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Equipment Discussions >> Mounts

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WayneJ
Carpal Tunnel
*****

Reged: 08/20/09

Loc: West Chester, PA
CGE Pro Declination "Play" Fixed
      #4327990 - 01/20/11 05:23 PM

A few people have encountered an issue with their CGE Pro where there was some play in the declination axis. I noticed this, as well, and finally decided to open the gear box and see what I could learn. The fix appears to be relatively simple.

Here is an image of the motor, gears, their support frame, and the support frame that attaches the motor drive to the mount.

Mounted to the declination axis is an aluminum plate where the gear box housing is mounted (it was removed prior to the photo). On this plate, a support frame is mounted (red arrows). The motor and gear assembly (black arrows) is mounted on the mount support frame by the two nuts on the mount support frame. These nuts attach to bolts on the gear and motor assembly frame.

The tension on these nuts controls the distance between the worm gear (under and parallel to the motor) and the declination gear. However, if these nuts are loose, the gear and motor assembly frame can move laterally relative to the mount support frame. This is what causes the "play" in the declination axis.

Also, this is a tuning issue with the mount. Setting the correct pressure to fully engage the motor's worm gear and declination axis gear is important to ensure minimum backlash in the gear without binding the gears against each other. So, by using the combination of nuts, the pressure and "tilt" of the gear can be accurately set.



At this point, play could result from 1) the nuts holding the motor and gear assembly frame to the mount support frame being too loose; or 2) the worm gear being too far from the declination gear. I found that when I wiggled the declination axis, the entire motor/gear assembly moved slightly.

Shown below is another view of the nuts holding the motor frame to the support frame. I turned each of the nuts clockwise 1/4th turn and eliminated the play. The worm gear seems to be firmly engaged with the declination gear and when I mounted a scope on it, the play is gone and everything appears to be working normally.

Those who are not able to get the motor fully secured without disengaging the worm gear from the declination gear could get some teflon washers and place them under the steel washer. It's possible that when they configured the mount at the factory, they didn't use enough spacers to keep the motor secure under heavy loads (I run my rig with about 60 lbs on it, so that may have help loosen things up).



Just be careful when fully removing the gear box covers that you are careful to remove the blue connector from the circuit board on the lower cover.

Regards,

Wayne


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ChadGray
sage


Reged: 04/09/10

Loc: North East Ohio
Re: CGE Pro Declination "Play" Fixed new [Re: WayneJ]
      #4328119 - 01/20/11 06:25 PM

So the two lock nuts (i am guessing 10mm) just need to be tightened a little to keep the motor assembly from flexing?

Seems like an easy tweak, but for $5k you would think this would be part of QC.


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Mike X.
scholastic sledgehammer


Reged: 06/28/10

Loc: Greece-Athens and Rome-Italy
Re: CGE Pro Declination "Play" Fixed new [Re: WayneJ]
      #4328167 - 01/20/11 06:47 PM

Wow some excellent work there Wayne, thank you for sharing with us you experience with the CGE-PRO.A very usefull post!

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WayneJ
Carpal Tunnel
*****

Reged: 08/20/09

Loc: West Chester, PA
Re: CGE Pro Declination "Play" Fixed new [Re: ChadGray]
      #4328256 - 01/20/11 07:17 PM

Quote:

Seems like an easy tweak, but for $5k you would think this would be part of QC.




I think it probably passed QC because you really don't "see" any movement of the gearbox relative to the support frame until you look at the end of a long lever arm (the end of the optical tube assembly) showing that the slop exists. The QC probably checked to make sure the block was secure and that the worm gear was properly meshing with the declination gear.

Regards,

Wayne


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ChadGray
sage


Reged: 04/09/10

Loc: North East Ohio
Re: CGE Pro Declination "Play" Fixed new [Re: WayneJ]
      #4328331 - 01/20/11 07:43 PM

So it is more structural. If they would add a little more support to the motor all would be happy.

Great post! This will help a lot of people.


