Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: wade16 on August 04, 2014, 02:28:49 AM

Title: What causes stepper motors to decelerate and then accelerate when moved?
Post by: wade16 on August 04, 2014, 02:28:49 AM
When I move the 3 axis, they  start to move and then they slow down almost to a stop, and then they accelerate up to the correct feed rate. How do I eliminate that problem?
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: Hood on August 06, 2014, 02:54:26 PM
Are you meaning jogging or via code or?
If code please attach and say approx where it happens.
Hood
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: wade16 on August 06, 2014, 03:08:16 PM
When I jog and when it feeds during the program run, the motors accelerate to speed and then almost immediately, the motor decelerates to a quick stop, and then accelerates back up to speed. This happens each time the axis changes direction or begins the initial movement. How do I insert the xml file?
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: Hood on August 06, 2014, 03:11:27 PM
either copy the xml and rename it something unique or zip it with a unique name then use the additional options button on the reply page to attach.
Hood
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: wade16 on August 06, 2014, 03:18:52 PM
I am sending the file.
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: Hood on August 06, 2014, 04:10:52 PM
Go into General Config and change to CV mode rather than Exact Stop.

It is always preferable to have an initialisation line in your G Code that sets modes such as CV or Exact Stop, G64 for CV.
Hood
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: wade16 on August 06, 2014, 04:13:05 PM
I will try  that and let you know. Thanks for the help.
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: wade16 on August 06, 2014, 04:21:01 PM
Hood,
I changed to CV, but it still happens when I rapid jog. Could it be a motor tuning problem?
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: Hood on August 06, 2014, 04:33:55 PM
I dont have a 32bit computer here to test with but will try tomorrow at the workshop if I remember ::).
Do the DROs show the axes moving like that?
What is the frequency and Time In Int on the diagnostics page?

Hood
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: Hood on August 06, 2014, 04:36:12 PM
I see you have backlash enabled and the shuttle accel on Gebneral Config seems quite big. Disable backlash and see if it helps, if it does reduce the shuttle accel.
Hood
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: wade16 on August 06, 2014, 04:49:45 PM
Where is backlash? I don't see it in general config. The shuttle accel is set on 1
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: Hood on August 06, 2014, 04:52:20 PM
Config menu then Backlash. You may have to restart Mach for it to take effect.
Hood
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: wade16 on August 06, 2014, 04:59:59 PM
That seems to have fixed the problem. All axis move in fast jog with no hesitation. Thank you very much.
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: Hood on August 06, 2014, 05:04:31 PM
If you need the backlash you could reduce the shuttle accel and see if it helps, maybe 0.05 or something. Dont use backlash myself so not sure what the normal settings would be but I would imagine you want it a short time.
Hood
Title: Re: What causes stepper motors to decelerate and then accelerate when moved?
Post by: wade16 on August 06, 2014, 05:07:49 PM
I will keep that in mind. Thanks.