Tuesday, May 08, 2012

CGEM mounts fail to autoguide correctly.
This keeps coming up on the chat board.
Many times confused with mechanical backlash.

Cause of DEC guiding problem in CGEM and a solution - rotor bushing fit with a bit of friction.
CGEM and CGEM DX Specifications ... (2012)
Motor Drive: Low cog DC Servo motors with encoders, both axes
"motor armatures are skewed to minimize cogging during low speed operation"
"Well, we are close. The encoders just keep track of motor movement.
"work" the encoders send information to the motor control board no matter which
direction in order for the motor control board.."
..." Call Celestron and talk to a service "engineer" and he will tell you what Ed,
Steve, and others are saying is true. They are working on a fix. "
Motor types in CGEM http://tech.groups.yahoo.com/group/CelestronCGEM/message/8894
String about http://tech.groups.yahoo.com/group/CelestronCGEM/msearch?query=%22low+cog+%22&submit=Search&charset=UTF-8
PHD DEC drift due to backlash ... (WRONG) - picture and links

My award for the most creative fix for CGEM cogging motors goes to Geert.

I finally got a good simple working solution.
It is not very nice, but it is very simple and best of all, it works as it

I putted a piece of cotton string with a couple of oil drops as a brake on the
motor axis.
The string is is about 2mm thick and the nice thing is that it is fastened with
the same screws which fastens the gear set to the motor so it can not move out
of place.
I added a picture of it in the file section under gvanhau.

Hope this solution is usefull for other who have the same problem.

--- In CelestronCGEM@yahoogroups.com, "gvanhau"


I have my solutions involving adding a separate motor for DEC autoguiding, offsetting polar axis, and using my "zero-backlash" homemade drive.

PHD autoguide is a joy to use on a backlash free mount.

Saturday, May 05, 2012

Big Moon - almost full on 5/5/12 ... with "the Lady"

Big Moon - almost full on 5/5/12 ... with "the Lady"

If the full moon looks a bit bigger and brighter in tonight's sky, you're not seeing things: It's just the "supermoon" — the biggest moon of 2012.
Lady in the moon outline shown at: www.flickr.com/photos/edhiker/1259776527/
News for big moon tonight. ...

The details of full moon and perigee:
(UT's) Full moon on May 6 at 3:35 -- Perigee May 6 at 4h UT at 220,160 miles. 33' 44"
That's 8:35 PDT Sat eve. and extremely full, just missed being eclipsed.