[nicubila]

I am facing a very annoying situation where I loose steps after 2-3h of work.
I have a 4 axes router, with the gantry being moved by 2 independent motors nema23, 3Nm.

One of the motors (Y) starts to loose steps, mostly after a period of work, 2-3h. Even though today when started the router, it lost steps for the first 3-4 very short runs (1-2min), then it went fine for the next 2-3h. The other motor (A) though is fine, no more than 0.05mm lost per 1h of work.

What i have tried so far:
- change the command of the motors, actually switch motor command pins between Y and A, and still y lost steps.
- checked the mechanical parts of Y, and all looks fine
- in the first 2h router can work at 6000mm/min on Y and A, but once starts to loose steps, even at 2500mm loses about 0.5mm (!!!) at a 5min run.
- checked the resistivity of both motors, and on all I have the 1.3ohm just like in the datasheet. SY60STH88-3008BF
- changed also with other bigger drives (EM806) but same effect.

So can it be that the Y motors is actually damaged even though it looks fine?
What i know is that a motor wither works or is damaged. Is that correct?

thanks
Marius

[awerby]

Lost steps are common in open-loop stepper motor systems that are driven harder or faster than the drivers or motors can go. It's rarely due to deterioration of the motors themselves. The simplest remedy is usually to ease off a little. You can lower your expectations of how fast the machine can move, and lower the acceleration and velocity settings to reflect that. If it's misbehaving initially and getting better after a short while of running, you might also try cleaning and lubricating the slides and screws first, and running them back and forth to distribute the oil. If you really need to go faster than your current system allows without errors, you might look into redesigning your motion control system.

Andrew Werby
www.computersculpture.com

[nicubila]

The thing is that loosing the steps happens even when the speed is lowered to 2500mm/min, at acc 100. For 2h works fine at 5-6000mm/min, acc 250, then not even at this speed.
I checked also:
- the motor shaft and pulley, they remain engaged (a scratched line is perfectly aligned)
- the screw and pulley, they remain engaged (again the scratched line is perfectly aligned)
- the lubrication seems ok, moves very easy.
- the nut moves very smooth on the whole length of the screw
- no movement can be detected if i try hard try very hard to move the Y gantry forward or backwards - it seems the screw is very well fixed.

In my view it can be either the motor or smth mechanical.

Anything else to check?

[wendtmk]

Are your drives getting too hot? Do you have heat sinks on your drives?

Mark

[nicubila]

No heating, and try used different drives, switched them....still the same.

[CarveOne]

The thing is that loosing the steps happens even when the speed is lowered to 2500mm/min, at acc 100. For 2h works fine at 5-6000mm/min, acc 250, then not even at this speed.
I checked also:
- the motor shaft and pulley, they remain engaged (a scratched line is perfectly aligned)
- the screw and pulley, they remain engaged (again the scratched line is perfectly aligned)
- the lubrication seems ok, moves very easy.
- the nut moves very smooth on the whole length of the screw
- no movement can be detected if i try hard try very hard to move the Y gantry forward or backwards - it seems the screw is very well fixed.

In my view it can be either the motor or smth mechanical.

Anything else to check?

The acceleration rate sounds like the problem to me. Try setting it to 30 and see if it works correctly. If yes, start increasing the number in increments of 10 or so until problems reappear. 100 to 250 is way higher than my DIY machines will handle. It may be causing any parts fastened with setscrews to slip.

[CarveOne]

How heavy is your gantry?

[nicubila]

it is mm/sec2, not in...just in case to be sure we talk same units.
when cold, router works as mentioned at 300mm/sec2 acc, 6000mm/min feed. and it used to do so 8h/day. the other motor on the gantry is identical but does not loose steps (maybe a couple during 1h run).

[nicubila]

found the problem, it was some bed dust in the ballnut. No sound, just losing between 0.2 and 0.6mm. Cleaned properly and works again.
Strange though that when trying to move the ballnut with hand, it worked fine for most of the time, then all of a sadden very stuck...