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vedder.se forums • VESC for art project
Page 1 of 1

VESC for art project

Posted: 31 Aug 2017, 18:58
by Davideo71
For a visual art project I've been learning about and experimenting with the VESC (4.12). I have a lot to learn but the BLDC_tool software is getting the VESC to work with my sensored 140 KV motor, so I'm already excited.

There are a few things that are particular for my project and it would be great to get some help on them.

1. I'm currently using a 3S powerpack, which turns the motor and is nice and light (great for my application). What are the consequences of this in comparison to the recommended 6S-12S ?

2. I'm noticing that the hall sensor registration seems to 'leak' with the Tacho counter ( VESC_Tool/Realtime Data/RPM ) not accurately reflecting the rotations of the motor at low speeds (especially when turning the motor manually). For my application it would be great if I can use the hall sensor to control position. Does anyone know what can be done to optimise accuracy? Is some leakage always to be expected?

3. It would be great if the motor was able to turn really slow. Now my motor has odd behaviour when dropping my duty value under 0.12 (FOC sensored) or 0.4 (BLDC unsensored), but it would be great if it could go a lot slower. I understand that I can add a second level of gearing but that would involve redesigning the prototype hardware and be a general headache, so any advice on settings to support slowest possible speeds would be appreciated.

4. I'm trying to understand the sound difference between the BLDC mode (noisy) and the FOC mode (soft and nice), could someone point me to resources on this?

Thanks!

Re: VESC for art project

Posted: 01 Sep 2017, 08:55
by ThierryGTLTS
Hi Davideo 71,

1. No problem, and you have more safety :!:
2. Hall sensors are not accurate enough for position control, use of the encoder is recommended.
3. If the motor needs to turn slowly with a low load, you'll have a low current and it would be interresting to increase the shunt value if so, and change firmware, but it depends of the mechanical load you have.
4. FOC wave is more like a sinewave with less harmonics, that explain the noise differencies.

Have a Nice Day.

Thierry

Re: VESC for art project

Posted: 01 Sep 2017, 12:03
by rew
2) It depends on how accurate you need the position. Hall sensors provide position information accurate to 6 positions per Electrical Revolution. Motors that are 140KV probably have 7 Electrical revolutions per single mechanical revolution. So you'd be able to resolve to 42 positions per mechanical revolution. Then if you have a 1:5 gearing, you'd have 210 positions per revolution. That is almost more accurate than the position of a 200 steps per revolution stepper motor! (the stepper could do halfsteps so, you can easly get 400 positions per revolution. If you go microstepping, the microsteps are often not equially spaced. )

Re: VESC for art project

Posted: 03 Sep 2017, 16:23
by Davideo71

Re: VESC for art project

Posted: 03 Sep 2017, 18:17
by rew
The "shunt resistor value" is not something that can be changed with BLDC_TOOL.

So: No, what he means by "change firmware" is to download the sources to the firmware, changing the "shunt resistor" value, and then compiling it and downloading it to your hardware.

Still I have been "playing" with my version that managed 140V and 80A today. Runs just fine at 1A too.

Re: VESC for art project

Posted: 10 Sep 2017, 21:30
by Vanarian

Re: VESC for art project

Posted: 11 Sep 2017, 10:34
by ThierryGTLTS
FW3.28 seems to have problems.

So I stay to FW3.27 which work fine for me.

Thierry

Re: VESC for art project

Posted: 11 Sep 2017, 12:54
by Vanarian

Re: VESC for art project

Posted: 11 Sep 2017, 15:48
by ThierryGTLTS
I use HW 4.12 with FW 3.27.

But I think HW 4.10 to 4.12 share same firmware version.

Thierry

Re: VESC for art project

Posted: 13 Sep 2017, 09:14
by rew