Celestron C8 - clock motor drive?

erick (Eric) · #1 10-08-2008, 10:12 PM

Anyone with experience of the original "orange tube" C8s?

I'm now the proud owner of one, about 70s vintage. Don't know how long since the RA motors have been used.

The socket is something I haven't seen before, but it has a plate saying 220V 50Hz - so it looked promising (hopefully designed for Australian and hopefully southern hemisphere rotation).

With no other information, I pulled the base apart and decided to replace the unknown socket with a suitable 240V plug.

Before that I ran a meter over the wiring to look for any shorts - active to neutral or either to earth. None - looking good. The two motors are wired in parallel to the power supply.

So I wired up the new plug, hoping active/neutral orientation wasn't important - I wouldn't expect it to be. Then I ran a little WD40 down the shaft of each motor below the cog.

Then powered on with the base disassembled. I could certainly hear one motor if I got my ear up close. I'm sure I could hear the other motor as well. No smoke, no funny sounds - good!

Reassembled the base, engaged the RA clamp and plugged in the power. OK, up close I can hear at least one motor ticking away. BUT - no rotation visible on the RA scale.

Gave up at that stage?

Any ideas what could be happening here? Have I just not done something correctly? I have found a copy of the original manual from the internet and read that carefully. I seem to have done everything correctly.

BTW, the RA clamp and RA adjustment knob seem to be functioning well.

Anyway, I'll get ahead with building my wedge. Even if I cannot get the drive working, that will make observing easier.

Thanks in advance
Eric

snowyskiesau · #2 11-08-2008, 01:28 AM

Eric,
I have an orange tube C8. It doesn't get much use but the RA motor works OK on 240V.
I'm happy to take things apart to take pictures etc. if it helps.

erick (Eric) · #3 11-08-2008, 09:25 AM

Thanks Geoff, it may come to that, but don't pull it apart just yet!

If you could just help me with the basics. So if you tighten the RA clamp, plug in 240 volts, then the drive starts and you can see the base turning against the RA scale on it? Just want to be sure I'm not doing anything silly here.

JohnG (John) · #4 11-08-2008, 10:04 AM

Hi

This guy has the disassembly and other tips and tricks for the old orange C-8, it is an old page but it is still up and running.

http://ngc1514.com/Celestron/celestron.htm

You may already have it, but..........

Cheers

JohnG

erick (Eric) · #5 11-08-2008, 10:10 AM

Thanks JohnG, yes I had found that site - especially the used sct pdf file, but had not seen all the disassembly instructions until after I re-plugged the motors.

The primary mirror in mine and corrector plate need a clean some time - so the disassembly instructions will come in handy, however scary (orientation, paper shims around the corrector!)

Ric · #6 12-08-2008, 10:54 PM

I cleaned the corrector plate on my C8, it started off as a scary exercise but in the end it was straight forward and not too bad at all.

I don't know if you have a manual but here's a link for the Celestron manuals for quite a few models.

they are a great scope and mine is still offering wonderful views even after 32 years.

http://www.company7.com/library/celestron/notes.html

snowyskiesau · #7 13-08-2008, 01:19 AM

Quote:

Originally Posted by erick

Thanks Geoff, it may come to that, but don't pull it apart just yet!

If you could just help me with the basics. So if you tighten the RA clamp, plug in 240 volts, then the drive starts and you can see the base turning against the RA scale on it? Just want to be sure I'm not doing anything silly here.

I've just plugged it in, tightened the RA clamp and so far, no movement at all!
[I must admit, it's been a while since I plugged it in at all.]

The motor seems a lot noisier than I remember

I'll have a play with it and see what I can find out.

erick (Eric) · #8 13-08-2008, 09:19 AM

OK, I'll pull the top off this weekend, blue-tac a couple of toothpicks to the top of the motors and set them running to see if they are rotating. I haven't counted the teeth, but they look like 40-50 turns per 24 hours so I should spot quickly what is happening.

snowyskiesau · #9 13-08-2008, 05:07 PM

I've pulled the base of the C8 apart following the instructions on this site .
The only change I made was instead of removing the 5/8 nut on the bottom of the base unit, I removed the circlip from the top. (the nut was too tight to easily remove)
This allows the main base piece, with the motors to detach.

I applied power (CAREFULLY! that's 240V exposed) and watched the gears - sound but no movement..
Looking at the top case of the motor, there is an inspection hole that shows the motor is turning.
Looks like a gearbox problem. If you hold the gear on the motor, there is no indication that it's trying to turn. There's a fair bit of backlash too.

