Argo Navis + G11

[mick pinner]

as some would know a while back l got a G11 with AN.
at the time l had some pointing issues which l discussed with some forum members to try and sort them out but with no luck, last weekend l decieded to go through the entire process again.
polar alignment is spot on, encoders do not slip, correct info entered into hand pad, values increase when scope is moved in the appropriate direction, cables are in the correct position.
two star alignment, go to first selected object no worries, all subsequent go to's are not even close, however select the two original alignment stars and will centre them perfectly.
is there someone in Melbourne with some experience with a setup like this that maybe able to help as there is nothing more l can think of, if not out with the Argo and in with the Gemini Go-To. any help appreciated.

[Jeff]

Hi Mick,

I can give you a hand if still required.

A few things to check are as follows:
setup Alt steps = +8192
setup Az steps = +8192
setup Mount = GEM exact (only requires single star align)

Hope this helps.
Let me know if you want to bring your rig over some time.

Cheers,
Jeff

[mick pinner]

hi Jeff, thanks for the reply, all these settings and procedures have been checked and rechecked thus the frustration.

[[1ponders] (Paul)]

I have exactly the same issue Mick. I've never been able to resolve the problem so I stick to one star alignment.

[gary]

Originally Posted by mick pinner

as some would know a while back l got a G11 with AN.
at the time l had some pointing issues which l discussed with some forum members to try and sort them out but with no luck, last weekend l decieded to go through the entire process again.
polar alignment is spot on, encoders do not slip, correct info entered into hand pad, values increase when scope is moved in the appropriate direction, cables are in the correct position.
two star alignment, go to first selected object no worries, all subsequent go to's are not even close, however select the two original alignment stars and will centre them perfectly.
is there someone in Melbourne with some experience with a setup like this that maybe able to help as there is nothing more l can think of, if not out with the Argo and in with the Gemini Go-To. any help appreciated.

Hi Mick,

Thanks for the post. Let's see if we can assist.

As you are aware, GEM's have the attribute that they can view any one point
in the sky from two different mechanical orientations of the mount/OTA.

Whenever the OTA is flipped over the meridian, the direction sense of the
Dec (Alt) encoder reverses. This is an attribute of spatial geometry rather
than some caveat of Argo Navis.

To appreciate this, position the OTA into the 3 o'clock position (the counterweight
will be at 9 o'clock). Point the OTA toward the horizon. Now, whilst raising the
OTA in Alt (Dec) only from the horizon, note which direction (clockwise or
counterclockwise) the encoder shaft rotates. Now flip the OTA over
to the 9' o'clock position, point it back at the horizon and repeat the
exercise. Notice how the encoder shaft rotates in the reverse direction
to what it die previously even though the tube is still climbing up
from the horizon toward the zenith?

The consequences of this is that your SETUP ALT STEPS sign must be
set consistently for the side of the mount you initially perform the FIX ALT
REF step and first star alignment. After that, you are free to flip the mount
and don't need to change the direction sense sign. If on some night you
setup the scope and want to perform the alignment on the other side of the mount to
what you normally do, simply reverse the sign and stick with it for the rest of
the night.

After performing the FIX ALT REF, when you go to align on the first star,
don't move the OTA more than 90 degrees in Declination. In other words,
don't cross the celestial pole to get to the alignment star.

In order to unambiguously ensure the tube is on the 'right side', when the
tube is on the East side, align on a star in the West and vice versa.

Please don't hesitate to drop me a line or give us a call if you should require
further assistance.

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au