just fine. using -30a battery regen, especially with dual, is insane as your battery is not equipped to handle that much charge current.


#37

I want to shoot a video with telemetry data where we can see what’s happening when the wheels lock up.
I got a hole in my trousers and a bit bloody knee from last week in a skate park, guess why? The wheels locked while braking on a concrete hill :laughing:

No but nothing extreme (see data below)
I have some telemetry data of 3 different motors on my mountainboard.

Interesting is that the batt regen while braking never came close to set limits, in most cases below 50%
So I don’t think it makes any difference when setting higher batt regen values.

The following pics show data of both motos together.


SK8 6374 149kv | 10T/50T gear drive | 200mm wheels
Settings: Motor max 80A | Batt max 50A | Motor regen -40A | Batt regen -15A

SK8_20181015


TRAMPA 6364 136kv | 15T/66T belt drive | 200mm wheels
Settings: Motor max 50A | Batt max 50A | Motor regen -25A | Batt regen -15A

TrampaMotor_20180215


UNIK 6374 150kv (sealed Maytech) | 10T/50T gear drive | 200mm wheels
Settings: Motor max 65A | Batt max 50A | Motor regen -35A | Batt regen -15A


#38

Try symmetric settings and your brakes will be super linear and very controllable. Benjamin Vedder does the same BTW. He knows why. Try -30A -30A or -30A and -25A.
Battery Max Regen defines the brake strength at speed and Motor Max Regen becomes more dominant with lower speeds. The transition between the two values can be very aggressive and uncontrollable when you have non symmetric values. Battery Max Regen will swell down very fast anyway and your battery can handle that short spike for sure.


#39

But as the thread title states it is about locking wheels at low or very low speed. Do you mean the transition is happening at this very low speed?

My brakes at higher speed are fine with -15A batt max regen each motor, I don’t want stronger brakes at speed.

The brakes are fine at lower speed as well so the only way to get it more symmetrical is to lower the motor regen to -20A instead of -40A which is half break strength. But I can test it for science just to know if the wheels lock, too.


#40

Do that, try -20 -20. They will be butter smooth.