Stalling Stepper Motor

solissydney (Ken) · #1 29-03-2010, 07:18 PM

What could be the reason for my RA stepper motor, intermittently, stalling when I press the fast forward button?

peter_4059 (Peter) · #2 29-03-2010, 07:21 PM

This can happen if the worm mesh is too tight.

solissydney (Ken) · #3 29-03-2010, 08:01 PM

Been there, done that. Even with a bit of slack (backlash) the stepper still stalls now and again.
With thanks

Ken

Bassnut (Fred) · #4 29-03-2010, 08:05 PM

Steppers dont like excessive load, is the OTA well balanced?. Try lowering the slew acceleration or slew speed.

[1ponders] (Paul) · #5 29-03-2010, 08:13 PM

What mount are you using?

solissydney (Ken) · #6 29-03-2010, 09:02 PM

It is a BIG one. An Astro mount (27 KG) with a 12 inch tube. Although I converted the tube to plywood the tube with all the gear on it comes in at only 15 KG.
The setup is well balanced. The gears are 15 cm in diameter. There is no slewing.
Fast forward, wait for it, is twice the speed of the drift of a star. I tried the stepper without any load, and of course there was no problem.
The problem, including the ST-4 guiding; see ( Astrophography and Imaging) "ST-4 problem" began without apparent reason about two month ago.
Actually, come to think of it, that was the time I slowed down the speed of the RA tracking, closer to what one normally would have it set at, namely precise tracking. Prior to that I had the tracking faster for the purpose of having the auto guider stopping the tracking only, rather than stopping and speeding up. Anyway, perhaps I should be looking for a stepper motor with more torque? Is their is such a thing?
Thanks for your inputs
Ken

Spanrz (Brett) · #7 30-03-2010, 10:13 PM

Stepper motors stall either due to load overcoming the magnetism (could be too low of current related or too much load), or the power switching between the coils is set too fast (slow the speed of the steps / power is cycling too fast around the coils).
Could be a controller problem as well, (either controller itself or the signals to the controller are wrong-i.e giving the controller a bum steer on what it really needs to put out).
I've got some NEMA 17 motors, small 6 wire motors (I think it's a Hybrid Motor). They put out a hellava grunt for such a small motor.
They have a max current of about 5amps, but 3amps is good enough. Anything over 3-4 amps and they get pretty warm.
Spent a lot of time mucking around with these motors and different current rates/steps.
Too much current made them really "torqy", but also made them hot real fast.
Too much speed or the wrong step, and they just stalled and buzzed.

bojan · #8 31-03-2010, 01:16 PM

Check power supply voltage..

solissydney (Ken) · #9 31-03-2010, 01:56 PM

Problem solved I believe.
It appears the gearbox is is the cause of my problem.
Thanks for your interest
Ken