I have the same issue on my thread, so far no solution i can see. My guess is that it’s using the battery regen braking current even at non regen speeds. I haven’t tried it, but i think raising battery regen would help with braking, but, obviously, put the cells at risk.
The reason i think this is because on 2.18 when i hit regen speeds, the braking felt similar to how it feels most of the time in 3.28
I had the r is 0 bug on my chaka vesc. I fixed it by running detection in bldc then running it on FOC again. No need to change control mode or even write any settings, just do the detection
I have FOC box’s and VESC X’s. Ive tried 3.26 and a both without issue. Also tried it on a TB VESC at 10S with FOC and lost a DRV.
I’m gonna raise the regen from -40A to -50A hope it helps a little with braking force at high speeds, it’s impossible to ride this way I feel pretty unsafe, I’ll also reduce the battery min from -10A to -8A as braking force at low speeds is too agressive
I think you got that backwards. I’m saying your braking at high speeds is weak because it’s using your battery regen current, so raise that and it should respond better. That’s my theory anyway.
I’ll do that later today, have you got the bluetooth module working on the new firmware in order to modify settings?
That’s correct! Battery regen is the value that will adjust your braking performance, as long as motor regen isn’t lower than battery regen. -30A is about right to get a good performance. You can set both values (motor/battery) same. Brakes get harder the slower you get. That’s the same as you experience in your car - same braking force against less kinetic energy.
Frank
Thanks for the confirmation Frank. Could you elaborate on why there is such a dramatic change in braking performance from 2.18 to 3.28? with dual VESCs and -8a battery regen on each VESC and -70A motor min, I had great braking response when below regen speeds.
What do you mean by “below regen speed”. You will always push currents towards the battery. You brake, you generate. Are you comparing BLDC 2.18 vs FOC 3.28?
Frank
You can’t regen while braking if the generated voltage by the generator (motor) is lower than the battery’s voltage. This should mean that you have to be going full speed or faster in order to regen brake.
This is at least my understanding from reading up on regenerative braking.
If you push current toward’s a system with higher voltage, it should just be dissipated as heat anyway
Source: Understanding Regeneration
A motor behaves as motor and as generator at the same time. In fact while a motor is ‘motoring’, that is doing mechanical work, it generates CEMF acting as generator, although the CEMF is lower than the battery voltage so the motor acts as a load and absorbs current.
In certain situations the CEMF may overcome the battery, in which case the generator component becomes dominant; the motor acts as a generator inverting the direction of its current and forcing it into the battery.
Bit that is at really low speeds only.
Frank
why would it be at low speeds? If you have a 40v battery, you need BEMF/CEMF to generate over 40v for it to charge the battery. The only way it generates that much voltage is for it to be traveling faster than full throttle speed.
I am afraid you are not entirely right. You can see the VESC as a synchronous multi quadrant power supply, it can step down the voltage (from a high battery voltage to a lower motor voltage, normal use) AND can boost the voltage (from the lower voltage motor to the higher voltage battery, regenerative braking).
So when the VESC reads negative motor / battery currents it does regeneratively brakes and charges the battery.
thanks for your input! I’ve been trying to find articles online about this and couldn’t source any good information besides the one I posted.
If this is the case, wouldn’t this bode even worse for f/w3.28? It means at any given speed a battery min value of -40 has the potential to inject 40 amps of charging current to the battery.
Sorry, I havent keep track of your issue, I just replied on the regenerative part 
.
Right, that’s why an adjustable battery min value exists. As I explained, you max braking performances is dependent on your battery. This is why you go for 3P+ setups and strong cells. A high discharge rated cell usually also performs better at charging. The dilemma of small packs at low voltage is capability to push/swallow Amps. Electric cars run on much higher voltage and have a bigger battery to cope with that. In consequence you can use lower discharge rated cells. Scaling things down to skate size is a challenge and you want to use the best cells possible. Long downhill/uphill sessions may be problematic, especially with low parallel cell count. You could strap an oven plate to your board and fry eggs while doing extended downhill sessions.
Frank
I get the relationship between regen current and cells. My question is two fold.
How is a recommended charge current of 40 amps for a 3P setup okay, if each cell has a rated max charge current of 4 amps. This is 13 amps per cell at the highest regen!
Why has the behavior changed from 2.18 and the brakes are now weaker at the same value. Was 2.18 just better in this sense and 3.28 just a downgrade?
Has nothing to do with the version of the software. Conservation of energy again… No software can dissipate energy into the universe.
Your cells can cope with higher amps, as long as its not a continuous flow for a long period. The longer you abuse them the shorter the life cycle. I rather have a strong brake than super healthy cells. Brakes are safety, healthy cells a bonus.
If you face very long 40A hills, better upgrade your pack to 6-8P. But: Full is Full and that’s the point where you should go up the hill again.
Frank
I think you’re missing my question again. You can have strong brakes at speed AND healthy cells on 2.18 as the braking was great with motor min -60 and battery min -8. On 3.28 it’s weak 80% of the time, and it’s only strong when you’re going jogging speed.
Found the problem. Benjamin uses the basic of watt control also for braking. That means when he identifies that with the actual duty cycle the full motor brake amps (motor min) can’t be reached he reduces the maximum brake current at the motor.
- 70A motor min
- 8A batter min
- 50% duty cylce
A maximum of only -16A is allowed (8A battery min / 0,50 duty cycle)
So for example at 75% brake you can only reach -12A at the motor.
Once it reaches lower duty cycle the brake power increases. That explains a lot and is the root cause for the strange braking behavior.
This results in a non linear braking which really isn’t a good idea. So only chance to have a good brake behavior is to set the battery min ridiculous high which is a bad idea as well.