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FSESC braking better in FOC than BLDC

Hi,
For some reason my brakes seem to work alot better in FOC than BLDC, at the exact same settings:

65a motor
-55 brakes

20a battery
-6 regen

My parts are:
-Meepo ER battery
-dual 6355 flipsky
-1:2 gearing
-FSESC 6.6+

In FOC, the brakes are very smooth and give a distinct ‘bite’ at high speeds.

In BLDC, the brakes feel like mush at high speeds, and they feel like mush until about 5mph where they suddenly get really strong and almost throw me off the board.

I hate FOC so I really want to get BLDC refined, has anyone experienced anything like this before?

Thanks!

2 Likes

maybe try and play with trotle curves?

1 Like

-6A regen? wat?
Moar

4 Likes

FOC uses all 3 phases simultaneously instead of 2 with BLDC. During acceleration this translates to directly to more torque for the same battery current at the same speed. Logically it makes sense this would extend to braking.

3 Likes

I’ve had exactly the opposite experience lol

4 Likes

I think it depends whether your braking is being limited by the motor current limit setting or the battery current limit setting. I would assume if he gets more braking force with FOC his braking is limited by the battery limit setting not the motor limit setting.

3 Likes

I think in BLDC the motor current is both the peak and the RMS current, but in FOC, the motor current limit is just the peak current— and the RMS current is the peak current per phase divided by sqrt(2). The FOC torque is the RMS motor current per phase * KT * 1.5

2 Likes

I run 80/80/-80/-12.5 on each motor for dual and 80/80/-80/-25 for single, and I feel like I get noticably better torque for acceleration and braking on FOC both single and dual.

2 Likes

Interesting. I got almost exactly the same performance from FOC and BLDC with slightly more torque in BLDC, and brake locking at low speeds on foc

3 Likes

If your acceleration is being limited by the motor current limit setting, I think it’s an interesting coincidence comparing the performance between BLDC and FOC that to get the torque,

with BLDC, it’s:

“Motor Current” * KT = Torque NM

and with FOC it’s:

“Motor Current” / 1.41421… * 1.5 * KT = Torque NM

^which gives ALMOST the same torque for the same “motor current” with BLDC and FOC, but for completely different reasons.

FOC should give more torque for the same battery current at low speeds, while providing lower top speed and less torque close to the motor’s top possible speed according to KV * battery voltage.

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That’s interesting, I wasn’t sure what the math behind it was. I switched back to BLDC after using FOC for a long time because the brake locking at low speed annoyed me so much

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new vesc default firmware, latest unity FW should fix this. if running ackmaniacs fw I have compiled 3.102 with Jeff’s brake fix applied.

low speed foc brakes used to suck but the brake fix makes it butter smooth, let me know if u want the link to Acks with the fix applied.

4 Likes

I honestly love the ability to lock up the brakes. I didn’t seem to notice a difference in braking power between bldc and foc. They both lock up nice

1 Like

It’s -12 total, should I bump it to -8 per side?

Please PM, thank you!

Is this on github?

2 Likes

depends how good you want your brakes, I’d say atleast 20-30A per side. (no you wont kill your battery unless you’re riding down mount everest on full break)

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That’s a lot, I’ve been okay with -12A battery minimum on a single drive, but -12A times two motors is a lot better and even -15A times two

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Yeah, I usually run it high. My motors lock if I pull full break on my carver(= no current flowing to battery) which makes cool skidmarks for the ladies (halp…I’m so lonly).
Just trying to point out that having 12A or 20A wont make or break your battery :woman_shrugging:

2 Likes

Will give this a try, thank you!