Re: odd parking position discrepancy


Hi Rolando,

Thanks, that is perfectly clear...I figured there was a good reason the "error" was so reliably repeatable.


John Collins


On 7/5/2017 7:43 AM, chris1011@... [ap-gto] wrote:
The Park positions, especially Park1 and Park4, will never be exactly parallel to the earth. There are a number of reasons for that, including the time it takes for the Dec axis to stop moving after the RA axis has gotten to the park position. During the Dec slewing the RA will be tracking at the sidereal rate, so that at the end of the park sequence it will be slightly off. The second reason is that atmospheric refraction is being applied so that the RA and Dec positions will be slightly high.

For the above reasons, when you re-start the system next time, don't Resume from Park4, rather use the more accurate Resume from Present Position. That is the most accurate way to start your mount after it has been parked. The mount always keeps track of the slight differences on the actual position, so let it resume from its internal known position. The only time I would ever use Resume from Park4 (or 1 or 2 etc.) is when starting with a fresh setup where the internal mount positions are not known or where you have moved the scope via loosening the clutches.


-----Original Message-----
From: john astro@... [ap-gto]
To: ap-gto
Sent: Tue, Jul 4, 2017 9:00 pm
Subject: [ap-gto] odd parking position discrepancy


John Collins from Oregon here. Wondering if anyone has seen/fixed this:

Historically, my CP3-controlled setup (AP 1600GTO, CDK17, STX camera)
would maneuver all night and return to park with no discrepancy at all
using SkyX native driver. Setting up a new observatory with CP4, APCC
Pro, and V2 driver, I'm seeing a discrepancy creep into results. I have
a digital level on the cw shaft....physically set RA and DEC to 0.00
degrees at park 4.....if I so much as nudge the scope out of park, then
repark using APCC pro for both moves, I have a 0.4 degree RA and a 1.1
degree DEC error when apcc reports parked. These discrepancies repeat
reliably...that is, there doesn't seem to be some loose thingy flapping
around...the errors are quite deliberate. The weird part is that SkyX
pro "likes" the erroneous numbers better, showing the scope parked
right-on-the money, whereas there is a slight offset in SkyX when the
park 4 numbers are "correct".

I'm sitting here in daylight just fiddling...will experiment tonight as
to what actually works........

This may be part of CP4/APCC new-guy syndrome, so feel free to bop me on
the head if needed...never saw this issue with CP3, but then I didn't
have this resolution before either. I've done the balance, lash,
etc........drawing a blank at this point. Any ideas?


John Collins



Posted by: john

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