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Gemini g11 issue:not balance, voltage or worm mesh

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#1 gillmj24

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Posted 25 July 2010 - 05:27 PM

I am having some RA motor stalling issues lately no matter how well I balance the scope. I have a Meade 10" sct that stays put when both axes are unlocked so I think balance is fine and I am not trying anything crazy like side by side or piggyback setups yet.

Anyway I can slew just fine in all four directions but if I let it sit for 5-10 minutes, then I hear a beep and it says TRACKING STOPPED! sometimes it starts out with "RA motor lags" before it stops tracking totally. If I turn off and on again the same thing happens. So it's not like the worms are binding or else it wouldn't slew again when I cycled the power right? I removed the motor and cover enough to see the RA worm through a small window. I spun the gear with a small Allen key and it moved fine so again I don't think the worms are the problem.

I took the battery out (which I replaced in January otherwise it kept resetting to Hollywood CA and January 1st) for 15 minutes and put it back but to no avail.

Also got a losmandy 18v adapter to use that 4-pin brown wire the previous owner supplied  but that didn't help much either. Whether I plug the 12v cable into my pyramid 5A 13.8v power supply or use the 18v converter and te 18v wire the same thin happens. Also tried my good Kendrick battery.

I know the Gemini g11 is sensitive to balance worm mesh and voltage but I thought I eliminated those three sources of problems. I swapped the ra and dec wires and then the dec motor stalled. Maybe that servo wire is bad? Hopefully the Gemini board is not to blame.

I did buy a level 4 chip v1.05 i wonder if that's to blame. The previous owner had really old firmware but didn't report any issues to me. I am posting here while I await moderator approval for the losmandy yahoogroup.
I had one good night last week where I really took the gemini for a test drive for the first time since I got it. It worked well for an hour or so but it's been downhill from there.

#2 saadabbasi

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Posted 25 July 2010 - 05:40 PM

If you swapped the wires and the problem shifted to DEC, I would check the wires carefully. Could be a bent pin.

I have not experienced this issue, but thats what comes to my head.

#3 rsbfoto

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Posted 25 July 2010 - 05:44 PM

I am having some RA motor stalling issues lately no matter how well I balance the scope. I have a Meade 10" sct that stays put when both axes are unlocked so I think balance is fine and I am not trying anything crazy like side by side or piggyback setups yet.

Anyway I can slew just fine in all four directions but if I let it sit for 5-10 minutes, then I hear a beep and it says TRACKING STOPPED! sometimes it starts out with "RA motor lags" before it stops tracking totally. If I turn off and on again the same thing happens. So it's not like the worms are binding or else it wouldn't slew again when I cycled the power right? I removed the motor and cover enough to see the RA worm through a small window. I spun the gear with a small Allen key and it moved fine so again I don't think the worms are the problem.

I took the battery out (which I replaced in January otherwise it kept resetting to Hollywood CA and January 1st) for 15 minutes and put it back but to no avail.

Also got a losmandy 18v adapter to use that 4-pin brown wire the previous owner supplied  but that didn't help much either. Whether I plug the 12v cable into my pyramid 5A 13.8v power supply or use the 18v converter and te 18v wire the same thin happens. Also tried my good Kendrick battery.

I know the Gemini g11 is sensitive to balance worm mesh and voltage but I thought I eliminated those three sources of problems. I swapped the ra and dec wires and then the dec motor stalled. Maybe that servo wire is bad? Hopefully the Gemini board is not to blame.

I did buy a level 4 chip v1.05 i wonder if that's to blame. The previous owner had really old firmware but didn't report any issues to me. I am posting here while I await moderator approval for the losmandy yahoogroup.
I had one good night last week where I really took the gemini for a test drive for the first time since I got it. It worked well for an hour or so but it's been downhill from there.


If I remember well when you have a stalling due to a MOtor LAg the mount does not beep.

It beeps when you have reached a set RA Limit be it on the Eastern or Western side.

#4 skybsd

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Posted 25 July 2010 - 05:49 PM

Hello Joseph,
Sorry to hear of the problem you're having there..,

From what I recall, this mount you have was working fine for your set up before this started happening, yes?

As long as nothing has changed in terms of your set up, but then, for no apparent reason, you've recently started experiencing this issue, I'd suggest that it might well be the gearbox that is slipping.

Its really simple to remove and check the gear meshing to see (visually check) if there's some degraded teeth, or other play in their meshing together.

Also, I know that you've done this a lot, but can you make sure to double-check your balance when the problem next presents itself again, please? That is, when your get the "TRACKING STOPPED!" error, hard stop Gemini, and just unlock the clutches to see if your payload is still as balanced as when you checked before starting off..,

You never know.,

Best of luck..,

Regards,

skybsd

#5 gillmj24

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Posted 25 July 2010 - 06:46 PM

Well I had the mount for a few months before really trying it out. So I didn't really have much success with it only because Astro time was limited this year.

