Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: cncbobuk on May 31, 2016, 03:35:34 AM
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I have finally managed to complete the new control system, (Mach 3 driving steppers through a UC300 motion controller) for my 1325 Chinese router and am generally delighted with the results. Everything runs much smoother and more accurately but................. I am plagued by occasional "clonking" from mainly the Z axis. I can only assume this is the drive losing or gaining steps and sounds the same as when the system is first turned on and power is applied to the drivers. It doesn't seem happen during program execution but very often does during initial homing or manually positioning for the start of job. Anyone any ideas where I should be looking first? Many thanks in advance. Bob.
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Any chance of a video - it could be backlash, a loose coupling, belt jumping teeth, drive issue :)
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Any chance of a video - it could be backlash, a loose coupling, belt jumping teeth, drive issue :)
Unfortunately there is nothing to see, I've checked the mechanical linkage, belt tension etc and all is well there, it does sound like an electrical issue as it's exactly as when the drive is first powered on.
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Mine all clonk when powered-up, its the stepper motors stepping into a known position.
If its doing this same thing at other times it sounds like the drive is disabling/enabling or a power fault - check the lights (if any) on the drive when it does it.
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Ok, I think I'll start by replacing the "Z" axis drive and see how it goes, maybe a faulty drive?
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Could be, could be just loose wire etc
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OK just to bring this back to the top, I've changed the Z motor and the driver and all is still the same :'(
Also checked the wiring and am sure all is good. Any further ideas where to look?
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any chance of sticking a video clip up on youtube??
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I'll give it a go but there really isn't much to see. Hopefully the sound if I can capture it will help. It's peculiar in that it only seems to do it when the axis is moving slowly, if I run it at rapid speed it appears to be OK.
Is it possible it could be something to do with the step per rev setting (currently 1600) resonating with something mechanically?
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I doubt it, steps per is relative only to distance travelled and the drive system mechanically.
So, travelling slowly it clonks, how slowly?
No clonks at rapid speeds or fast moves?
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I would suggest you have someone look at the pulse signal from pc and the drive with an o'scope.
May be that you have ringing on the pulses.
RICH
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Ok guys, a bit more info. I've checked the pulse train to the drive with a scope and there does not appear to be any "ringing" or interference there. I then tried different feed rates to try to see if any were worse than others. The problem is particularly bad at between 400-650 mm/min becoming ridiculous at about 570. I've taken a short video as suggested and attach here, as you will see or should I say hear there is a big problem. As I said previously this seems to disappear completely at rapid feed rates.
Video here https://youtu.be/d1a2sbQnat0 (https://youtu.be/d1a2sbQnat0)
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WOW, that sounds rough ;)
My only guess is resonance in the motor, I have not met this yet so have no idea how to tune it out if it is that. Some say adding mass to the motor shaft is a fix but only what I've read.
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Hi Dave, thanks for your input, that does sound like a reasonable assessment. The problem was there when I first got the machine with an NcStudio controller. It was my motivating force behind upgrading to the Mach 3 platform. In desperation I will try adding some mass to the motor shaft or would changing the driver current settings maybe help?
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The current settings should be matched to the motor I think, up to but not over the motor spec. Micro-steps is usually 1000 i think but can be others, try a google on stepper motor resonance.
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Dave, you may have just solved my problem. I did a little research on motor resonance and it's a little cleared now. Before adding mass to he motor I decided to play with the current drive, now halved from the original manufacturers setting and low and behold everything is much smoother and after 10 x 100mm cycles up and down the axis has returned to exactly zero. Tada!
It all goes to prove there's a lot to learn and often the simplest things can have the most effect. I'll continue to play with the settings to see if I can perfect them.
Regards and thanks again.