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LLEEGE
True Blue
*****

Reged: 03/03/05

Loc: Cloud-chester,NY
Re: CGE Pro Declination "Play" Fixed new [Re: ChadGray]
      #4329247 - 01/21/11 08:27 AM

I've been through all that routine. My issue is the DEC gear is either not perfectly centered on the axis or not perfectly round. There is no play at 0° or 180°. When I slew the DEC 90° or 270° there is play. When I adjust the spring tension @ 90 or 270° there is not enough "in" travel to completely remove the play. When I then slew back to 0 or 180°, the worm binds and the motors stall.

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HowardK
Pooh-Bah
*****

Reged: 10/20/10

Re: CGE Pro Declination "Play" Fixed new [Re: WayneJ]
      #4330257 - 01/21/11 05:11 PM

Wayne....are those two nuts the ones that are hidden under the aluminium caps on the outside of the DEC housing?

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jrbarnett
Eyepiece Hooligan
*****

Reged: 02/28/06

Loc: Petaluma, CA
Re: CGE Pro Declination "Play" Fixed new [Re: LLEEGE]
      #4330595 - 01/21/11 07:44 PM

Would a tilted gear mimic the behavior of an out-or-round gear?

Regards,

Jim


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WayneJ
Carpal Tunnel
*****

Reged: 08/20/09

Loc: West Chester, PA
Re: CGE Pro Declination "Play" Fixed new [Re: jrbarnett]
      #4331095 - 01/22/11 12:15 AM

Howard -- Yes, they are

Jim -- It could. I used to repair Criterion mounts back in the late 70's and early 80's. The worm gear would get askew with respect to the RA gear and have a problem similar to what Lleege is experiencing. It took some trial and error to get it re-seated properly.

Regards,

Wayne


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HowardK
Pooh-Bah
*****

Reged: 10/20/10

Re: CGE Pro Declination "Play" Fixed new [Re: WayneJ]
      #4331242 - 01/22/11 03:05 AM

Wayne.....thanks....I have tried tightening these 2 nuts but could not prevent the slop in the DEC....noticable when gently rocking the front or rear of my OTA.....it didn't seem to make much difference even when the nuts were locked down tight........ other ideas as to what I can do?

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WayneJ
Carpal Tunnel
*****

Reged: 08/20/09

Loc: West Chester, PA
Re: CGE Pro Declination "Play" Fixed new [Re: HowardK]
      #4331694 - 01/22/11 10:47 AM

Howard -- I'd remove the covers to the gear box and then mount the scope. Get the scope to rock (gently) and watch the gear/motor assembly and see whether it's moving. If the nuts are overtightened, it will pull the worm gear away from the dec. gear and the play will be the result of the two gears not being fully engaged. If that's the case, you can put spacers under the steel washers (they should be easy to get at a hardware store).

No matter what, the best thing is to look in the gearbox and watch what happens when the dec axis "slips". Just remember that there is a blue power connector attached to the bottom cover (it comes off in two parts -- the top has the 4 philips head screws and the bottom has the 8 5.5mm hex nuts -- slowly remove the bottom cover and unplug the blue connector). You'll also need a small philips head to remove the encoder sensor (it's the little roller that presses against the declination axis). It remains connected to the lower cover.

Celestron's gearbox design, by the way, is basically the same design that's been in use since the 1960's. On the upside, it's a well proven design that's very reliable and adjustable. The downside is that it's really no better than what we started using 40 years ago and uses some "kludges" to improve performance... which means that getting it to perform "right" can be a huge pain in the neck.... but it can be done.

By the way, I had mine out last night and was able to check the tracking. Clouds were coming and going, so I only ran a few exposures and watch the tracking graph (I use metaguide) and the stars were respectably small and well shaped for the seeing in exposures as long as 6 minutes -- which is where moonlit sky saturated the sensor).

I had the lowest tracking numbers I've ever had... and the wind was blowing a steady 5-10 with some gusts to around 20... just what I'd hoped for when putting my 30'ish pound dslr rig on this mount

Regards,

Wayne

p.s. If you can't figure out what nuts/screws to turn after looking at the gear and seeing what's happening, put it in an email to Celestron support. I'm sure that if you can give them a clear indication of where the slippage is occurring, they'll know how to fix it. It's a very hard problem to diagnose without a scope on the rig to help visualize the problem.