Thanks for the suggestions. When centering (when I had it out without settin up Gemini) there is virtually no backlash in either axis.

Where would the bent pin be in the ra wire or on the Gemini board?

#6 saadabbasi

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Posted 25 July 2010 - 07:01 PM

Well, if it changed, I'd reckon its the wire as it shifted along with the wire, didn't it?

#7 blueman

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Posted 25 July 2010 - 07:32 PM

No backlash might mean that the mesh is too tight. You want 1-2mm movement at the end of the counter weight shaft.
Blueman

#8 gillmj24

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Posted 25 July 2010 - 08:19 PM

I meant when you switch directions with the hand controller, the reverse in direction was instant.

I thought that was a good thing... I'll go measure the movement at the end of the shaft and report back.

#9 gillmj24

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Posted 25 July 2010 - 08:26 PM

Yes, I can wiggle the end of the CW shaft a couple mm back and forth with the clutch tight.

Yes, I then unlocked the clutch to make sure it was still balanced and it was.

I just rstarted things in the home position - CW down, Dec 90 - and now it won't slew at all in RA in either direction.

THis is with my 12v cable plugged into my 13.8V 5A Pyramid supply (the one like AP sells) since it doesn't seem to want to power on at all with the Kendrick 18 volt converter in anymore.

If you still think it's a gear mesh issue - and I prefer that to having to replace the gemini board - please let me know of a photo tutorial to fix this.

I;m sure there is one on the yahoo group and hopefully they'll be back at their desks tomorrow to accept me.

#10 David Pavlich

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Posted 25 July 2010 - 08:47 PM

Hey Joseph...just to eliminate the weight or balance issue, I'd stick a lighter scope in there first. Get it balanced and see if the same problem creeps up. If the problem shows up with a light load, I'm guessing that there's some sort of binding going on.

David

#11 skybsd

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Posted 26 July 2010 - 01:07 AM

Hello Joseph,

Yes, I can wiggle the end of the CW shaft a couple mm back and forth with the clutch tight.

Yes, I then unlocked the clutch to make sure it was still balanced and it was.

I just rstarted things in the home position - CW down, Dec 90 - and now it won't slew at all in RA in either direction.

THis is with my 12v cable plugged into my 13.8V 5A Pyramid supply (the one like AP sells) since it doesn't seem to want to power on at all with the Kendrick 18 volt converter in anymore.


I take it that the DEC slews work fine still?

What does Gemini say when you try to slew in RA and see nothing happening?

Can you hear the RA motor whilst you see no movement?

Did you check the gearbox as yet?

Regards,

skybsd

#12 gillmj24

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Posted 26 July 2010 - 06:02 AM

It says Motor stalled and tracking stopped. I was just approved on the yahoogroup so I'll check their files section tonight.

#13 blueman

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Posted 26 July 2010 - 12:44 PM

You will need to remove the worm cover and take a look at everything. Check the set screws on the Oldham coupler, check to see there is nothing loose. Look to see that the worm is properly greased and nothing is there like dirt or other contaminates.
You may have to remove the motor and gear box to check the smooth turning of the worm. You might be able to just loosen the Oldham coupler on the gearbox side and turn the worm with your fingers without removing everything.
The problem sounds like something is binding. It could be anything from the motor or gear box to the worm.
Blueman

#14 gillmj24

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Posted 26 July 2010 - 01:38 PM

Can I try removing the motor from the worm and see if the Gemini will run the motor?

The guy I bought it from suspects a bad cable.

#15 gnowellsct

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Posted 26 July 2010 - 02:24 PM

Cable failure is a major thing on all scopes.

The G11s *prefer* to run on 18v. Assuming you have enough backlash in the setup 1-2mm, err on the 2mm side, voltage is a major cause of slewing problems.

Among the people I observe with I don't know anyone with a go-to system who has not, at one time or another, experienced slewing errors. That's why I settled in with push-to.

regards
greg n

#16 gillmj24

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Posted 26 July 2010 - 08:24 PM

OK more tinkering and an update:

I swapped the two cables, but that didn't change anything.

I put the RA motor on the Dec cable, then it said Dec stalled (one expected that)

Then I took the RA motor OFF the mount, to se what would happen, to eliminate motor-worm binding as the cause.

After a few seconds of tracking, the motor STOPPED! Same RA motor lags! then MOTOR STALLED! errors appeared.

I gave the little exposed sprocket a nudge and then it resumed tracking. After that point, I could slew in both directions with ease, at the lower speed that I had set thinking this was a voltage issue at first.

Looks like I need a new motor. I took the encoder cover off and it did not appear as though the encoder was bent but it doesn't take much for those to fail. Could a bad enocer be causing this?

Seems like a new motor should fix this.

