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Help with jerky motion - again!
« on: September 04, 2018, 08:00:34 AM »
Hi,
I would really appreciate some help with jerky motion on my milling machine.

I've read many many post and tried lots of different options and I still have the problem.

So, if I hold the arrow keys down, then motion is smooth.
If I use an external MPG then the motion is smooth.
If I push the RefAllHome button then the motion is smooth (this I find odd).

But if I type a simple command like G0X10 (for example), then the motion is significantly jerky.
This affects all three axes equally. If it runs smooth then all 3 axes are smooth. It is runs jerky then all 3 axes are jerky.

Also if I type:
G64
G0X10  (in mm)
then then the motion is jerky.

It follows that if I load a g-code program then the motion is jerky.

I've tried all the combinations of CV and FullStop modes with no difference. Not that I would expect any difference with a simple one command of G0X10.

I've tried all sorts of motor tuning options of fast acceleration fast speed. slow acceleration slow speed, etc. And still I get jerky motion with the G0X10 command.

My setup is a Bridgeport CNC Interact with upgraded servo motors using Mach3 version R3.043.
 

Thanks
Craig

Offline ger21

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Re: Help with jerky motion - again!
« Reply #1 on: September 04, 2018, 08:10:45 AM »
If you are using the parallel port, run Drivertest.exe in the Mach3 folder, and watch the pulse rate. It should be very stable.

Also, open Windows Task Manager and monitor the CPU usage.

This sounds like a problem with the parallel port or the PC.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Help with jerky motion - again!
« Reply #2 on: September 04, 2018, 09:04:31 AM »
Hi Gerry,
Thanks for the quick response.
I forgot to mention that I'm using Pokeys 57CNC with USB interface.

I just checked the CPU usage whilst it was implementing a very jerky G0X100 move, ie a move of 100mm and the maximum CPU usage registered 25%, well away from 100%.
Also there's 2G of free memory available, so not running out of memory either.

regards
Craig

Offline ger21

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Re: Help with jerky motion - again!
« Reply #3 on: September 04, 2018, 09:17:22 AM »
My guess is that this is a Pokeys issue, as it's something I've never heard of before.
You might want to contact them.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Help with jerky motion - again!
« Reply #4 on: September 07, 2018, 09:36:06 AM »
Hi,

Just an update on progress.
I really really need this issue resolved, so I will continue until I find a solution. Since I imagine there are plenty of people out there successfully using Mach3, Pokeys 57CNC via USB and servo motors (with just step/dir mode), then there must be a solution. Not forgetting also that I can get perfectly smooth operation under some conditions.

Whilst testing Mach3, the laptop I was using for Mach3 died, so I have replaced it with a new PC based on a motherboard from MSI (H110M pro-vd) and using the same HDD. And I still have the same issue. So whatever the problem, it would appear not to be PC HW based.

Just to explain what's happening with the jerking. If I use G0X10 to move 10mm, it seems to split the move into about 3 segments and the motor ramps up and down for each segment. This gives the jerky motion. Now I don't know how Mach3 works, nor how Polabs USB driver works for the 57CNC. So I can't see whether Mach3 is splitting the move command into smaller segments and the Pokeys board is just following what it's told, or Mach3 is passing the correct move command to the Pokeys board and it is causing the segmentation and jerky movement. I still need to check with Polabs.

I did also try an old fix using RMClock, which stops the CPU from going into sleep mode by always giving it something to do. This also made no difference. I just wondered if the CPU was regularly going into sleep mode (to save power for example) and this was causing Mach3 to split up the move into segments. But I'm sure others would have had this same issue and I would have read something about this on the board.

regards
Craig

Offline Tweakie.CNC

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Re: Help with jerky motion - again!
« Reply #5 on: September 07, 2018, 10:43:16 AM »
Hi Craig,

While you are checking the sleep thing it may be worth checking your USB hubs to make sure the power management does not allow sleep.

Do you have a USB memory stick connected when you are running Mach3 ?
Are you running your Gcode file direct from the C drive ?

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.

Offline ger21

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Re: Help with jerky motion - again!
« Reply #6 on: September 07, 2018, 11:36:44 AM »
If it's not a USB issue like Tweakie says, then my guess is still the Pokeys. Have you contacted them?

It's the Pokeys that controls all the motion, not Mach3.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Help with jerky motion - again!
« Reply #7 on: September 10, 2018, 12:35:49 AM »
It was very jerky until about the 5th step over and it went smooth, and then on the 6th step over it was jerky again
Re: Help with jerky motion - again!
« Reply #8 on: October 02, 2018, 04:03:32 PM »
Hi Gerry and Tweakie,

Thanks for your comments on this.
I have now resolved the issue.
Gerry's hunch was correct, it was the Pokeys controller.

I opened a ticket with them and they were very helpful and went through the problem with me.
The Pokeys software comes with a really helpful troubleshooting feature. This showed I had slow USB communications, at approximately 8ms.

The issue ended up being related to the USB drivers I was using.
As it turned out I couldn't fix the problem using USB.

The solution ended up being for me to use the Pokeys ethernet input instead of USB.
The troubleshooting feature now shows a communications time of about 0.5ms and this 16 times speed improvement resolved the jerky motion.

Thanks again for your help.

best regards
Craig