Re: AP900 Dec backlash

Jeff <jlc@...>


By any chance were you using The AP Ascom driver?

Fyi, with the new 1200, after installing the Ascom driver and running
PemPro, I ended up needing a ton of backlash compensation.
I tried compensating this w/ the handpad setting which was very odd.

Turns out the default backlash compensentation _setting_ in the ASCOM AP
driver was like 25, which it then loads into the controller.

(I.e. after I installed the driver, the "default value in the UI" was like
25 secs. This didnt show up in the handpad, but visually in the eyepiece it
was very obvious. It took me like two weeks to figure out what was causing
the odd behaviour with the 1200. Powercycling the mount cleared the
problem, but whenever I wanted to control the mount w/ software I'd get the
bad backlash.)

However, this was in RA. Dec was zero, iirc.

Just something to check.

If there was alot of backlash, I'd expect it to be noticible with the "hand"
test. But I could be wrong.


From: ap-gto@... [mailto:ap-gto@...] On Behalf Of
John Winfield
Sent: Saturday, April 21, 2007 2:52 PM
To: ap-gto@...
Subject: [ap-gto] AP900 Dec backlash


I've recently bought a used AP900 and just ran the backlash tests in
Ray's Pulseguide app.

I found a load of Dec backlash - so much that the tests didn't reverse
direction at all.
I needed a backlash setting of 87 in the driver to correct for the

Today I went to follow the instructions on the AP website to adjust
the Dec worm adjustment (using the advice of finger pressure rather
than a hammer!).

The first thing I noticed was that the grub screw locking the hex bolt
in place was still present, so presumably the adjustment had never
been done before since the instructions say to remove and discard this
However, although I could loosen the grub screw, I couldn't remove it
completely - it unscrewed to the point of contacting the Dec motor
housing but I couldn't get it out completely. Is there a trick to
removing it?

Secondly, once I had loosened the bolt and retightened with finger
pressure pushing on the motor housing, the instructions said to remove
the shaft cover and ensure the shaft could be rotated by hand without
binding. However, I couldn't remove the shaft cover.
Does it screw on, or is it a push fit? Any tips for removing it
without marring?



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