Stepper motor "skipping"

[John T]

Hi Art,
This question is not directly related to Gearotic - but it is related to the CNC machine.
I'm using a CNC Midi from WidgetMaster.
The spindle is from Wolfgang Engineering and the CNC uses 200 (I think) Gecko stepper motors.  The CnC controller is a Hobby CNC unit.

The issue is that occasionally, like once in 10 hours of use, the x-axis stepper motor will "buzz" without moving and when it starts moving again (on its own) its several inches away from where it should be.

Since its intermittent it isn't and out and out failure and I having difficulty tracing it down.  I think it might be related to the stepper motor speed - I normally run at 100 inches without any problem but occasionally I'll have an easy cut and I'll speed things up to 250 inches.

The question is - Do you think I have a dying stepper motor, faulty cmc controller or a bad setting on Mach 2?

I know you can't solve this at a distance but you might be able to point out a likely direction.

John

[ArtF]

John:

  I suspect your hitting the power inversion of a stepper, they lose power as they go faster. Acceleration is very important to
steppers, they like smooth increases and decreases in speed. When it buzzes, it means you lost phase with the motor, its
armature is out of sync and will lose position until the speed slows down enough that the power increases enough to grab and stay in sync again.

  You probably dont have any problem. To minimize this you should maximize the micro-step count of your drivers, usually the higher the micro-step count the less likely they will go out of phase. If this is driven by printer port you may have
timing issues, if driven by an external engine its probably just speed and acceleration. Ensuring your screws are clean and lightly lubed can help as well. All that having been said, I suspect if you lower the acceleration setting by 5% you wont see it
again...

Art

[John T]

Thanks Art,
You've saved me a lot of worry if nothing else.  I'll just be a little more patient.

John