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Declination On CG5 Will Not Calibrate

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#1 galico

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Posted 21 November 2012 - 12:26 PM

I have a CG5 carrying a 17 lb payload. I am not able to get my guide scope using a LodeStar and PHD to successfully calibrate in Declination. RA calibrates real fast.
When you move the Declination with the hand control there is about a 3 tooth rotation before the the drive gear on the worm gear actually moves. The worm gear has no slop. If you rotate it while unattached to the mount the drive gear on the worm gear shaft and the worm gear act nicely as one.
The stepper motor and reduction gear assembly seem to be the culprit. The reduction gears appear to be a hard plastic and I think are sloppy. No amount of backlash adjustment on the hand control seems to cure the problem.
There is a very fine line in the adjustment of the worm gear engagement with the Dec. Axis Gear. I can eliminate the slop in the gearbox by increasing the depth the worm engages, however when this is done, unusually it is to tight and the Dec will not move.
Any suggestions?

Steve

#2 Cliff Hipsher

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Posted 21 November 2012 - 12:38 PM

Google CG5 Backlash and you find a ton of stuff....

The CG5 and the Meade LXD-55s are similar...

#3 RTLR 12

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Posted 21 November 2012 - 12:50 PM

Have you checked the end play of the worm gear shaft?

Stan

#4 galico

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Posted 22 November 2012 - 12:47 PM

Rod and Richard, Stan and Cliff,
Thanks for the input. I investigated the numerous postings regarding the CG5 that are on the web (Cliff you were very correct and I am glad I looked). Several by Uncle Rod, who in one posting did a great job in defending the quality of CG5.
I am using PHD. With the collection of replies I got on CN and further reading I have come up with some consensus:
-Use Bigger Steps on PHD-I will try 1250ms on the Dec. The RA works great with 750ms.
-Try 0 setting for backlash since PHD rewinds the motor prior to sending the pulses.(I never got my GPS 11 to calibrate until I set the Backlash on both drives to 32 as per Lenny's advice)
-Set the Autoguide Rate to 90% on the Dec. Changing this and observing on the bench the response was significant. While set at 50%, when a the reverse direction button is pushed, the take-up would occur and then then the gear would cease to move for several seconds. Set at 90% there is no delay.(This was observed after I preformed the dis- assembly described below)
-Front-lode the balance as suggested by Rod and Richard.

I disassembled the Dec. Drive again last night. I took apart the reduction gear assembly. There is one Nylon gear and the rest are made of some lightweight cast material. The gears all looked good. I greased the gears with SuperLube quite heavily. When I re-installed the reduction gearbox I noticed that I could minimize the slop by carefully balancing the torque I applied to the housing. Also, when I engaged the motor gear to the worm drive gear I was careful to balance the three screws that hold the motor assembly.
I noticed a complete different response after preforming this procedure coupled with the change in Autoguide Rate.

If the sky clears tonight I will test it out,once the grandkids are gone and the turkey is gobbled up.

Happy Holidays, may Santa bring you Clear Sky's.

Steve
PS. I am going to post this on CG5 user group.
--- In NexStarGPS@yahoogroups.com, "Rod Mollise" <rmollise@...> wrote:
>
> Steve, Richard's suggestion is a good place to begin, and combined with
> making the calibration steps in PHD (if you are not using PHD Guiding, get
> it) bigger tht should do it.
>
>
> Uncle Rod Mollise
> Contributing Editor Sky and Telescope Magazine
> Uncle Rod's Astroblog:
> <http://uncle-rods.blogspot.com>
>
>
>
> -----Original Message-----
> From: NexStarGPS@yahoogroups.com [mailto:NexStarGPS@yahoogroups.com] On
> Behalf Of Richard Richins
> Sent: Wednesday, November 21, 2012 11:56 AM
> To: NexStarGPS@yahoogroups.com
> Subject: Re: [NexStarGPS] Uncle Rod, I need your help! Problem with CG5
>
> Hi Steve,
>
> I'm not Uncle Rod, but maybe I can offer a suggestion. I had similar issues
> with my C11, and learned that if I hung a bag of rocks from the front or
> back of the scope to make it a little front or back heavy that my backlash
> decreased pretty dramatically. The idea is to maintain contact between
> those gears so that there is little or no slop possible. Don't add so much
> weight that you overtax the motors. The approach also works for minimizing
> backlash in RA.
>
> I used a Crown Royal bag, and if I couldn't find a few appropriate rocks,
> then wrenches or pliers or whatever I had available would go into the bag.
> Just need a pound or two.
>
>
> rr
>
>
>
> On Nov 21, 2012, at 10:31 AM, galico1952 wrote:
>
> > Hi,
> > I know this is a bit off subject but since nobody is posting I thought I
> could find Uncle Rod and get some sage advice.
> > Here is the problem:
> > I have a CG5 carrying a 17 lb payload. I am not able to get my guide scope
> using a LodeStar and PHD to successfully calibrate in Declination. RA
> calibrates real fast.
> > When you move the Declination with the hand control there is about a 3
> tooth rotation before the the drive gear on the worm gear actually moves.
> The worm gear has no slop. If you rotate it while unattached to the mount,
> the drive gear and the worm gear shaft and the worm gear act nicely as one
> unit(even when clamped).
> > The stepper motor and reduction gear assembly seem to be the culprit. The
> reduction gears appear to be made of a hard plastic and I think are sloppy.
> No amount of backlash adjustment on the hand control seems to cure the
> problem.
> > There is a very fine line in the adjustment of the worm gear engagement
> with the Dec. Axis Gear (the big tubular main drive gear). I can eliminate
> the slop in the gearbox by increasing the depth the worm engages in the main
> drive, however when this is done, unusually it is to tight and the Dec will
> not move.
> > Any suggestions?
> >
> > Steve
> >
> >
>
>
>
> [Non-text portions of this message have been removed]
>
>
>
> ------------------------------------
>
> Yahoo! Groups Links
>






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