Stepper motors Vibrating BADLY on new PRS Alpha help!!

[dray]

My steppers are vibrating badly when moving and cutting on occasion. Brand new PRS Alpha. Its like its not changing gears or something.

At first I thought it was the X carriage being slightly squewd or something so I toom the steppers out and ran it and they both vibrate and shudder. Why is this happening?

Thanks

[harryball]

My PRT Alpha did something similar after I got it running. I finally figured out it would only do it when the Z was moving at the same time as X and Y. It turns out the pinion was only about 50% engaged into the track on the Z axis. This seemed to create the dramatic vibration and sound only when the Z was moving slow and additional forces were being applied.

I removed the assembly, the pinion didn't appear loose but it had marks showing some wear on it. I made the adjustments and cleaned everything up and reassembled. It's been fine since. I guess I need to send shopbot an email, they were going to send me a new pinion to replace that one but I forgot to follow up on it. I probably should order some extras as well to have on hand.

So the moral is, it'd be a good idea to inspect all the pinions and tracks, make sure they are 100% engaged (not hanging off the side) and the springs are tensioned correctly etc...

EDIT: I'm not sure I understand your post completely when I read it again... you're saying with the stepper hanging free it vibrates badly when moving? All of them?

Let us know how it turns out.

Robert

[richards]

Stepper motors can vibrate excessively at certain low speeds due to 'harmonics'. It's something that is native to most steppers and only happens at low speeds. For instance, the PK296B2A-GS3.6 motors that I have on my test bench sound like they're going to come apart when running the 'corner' portion of the doors program that Bruce Clark and I wrote. (This is particularly evident when using the G-code version of the program.) All other cut segments sound fine.

Unless there is something truly out of the ordinary occurring, you'll probably find that the vibration only happens when running the motors slowly. I would run some speed tests and find the area that the motors vibrate and then not use those speeds when writing cut files.

I believe that you have gearboxes on your PRS-Alpha, so I can't tell you at what speeds the resonance is likely to occur. Most of the stepper motors that I've run on my test bench tend to vibrate excessively when run at about 100 pulses per second. Large motors vibrate much more than small motors (at least the PK and PH series that I've used in the 23 frame size and the 34 frame size - the round PH motors have more of a problem than the square PK motors). In reality, its a stepper thing that is very common and nothing to worry about.

In fact, if you're lucky enough to have driven a chevy pick-up truck from the 1940s and early 1950s, you'll most likely have found that 1st gear (compound) had a top speed of about 10 mph and caused the whole truck to shake and vibrate like it was going to fall apart. It didn't hurt the truck, but that very low gear ratio really helped around the farm where a lot of trucks were used in the fields and had to be run at 'walking' speeds. In similar fashion, the resonance area of a stepper motor is proof that the laws of physics really work and that stepper motors are not exempt from those laws.