View single post by Robert
 Posted: Sat Mar 9th, 2019 04:45
Robert



Joined: Mon Apr 2nd, 2012
Location: South Lakeland, UK
Posts: 4066
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 It's a massive challenge, I know a little about the stars but really getting into it with a proper mount, albeit old, I reckon it's about 1985 ish.  It must have been very advanced in it's day because it uses stepper motors, even now there are manufactures who are still using DC synchronous motors nearly 35 years on.

Think 'star drift' is a factor, I couldn't lock on to Polaris because I couldn't see it clearly enough so I used the Ursa Minor group instead right next to Polaris, which is also etched into the polar finder. in the 35 years since the mount was etched I believe the stars have drifted.  I also need to do tests to check the alignment of the scope.  Given the polarity of the motor had been swapped I don't take anything at face value.

There seems to be a regular deviation in the mount which I need to understand, it may be caused by hard grease on the worm wheel having solidified and causing a regular change in resistance.  I am hoping it will be 1/144 of a day interval because thats the worm gear ratio, it might also be the meshing of the 40 tooth drive wheels between the motor and the worm shaft. For a delicate mechanism it's a pretty crude drive, with an open pair of gears and one imprecise bolt to secure the motor in position, you can't turn the motor shaft because it's geared back by 1/120th down-gearing, unless somebody has in the past and bent something in the  motor drive.  Anything is possible, it might even have been dropped.

Given the use of stepper motors, I could make my own driver controller, I have all the bits with an Arduino programmable controller right here.  Will post pix later.



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Robert.