Can FOC be used on a 10S BLDC motor powered by a 12S battery?

Discussions regarding the Field Oriented Control (FOC) implementation on the VESC.
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Location: San Francisco, CA

Can FOC be used on a 10S BLDC motor powered by a 12S battery?

Postby Hackerboysf » 16 Feb 2018, 20:04

My son and I just completed converting a kick-scooter to electric. The build includes a Maytech VESC hardware version 4.10 (although the seller said it was 4.12... don't know if this matters or not) with firmware upgraded to 3.34 using the VESC Tool. The motor is a Turnigy 6364 190KV, which says it's rated for up to 10S. The inputs are two ADCs- a thumb throttle on the right (ADC1) and a twist throttle on the left (ADC2) for the regen brake. Control Type is Current No Reverse Brake ADC2.

We got it running using an 8S LiFePO battery (running around 26V) and it was running well in both BLDC and FOC modes. The quiet running was really great. Unfortunately that voltage didn't have enough power to carry my boy up the hill we live on, so we swapped out that battery for a 12S LiPo bike battery pack we had from an old go-kart project. Wow, that changed things, and it runs great in BLDC mode.

However, when we try to get it running in FOC mode, we can't get past the RL test. We keep getting the error message saying "R is 0. Please measure it first." So we can't complete the parameter settings required for FOC setup. When I put the 8S battery back on it I am able to go through all the processes, apply all the parameters, and then FOC works fine. Unfortunately, those parameter settings don't work when I put the 12S battery back on and try FOC mode at the higher voltage.

My question is this: is it possible for this build to work with the higher voltage in FOC mode? Or is the fact that the motor is only rated to 10S voltage going to make it impossible to find any parameter settings that would make FOC work at that voltage with that motor? If it is possible, how might I make the system read the parameters that would work?

Any input will be very much appreciated. Thanks in advance.
Edit: This was driving me nuts, so I pulled out the 8S battery pack and a DC power supply and hooked it all up to the system so I could have a variable power supply to test with. All the way from 27V up to 44.1 volts the system read the parameters pretty much exactly the same:
Anything higher than 44.1 V input resulted in the "R is 0..." message and the system not operating in FOC mode.
I recorded the scooter operating in both BLDC and FOC modes, and tried to upload the recordings but got a message saying MP3 is an invalid extension, so I can't share those. The upshot is that at 42.0V with this motor there's not all that much difference in the sound between FOC and BLDC, so I'm just going to forget about it.
Last edited by Hackerboysf on 27 Feb 2018, 18:10, edited 2 times in total.

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Re: Can FOC be used on a 10S BLDC motor powered by a 12S battery?

Postby arvidb » 16 Feb 2018, 21:43

It should work.

The "10s" limit of the motor is an rpm limit (i.e. if you apply the full voltage of a 12s pack without a software rpm limit the motor could shake/rip itself apart), and shouldn't affect the FOC parameter measurement... (You should set the limit to 8000 rpm BTW: 190 rpm/V * 10 cells * 4.2 V. Multiply the 8000 rpm by the number of pole pairs of your motor to get erpm for the VESC.)

Unfortunately I don't know why your setup doesn't work. Maybe you could play with the detection motor current a bit and see if that helps?

Posts: 2
Joined: 16 Feb 2018, 19:08
Location: San Francisco, CA

Re: Can FOC be used on a 10S BLDC motor powered by a 12S battery?

Postby Hackerboysf » 19 Feb 2018, 00:27

Thanks for your reply, Arvidb.
I thought FOC mode ought to work, too, but the best I've been able to get is for it to rev up a few times in FOC, but then it goes back to just moving a tiny bit, and then nothing except a tiny shudder when I throttle it up.
I did try messing with the current settings, but I think that may only be relevant for the lamda calculation since it didn't seem to make any difference.
Thank you for the RPM advice.
It's not too bad in BLDC mode. The quietness difference between BLDC and FOC mode isn't really very significant at the higher voltage. At this point it's more academic curiosity that's driving it.

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