Quote:
Originally Posted by mick pinner
set up the Argo tonight and tried to do an alignment and then a goto to check accuracy.
G11 polar aligned, time, date, location entered.
encoder directions are both positive values when scope moved in ra/dec with scope on east side of mount.
acrux as alignment star then picked ngc3372 as goto object, moved scope until values read 0 on both axis, scope ends up on western side of mount pointing to the west of the southern cross? nowhere 3372, can anyone pinpoint something l am doing wrong. l have repeated this a couple of times with the same result. thanks.
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Hi Mick,
Chances are one or both of the encoder direction sense signs (the +/-) signs
in SETUP ALT STEPS and/or SETUP AZ STEPS is incorrect.
In particular, your SETUP ALT STEPS sign might be the one to scrutinize
first.
As you know, GEM's have the ability to point to just about any point in the
sky using the mount in two different orientations.
When you perform the alignment operation, the SETUP ALT STEPS sign
has to be set consistently with the 'side' of the mount the OTA is
on.
To appreciate this, try setting the mount so the Dec cross bar is
horizontal, with the counterweights on one side and the OTA on the other,
like a pair of weigh-lifters dumb bells. Now point the OTA to the horizon
and then raise it in altitude toward the zenith. Whilst you are doing so,
take note of which 'sense' the encoder shaft is rotating (i.e. either
clockwise or counter-clockwise depending upon your frame of reference).
Now rotate the scope in RA only by 12 hours so that the Dec axis is horizontal
again but the positions of the OTA and counter-weights are swapped.
Again slowly raise the OTA from the horizon to the zenith. Notice that
even though you are raising the OTA up in altitude, the sense of the encoder shaft
rotation has reversed compared to what it was previously?
This is an attribute of three dimensional geometry rather than some
caveat of the Argo Navis.
One can perform the initial alignment with the OTA on either side of the
mount as long as the SETUP ALT STEPS sign is set consistently for that
side you are aligning on.
When attempting to align on a star that is in that circumpolar region of the
sky, one has to think more carefully because as one goes from the horizon to
the pole, declination decreases as you get closer to -90, reaches the
minimum of -90 at the pole itself and then starts to increase again the
higher in elevation you go.
For this reason, say you have previously determined the Alt encoder
direction sense for the when the OTA is on a particular side of the
mount. When you choose the first alignment star, do not cross the
celestial pole.
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