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HowardK
Pooh-Bah
*****

Reged: 10/20/10

Re: CGE Pro Declination "Play" Fixed new [Re: WayneJ]
      #4331795 - 01/22/11 11:28 AM

Thanks a lot Wayne...but you know i think I will just live with this slop...I just don't want to mess with the worm and gear spacing by fooling around with those 2 nuts...I really wish Celestron would have made sure things were accurately aligned when they shipped the mount....I use a Mallincam and guide so 2 or 3 minute exposures are pretty tight...

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jarin
sage


Reged: 10/03/09

Loc: Northern VA
Re: CGE Pro Declination "Play" Fixed new [Re: HowardK]
      #4332461 - 01/22/11 04:10 PM

I'd first start with adjusting the DEC spring assembly myself before any other adjustments. You can loosen/tighten the large brass screw quite readily and easily. Directly below it is another small bolt that limits the maximum travel distance of the worm into the gear teeth, regardless of spring pressure. If you want the worm to be able to extend futher, adjust the bolt accordingly. Pretty simple design.

Although it sounds like LLEEGE has tried all this...

On my mount the DEC has no play around the entire gear. The only fault I've ever had with the mount was the grease wasn't applied terribly carefully between the gears. 5 or 6 q-tips later everything was cleaned up nicely.

Jeff


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LLEEGE
True Blue
*****

Reged: 03/03/05

Loc: Cloud-chester,NY
Re: CGE Pro Declination "Play" Fixed new [Re: jarin]
      #4332645 - 01/22/11 05:55 PM

I've had the DEC apart and made every adjustment possible. Nothing eliminates the play.

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HowardK
Pooh-Bah
*****

Reged: 10/20/10

Re: CGE Pro Declination "Play" Fixed new [Re: LLEEGE]
      #4333614 - 01/23/11 05:03 AM

I have also adjusted the brass screw and the 2 nuts but cannot stop the play.......i don't understand how Wayne managed this fix

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WayneJ
Carpal Tunnel
*****

Reged: 08/20/09

Loc: West Chester, PA
Re: CGE Pro Declination "Play" Fixed new [Re: HowardK]
      #4334359 - 01/23/11 01:16 PM

You need to look and see where the play is coming from. In my case, it was the assembly that holds the worm gear moving relative to the support frame that attaches it on the mount.

If you removes the gear housing covers and mount a scope, you can watch the worm gear and see where the play is coming from. In your case, it sounds like the teeth are not fully meshed with the gear. If you look and see that they are, then watch the worm gear itself -- is the entire thing moving? Is it the motor itself or the metal it's attached to also? Keep looking... these systems are far too simple to hide it.

Basically, you have to see exactly what's able to move freely (that's the play). Once you know what's slipping, it's easy enough to fix it, although sometimes it's counterintuitive to know how. For example, tightening the two nuts on the bottom of the support frame will increase play if you pull the worm gear away from the declination gear.

Wayne


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LLEEGE
True Blue
*****

Reged: 03/03/05

Loc: Cloud-chester,NY
Re: CGE Pro Declination "Play" Fixed new [Re: WayneJ]
      #4336185 - 01/24/11 08:33 AM

I've been inside the mount more then I care to. My play is in the worm/gear mesh. This is not from the spring loaded worm block. The amount of play varies, depending on where it is slewed.

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HowardK
Pooh-Bah
*****

Reged: 10/20/10

Re: CGE Pro Declination "Play" Fixed new [Re: LLEEGE]
      #4337452 - 01/24/11 06:17 PM

Lleege......are you just going to live with the play in DEC?.....do you think it affectsvthebperformance in any way?

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LLEEGE
True Blue
*****

Reged: 03/03/05

Loc: Cloud-chester,NY
Re: CGE Pro Declination "Play" Fixed new [Re: HowardK]
      #4337958 - 01/24/11 09:29 PM

I haven't had a chance to evaluate it since its return. It is mounted in my club's dome and the weather has been poor. If it still has issues, it's back for the last time.

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HowardK
Pooh-Bah
*****

Reged: 10/20/10

Re: CGE Pro Declination "Play" Fixed new [Re: LLEEGE]
      #4338526 - 01/25/11 04:49 AM

Ok.....i understand.......please let us know the performance when the weather changes for the better.........btw........did you send the mount to celestron because of the play in the DEC......?

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