G11/Gemini slewing problem. Any thoughts?

[[1ponders] (Paul)]

We are using the 2032. I've just swapped it out and no difference. AAAARRRRGGGHHHHHHH!!!!!!!!!!!

btw the old battery was only 11 months old.


I'm going home.

[JohnG (John)]

Paul, the reason I asked if the motor was getting warm is that there could be a high point on the gear and the clearance might be tight on that point of the worm.

[allan gould]

Paul
On reading your posts- do you remember at Astrofest last year I was suddenly having problems with motor stalls as well as dec runaways? Was fixed by Acropolite when he changed over my cables. It turned out the one of my cables would give intermittent contact with temperature changes and gave this weird problem. I had it initially when I got the scope and then it went away for 3 years. Then cam,e back last year at Astrofest. You could try new cables. Mine now are internet cables - work great.
No problems now but I always suspect the 2032 then the cables if I get a problem Remember to wait 15 min after changing the battery and do a cold start.
Allan

[Omaroo (Chris Malikoff)]

Really keen to hear your ultimate findings Paul. My G-11 was delivered with Gemini and until what I ordered (standard Digital Drive & steppers) came through, I had the Gemini on loan. It was always stalling on me and I rapidly became tired of the "RA Stalled" messages I continuously got. I had the scope very well balanced in 3-D and the worm gap was perfect - not tight but no slop at all. It turned out that the RA servo was stuffed ex-factory, and the Dec servo was only marginally better because I did swap them as part of the diagnosis. This kind of fixed the problem, but on occasion it still stalled.

I eventually recieved the Digital Drive and replaced the troublesome servos with steppers and the simpler logic. Never had a problem since, and intend to add an ArgoNavis to it. I have found that the worm does need clearance maintenance periodically though.

[Bassnut (Fred)]

The controller sees a stall by the encoder feedback stopping. If the motor is still turning and you get a stall fault, the controller isnt seeing the encoder signal. Since its doing it on both motors, the cable might have a bad connection on the encoder wires. I cant work out exactly whats going on when you swap only one end of the cables, try swapping the 2 cables round totally and see what happens.

I dont get the "working sometimes" part unless theres an intermittent connection/wire. If the problem was balance/gears and you are playing with these during testing, I would have expected a "lag" error sometimes, (especially just before a stall), ie not a total stall, but enough drag for the controller to see the motor not going as fast as expected, this is probably not a connection/wire fault. If you get lag and stall faults, its probably mechanical.

If you only get stall faults, get your mutimeter out and compare the pin to pin connections end to end on both cables and wiggle them while your doing it. Of course any difference bettween the 2 is bad.

[[1ponders] (Paul)]

Ok, I'm home now and able to think more clearly.

John, the motors don't get hot at all. even after slewing all over the place until a stall. Motors are still cool.

Allan I've swapped both cables over still stalled, even ran RA from Dec the dec port and Dec from RA port and used the Dec buttons to move in RA etc. Still stalled.

I know where you are coming from Chris. This has been an ongoing problem, only now it is much worse. I've rebalance the scope and rechecked the RA Worm connection so many times now I could do it in my sleep. The stall only occurs when the scope passes the meridian to the west, never on the east. It will go for weeks with no problem and then suddenly it will start this rubbish. If I remove the motor and gear box I can turn the RA Worm with my thumb and one finger so it is definitely not too tight. There is the occassional tightish spot, but still turnable by finger. Hell tonight I totally loosened the worm so it wasn't touching and released the clutch and it still stalled!!!

Fred that is what happened when I removed the motor and let it run free. It still showed a stall but the motor still kept turning. Doesn't happen when its connected though. The whole thing just slams to a stop. Sometimes I can hear the motor struggling, but when I take it off I can turn the worm by hand without a strain. Even dropping slew and goto speeds haven't made a difference. I don't just get "motor stalled" Fred, I also get "tracking stopped" and that can occur after a successful goto.

I need a drink.

