High speed issues with bike hub motor

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imval
Posts: 12
Joined: 02 Sep 2016, 13:07
Location: Rouen, France
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High speed issues with bike hub motor

Postby imval » 02 Sep 2016, 13:39

Hello all :)

I have a ebike project actually running pretty well based on Arduinoes and Vesc. Here are the technical details :

Homemade VESC with short wires and two caps on the power lines
Arduino driving the VESC by serial commands from the throttle and stuffs
13S Lithium Ion 17Ah battery with BMS protection.
1500W noname chinese hub motor from an Aliexpress supplier mounted on a 26 inches rim
Like this one :

Actually it is running pretty well, I know that 13S is not recommended, and I am not using regenerative braking for this reason (Avoiding magical fireworks and surprise smoke in my battery/vesc box)

The only issue I have is when I am running at aproximately 50km/h i start feeling small "hiccups" in the thrust from the motor and if I maintain it it will go into error "ABS_OVER_CURRENT".
I configured my Max Motor Current to 90A, Max battery current to 50A and Absolute current to 130A.
I am driving the VESC in Current mode and I am not asking for more that 40Amps on the command so I don't understand why I'm getting this kind of error.

Could it be because my caps are too weaks ? Or a configuration is not correct ?

You can find detailed configuration screenshot and faults on terminal at this link :
https://drive.google.com/open?id=0B7k-d ... W9SM21RMGc

Thanks for your help !
And thanks to Benjamin for his amazing work ! :D

pf26
Posts: 310
Joined: 28 Mar 2016, 14:37
Location: FR Valence
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Re: High speed issues with bike hub motor

Postby pf26 » 05 Sep 2016, 12:18

Do you use BLDC or FOC mode (couldn't see on your config captures) ?
If BLDC, then I suspect the change from BLDC with hall sensor to sensorless (above a certain RPM, the control mode goes sensorless), but the ERPM limit seem to be set at 2000, so well above your RPM during fault (around 1100).
In you fault records, it seems strange that the duty cycle is only around 0.2 (this would make around 10 volts only, so it is very likely not to fit with the actual motor voltage at that speed - and thus, it explains the current spike)

Interesting to see that 13s can work for Vesc without regen.. But it is quite a bit frustrating for an Ebike not to use regen..

imval
Posts: 12
Joined: 02 Sep 2016, 13:07
Location: Rouen, France
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Re: High speed issues with bike hub motor

Postby imval » 05 Sep 2016, 13:16

Hi,
I'm currently using FOC, I'll try with BLDC. But FOC is so much more comfortable as it's almost noiseless and vibrationless !
Do you think that it could be because of one of my voltage divider resistor is bad ?
I'll check the values asap.

Yes i know that it's quite frustrating, maybe I'll try again with proper parameters, and now that i have received some spare DRV8302, I'll be able to change it if it goes to magic smoke haha :D

Thank for your answer !
Have a good day

pf26
Posts: 310
Joined: 28 Mar 2016, 14:37
Location: FR Valence
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Re: High speed issues with bike hub motor

Postby pf26 » 05 Sep 2016, 15:19

Possibly you are getting near what max output voltage FOC can achieve (without field weakening).
You may try with sligthly more charged batteries, to see if the problem occurs at higher speed (this would confirm that the issue is voltage related).
Probably BLDC mode will reach higher speeds with the same battery voltage (because output is not sinusoidal).

With FOC, voltage divider resistor are only used to start an already running motor, so it should not be an issue here.

As for regen, I advise you to try using a anti-spike diode soldered between +V and ground very near the DRV chip pins (maybe several 1.5KE56A in parallel ?). Also you need to make sure your VESC regen current is lower than BMS max regen current.
I am not sure it will work, I never tried, but if you are not afraid of DRV soldering, why not ?
It is almos certain that with regen, 13s without VESC mod will blow the DRV8032.

imval
Posts: 12
Joined: 02 Sep 2016, 13:07
Location: Rouen, France
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Re: High speed issues with bike hub motor

Postby imval » 06 Sep 2016, 08:56

Hi pf26,

As far as I remember, it happens even when my batteries are fully charged. It only occurs when I'm at high speed.
I will try with BLDC mode as soon as possible and keep you updated !

I think that these diodes are to close to the max battery voltage when fully charged which is 53,3v (breakdown voltage = 53,2v).
I also might need to add bigger capacitors with low ESR.

Thank you for your help :)

pf26
Posts: 310
Joined: 28 Mar 2016, 14:37
Location: FR Valence
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Re: High speed issues with bike hub motor

Postby pf26 » 06 Sep 2016, 11:44

The question was, does it happen at the very same speed, or does the speed limit depend on battery voltage ?
You can get the voltage and speed in the faults records.

As for the protection diode, you are correct. A a small resistor and/or inductor is required in series, coming from the high voltage rail, before supplying the DRV PVDD2 inputs near C39 capacitor. This would prevent voltage spikes to reach and kill the DRV.
Actually, there were inductors in series between high voltage FETs and DRV VDD in early versions of VESC - they are now removed and the proposed modification is rather difficult on the new pcbs unfortunately. (but still possible, you need to drill out 3 little via located under a FET, near R1 - and add the inductor/resistor between there and C39 high voltage pad, near P3 text.
Last edited by pf26 on 07 Sep 2016, 07:39, edited 1 time in total.

imval
Posts: 12
Joined: 02 Sep 2016, 13:07
Location: Rouen, France
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Re: High speed issues with bike hub motor

Postby imval » 07 Sep 2016, 07:09

Hi,

It happens almost exactly at the same speed, when I am going around 50km/h.
I don't feel a significant change un speed when the battery is full or not. I may try with another battery, I have a 3S lipo laying around.

Last night, i tried with BLDC mode and I have the feeling that it has more torque than with FOC mode, maybe it's just me :)
But the noise from the BLDC mode is really annoying and my disk brakes are resonating, horrible :?

I'll do more testing and keep you updated as soon as possible ;)
Thanks !

imval
Posts: 12
Joined: 02 Sep 2016, 13:07
Location: Rouen, France
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Re: High speed issues with bike hub motor

Postby imval » 12 Sep 2016, 12:40

Hi all,

I've done more testing during the weekend and I think that my caps are the issue, I think they don't have enough capacity to handle the high speed commutation and current when going fast.
When the wheel is not touching the ground, i reach aproximately 70km/h but when i ride it, i cannot reach more than 51-52km/h even in big downhills. I feel "hiccups" and if I continue to push the throttle, it goes to "ABS_OVER_CURRENT". After a short ride trying to push it to maximum speed several times, the caps were pretty hot on arrival.

I'm waiting for sparkless XT90 plugs to come, and when I will mount them I'll change the caps to put bigger capacity / lower ISR and I'll try again :)

Stay tuned ! :)

dima
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Joined: 09 Oct 2016, 05:13
Location: Canada
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Re: High speed issues with bike hub motor

Postby dima » 09 Oct 2016, 05:21


pf26
Posts: 310
Joined: 28 Mar 2016, 14:37
Location: FR Valence
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Re: High speed issues with bike hub motor

Postby pf26 » 10 Oct 2016, 08:47

On this picture, you can see the 1.5KE56A soldered in parallel with C39, and the arrow points to the 3 little vias.
Image
I think there is no other way then drilling the vias, since this track is internal (inside 4 layer pcb).

Beware that there is absolutely no waranty on this. I don't recommend to do it unless you know what you are doing and ready to repair your Vesc if necessary.


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