Quote:
Originally Posted by astroron
(1)Do you use external power or internal batteries?check batteries for charge.
You will get poor results with low batteries.
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Hi Ron,
Thanks for the response which is appreciated.
As long as the internal batteries are not completely depleted, in which case the
unit would not power on successfully at all when the encoders are attached,
"low" voltage levels will not affect pointing performance. At its heart, the system
is using digital electronics and the processing itself is CPU-based and largely
arithmetic in nature. The arithmetic results are not affected by the voltage level
and in any case, Argo Navis has sophisticated power circuity that is designed
to squeeze as much life as possible out of a set of regular alkaline cells.
Quote:
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Have you done the 360deg test?
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As Eric also kindly suggested, the Daytime Encoder Test which is detailed on
pp 116-117 of the User Manual under a section of the same name, is the recommended
first test.
In most instances, large pointing error residuals are usually the result of
what we call "Category 1" which are described on page 115 of the User Manual.
These include setup errors and encoder installation errors, such as a slipping
bolt. It is worth reading pp 115-116 of the User Manual for additional important
information. For example, if one has SETUP REFRACTION set to ON but the
local timezone and time in SETUP DATE/TIME is significantly incorrect or the
location in SETUP LOCATION has been set for some other part of the world,
then large refraction corrections may be incorrectly applied.
As mentioned, the Daytime Encoder Test can be useful to catch some
types of common encoder installation errors.
Here is a synopsis of the Daytime Encoder Test.
Power the Argo Navis unit OFF.
Using a high-powered eyepiece or reticle eyepiece, sight and center a distant
terrestrial object. For example, I often like to use power pole insulators.
Now power ON the unit.
DIAL up MODE ENCODER and press ENTER.
Spin the DIAL until it shows AZ/ALT ENC STEPS.
The two values shown in the lower line of the display should both be zero.
Now rotate the mount in Az through 360 degrees and reacquire the target.
Note the left-hand displayed value. It should be ideally within a step
or two of the original zero reading. Keep in mind that with your
10,000 step encoders, when the value reaches 9999 it will wrap back to 0000.
Once satisfied, try rotating the mount again in Az but in the counter direction
to what you previously did. When you re-center the target, ensure that the value is
again within a couple of encoder steps.
Now try swinging the scope in Az back and forth a few times, to try and
induce an encoder slip if something mechanical is amiss, such as a loose
set screw. Again re-center the target and check that the Az encoder value
on the display is within a step or two of zero.
Now do the same procedure, but this time on the Alt axis.
With your Dob, obviously you will not be able to rotate the tube through
a full 360 degrees. Instead, rotate the tube all the way through its full travel
above and below the target before re-centering it, this time taking note
of the right-hand displayed value, which should be within a step or
two of zero.
Sometimes when we ask users if they performed a Daytime Encoder Test,
they respond, "Sure, I did it during the night".
The advantage of performing the test during the daytime is that it is
easier to find a fixed object. Stars won't do as they have apparent motion
due to the Earth's rotation. The other advantage of performing the test during the
daytime is that if something is amiss mechanically, you can literally get
down on hands and knees and inspect up close the encoder installation.
At night, its is dark, often cold, damp and sometimes you are tired.
During the day with the benefit of sufficient light and a clear head, it is
often easier to spot something that is going wrong.
If the mount does not pass the test, then you have some work to do
to find the cause. On the LighBridge, if the Az axis fails the daytime encoder
test, check that the Az pivot bolt is staying fixed with respect the ground board
when the scope rotates. The LightBridge installation kit comes with a nut for
fastening on the bottom of the new Az pivot bolt where it protrudes through the
bottom of the ground board. If need be, remove the large Az pulley and timing
and check that the bolt is secure.
Quote:
Use Auto adjust on when doing Fix Alt Ref.
I am sure Gary will come in on this , but these are a few things to go on with.
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Mbaddah resported using AUTO ADJUST ON in a subsequent run, which
is recommended.
An important check is to now determine after one aligns the unit, whether one can
reliably GUIDE back to the two alignment stars and whether over a period of,
say, 15 minutes, do the alignment stars remain zeroed?
What we call "Category 2" errors are those that result from any
geometrical, gravitational flexure or eccentric bearing errors within the mount
itself. These can be analyzed with the in-built TPAS feature. However, before
reaching for the "heavy guns" which TPAS provides, the possibility of any
Category 1 errors needs to be ascertained first and this is where the Daytime
Encoder Test is once again an indispensable aid. It won't catch all encoder installation
related issues, but it can catch many of the important ones.
After Category 1 errors have been eliminated, If he pointing error residual appear to
increase the further one gets away from either of the two alignment stars, then it can
be a hint of a Category 2 error.
There is a built-in system called TPAS which can do this precisely in a quantitative
fashion, but often an anecdotal account can be telling enough. Keep in mind that
the two GUIDE angles aren't necessarily the best indication of a pointing error
residual, since the angular offset has been then decomposed into the two axis
of motion of the mount. Since the mount uses a spherical co-ordinate system,
the Az axis reading would need to be weighted trigonometrically by where the
scope happens, something not necessarily easy to do "in the head". Angular
separation in terms of eyepiece fields or a fraction thereof is a better metric
if performing the measurement manually without the benefit of TPAS.
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
to be elevated in Alt