Next step - pull off one of the motors and see if the gearbox can be accessed.

dannat (Daniel) · #10 13-08-2008, 06:03 PM

Eric, if its making a slight noise maybe the motor is a bit stuck - my father is a sparkie and if he came across an old motor that hadn't been kicked over in a while he would give it a real good whack with a heavy screw driver, he said it got things working about 50% and that they were a bit stuck from not being used
try it if you are game, cheers daniel

snowyskiesau · #11 13-08-2008, 06:15 PM

Well it looks like patience is required when watching the motors turn

According to the markings on the motor, they are rated as 1 RPH - that's revolutions per HOUR! No wonder I couldn't see them turning.
I took erick's idea and stuck a small piece of copper wire (no toothpicks) to each motor gear. After 15 minutes, the movement is obvious.

I'm going to give everything a good clean, apply some grease and reassemble.

erick (Eric) · #12 13-08-2008, 08:09 PM

Copper wire - yes, I like that idea. 1 rev per hour - really? Perhaps it is 24:1 big gear to the gears on the motors. I was guessing more like 40-50:1. But they are clock motors, so it makes sense that they are 1 rev per hour.

Geoff, please let me know if you can see the base rotating when you have it all together and exactly what is the position of the clamp.

snowyskiesau · #13 13-08-2008, 08:28 PM

Eric,

It's all back together and working

The problems I found were:

1. There was a broken shim under the circlip that holds the base together. This allowed the base to lift so that the large gear was sitting on top of the two small motor mounted gears. (hope that makes sense). When the motors turned, as the gears were not meshed, the forks didn't turn. I fitted a new shim but it's still a little loose.

2. The spring that is supposed to hold the degree wheel in place, didn't. As a result, the degree wheel was turning with the forks. This made it appear that the forks weren't moving.

To get the motor gears to mesh properly, I had to release the screws holding the motors and wiggle the motors a bit while the were running. This only took a few seconds to click in. I also had to apply some grease as there was next to none present. Still have to work out the correct fitting for the spring.

The clamp was in the locked position for it to work properly. It's also quiet.

erick (Eric) · #14 13-08-2008, 09:07 PM

Thanks Geoff - I have a bit of work to do then! But your experience will really help! Thanks.

erick (Eric) · #15 17-08-2008, 11:15 AM

OK, just pulled it apart again. This time I disconnected the arms from the base so I now have the OTA and arms put to one side.

I used toothpicks balanced (couldn't find blue-tac!) on the drive cog of the two motors and they are both definitely turning. Obviously, when I put it together the cogs weren't meshing? Anyway, time to clean it all down and re-grease. I'll start on that, then follow the various instructions to rebuild it properly.

Thanka again!
Eric

snowyskiesau · #16 17-08-2008, 06:40 PM

Eric,
If it's any help, I had to loosen the two screws holding one of the motors to get the gears to mesh properly.
With the motors running, wiggle the top of the base (where the arms attach), you'll hear a click when the gears mesh.
Then just tighten the motor mount screws while pushing the motor towards the centre of the base this makes sure the gears stay meshed.

erick (Eric) · #17 01-09-2008, 09:02 PM

OK, finally all done. Yes, the spring jumped out and I couldn't really work out where it went back?? But I shoved it in somewhere and hammered and screwed it all together! Thanks Geoff, I used your guidance.

I have fine RA control when I unlock the RA clamp, and driven RA (in the correct southern hemisphere direction) when I lock it. The indicator scale doesn't turn freely - but I don't care - I have what I want.

All nicely cleaned off and re-greased as well. Set it up today on my new (second-hand) wedge, leveled and pointed roughly south and waited for evening so I could see whether I had satisfactory RA drive for observing. Clouds rolled in and it started raining! Surprise, surprise! All packed away for another night - but I'm feeling hopeful.

snowyskiesau · #18 01-09-2008, 09:12 PM

Eric,
Glad it was nothing major like the motor. I found the manufacturer of these and asked for a price. They are only OEM and didn't want to talk quantities of less than 200!

erick (Eric) · #19 19-10-2008, 10:45 PM

Grumble.... my RA drive has collapsed - clutch has stopped working. I think I never had it together properly. I'm going to have to pull it apart again and try a second time.

erick (Eric) · #20 20-10-2008, 05:08 PM

It spins freely now and there are tinkling sounds coming from the fork base

Hope it's a few screws that have worked loose and not pieces of broken metal

Cannot look at until next weekend or later!