High speed issues with bike hub motor

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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, 17:13

@xlv: I don't get it. My idea was to replace the existing tracks between battery voltage and C39+ by a small resistor and/or inductor in series. So that voltage spikes during regen are not propagated to the sensitive DRV power supply pins. I think it is useless to add a more inductive path unless you cut the existing pcb track. Now there are 2 parallel copper tracks on both .gbl and .g3 layers, therefore I proposed to drill those 3 little vias.
Most likely, just drilling the top of those vias on the DRV side is enough.

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 » 01 Mar 2017, 11:13

Hello all,
Some updates after a few months : for short, i still have the issue.

I also had some "fireworks" because of bad handling of the VESC (Vbatt+ wire touched a +5V pin, very bad) and had to make a new VESC.
I also purchased big brand new low ESR 2200µF caps and put two in parallel. But still the same issue ...

In FOC mode, the motor (and bike) behave really nicely up to aproximately 50km/h and then I feel some "hiccups" in the drag and finally it goes into safe mode, disabling the motor for 3 seconds. When the wheel is not dragging anything (freewheel in the air), it goes up to 70km/h.
And I don't think it's because of a low current limit because the ABS_OVER_CURRENT limit is set at 130A and I'm pulling "only" 60A maximum when full throttle in current mode. And even when I'm going downhill and not pulling that much current, i got the error code.

EDIT : I just thought about the switching frequency when browsing this post : viewtopic.php?f=7&t=507
As I'm running on a 13S battery, 53,3v fully charged, can the switching frequency of 20kHz by default be an issue for my VESC ?

It's a really strange behavior and I don't understand what could be causing the issue, everything on the board is basically brand new.
Hope you have some ideas guys :D
Thanks !

rew
Posts: 943
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.
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Re: High speed issues with bike hub motor

Postby rew » 01 Mar 2017, 23:03

The "does nothing for 3 seconds" means that it is getting an error code.

What you could do is to trigger the error, go home and do NOT turn off the VESC before connecting it to your computer. When you fire up BLDC_tool, you need to go to the terminal tab and type "faults". This will list the faults that happened since startup.

That should provide a hint....

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 » 01 Mar 2017, 23:13

Yep I know that behaviour and the error code is ABS_OVER_CURRENT ;)
And as i mentioned in the first post, here you can see some screenshots, with the error code as well : https://drive.google.com/drive/folders/ ... W9SM21RMGc

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 » 02 Mar 2017, 10:31

I think you are very likely to kill your VESC in such a config. And this may be quite dangerous when the Fets die in the ON state at +50kph..
I would reduce the max battery current (30-40Amps ?), so that with higher duty cycles, your motor current gets progressively reduced.
What kind of battery do you use ? Its voltage is likely to drop when you draw near to 60 Amps.. Also there is a large voltage drop due to the motor windings resistance. This explains probably why your max speed is lower at higher loads (ie high currents) than unloaded.
It is interesting to use a little bluetooth module connected to the VESC Uart, and the Android VSC monitor App to record your parameters (currents, power, speed..) in real time before the fault occurs.

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 » 02 Mar 2017, 10:39

Hopefully I have a good BMS that already proved it's ability to cut the load if anything wrong happens.
I already tried this, but even with 20Amps max batt current I can't reach higher speeds and still experience the hiccups and ABS_OVER_CURRENT.
I use a battery made from 18650, custom made with a 45-50A continuous BMS, and even with a high load around 60A for a few seconds, the battery voltage goes down to "only" 46-48v when fully charged.

This was my first thought that when loaded the winding resistance would reduce the max speed, but even when I'm going on a steep downhill, faster that 50kph and trying to apply a very small amount of current, I feel the hiccups, that's why I don't think it's because of the current draw or the battery.

I'll try to find a solution for logging everything, like with a laptop in backpack, as my ebike system already use the uart to control the vesc.


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