CGEM tuning dillema

[Lognic04]

Hi all,
Last night i went out and started guiding for the first time with my CGEM. i was getting an ra/dec orthogonality error, and odd graphs so i ran the guiding assistant, and lo and behold, there was an INCREDIBLE amount of backlash in the 'south' direction https://cdn.discordapp.com/attachments/247338197921693697/315473403727446017/20170520_225603.jpg
So today i wnt about tuning it with a diy guide, and eventually stopped it from binding in every position , but then i had the issue of only the raised areas were smooth and then most of the areas were subject to lots of backlash and were too loose. I am at a loss of what to do now. Thanks
:help::help::help::thanx:

[Lognic04]

here was a graph before the tune, i will try and get one tonight after the tune https://cdn.discordapp.com/attachments/247338197921693697/315465470067081216/20170520_222653.jpg

[casstony]

Balance East heavy to keep the RA axis teeth engaged and the worm pushing and also have some imbalance on the Dec axis.
The CGX spring loaded worms avoid this issue, although I imagine some imbalance might be wise to cope with backlash elsewhere in the drive train.

[ChrisV]

I've got a fairly new CGEM mount and its a bit spikey when guiding but not as bad as yours. Can't help you much with you problem, but I turned up the 'min movement' a but and its okay now.

Also the binding isn't even throughout a full rotation on my mount. I think its just a problem with the CGEMs. In fact I returned my first mount to Bintel as it was so bad. They said it was a dud and replaced it (good service). The replacement still isn't even but I get OK guiding.

I made do with making it as tight as I could without binding anywhere through a full rotation. And imbalance a bit as casstony says. Thats was easy to do in the DEC axis, but not so easy in RA as that is a bit stiff on my mount.

You mention you found a DIY tune guide. I can't find one anywhere other than adjusting the worm gear meshing. Does the DIY tune you found include instructions for disassembly to clean it all out?

[Lognic04]

Hi All, The dramatic spikes are most likely because i am guiding at 1330mm. I only adjusted the worm mesh.

[Lognic04]

Is it ok to have a stiff axis but it is definitely not binding?

[casstony]

So long as the motor doesn't stall or sound like it's groaning/working too hard you should be ok. If the ring gear/shaft is out of round you would expect to have more obvious backlash in some positions of rotation than others.

Stiffness in the axis usually refers to the thickness of the grease Synta/Celestron use and/or how tight the tensioning nut is on that axis. It doesn't have to spin freely but there shouldn't be stiff resistance either (with locks disengaged).

[LewisM]

The CGEM I had was really worse than yours Logan in both axes. No matter what I tried, it just would not improve. The answer apparently is the hypertune kit available in the USA, as the OEM gears and worms are not the best.

https://www.deepspaceproducts.com/hypertune-do-it-yourself-kit-for-the-celestron-cgem-mount_8_4227_8666.html

I could see with my own eyes how much wobble/oscillatory motion there was in the RA and Dec gears when NOT meshed to the motor - so out of spec to be unacceptable.

The kits aren't cheap, but they are pretty much the only solution if your gears and worms are as out of spec as mine were. Not much help, but it's the best you can do with these short of rebuilding it entirely.

Mine simply would not reliably guide with PHD or MaxIM. MaxIM's algorithm was having hissy fits, telling me X didn't move, then next Y didn't move and so on - SO much backlash despite fiddling.

[Tony_]

I have a lot of backlash in my CGEM dec also. I overcome it by switching off guiding in one direction so it only adjusts for dec drift. You can try backlash settings etc. but the easiest is guiding dec in one direction only.


Regards,
Tony.

[Lognic04]

Update:
Hi all, i have adjusted the dec, to the point where there is absolutely no backlash! tonight i will be going on to the RA axis, so i will let you know how that goes :D

[toc]

There will always be some level of backlash, no matter how much adjustment is made. Even if you have no play in the gear-worm block, there will be some from the motors.

[Lognic04]

Update:
I must have been doing something wrong the first time, i can get it really smooth now. Only thing is, it shifts a lot when i tighten the housing bolts???