Stalling DEC motor?

E_ri_k (Erik) · #1 22-03-2012, 10:49 AM

Does anyone have any ideas why I would be getting the error "DEC Stall" on my gemini 2? Thought the worm may have been a bit tight, so I adjusted it a little, and even with a lot of play, it still stalled. Even with the motor removed completely from the mount and gear box, it stalls under no load at all. RA works fine.

After playing around a little I noticed it will only stall on speeds above 500. swapped motors around, and it is definitely the DEC motor. I'm thinking something is broken?

Its running on 12V 10 Amps.

What do you guys think?

multiweb (Marc) · #2 22-03-2012, 11:43 AM

Just ramp up your voltage from 12V to 16V with a DC to DC converter from JayCar and you won't have any more stalls.

E_ri_k (Erik) · #3 22-03-2012, 04:04 PM

Ok thanks. ill give that a try

wasyoungonce (Brendan) · #4 22-03-2012, 05:55 PM

Nah...shouldn't stall if removed from gear box.

Try swapping motors see what prevails.

multiweb (Marc) · #5 22-03-2012, 05:59 PM

Quote:

Originally Posted by wasyoungonce

Nah...shouldn't stall if removed from gear box.

Try swapping motors see what prevails.

Yeah , too low voltage will do that. Had the exact same problem. Even took the worm completely off the meshing and it would still stall. Just low voltage. That's all. 16V will fix it. If not then the motor has been damaged (likely overheating) and needs changing.

wasyoungonce (Brendan) · #6 22-03-2012, 07:19 PM

Quote:

Originally Posted by multiweb

Yeah , too low voltage will do that. Had the exact same problem. Even took the worm completely off the meshing and it would still stall. Just low voltage. That's all. 16V will fix it. If not then the motor has been damaged (likely overheating) and needs changing.

Jeez...I've felt the motor torque on the pinions (of a G1) with them driving @12V (normal rates)...damn...no way to even attempt to hold them. But with no load...I am surprised.

Lots have complained about Gemini @12V...I've personally never had an issue but that doesn't mean much.

What are the G2 drive H bridge drivers like? Maybe there is a change wrt this.

E_ri_k (Erik) · #7 22-03-2012, 09:40 PM

Yeah, I tried swapping the RA and DEC motors over. Same thing happened. The DEC motor on the RA axis slewed perfectly, but the RA motor on the DEC axis stalled. So I guess it cant be the motor.

I think I will try the 16 volts and see cross my fingers.
I'll keep you posted.

Thanks so far!

Barrykgerdes · #8 22-03-2012, 10:46 PM

Did you say 12volt at 10 amps. I would think 12v at 1.0 amps would be more like it. If so you have a problem with the motor control. 16 volts may cause problems. Try to put a meter across the motor power supply and see what voltage is being delivered. It should be close to 12v at full speed. However I would expect it to be pulse width modulated for control and you may need a CRO for an accurate assessment.

Barry

E_ri_k (Erik) · #9 22-03-2012, 10:55 PM

Barry, yes I mean "10" Amps. That is the maximum current output of my power supply. I'm sure the G2 is not drawing 10 Amps though. I am looking at a 15V 5 Amp power supply at the moment for $160.

[1ponders] (Paul) · #10 23-03-2012, 09:52 AM

Erik, I can fully understand your frustration. We have been battling the exact same problem with a G11 (G1 V4 gemini) for years now at the Mapleton Observarory. We have tried everything, including swapping power supplies, cables, gearboxes. Frankly I think its in the hand controller or the connection from the HC to the Gemini.

I've also had it happen occasionally on my home Gemini. I'm not sure if I solved the problem or not, but it hasn't happened in a while and I've never really found a satisfactory answer on the net, even after emails with Scott Losmandy. Good luck with it, I hope you solve it.

wasyoungonce (Brendan) · #11 23-03-2012, 10:55 AM

Quote:

Originally Posted by E_ri_k

Yeah, I tried swapping the RA and DEC motors over. Same thing happened. The DEC motor on the RA axis slewed perfectly, but the RA motor on the DEC axis stalled. So I guess it cant be the motor.

I think I will try the 16 volts and see cross my fingers.
I'll keep you posted.

Thanks so far!

Did you try swap cables as well?

G1 uses a H bridge to drive the motor and this is controlled by the encoder pulses it sends back which are read by various RA/DEC programmed (PAL) chip-sets.

G2...from what Rene said...a similar set-up aka a H bridge and reads encoders (same motors as G1) ...albeit with newer & different chip-sets than G1.

E_ri_k (Erik) · #12 23-03-2012, 11:10 AM

I will try a cable swap next chance I get. If I have no luck I'll try the 16 volt power supply and hope it works. I hope its not going to be too frustrating!
As for the hand controller, last month I lost all my catalog objects, and found out that the SD card was corrupt and had to replace all the files. Maybe its connected to that problem somehow?
Ill keep you posted.
Thanks.

