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Slaved X and A Axis Problem
« on: November 21, 2014, 01:56:58 PM »
Hello,
New to forum and first post...
I have a DIY 30x40 cnc based on CNC parts machine. I'm running slaved ball screws on the x axis and nema 23 425oz/in motors.
My problem is that the two sides (x and a) do not run perfectly in sync. If I run the calibration test on the left side of the machine, it will not be the same on the other side.
I've turned the velocity way down and still have a problem. The question is, in the Mach motor setup, can the steps be different on the slaved axis to compensate for the difference in the
movement side to side of do they have to be identical. I did notice that when I calibrate the x axis, the correction only appears on the x motor and not the A. If I try to calibrate the A
axis by itself, the motors do not turn.
At this point I have many hours trying to solve but have not come up with an answer yet.
Any help is greatly appreciated..
Thanks
Art

Offline TPS

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Re: Slaved X and A Axis Problem
« Reply #1 on: November 21, 2014, 02:20:46 PM »
Hi,

why dont you rum both sides with the same step/dir signal's (paralell).
ok. referencing is a little bit tricky, but the normal run is 100% sync.

Thomas
anything is possible, just try it.
if you find some mistakes, in my bad bavarian english,they are yours.
Re: Slaved X and A Axis Problem
« Reply #2 on: November 21, 2014, 02:25:46 PM »
Thanks for the reply,
Not sure I can do that with the Gecko 540....

Offline ger21

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Re: Slaved X and A Axis Problem
« Reply #3 on: November 21, 2014, 07:28:17 PM »
What pitch are the ballscrews, and what are your velocity and acceleration settings?

When slaving, both axis must use exactly the same settings. I would guess that the calibrate function either won't work correctly, or you'll need to copy the settings to the slaved axis.
If the two axis are not moving in sync, then most likely, one (or both) motors are losing position. This can happen for a variety of reasons.
Generally, 425oz motors don't perform very well unless you run them  at 70V or more, due to their high inductance. They can easily lose position if you're trying to spin them fast.
Also, it's very common with modern PC's for the G540 to require a very high pulse width. This is due to the PC having a weak parallel port. Try setting the pulse width in the motor tuning screens to 15.
Gerry

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

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Slaved X and A Axis Problem
« Reply #4 on: November 21, 2014, 09:40:32 PM »
Thanks Gerry,
I'm kind of stuck with the setup I have now. It looks like the Gecko won't go past 50V and I'm at 48. Kind of maxed out there.
What steppers would you suggest based on the Gecko???
Before I do that I'll change the pulse and see what happens...

Offline ger21

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Re: Slaved X and A Axis Problem
« Reply #5 on: November 21, 2014, 09:43:50 PM »
Again, what is the pitch of your screws?
Gerry

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

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Slaved X and A Axis Problem
« Reply #6 on: November 21, 2014, 09:51:24 PM »
.19685 inch/turn

conversion from metric.....

Offline ger21

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Re: Slaved X and A Axis Problem
« Reply #7 on: November 21, 2014, 10:04:25 PM »
5mm? Those are a very poor match for the motors you have, as they require high rpm to get any speed.
Ideally, you'd want 10mm pitch screws, and 381oz, 3.5a motors. Those are the best match for the G540.
With 5mm screws, you might get slightly better performance with even smaller motors, like 270oz.
But generally, the 381 oz motors are the best all around choice for the G540.
Gerry

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

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Slaved X and A Axis Problem
« Reply #8 on: November 21, 2014, 10:19:41 PM »
I had that feeling when I started to run all the numbers and saw that the motor had to run high velocity to get anywhere.....
I'll have to decide now based on finances!!!
Thanks
Art
Re: Slaved X and A Axis Problem
« Reply #9 on: November 22, 2014, 07:26:01 AM »
OK, slept on it last night....What if I used one of my original motors, tied to two axis together and geared it down by half. That would essentially put double the
load on the motor and allow it to turn 1/2 as fast at higher velocities..
Do you think that would work??