Re: AP 900 problem

Michael Cater <nitemike1@...>

I have had no problem with the calibration function of the ST4 as long as I calibrate for about 10 seconds in both axis. When the guiding starts it seems to work well for several minutes and then the numbers on the screen progressively increase in the RA axis (as in periodic error). After a few minutes the values improve only to increase again in a few minutes of guiding. Eventually, the values reach the E value (>9) which means the ST4 can't find the guide star. I will probably try my friends ST4 this weekend to see if the issue is my ST4.


chris1011@... wrote:
In a message dated 2/14/2008 6:02:21 AM Central Standard Time,
nitemike1@... writes:

I am new to the group. I have an AP 900 mount (V 4.12) that I bought
on Astromart. It tracks very well and the GOTO function works
flawlessly. However, I have been unable to get my ST4 to guide for
more than a few minutes at a time. I tried using the periodic error
function to correct any flaws in the RA worm but to no avail. I don't
know whether the problem is in the ST4 or the stepper motors. What
would you suggest? If it is the stepper motors is replacing them a
major expense/problem?
1) the 900 servo mount does not have stepper motors. If it tracks very well,
then certainly the servo motors are working properly.

2) An ST4 is not an easy beast to work with. If it does not work properly,
then it will not interact with the mount. If the relays are shot or stuck in an
open or closed position, then it will not work no matter what you do with the
mount, so the first thing you need to do is find out if the 4 relays are doing
their job properly. Next thing is to make sure that the connector cable from
the ST4 to the mount is of the proper type. You will need to the trace the
pins back to the relays with an ohmmeter to make sure that the proper pins are
opening and closing when the 4 direction buttons on the ST4 are pushed. If the
ST4 is not set up properly, you can forget about using it to guide the mount.

3) you mention that you tried to use the periodic error function to correct
any flaws in the worm. What flaws are in the worm that you are trying to
correct, and how are you setting up the periodic error compensation to do this? Are
you guiding by hand and loading the PE curve this way? Are you using PEMPro?
What is your method for loading the PE curve?


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