E_ri_k (Erik) · #13 24-03-2012, 11:19 AM

Ok, so a cable swap did nothing. Tried a few other things also. So:

The DEC motor stalls in the DEC port under no load.
The DEC motor stalls in the RA port under no load.

The RA motor works fine in either port under full load.

To me it sounds like a motor issue??

I haven't got a 16 volt power supple to test yet. Having trouble finding one.

asimov (John) · #14 24-03-2012, 11:41 AM

If your RA motor is running fine under 12V then I'd say the answer is obvious.

Barrykgerdes · #15 24-03-2012, 12:22 PM

Hi I have a thought on this.

The old LX200 classic had inverter drivers referenced to a fixed voltage to handle the motor drivers that were l2724's. The RA motor driver was supplied with the main supply rail 12-18 v but the Dec was supplied from 5 volt. The effect I noticed was that some Dec drive worked better than others. A later mod changed this supply to 12 v.

The LX200 design was probably from manufactures specs (no copyright problem). I would expect the Gemini drive to have been done the same way so maybe the motor drive circuitry should be examined for the Dec verses the RA.

Barry

wasyoungonce (Brendan) · #16 24-03-2012, 02:44 PM

Quote:

Originally Posted by E_ri_k

To me it sounds like a motor issue??

Yep ...motor bad. They can be repaired by yourself or I believe send back to Losmandy (maybe thru your dealer). You can buy a new one but at $200...ouch!

There is another guide on repairing Gemini motors..probably by Rainer...I'm not at home so sorry I don't have a link.

kinetic (Steve) · #17 24-03-2012, 03:03 PM

Quote:

Yeah, I tried swapping the RA and DEC motors over. Same thing happened. The DEC motor on the RA axis slewed perfectly, but the RA motor on the DEC axis stalled. So I guess it cant be the motor.

Quote:

Ok, so a cable swap did nothing. Tried a few other things also. So:

The DEC motor stalls in the DEC port under no load.
The DEC motor stalls in the RA port under no load.

The RA motor works fine in either port under full load.

To me it sounds like a motor issue??

Erik,

I certainly know NIL about the Gemini system but I know a little about steppers.
Brendan sounds on the money...it may be the bridge driver circuit on the
DEC axis has a component fault or simple connectivity problem.
It's also a little difficult to understand your two posts above...
Don't they sorta contradict each other?

One other thing, the tiniest piece of metal inside a stepper when
fouled against the spinning rotor permanent magnets and stationary
outer metal cage with the windings will cause these stalls.
Can you spin the motor freely? You will feel a smooth 'lumpiness' or
friction as it settles on it's 'steps'.
If there is metal or grit inside it will grab randomly.
Moisture/rust in the bearings (motor)will do this too.

Edit: Ahhh I followed Brendan's links....Hmm it has brushes
and an outer permanent magnet!....Hmm, what sort of stepper is
that?!!! Is it simply a DC servo/motor with encoder feedback for speed control???

FWIW.

Steve

wasyoungonce (Brendan) · #18 24-03-2012, 07:54 PM

Quote:

Originally Posted by kinetic

Erik,
....
Don't they sorta contradict each other?

........
......Is it simply a DC servo/motor with encoder feedback for speed control???

FWIW..Steve

Yeah he has contradicted himself but the last test points it to be a motor problem. Its confusing at the best of times and easy to come to the wrong conclusions without a logical test method.

I've done (or shall I say failed to do) this more than once.

The Gemini motors are H bridge driven DC servos with encoder feedback. Since this is a Gemini2 then the control is quite different to the G1. However his last tests did indicate it to be the motor issue...IMHO

.

Which in itself is odd...I assume it's reasonably new...maybe a motor was damaged by a bad balance?

E_ri_k (Erik) · #19 24-03-2012, 10:53 PM

Ok, yep I did contradict myself! Haha. It made sense in my head what I was typing, but I guess it didn't read too well!

So what I meant was that the motor which is stalling, stalls when plugged into the DEC port AND the RA port on the gemini 2 panel. The Good motor currently on the RA axis, works without a problem, when plugged into either port on the gemini 2 unit.

To me that sounds like the motor is buggered, and the circuitry inside the Gemini 2 is OK. Yes?

Sorry if I confused you guys....

The motors are not all that old, about 3 months. I do keep my mount permanently set up in my shed outside, so moisture may be getting into them, but I don't think much would be. The gemini 2 unit comes inside every night though.

E_ri_k (Erik) · #20 07-04-2012, 10:44 PM

Ok, so the motor is stuffed, it stalls no matter what now. I was thinking about getting the Maxon motors when I bought the gemini 2 upgrade kit, but didn't because of the $350 price tag!

So I'm thinking about swapping to the Maxon motors, as one is stuffed anyway. The question is, do you think I could get ONE now, and run with one of each motor while I save for the second? Without any problems?

Thanks.