Photo of my RA drive. Its an ETX-105.

[russ_watters]

Attached is a photo of my RA drive. Its an ETX-105. The only visible problem is too much grease, but that's not a fatal issue. There are no chipped teeth, burrs, or anything else visible that could cause the problem.

I watched run it for several minutes, then turned the scope off and moved it by hand. Moving it by hand, everything appears smooth. When electronically driven, every now and then, for no reason I can see, it starts oscillating back and forth for about a second, then resumes moving (and corrects itself). It does not happen at regular intervals - sometimes it happens 5 times in 10 seconds, sometimes the drive runs smooth for minutes at a time. Seems to me like it could be an electronic issue.

Do you know much about the new Autostar feature, "[drive] percent"? It corrects for backlash and "looseness" (the gears have to move a little before they start moving the scope) in the drive when manually slewing. I've gotten good results with it fixing issues like "creep after beep" and slow response times, but could that have anything to do with the tracking rate? Perhaps I need to play with those values some more...

I think I'll call Meade tech support to see what they have to say.

 

[turbo]

Since you have looked at the drive train while it was operating, did you notice if any of the gears have a period of 30 seconds or so (or any period that could divide evenly into the minimum period of the oscillations)? There could be a very tiny piece of plastic or nylon floating around in all that grease causing some binding periodically. BTW, that IS quite a bit of grease in there and I would be a bit surprised if the scope did not give you drive troubles on cold nights.

 

[russ_watters]

I've cleaned off some of the more critical surfaces (a greased clutch plate? c'mon ), but I guess I'll clean out the whole ra drive gear assembly.

 

[turbo]

I've cleaned off some of the more critical surfaces (a greased clutch plate? c'mon ), but I guess I'll clean out the whole ra drive gear assembly.

That's probably a good idea. On colder nights, you could easily get ropes of grease forming (like taffy) and feeding into one or more parts of the drive train, and causing periodic binding. You might want to check with Meade before trying this, but in cold weather situations, that entire train would probably be better lubricated with a light coating of silicone. It would give less loading (requiring fewer corrective guiding measures) on the RA drive, and would make your scope's drive last longer. If you ever observe in a COLD environment, and your RA drive has to pump cold stiff grease, you can bet that those little nylon gears will get sloppy PDQ. If the RA drive is being stressed, the scope will soon be useful for little more than bird-watching and casual sky-gazing.