G11/Gemini slewing problem. Any thoughts?

[[1ponders]]

We are having a problem with the G11 at the Mapleton Observatory. The RA keeps stalling and displaying "Motor Stalled" or "Tracking Stopped".

I did all the normal things, checked balance, checked worm alignment and mesh, even loosened it right off. I then swapped the dec motor with the RA motor, and drove the Dec motor same problem. RA (dec motor) kept stalling. Then put the RA motor back on the RA cable and ran the RA motor unconnected to the mount, "Tracking Stopped". Ah Ha I thought, the motor is stuffed. But no! I connected the Dec motor (again not connected to the scope)...."Tracking Stopped", "Motor Stalled" and then connected the Dec cable....np, the motor ran fine.

So how can both motors run fine when connected to the Dec cable, but both motors stalled when connected to the RA cable?:confuse2::confuse2: :confuse2: Would a poor connection cause this problem?

[[1ponders]]

Nope, I just swapped the cables over and same problem. :confuse2:

[[1ponders]]

Weirder and weirder. No moters, press the handpaddle RA buttons...Tracking Stopped!!!

[renormalised]

Sounds like there's something screwy with the controller chip on the PCB, or the connector you plug the cables into for the RA encoders/motor is faulty. You may have to lift it out and check underneath the PCB to see whether you have worn or loose soldering. If it's not that, then a multimeter check of the pins in the connector might be warranted. If everything is OK there, check your handpaddle.

[JohnG]

Hi Paul

Check your power supply, Motor Stalled or Tracking Stopped can usually be traced back to insufficient voltage.

Cheers

[renormalised]

Come to think of it....check all the connectors and pins on the PCB's. It could be something as silly as a frazzled resistor!!!

[renormalised]

Problem is they're getting enough juice to the DEC motor, so unless the cable to the RA box is faulty, you'd think they'd be getting it there too.

You maybe right though.....

[h0ughy]

try the voltage?

[[1ponders]]

Running on 16V John so should be np there. The Dec is fine.

I've just put it all back together and given it another run and it keeps stalling about 45 deg with the scope on the west. I've turned it off and tried to get it going but tracking refuses to start, and the screen says motor stalled. But I know if I pull it off and put it on the dec drive it will work fine. ?????

[allan gould]

Paul
It could be that the 3 volt battery is beginning to loose juice. Swap it over. Believe me had the same problems and it WAS the 3 volt battery. Really weird.
Allan

[renormalised]

Was anyone trying to take a piccie of Zeta Reticulii???. That might be your problem. The gov'n doesn't want you to find out about the little Grey fellas, so they've sabotaged the scope:P:P:D:D

Gotta pullout a conspiracy theory somewhere!!!!:eyepop::P:P:D:D

[renormalised]

Is that much the same as the CR2032 battery on a MB??. If so, then I can understand why things might go haywire, especially if it's being used to keep the onboard electronics upto speed.

[[1ponders]]

That was my thought as well at first Allan, but this is just so damn weird. I'll do that this week and see how it goes.

[JohnG]

Does the motor get warm at all.....

Allan is right about the battery in the control unit, it can cause some weird responses, if it is more than 12 months old, it should be replaced anyway.

Cheers

[[1ponders]]

Ok if the motor stalls and I swap the cables over at the motors, no go. But if I swap the cables over at the controller then away it goes again......until it stalls. :doh:

[[1ponders]]

New battery this week!!!

[JohnG]

When it is running, does the motor get warmer than normal..

[allan gould]

That little 3 volt bugger and the stupid 1 line handset are the achilles heel of the Losmandy mount

[leon]

John, although I did consider changing my battery in the Gemini Unit, I have to admit I got slack and did not do it as yet.

So from date of purchase it is still running like a dream and into its third year.

Leon :thumbsup:

PS, I agree one night it will give me grief, I expect :shrug:

[JohnG]

There are 2 different types, the older Gemini's have the CR 2032 which is good for around 12 months but the newer Gemini's have a different battery which is rated for a bit longer, from memory, the one Paul has in the Observatory is the older version.

[[1ponders]]

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. :mad2:

[JohnG]

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]

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]

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]]

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]]

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]]

Fahim, if I had the remotest idea of what you are talking about I'd say Id look into it. :lol: 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. :lol:

[Omaroo]

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 :shrug: You'd have it nailed in 10 minutes.

[[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. :P 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 :lol: ) they you can forget it!!

[Omaroo]

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. :shrug:

[[1ponders]]

Oh yeah.....that I can do:D


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

[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]

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]]

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. :sadeyes:

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:thumbsup:

[[1ponders]]

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

[Bassnut]

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

[[1ponders]]

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.

[acropolite]

Paul, what Bird described is a common occurence with RJ sockets in telephone handsets, the constant movement either cracks the cct board tracks or if the solder joint is at all fragile it simply cracks that.

Often the cracks are hairline, best remedied by soldering a piece of wire back along the track.

