Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: alevitt53 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
-
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
-
Thanks for the reply,
Not sure I can do that with the Gecko 540....
-
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.
-
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...
-
Again, what is the pitch of your screws?
-
.19685 inch/turn
conversion from metric.....
-
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.
-
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
-
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??
-
Why just use 1 motor? If you have an easy way to add a belt reduction, then do a 1:2 reduction, but still use both slaved motors.
-
Progress... I put a belt drive on each of the X and A axis to reduce the motor speed in half. I made sure there was no mechanical slippage by filing a flat on the shaft of the motor and ball screw shafts.
I ran a simple test pattern to put a 1/4 inch hole in the corners of a 10x10 square and I have 1/4 inch dowel pins for measurement. No matter how many times I run it, the A axis is ALWAYS .015 shorter
than the X axis. I retightened all the pulleys but to no avail. Then I switched the two axis wires on the Gecko G540 to see if was the driver. The same side was still short......
I have run out of ideas to try....Could the motor/motors be bad???
Any help would be greatly appreciated.