Y axis occassional chatter and binding

[dcg44@fairfieldglade.com]

RE: prt96 with Model PK299-01AA Vexta Stepping Motors. Problem discovered while running an engraving program - y-axis lost its location i.e. printed two steps in one line and then offset another line by several inches. In troubleshooting found that there was a chatter in y-axis movement that under right conditions caused axis to bind. Took one of x-axis motors and replaced y motor - problem disappeared - movemet of y-axis was smooth. Has anyone encountered similar problems with stepping motors?

[Mayo]

The only times I have experienced similar problems, I could trace it to power fluctuations. This usually happens for me when I turn off either the router or the shop-vac before the shopbot has come back to home position and the file has ended. Whatever change in voltage that occurs while the stepper motors are still moving, is sufficient to sometimes cause it to not work correctly on the next file. If I shut down the control box and computer and reboot, everything goes back to normal. You will probably need to reset your home position (x, y, and z zero)

[dcg44@fairfieldglade.com]

appreciate the feedback, but this does not expain why the problem only exists with the one stepper motor. when i replace the y stepper with one from the x axis, the problem disappears and when i return the original y-stepper motor to the y axis, the problem returns.

[bill.young]

Donald

Have you checked the connection at the plug on the Y motor? Look into the plug where the wires go and make sure that you can see a little bit of bare wire at the connection point. If the wire is too deep in the plug and the connection is made partly on the insulation, you might get an intermittent connection. Also cneck for stray wire strands that might be shorting out.

Good luck,
Bill Young

[sea_nc@bellsouth.net]

Donald,

Check set screw(s) on Y pinion gear to make sure that they're tight and seated on shaft flat.

Also, assuming that your wire connections are OK, your Y axis problem could be due to (1) how the motor is mounted, and (2) hold-down tension on your Y car. A turnbuckle that is too loose or too tight, a motor mounting bolt too tight or too loose, or a motor that is angled excessively can easily produce the type of performance problem you explained. When you swapped your Y stepper motor with the X motor you would have, of course, removed the motor mounting bolt and unhooked the turnbuckle to remove a motor and retightened the bolt and turnbuckle to reattach a motor. Getting the bolt/turnbuckle tension "right" after the swap could have solved the problem rather the X motor per se. As for why Y motor didn't perform well when reinstalled, that might be due to bolt/turnbuckle tension being insufficient again. Alternatively, the Y motor may differ from X because of a bent motor bracket or loose pinion gear. The fact that the X motor swap solved the problem (over the longterm?) suggests that your hold-downs are OK.

If you have an intermittant motor wire connection it could explain a performance problem, as Bill suggested, but it can lead to a blown driver on the control board (a bigger problem). If you suspect you have a loose connection be careful during troubleshooting not to unplug any connections while the control box is turned on because that can blow a driver.

Dave

[Ted Hall, ShopBot]

Hi Donald,

Lots of good suggestions here ... If none of them solve the problem, let's consider something being wrong with the motor. I am pretty impressed by the effect of your swaping the motor. Assuming the pinion is tight and no teeth are damaged, we could have some sort of electrical problem with the motor. The motors hardly ever fail, but if this is where all the evidence points, we'll send you one out on Monday. Give us a call to let us know.

[dcg44@fairfieldglade.com]

Thanks to a good conversation with Ted Hall, I believe the problem has been solved! Turns out it was an RF problem with the Shopbot controller too close to the CPU. I recently did an equipment relocation to 'clean up' the work area and give the controller and computer a little more protection from dust etc. Seems that the cpu was emmitting spurious rf that only impacted the y-axis periodically. Since separating the controller and computer, there has been no duplication of the problem.

My thanks to all who took the time to help out and my sincere apprecition to Ted Hall of Shopbot who not only took the time on his day off, but had the patience and knowledge to work throught the problem with me.

[sheldon@dingwallguitars.com]

OK, that brings up the question is this an isolated problem or is there a recommended separation distance for the controller and computer?

Mine are right beside each other in an enclosure.

[bob buttons]

i cannot see how rf interference would effect a motor?? i think something else fixed the problem and the relocation of the controller was just coincidental not the cure.

[don guckenberger]

comments to the last two entries. You will have to talk to shopbot on recommended distances for separation of units. In my case, I had built a shelf that essentially laid the controlled on top of the cpu. I now have the traditional along side the cpu configuation. The controller is a few inches from the cpu. Ted Hall stated that the version controller I have is very susceptible to electrical interference and that they have made changes to the new models.

the aanswer to the second entry is that rf did not affect the motor. what it did do is affect the electronic circuitry in the controller that inturn sent erroneous signals to the motor. this is a typical problem with any type of electronic device - which is why computers must meet FCC regulations.

[joa]

That's funny, I've just recently *again* started having this problem. The y axis will shake during certain movements and cause the zero to drift. I can see it happening. I'm still narrowing the cause down but so far it appears that when I change the tension on the bottom two bearings it makes a difference. Today I bought six new bearings and plan to replace all of them on the machine. We'll see if this does it.

My theory is that the offset torque from the r&p is causing the y-axis to rack and stalling the motor. Usually after I "play" with the tensions it solves things for a while. Hopefully the new bearings (the old ones were pretty loose) will help. I'll keep you all posted.

Joa