Jerky movement of steppers with UCCNC but not with Mach3

If you have a question about the software please ask it here.

Jerky movement of steppers with UCCNC but not with Mach3

Postby Mrgreenjeans » Tue Sep 04, 2018 2:28 am

I've been noticing UCCNC movement is harsh and jerky with certain gcode. I've looked around and trying to get it to not be so jerky but all the setting's I've tried don't get me there. I have seen some improvement by changing the velocity and acceleration but still not smooth. I'm running imperial units and tried some settings I've seen on the forum and to be honest it's been an improvement but no where near as smooth as Mach3 so I'm guessing I have some settings configured incorrectly and looking for some help. I'm running 1.2047 and below are my axis settings and cv settings as well as some gcode that makes a 4.5" circle that I'm using as a comparison. Velocity and Acceleration are basically the same in Mach3.


CV Settings
https://drive.google.com/open?id=1OhGs-V5eQBAxbIBj8DyPR3S8zX_A2_5K

Axis settings
https://drive.google.com/open?id=1182PjxQ_FL-FjHzAmJTA7KzoIAWbe0Sh
GCode
https://drive.google.com/open?id=17gP0M_VPZVwMUf4xNGF4uHF8lkOne_Xa
Mrgreenjeans
 
Posts: 6
Joined: Wed Jun 13, 2018 10:46 pm

Re: Jerky movement of steppers with UCCNC but not with Mach3

Postby spumco » Tue Sep 04, 2018 4:39 am

1. Your "circle" is a series of tiny lines. UCCNC is trying to move through each line segment accurately - jerky as it has to slow down and speed up at each direction change. I'm guessing Mach3 is fudging it, resulting in smoother perceived motion.

You should try coding an actual circle or set of connected arcs and see how that sounds (G2/G3).

2. Try turning the linear error and addition settings down and see if that helps.
spumco
 
Posts: 306
Joined: Mon Oct 03, 2016 10:10 pm

Re: Jerky movement of steppers with UCCNC but not with Mach3

Postby cncdrive » Tue Sep 04, 2018 6:19 am

Try to higher the Linear additional length to e.g. 1 and Linear unify lenght to e.g. 2., because how your settings are now these are too low, they are comparably small as the tiny line segments in your code,
and so these tell the UCCNC to stop the lookahead if the next line is longer than the Linear additional length and also do not put more length together than the Linear unify length.
So, if these are so small then basicly the looking ahead will not work, or will only have very minor effect on your code.
cncdrive
Site Admin
 
Posts: 4695
Joined: Tue Aug 12, 2014 11:17 pm

Re: Jerky movement of steppers with UCCNC but not with Mach3

Postby Mrgreenjeans » Tue Sep 04, 2018 3:48 pm

spumco wrote:1. Your "circle" is a series of tiny lines. UCCNC is trying to move through each line segment accurately - jerky as it has to slow down and speed up at each direction change. I'm guessing Mach3 is fudging it, resulting in smoother perceived motion.

You should try coding an actual circle or set of connected arcs and see how that sounds (G2/G3).

2. Try turning the linear error and addition settings down and see if that helps.


Thanks for your suggestions. I should clarify that gcode actually starts with a pilot hole in the center then after about 180 lines it starts doing the 4.5" circle. I'm only talking about the 4.5" circle not the pilot hole path. The jerky motion is not just a perception but is both visually and audibly noticeable. Almost as if there is no slow down for direction change but instead an immediate stop at each direction change. With Mach3 it's also visually and audibly noticeable that it slows and speeds up (smoothly) throughout the path and that's what I'm trying to get UCCNC to do.

I've increased the Linear addition length to 1 and Linear unify length to 2 as per cncdrive recommendation and that seems to help some, similar to how changing the acceleration and velocity did but still not really smooth sounding. Visually it seems a lot smoother but the steppers sound like they're still abruptly starting & stopping at times just not as bad as before.
Mrgreenjeans
 
Posts: 6
Joined: Wed Jun 13, 2018 10:46 pm

Re: Jerky movement of steppers with UCCNC but not with Mach3

Postby Mrgreenjeans » Tue Sep 04, 2018 3:49 pm

cncdrive wrote:Try to higher the Linear additional length to e.g. 1 and Linear unify lenght to e.g. 2., because how your settings are now these are too low, they are comparably small as the tiny line segments in your code,
and so these tell the UCCNC to stop the lookahead if the next line is longer than the Linear additional length and also do not put more length together than the Linear unify length.
So, if these are so small then basicly the looking ahead will not work, or will only have very minor effect on your code.



