You are here

Best way to stop "de-sync" of motors

12 posts / 0 new
Last post
Paul15578
Offline
Last seen: 4 years 2 weeks ago
VESC Original
Joined: 2017-09-15 15:36
Posts: 26
Best way to stop "de-sync" of motors

Hi Guys

When I accelerate on grass with 200mm tyres,
if I have the motors set to say 75A each, and I take off full speed, I get a violent wobble of the rear truck and motors stop partially suddenly. Which I am calling a de-sync of the motors. 
It will pass this after a fraction of a second, and then continues normally, I believe its just occurring at peak current. 

Is this a matter of lowering the amps? (as it cant handle approaching the limit and thus spazzes out?)

Or modifying the observer gain and just see what happens?

Do I need to adjust the "time constant" in the motor setup?

Thanks for your help

Regards

Paul

Paul15578
Offline
Last seen: 4 years 2 weeks ago
VESC Original
Joined: 2017-09-15 15:36
Posts: 26

Anyone had this? 
If I reduce the current to 65A it doesnt happen at all. The motors are rated to 65A so do you think the motors cant handle the current? I thought they would just heat up quicker if over the max amps?

Paul15578
Offline
Last seen: 4 years 2 weeks ago
VESC Original
Joined: 2017-09-15 15:36
Posts: 26

Anyone out there?

Fotherja
Offline
Last seen: 4 months 1 week ago
VESC Free
Joined: 2017-11-02 01:59
Posts: 3

Perhaps the motor laminations are desaturating because of the high currents above the motor specs. This would effectively change the inductance of the coils and make it difficult for the VESC

benjamin
Offline
Last seen: 23 hours 21 min ago
VESC FreeVESC OriginalVESC Platinum
Joined: 2016-12-26 15:20
Posts: 487

Sounds like the motor saturates. There is a saturation compensation parameter in the advanced settings that you can experiment with. The help text for it explains how it can be used.

Paul15578
Offline
Last seen: 4 years 2 weeks ago
VESC Original
Joined: 2017-09-15 15:36
Posts: 26

Thanks alot Fotherja and Benjamin

Can you tell me what else the "saturation compensation" could be called?

It would be great if there was more technical information about each setting in the help, (rather than sometimes just how to set the setting) More about what the setting does would be superb.

Is there ever going to be a manual?

Thanks

Paul

 

Paul15578
Offline
Last seen: 4 years 2 weeks ago
VESC Original
Joined: 2017-09-15 15:36
Posts: 26

Sorry - found it in FOC - sensorless, (not in advanced)

And great it has some good information attached to the help, thanks

Paul15578
Offline
Last seen: 4 years 2 weeks ago
VESC Original
Joined: 2017-09-15 15:36
Posts: 26

Hi Guys

Are there any other settings that I should concentrate on to stop the desync of the motors. I believe it may be when the motors can properly work out their position. 

If I go full throttle from 8kmh it doesnt happen, but any speed lower than that it does happen. 

I have adjusted observer gain from 30 to 60 which helped a little. And saturation compensation to 10% which also helped.

Anything else please?!!

Regards

Paul

josh
josh's picture
Offline
Last seen: 1 year 15 hours ago
VESC Original
Joined: 2017-05-24 12:15
Posts: 92

What are the specifications of the motors? Most well designed 6355 motors should be able to handle that power although 75A is high. I have not experienced motor saturation myself so I can not comment on if it is that or not. See if you can do a capture of this in VESC tool under Data Analysis -> Sampled Data and post some images of it. That might be a good place to start. 

Cheers!

Paul15578
Offline
Last seen: 4 years 2 weeks ago
VESC Original
Joined: 2017-09-15 15:36
Posts: 26

Hi Josh

It seems the motors can handle the 75A after all, albeit they do heat up with lots of fast takeoffs.

I increased the sensorless ERPM from 2500 to 8000, as it appeared to be happening low down in the very early sensored zone with motor high current.  (5000 setting still had the startup desync problem)

There doesn't seem to be any problem now with that higher settign, but I guess the startup is not exactly as smooth as it was before? I dont really understand it all properly.

Can anyone comment? Or offer other options of what could be adjusted so we can keep the sensorless EPRM lower or is that not an advantage anyway?

Regards

Paul

 

 

josh
josh's picture
Offline
Last seen: 1 year 15 hours ago
VESC Original
Joined: 2017-05-24 12:15
Posts: 92

Hey Paul,

What motors are you using? Did they come with integrated hall sensors or did you add them yourself? I had a batch of motors which contained non-latching hall sensors which caused some issues during sensored operation. I made a post on here a while back about it here: http://www.vesc-project.com/node/170. It is possible this could be the issue. Have you tried running with lower current? If it is current related, you could get higher KV motors, run lower current, and use a more aggressive mechanical reduction on your pulleys.

Cheers!

Dillon
Offline
Last seen: 3 months 3 weeks ago
VESC Original
Joined: 2017-08-14 11:48
Posts: 34

I am running into the same problem. I have a large motor that runs max at about 4K RPM. Setting the saturation to 15% seems to help, but it still occurs. In my application, it will do the scary de-sync for a very long period of time, in fact until I start cutting power back. Then it will all of the sudden accelerate very quickly when it re-syncs, almost throwing me off my board every time. Very scary. I think I will use high RPM motors in my production unit to avoid this issue. I think it may be partially caused by the cogging torque of my motor.