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Tracking Platform Motor "Knocking"

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#1 Tom Polakis

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Posted 22 September 2013 - 06:10 PM

I have used a compact equatorial platform with my 10-inch Dob for nearly 15 years now, and motor has developed a problem. After running for a period of typically a half hour to an hour, it begins a sort of knocking sound whose frequency varies randomly between 2 and 4 times per second. Each one of these knocks gets transmitted up to the eyepiece.

This YouTube video is a recording of the sound it is making.

If I remove any load from the platform, or take the motor off it, it runs without this issue. Adjusting the clutch plate on the back of the assembly does not help, nor does any cleaning of the platform itself.

Tom O. at Equatorial Platforms gave me a sort of high price to repair it, so I'd like to take a shot at it myself. I wouldn't mind replacing the motor, but I don't know how easy this one with the phone jack would be to find. Photo attached.

Has anybody else had this problem with platform motors or drive motors in general? Do you know of a good source for this type of motor? Thanks.

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#2 Quintessence

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Posted 22 September 2013 - 09:15 PM

It would be helpful to know exactly what type of motor it is. Your photo seems to suggest as many as six leads to the motor -- but are all of them used?

A broken lead or a defective controller seems more likely than a bad motor. Motors are far simpler than controllers -- and if the motor was once working properly, it's more likely that something feeding the motor went bad than the motor itself.

I'm not an expert at all -- but knowing the type of motor employed would seem to be useful info for those are are experts.

Charles

#3 Quintessence

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Posted 22 September 2013 - 09:32 PM

After listening to your video and also based on your photo, I would hazard a guess that the motor is a unipolar stepper.

Judging from the video, I don't think the motor is the problem. It's more likely a bad lead or a bad motor controller. But again -- my knowledge of electronics is fairly limited.

Besides positively identifying the type of motor, a good starting point would be to use a basic multimeter to verify the continuity in the leads. You could also use the meter to see if one of the windings in the motor is bad. You could also check the current being sent to the different windings from the controller with the meter.

You only need a really basic multimeter to check these things.

Beyond those simple suggestions, you will need to enlist the help of someone who IS an expert.

Charles

#4 Megabusa

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Posted 22 September 2013 - 10:03 PM

I hope I'm wrong but I think I'm right , I've seen this type of thing before but not with telescopes Mounts , but with things of age , and you said 15 Years old , After time on transfer cases or anything like that and with ELC motors both have some kind of bearings , after time these wear down and when it gets hot the Gears stop lining up because of worn out bearing and starts to skip , sometimes cased by the armature moving back and forth ,Not enough lube, but mainly just ware, Even though you take the Motor out and move it , No knocking sound , But it also is not under the load of the motor , so it still could be the transfer case . I don't think anybody could know with out taking it apart for sure . If this is the case ,I'm sorry to say it may need to be replaced and if it is the case , look at the bright side , You got 15 years out of it , That's not bad

#5 Megabusa

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Posted 22 September 2013 - 10:11 PM

I'm also looking at the other posts , and maybe they are correct , I would really like to know when you find out the problem, that way I could start looking a different things if it happens to me . I hope the best for ya .

#6 John Carruthers

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Posted 23 September 2013 - 09:05 AM

That's exactly the motor used on Orion eq5/eq3 mounts.
Try it with 12V instead of the suggested 9V.

If you suspect a clicking gear the gearbox is easily dismantled. Unclip the spring clip holding the motor down, (sometimes a simple misaligned motor is the cause of the click).
Remove the gearbox from the mount and turn it over. You will find 2 crimps holding the backplate on. If you carefully ease these away you can remove the backplate from the various axles and pinions.

#7 nevy

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Posted 23 September 2013 - 02:41 PM

You can get a new motor for about $40
http://www.amazon.co...escopes/dp/B...

#8 Tom Polakis

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Posted 24 September 2013 - 09:04 AM

Thanks for the comments and suggestions. I will look into it this week, and report back.

Tom

#9 Tom Polakis

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Posted 10 October 2013 - 09:51 AM

A couple weeks ago, I asked about this problem, and received some good suggestions. As it turned out, neither the motor or the gearbox were related to the knocking. A close look at the roller that is driven by the motor revealed that it had ratcheted its way axially forward, causing it to intermittently rub against one of the two rails that surround it. Simply centering the roller between the rails solved the problem.

At a star party this past weekend, I came across a friend's platform, and noticed that it was making the same knocking noise. He said that it didn't bother him, so I kept my suggestions to myself.

Tom






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