Given what you have described that would be a good starting point. If your soldering skills are a bit average, get someone who is proficient to do it, as too much heat can quickly destroy the fine tracks that usually connect to the RJ PCB sockets.

[leon]

Bloody hell, this is getting to much for me. :scared:

Paul, I wish you well.;)

Leon :thumbsup:

[[1ponders]]

:rofl: geez you make me laugh sometimes Phil. :rofl: "a bit average" doesn't even come close. Absolutely woeful might be closer. Completely incompetent would be better. :P

[Hagar]

Hi Paul, with you r statement above it is indicating it is something mechanical rather than an electrical problem unless you have a cable dragging or moving in this position.
Have you tried loosening the the clutches fully and then operating the drive through the full range. If it still stalls it may be a tight spot on the worm gear.

I don't see you have much to continue with other than trying to eliminate one thing at a time. next would be to mechanically disconnect the servo and drive it again without load. If the motor again stalls I am afraid you are looking at cables or electronics.

If it looks like being an electronic problem have a good look with a magnifying glass for a dry solder joint. Sometimes these will only show up when current is passed and the connection heats up a little.

Good luck.

[[1ponders]]

Doug, I've done everything you've suggested including running the servos unattached and Motor Stalled still comes up. There are no cables snagging, I've dropped the worm right down so it isn't touching the gear as well as releasing the clutches completely. I've swapped motors, cables, gearboxes, run DEC through RA and visa Versa, used the Dec motor in place of the RA motor, yet when it stalls and I remove the motor I can rotate the worm by hand with no difficulties at all. It has me totally stuffed. I believe that there is something electronic, possibly in the encoders or as Phil has suggested in the RA socket, but it's the repeatable positioning of the stall that's got me. As you suggest it sounds mechanical, but given everything I've tried I don't see how it can be.

[[1ponders]]

JOI is there any difference between the servo motors used for V3 Gemini and V4 Gemini.

[Shano592]

A good rule of thumb is to change these batteries on April Fool's Day, along with your smoke alarm batteries, and any others (like car remote and motherboard batteries).

That way, you have a fixed "maintenance" schedule, on all items like this.

[Bassnut]

Measure the supply voltage under load punk, do the easy obvious tests :whistle:

If the motor is stalling not even connected to the mount, forget the mount.

[leon]

Hmmm, Fred i might have to agree there, so to try the set up with a L4 Gemini unit probably wouldn't help either, :shrug: what about if someone sent Paul a motor, to try ;)

Leon :thumbsup:

[[1ponders]]

The hand paddle is saying the motor is stalled but the motor is still turning :screwy:

[leon]

Gees Paul, what are we going to do with you, mate, :shrug: you have lost me. do you wont me to send you a hand paddle, as I'm away for two weeks, come Saturday.

Leon :thumbsup:

[JohnG]

If you have confirmed the motor is actually running but the hand paddle is showing otherwise, change the hand paddle cable, if you have a spare or can get hold of one, they are Mac cables I believe, replace it.

Give the cable a wiggle and see if that clears the problem, I had an intermittant problem show up when I had my Gemini, I replaced the hand paddle cable and the problem disappeared.


Other than that I am out of ideas....


Cheers

[Hagar]

If the motor is still turning it would indicate a feedback problem from the motor encoder or a hand paddle problem. Back to cables or hand paddle or cable or a crook solder joint in the connection area on the main board.

[acropolite]

I'm not sure what the G11 motors and encoders look like but if they're seperate, the controller is probably checking the encoders (how else would it know the motor had stalled?) and not seeing them turning therefore deduces the motor has stalled.

[Hagar]

If it is similar to V4 then the motors and encoders are in the one unit. It would indicate that the encoders are fine if they work OK connected to the Dec drive cable.
The problem must be in cables or main board or hand paddle or any combination of these.

[bird]

The motor cables contain wires for both power to the motors and reading back the encoder signal from the motor to see how fast the motor is turning.

Sounds to me like the latter signal is not getting through, ie a broken wire in the cable or a bad solder joint.

For what its worth, a broken wire in the cable may also explain why the mount seems to stall at a certain point, maybe the cable is being bent just right to go open circuit.

You could check this by swapping the RA and DEC cables and see if the problem moves with it, or flexing the RA cable and see if you can provoke the problem.

cheers, Bird

[[1ponders]]

Yep, done that too bird. I have a sneaky suspicion that acropolite may be on the money with a break in the socket on the gemini side.

Leon has offered to lend me his V4 gemini, will it work with the motors I have and will he need to send his cables and hand controller as well?

[h0ughy]

http://www.ovision.com/Losmandy_PresentationNS_english.htm l just as a small distraction, what about the item in the link - might rule out the worm drive

[[1ponders]]

I've done a bit more with it, taking into consideration some of the suggestions and advice and it looks like its the RA motor. I'll send the whole kit and kaboodle away to get looked at but I think that is all that is needed.

[[1ponders]]

I've been tempted by those for my G11 Dave, but unfortunately the money for them has been tagged for other needs....like food and bills. :lol: