Stalling Stepper/Gearbox

[solissydney]

Hi.

I am looking for a replacement stepping motor/gearbox for my Astro Mount. The setup stalls on occasion, even when on the workbench as you see it on the image. The stepper on its own is fine, but not when mated to the gearbox. I find on the WWW that it is difficult to actually find a place that sell such items in order for me to travel to in order to speak to a human about my problem.
Ken

[bojan]

This looks like Crouzet gearbox.. ( I was using one -the same housing- a long tome ago... it was from washing machine timer, plastic gears)
http://www.beikimco.com/press/pr_ovoid_gearboxes_071410.php

Very hard to find these days. And expensive..
The whole thing looks like home made to me?

My suggestion then would be to open it and have a look inside..
Most likely you have broken gears...
There are places where you may find suitable gears, like SPI.
The other way may be to determine the reduction ratio of the gearbox.. and then see what can be done next in terms of replacing the whole thing with assembly of similar characteristics.

[solissydney]

Thanks Bojan.
Crouzet told me they don't make any gear boxes for the hobbyist, it was a special order then.
The gearbox is fine, was taken apart and lubricated. The rotation of the output shaft is one turn each 4 minutes. Will look up SPI

Ken

[solissydney]

Hhmm, millions of companies by the name of SPI. What does it stand for?

Ken

[bojan]

So, does it still stall when motor is on it or not?

If all gears are OK, maybe it is just too tight meshing at motor shaft?

If you do have broken gears, it should not be hard to determine the overall reduction ratio (by counting the teeth of each gear).. from there, perhaps something suitable could be found.
I may have something in my drawers.. just let me know the reduction, and shaft diameters/coupling

[bojan]

it is this one:
http://www.sdp-si.com/Press/New/Belts2_5.htm

Also, small parts and bearings:
http://www.smallparts.com.au/hobby/

[solissydney]

I did one more test on the stepper only Bojan
With light pressure using two fingers on the output shaft I felt the stepper stalling some of the time, other times I was unable to prevent the shaft turning.
So, the problem is the stepper only, not the gearbox.

Do you think it might help taking the stepper apart?

ken

[bojan]

First, make sure it is electrically OK (all windings are OK.. same resistance and so on).
Steppers are easier to find.. you just have to determine the working voltage and number of steps/rev.
Perhaps this is written on the label ?

The problem may be the mount wiring as well.. broken connectors, cold joints, broken wire... short circuit...

[solissydney]

The "TEAK" stepper looked OK inside.
Will try to work out working voltage and steps
Thanks Bojan
A friend of mine build the controller box and converted the old setup from 240/12V to the present setup many years ago.

[bojan]

The stepper is probably from old 5.25" floppy drive.. 100 or 200 steps/rev (TEAC ?)

[solissydney]

That is the size of my Dec stepper Bojan.
The RA motor, the problem stepper, is bigger at 40 mm by 40mm. Height is about 33 mm. Perhaps the reason it does not have enough torque any more, after many years of usage , is that I went from a ten inch to a twelve inch some time ago.

Ken

[bojan]

That is not the reason..
Most likely it just went faulty (one of phases are disconnected, either inside motor (less likely) or the cable is faulty (more likely).

It looks like NEMA17 size
http://www.linengineering.com/site/products/size17_18.html

[solissydney]

Which do you suggest? High torque? or Standard
Ken

[bojan]

Standard is quite OK.

Have a look at ebay..
Or Computer swap meetings.. look for old floppy drives.

Also, determine what type of motor is yours: bipolar or unipolar (count number of wires: 4 wires means it is bipolar, 5 or 6 means it is unipolar)

[solissydney]

5 mm shaft, 6 wires.
Bojan, you have been most helpful. Greatly appreciated. Many thanks

All the best
Ken

[bojan]

So this is NEMA17, 12V (most likely), unipolar motor, like ones used in 5.25" floppies.
The only unknown now is number of steps/rev. If I had it in my hands, I would be able to tell if it was 100 or 200s/rev..


No worries, always glad to help :thumbsup: