Mid run stop and then RUN-AWAY GANTRY!

[JayCop]

I was running table surfacing program made in cut 2d which was about half way through when all of a sudden the gauntry stopped when it should be going in the x- direction paused, then when the Yaxis made its stepover the X continued in the X+ but thinking it was at X zero. Luckily I was standing there watching and stopped it from running off the tracks.( Note to self stop being lazy and hook up the dam estops!) Thinking this my have been just a fluke I re ran the program from the beginning after re-zeroing the X axis. However it seems it wasn't a fluke on the next run it did the exact same thing. Im not sure that it was in the exact same spot but if not it was dam close.

What could have caused this not only to happen but twice?

Some info on my machine. It was made with buildyourcnc electronics ie. ps, bob, driver, and steppers. It is a steel welded frame with with CNCRouterParts linear motion on all axis, R&P on X and Y, and Acme on the Z.

[JayCop]

Please let me know if any other info is needed. I'm going to run the program again today and see if it happens a third time.

[awerby]

That sounds like lost steps. The gantry was probably too heavy for those motors and drivers to push (probably over a slight rough spot in the slides) so it stopped moving, but thought it had done what was commanded. Once it got going again, it started from where it thought it was.

How heavy is this gantry, and if you run it by hand, do you notice any rough spots? Which motors, drives and power supply did you use? Did you get the 70 volt system, the 36v, or the 24v? The 23 frame motors or the 34 frame?

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

[BanduraMaker]

When this happened, did the sound your machine makes change drastically? I've had things like this happen when I was sorting out my machine and it was a result of the stepper stalling and missing massive amounts of steps during the stall.

On my machine, the sound of steppers stalling is quite obvious and I can usually hear even a few steps missed. I solved the problem by oiling my ballscrews and taming down my accelerations and velocities.

Depending on your drivers etc, it can also be a resonance issue. I haven't had that problem but others were able to eliminate resonance issues by making dampers that attach to the stepper shaft.

Good luck!

[kennl]

Did you check the line of gcode where this happened to make sure it compiled right? Can you run a simulation with your cam program and see if the sim does it also?

kenny

[JayCop]

Sorry for taking so long to get back to you guys. I believe that my problems are caused from missed steps. I will be getting a new gecko g540 in the next couple days and report back to see if that helps.

I have a 36V power supply which I may upgrade if I find I am still having problems. The gantry only weighs about 100lbs which I hope is not too much of a problem for the two 380oz motors which drive it. With out the motors engaged the gantry moves down the tracks with very little effort.

[leix_99]

100 lbs is quite a heavy gantry but "should" be no problem with tandem motors driving it... No idea, try cleaning everything up and checking all the stepper cables and drive cables to see if there is something loose, it happened to me the other day while testing, it worked fine but suddenly started making crazy things due to a loose cable!

[JayCop]

Thanks for the reply Leix. I have gotten the new G510 and redid the wiring at that same time. It did resolve my problems with missed steps. Since I did the wiring and the new drviers/bob all at the same time I can not be sure which one was cause the tremendous amount of lost steps.