[netwolf]

I had similar issues with my Sitech Controller and Gemini Motors, turned out i needed to add some pullup resitors to the Encoders. At slow slew speeds the motors would turn without issue, but when slewed at high speed the motors would stall. Essentially the encoders were lossing position.

The newer sitech controller comes with the pullup resitors but the old one did not. From your intial descriptuon it seems the issue is on the RA output port of your Gemini. Might it be possible that similar pullup resistors on this output are faulty.

[[1ponders] (Paul)]

Thanks for all the feedback guys. Sorry if I've not sounded grateful, I am. It's just been and ongoing issue that I can't seem to resolve.

now the next important question, can someone pm me the name of a reliable, reasonably priced Gemini mechanic.

[[1ponders] (Paul)]

Fahim, if I had the remotest idea of what you are talking about I'd say Id look into it. If it's not outside the little black box I don't touch it. I think it has something to do with sticking a screwdrive into a GPO when I was about 8.

[Omaroo (Chris Malikoff)]

There's got to be another G-11/Gemini user, between Noosa and Brisbane, that your can swap out whole components with on the fly to diagnose the problem Paul You'd have it nailed in 10 minutes.

[[1ponders] (Paul)]

If I had a modercom of electronics capability, I'd have a go at whacking a multimeter on a few parts, but I have problems working out where to plug the leads into the multimeter. Seriously, give me a chainsaw and a forest and I'll build you a house (no steel pleeease), but if it's electronic and it ain't modular (as in, I do a pretty good job of the home entertainment system ) they you can forget it!!

[Omaroo (Chris Malikoff)]

Originally Posted by [1ponders]

If I had a modercom of electronics capability, I'd have a go at whacking a multimeter on a few parts, but I have problems working out where to plug the leads into the multimeter. Seriously, give me a chainsaw and a forest and I'll build you a house (no steel pleeease), but if it's electronic and it ain't modular (as in, I do a pretty good job of the home entertainment system ) they you can forget it!!

LOL! By "component" Paul - I meant whole Gemini assembly, whole RA motor assembly, whole Dec motor assembly, a cable, the other cable. If it were none of these then you probably have a mechanical prob.

[[1ponders] (Paul)]

Oh yeah.....that I can do


btw now you know why I have a Digital Drive and an Argo Navis

[netwolf]

Sorry Paul, did not mean to get complex there. I think your best bet at a Gemini mechanic would be Peter Ward. BTW how about building everyone a backyard observatory. If you need a short term fix, I still have a Digital drive kit packed from its last round trip.

[bird (Anthony Wesley)]

Paul, sounds like a bad connection in the socket on the controller, maybe check inside the box to see if you have a broken solder joint or crack where the motor socket joins the board.

Also check (but I'm sure you've done this) the RJ45 socket, clean the wires etc.

Sounds to me like the feedback from the motor to the board is not working, so the board doesn't think the motor is turning. The board stops the motor power so that it doesn't burn out, which would likely happen if the motor really was stuck.

cheers, Bird

[[1ponders] (Paul)]

The more I look into it bird the more I'm hoping that is all it is. I've swapped everything external to the box around (cables, motors, gear boxes, run dec from RA and visa versa) and the same problem occurs each time. The alternative is not something I want to think about. If the mother board needs to be replaced then I don't know what I'll do as I'm not sure there would be mother boards available for V3 Gemini still available.

[leon]

This is interesting reading, but I do feel for you Paul.

However not one person here has mentioned the Maxxon motor upgrade that Peter Ward suggested, or nearly insisted i get when I bought my G11 from him a couple of years ago.

The difference is between driving a 4 cylinder car, to a super charged V8, and it is true, they a awesome, and powerful, and never stall, even with a bit of a balance issue.

A bit pricey, but if they are added before shipment, it dosen't make a lot of difference.

Leon

[[1ponders] (Paul)]

Motors and new Gemini V4 might end up being an option Leon

[Bassnut (Fred)]

You say you have 16v supply. Have you checked the voltage while the motors are working, when you get the stall?.

[[1ponders] (Paul)]

No I haven't Fred, but it's strange it only happens in RA and always on one side of the mount in the same spot.