VESC for art project

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Davideo71
Posts: 2
Joined: 30 Aug 2017, 14:12

VESC for art project

Postby Davideo71 » 31 Aug 2017, 18:58

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!

ThierryGTLTS
Posts: 85
Joined: 09 Aug 2017, 11:10

Re: VESC for art project

Postby ThierryGTLTS » 01 Sep 2017, 08:55

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

rew
Posts: 924
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: VESC for art project

Postby rew » 01 Sep 2017, 12:03

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. )

Davideo71
Posts: 2
Joined: 30 Aug 2017, 14:12

Re: VESC for art project

Postby Davideo71 » 03 Sep 2017, 16:23

ThierryGTLTS wrote: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.



This sounds like something I should learn more about. Do you know of any resources that explain more about this? When you say; change firmware, do you mean change the values in the BLDC_tool or are there existing firmware versions that are more suitable?

I'm not sure how to estimate and qualify the mechanical load but I'm aiming for the device to be able to pull about 10 kg up vertically (but more would be nice and less would be acceptable). hopefully I'll have a more exact handle on that as my prototype develops.

Thanks for your advice!

David

rew
Posts: 924
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: VESC for art project

Postby rew » 03 Sep 2017, 18:17

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.

Vanarian
Posts: 9
Joined: 23 May 2016, 11:27
Location: Nissa

Re: VESC for art project

Postby Vanarian » 10 Sep 2017, 21:30

rew wrote: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.


Hi rew ! It sounds good ! Me I'm finally starting to play with the BESCs after a long wait (50v max version with separate power board). Also had to resolder a smd resistor I blew.

Wanted to ask : did you test VESC-Tool firmware 3.28 ? Which hardware number should I choose to start the monsters? Do you have a "custom" one or should I choose another ?

ThierryGTLTS
Posts: 85
Joined: 09 Aug 2017, 11:10

Re: VESC for art project

Postby ThierryGTLTS » 11 Sep 2017, 10:34

FW3.28 seems to have problems.

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

Thierry

Vanarian
Posts: 9
Joined: 23 May 2016, 11:27
Location: Nissa

Re: VESC for art project

Postby Vanarian » 11 Sep 2017, 12:54

ThierryGTLTS wrote:FW3.28 seems to have problems.

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

Thierry


Hi Thierry thank you for feedback. Which HW number did you choose for configuration in VESC-TOOL ? I think you run Rogier's VESC too right?

ThierryGTLTS
Posts: 85
Joined: 09 Aug 2017, 11:10

Re: VESC for art project

Postby ThierryGTLTS » 11 Sep 2017, 15:48

I use HW 4.12 with FW 3.27.

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

Thierry

rew
Posts: 924
Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: VESC for art project

Postby rew » 13 Sep 2017, 09:14

Vanarian wrote:Wanted to ask : did you test VESC-Tool firmware 3.28 ? Which hardware number should I choose to start the monsters? Do you have a "custom" one or should I choose another ?

I have not had time to test my hardware with newer firmware. I have a github with a clone of benjamin's firmware. That's what I use.


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