Tonight's testing was done with the Pyramid power supply and the 12v cable. For some reason the 18 volt wire is not powering the mount. I don't know if my new 12v-18v converter is bad, the Gemini LED won't even light with it connected. Horrified, I put back the 12v cable (running at 13.8v) and it powers on fine.

Anyone know which pins on the 3 prong (one the side going to the converter, 4 pins going into gemini) to test with a multimeter? I tried all combinations but they all came up with 0 volts.

#17 gnowellsct

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Posted 26 July 2010 - 09:52 PM

If you can afford it I would order the MAXON motors and keep your remaining good motor as a spare. The Maxon motors are much tougher. They cannot "power through" tight spots in an incorrect worm mesh but they will be less prone to give up the ghost.

Clever diagnosis. Don't rule out the 18v however.

Greg N

#18 gillmj24

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Posted 26 July 2010 - 10:31 PM

Where to purchase the maxon and how much?

Losmandy's site just says if you get a new Gemini retrofit kit with the maxon motors it is $200 more.

Oh I jiggled the wires while running the motor away from the mount and I don't think it made a difference.

#19 gnowellsct

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Posted 26 July 2010 - 10:46 PM

You get the motors from Losmandy, and you need to call. I don't remember the total price. It appears one of your servos is bad, that leaves you with one good one. There is a market for both these and the steppers. But the Maxons will set you back a bit. regards Greg N

#20 David Pavlich

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Posted 27 July 2010 - 08:22 AM

PM Sent.

David

#21 gillmj24

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Posted 27 July 2010 - 12:14 PM

Thanks all.

Anyone with experience with the Kendrick 18volt adapter or the 18volt battery? They say the adapter is the same thing that the 18volt battery uses, the latter is just a cleaner setup.

I tried hooking my multimeter up to the pins but could not get a voltage reading.

#22 gillmj24

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Posted 27 July 2010 - 08:56 PM

Well, if it changed, I'd reckon its the wire as it shifted along with the wire, didn't it?


clarification: when I say I swapped cables I mean I first switched the ra cable with the dec cable so that the ra output on Gemini was still goin to the ra motor, the sec to the dec motor. No change so probably not the wire.

Then I connected the ra motor to the dec output if Gemini causing it to say dec motor stalled. Now, It was "tracking" at sidereal rate driving the dec motor and the dec motor was not lagging or stalling. The ra motor stalled but since it was connected to the dec output of Gemini, naturally the handbox said "MOTOR STALLED: D"

Then I removed the ra motor from the mount and ran it connected to the ra output again, and it wa still stalling until I nudged the sprocket (that turns the mount's worm) with my finger. When the mount was disconnected I could spin the sprocket very easily. So it doesn't appear to be a mech issue with the servo. I think I tried this with the servo connected to the dec output of Gemini and it did the same thing. So I think I have luckily shown it isn't the Gemini that's at fault.

#23 gnowellsct

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Posted 27 July 2010 - 09:36 PM

Thanks all.

Anyone with experience with the Kendrick 18volt adapter or the 18volt battery? They say the adapter is the same thing that the 18volt battery uses, the latter is just a cleaner setup.

I tried hooking my multimeter up to the pins but could not get a voltage reading.


I would ask on Yahoo! Losmandy or yahoo! Gemini what people do for converters. There may even be a recommendation in Losmandy Yahoo DATABASE where we keep lists of parts.

The Kendrick battery things are outrageously expensive IMHO. I like Kendrick, have met him, want him to succeed, but the battery stuff, I just have a hard time with that.

Greg N

#24 gillmj24

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Posted 31 July 2010 - 04:03 PM

The cylindrical fuse inside the cigarette adapter of the Kendrick converter blew.

It is a 2A 250V fuse but my Kendrick battery has either 5A or 10A output. I am rummaging through other cigarette lighter stuff (car chargers for long lost cellphones mostly) and the closest fuse I have is 3A 250V. Is that okay to use just in case the clouds stay away tonight and I go to the local star party?

Oh and David kindly offered to let me try his spare motors and buy them if they fixed the problem and if not I'd only have to pay to ship them back. I am testing one connected to the RA output of Gemini and it's been tracking for 5 minutes now with no problems!

Thanks very much Dave and everyone here!

#25 mclewis1

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Posted 31 July 2010 - 06:46 PM

3a should be just fine but I'd like to know why the 2a blew. Stalled motors will indeed draw more current and if you've got that part licked then you should be fine with the 3a fuse. If you've still got a stalling problem then putting the 3a in will increase the possibility of frying something in the Kendrick 18v adapter.

Having only 2amps of current available with the Kendrick adapter is not much headroom since the mount will easily draw over an amp slewing with both motors. I'd personally be a lot happier with a 12v source that's capable of more than 2-3amps when required rather than an 18v source that's limited to 2amps or less.






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