Thanks for your suggestions.

I've tried the settings you've suggested and they do seem to help some. See my previous post to Spumco. Any other suggestions you could make?

Thanks
Mrgreenjeans
 
Posts: 6
Joined: Wed Jun 13, 2018 10:46 pm

Re: Jerky movement of steppers with UCCNC but not with Mach3

Postby ger21 » Tue Sep 04, 2018 4:32 pm

Try increasing the two error tolerance settings, to at least .005-.007.
Gerry
UCCNC 2022 Screenset - http://www.thecncwoodworker.com/2022.html
ger21
 
Posts: 2663
Joined: Sat Sep 03, 2016 2:17 am

Re: Jerky movement of steppers with UCCNC but not with Mach3

Postby cncdrive » Tue Sep 04, 2018 4:58 pm

Well, the thing is that mach3 may be smoother in some cases, but you do not know how much error it will make on the path to be smooth. There is no path error tolerance settings in mach3 and so it may "fly" in some codes, but the result is unpredictable which is especially an issue if you do precise work where you want to know the tolerances.
Also mach3 often overaccelerating your settings is how it achives fast and smooth operations, however this involves the risk of stalling the stepper motor, because the software then using higher accelerations than what you setup. We measured out upto 8x accelerations... So how and why mach3 is often smooth is cheating which involves risks which are dangerous.
cncdrive
Site Admin
 
Posts: 4695
Joined: Tue Aug 12, 2014 11:17 pm

Re: Jerky movement of steppers with UCCNC but not with Mach3

Postby Mrgreenjeans » Tue Sep 04, 2018 8:09 pm

ger21 wrote:Try increasing the two error tolerance settings, to at least .005-.007.


Thanks for the suggestion. I've set both Corner error and Linear error to .005. I think in combination of this change and the others suggested by cncdrive it's not to far off from what I was hoping to achieve. Still not as smooth but a world away from where it was. Thanks to all for the help.
Mrgreenjeans
 
Posts: 6
Joined: Wed Jun 13, 2018 10:46 pm

Re: Jerky movement of steppers with UCCNC but not with Mach3

Postby ger21 » Tue Sep 04, 2018 11:27 pm

Then try a little higher.
The difference between UCCNC and Mach3 is that UCCNC will follow the path exactly, unless you specify how far away it can deviate.
Mach3 just tries to maintain velocity, regardless of how far it may stray from the path.

Because of this, If your machine can accelerate fast enough, you can run at much higher speeds than Mach3, while actually having a higher level of precision.

What CAM are you using for this? If it was coded with G2/G3 moves it would be perfectly smooth.
Gerry
UCCNC 2022 Screenset - http://www.thecncwoodworker.com/2022.html
ger21
 
Posts: 2663
Joined: Sat Sep 03, 2016 2:17 am

Re: Jerky movement of steppers with UCCNC but not with Mach3

Postby spumco » Wed Sep 05, 2018 5:01 am

Sorry if my "lower the settings" advice was bunk. It just seemed like .100"/0.050" was a bit high for an inch-units machine.

And when I looked at the code there wasn't a single G2 or G3 move in it. Maybe I missed something, but even if you ignore everything but the 'circle' it should still look like a faceted part from all those little moves.

I was thinking the OP might just run a test code of a simple G2/3 circle - whatever diameter - to see if the noise/jerking is minimized or eliminated.

I'd also be intereseted in seeing the CAD and knowing what CAM generated this code.
spumco
 
Posts: 306
Joined: Mon Oct 03, 2016 10:10 pm

Next

Return to Ask a question from support here

Who is online

Users browsing this forum: Google [Bot] and 28 guests