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Old 23-02-2009, 01:53 PM
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gary is offline
Join Date: Apr 2005
Location: Mt. Kuring-Gai
Posts: 5,443
Arrow Encoder direction sense establishment

Originally Posted by nightstalker View Post
Sure is kev.. my encoder mounting seems ok .. I get a very small deflection on one point on one of my alt axis .. I'm thinking its one or both of my alt bearings arn't exactly the same at this point .. anyway the amount of movement at the end of my tangent arm is 1/2 mm and would then likely be much smaller again if measured closer to the encoder and if my thinking is right??.
If the movement of which you write is toward and away from the side of the
rocker, then of course the arm will deflect less in distance if measured toward
the encoder end, but the angle by which it deflects will be the same, irrespective
from which end it is measured.

if the movement is radial, toward or away the Alt axis, the radial distance the
arm moves by will be the same irrespective of where it is measured along the arm.

Gary I reset the encoder resolution to 10 000 steps on both axis
thats right isn't it ?
That is correct.

To determine the encoder direction senses, you may find the following
alternative procedure beneficial -

To check the SETUP ALT STEPS sign, point the Optical Tube Assembly (OTA)
to the vertical and DIAL up MODE FIX ALT REF, ALT REF=+90, AUTO ADJUST
OFF and then press ENTER. Now DIAL up MODE ENCODER. The right-hand
displayed value should be close to +90 degrees. Now push the OTA
downward in Altitude toward the horizon. The right-hand displayed value
should decrease, +89, +88, ... +3, +2, +1, 0 as you go from the zenith
toward the horizon. If not, reverse the SETUP ALT STEPS sign and repeat
the test.

Once the ALT STEPS sign is correctly established, perform a FIX ALT
REF and two-star alignment. Now DIAL up MODE RA DEC (not MODE
ENCODER). Point the OTA at the approximate intersection of the
meridian* and celestial equator* (see below). Now sweep the OTA from that point
toward the East, roughly following the celestial equator. RA (left-hand value) should
be increasing on the display (it will wrap at 23:59.0 back to 00:00.0).
If it is decreasing, reverse the SETUP AZ STEPS sign and repeat the

One you have established the signs, try the following test as well.
Firstly, go to MODE SETUP, SETUP GUIDE and set the number of GUIDE
DECIMAL to 2 DECIMAL PLACES. Perform a FIX ALT REF and two-star
alignment. GUIDE back to one of the original two alignment stars. Note
that the display shows close to 0.00 0.00. Wait 15 minutes and GUIDE
back to the same star. Does the display still show close to 0.00 0.00?
Now GUIDE to a third star, well away from the original two in some other
part of the sky, and check that the angular error residual of this third
star is small.

As mentioned in the User Manual, irrespective of which way the
arrows point in GUIDE mode, always push the scope in a direction
that makes the GUIDE angles closer to zero. One can later change the
convention of which way the arrows point using SETUP GUIDE as a
matter of personal preference for your particular installation.

Once you have correctly established the encoder direction senses,
we also recommend you use AUTO ADJUST ON when you perform the FIX
ALT REF step. To set it up, DIAL up MODE SETUP, SETUP ALT REF and
enter a value of +090.000. Then when you perform the FIX ALT REF
STEP, DIAL up ALT REF=+090.000 AUTO ADJUST ON. Perform your two star
alignment as normal. The WARP factor should then be 0.00 (A) where
the (A) indicates the ALT REF point was automatically adjusted. If
you see a non-zero WARP factor when AUTO ADJUST is ON or an (X)
instead of an (A), it means something is amiss, such as a
misidentified star or cable not plugged in. Keep in mind that though
a WARP factor of 0.00 is a prerequisite for good pointing
performance, it does not necessarily guarantee good performance. The
reason is that the AUTO ADJUST mechanism bends over backwards to
correct the ALT REF point so as to produce a WARP factor of zero
wherever possible, even if you have misidentified the alignment

spose I'm not to far from giving it a try .. not sure how a two cloud alignment will work out but we'll see
Hope you have some clear nights ahead!

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Phone +61-2-9457-9593
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