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CGE stops slewing

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#1 RedBarnBandB

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Posted 28 July 2010 - 01:07 PM

My four year old CGE slews OK in RA both directions and OK in one direction in Declination but not the other. It begins slewing but then crawls to a snails' pace. I've checked for mechanical issues but can find none. I cleaned the brushes on the motor and this helped just the slightest. It has been suggested that it sounds like the motor. A Pittmann reseller took my contact information but will not correspond with me and Celestron tells me that they do not sell parts. Any suggestions on a fix? Where might I be able to get another motor?

#2 Asimov

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Posted 28 July 2010 - 01:50 PM

Yeah could be the motor - might not be too - Anyway as you have noticed, you won't find a part for that baby unless you find one 2nd hand. Check the forsale section of this site..

#3 RedBarnBandB

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Posted 28 July 2010 - 05:37 PM

Yeah, I was afraid that this is what I'm looking at. I'll check here. Otherwise, I might be putting this up for sale "as is". Perhaps someone else has another CGE in the same situation. Thanks.

#4 LLEEGE

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Posted 28 July 2010 - 06:09 PM

Could be the encoders.

#5 jbattleson

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Posted 29 July 2010 - 09:33 AM

Try contacting Jim. His CN name is "Counterweight".
He had a CGE that died and was selling the parts here on CN back in early June.

#6 CounterWeight

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Posted 29 July 2010 - 10:11 AM

Hi - just noticed this thread.

If the enconder was bad chances are it wouldn't work in either direction, at least if missing encoder data, mine just runs aimlessly in both directions.

BandB, first thing I'd try is to loosen the entire worm blok assy without and wieght - strip off the ota and cw/shaft, cw's, loosen the two hex bolts under the motor block in the head assy, and try repositioning the worm gear. The screws are a bit difficult to break loose (mine were loc-tited or thread locked) but can be done with a shallow 'I think' 11mm box end wrench.

It's extremely difficult to view the worm to gear mesh as the motor block assy obscures the view, can be seen from extreme side angle though after top cover removed. There should be some thin spacers between the motor block and the head housing on the same side as the worm gear exposure.

If you've cleaned the brush motors you must be pretty familiar with all this already. My question is how does the motor behave under 'no-load' condition, and follow up is how did those little motor bearing feel when turned by hand? Same goes for the little bearings holding the worm. All can be adjusted from the outer side, you may need to make you own tool from a flatblade screwdriver or possibly better an offset flatblade if you dont have a tiny inside bearing
sleeve tool. Also these have some sort of loc-tite or thread lock on them so can be a little tricky to break loose.

Anyway, it all falls under the mechanical checks near the motor/worm assy, then checking the orintation of the worm wrt the main gear for the head assy. I imagine it much more likely to become sloppy with wear than binding in one direction - so this is a long shot. Another long shot is to check the feel of the tapered and radial thrust bearings in the head assy for any directional binding. It's east to do when the motor block / worm removed, or otherwise not in the mechanical path. These can be replaced on the cheap from any good bearing company if need be. I bought replacement tapered bearings for I think about $25- and the little radial(s - upper and lower different size)) were much less.

EDIT - oops! just read you already checked the mechanicals... sorry about that. You're right Pittmann won't talk about the motor assy, it's proprietary to 'C'. I tried too a while back and no joy there. When I was corresponding with the folks at 'C' they wanted quite a bit of $$ (I think it was ~$400) for the entire motor/worm assy and was no sub-assy other than the tiny bearings (mentioned above) they'd talk about.

#7 RedBarnBandB

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Posted 29 July 2010 - 01:56 PM

Thanks for your consideration on this. Yeah, I did take a little bit of the load off the motor bearings and the armature rotates fairly smoothly in both directions. The plastic spacers are in place. I did my testing with no scope or counterweight and the outcome is the same. Are you the guy who was selling CGE parts a while ago? Again, thanks.

#8 CounterWeight

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Posted 30 July 2010 - 12:16 AM

PM sent - you'll see a blinking envelope towards top of page...

[edit] OK .. so then you did test the feel of the DEC assy for worn/bad bearings when the motor was out? I recommend doing from either end of the bearing shaft with a wrench - if there is a bad bearing it's easy to feel.

#9 RedBarnBandB

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Posted 31 July 2010 - 06:11 AM

The motor turns freely. Well, I can feel a slight lack of complete smoothness and when I loosened one bearing this decreased. But why would a bearing problem act in only one direction?

#10 Asimov

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Posted 31 July 2010 - 10:18 AM

I think you'll probably end up finding it's not a motor or encoder problem. I have a somewhat similar problem with my CGE - My slew rate is stuck on rate 9 on one axis, along with no ramp up or down. The culprit is a cooked chip on the MC board in my case.

Could be a faulty/broken wire somewhere on yours though. The trouble is, they are so hard to diagnose. I wish I was more knowledgable in electronics, drives me nuts.

Good luck with it.

#11 CounterWeight

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Posted 01 August 2010 - 01:45 PM

There is also a lot of CGE experience at the yahoo group for the mount...

As far as bearings go, I'm no expert, just that it is relatively easy to completey check vs. the electronincs. And many have reported better perfromance re-lubing them including myself. There is a whopper of a nut one the bottom or lower end of each shaft where you can adjust the bearing pre-load, but getting loose can be a chore. I believe Joe C. had a fairly complete method there with images. I had ordered several extra boards for help TS'ing the electronics. One of the issues I had was a warped bearing, but couldn't nail it until I disassembled the entire shaft and inspected them.






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