Re: AP900GTO - DEC stiffness

chris provost <lineman_16735@...>

Roland has always said it is best to use 1x gor an ag rate.  I can't remember why but I had a similar issue as you and once i switched to 1X guiding is perfect in dec.

--- On Sun, 3/21/10, Stefano Cancelli <scancelli@...> wrote:

From: Stefano Cancelli <scancelli@...>
Subject: Re: [ap-gto] AP900GTO - DEC stiffness
To: ap-gto@...
Date: Sunday, March 21, 2010, 8:47 PM


Howard and Rick,

Thanks for the information. I'm pretty sure backlash really is set to 0, I'm
using Ray's latest ascom driver. I'll keep working on it but for now, if I
keep aggresiveness really low.. around the 2 range in MaxIm DL and guide
speed at .5x it's manageable. My max move is set to .3 secs and the dead
zone is currently set to .02 secs. It takes a while for the guide star to
center after a dec dither at these low aggressiveness values, but its not
that big a deal since CCDAP does all the heavy lifting :)

Rick, yes dithering moves the guide star between exposures randomly within a
user defined box. CCDAP has an enhanced dithering pattern rather than random
that works great even if you have just a few exposures. Dithering makes a
huge difference when combining since the rejection algorithms have no
problem identifying outliers and eliminating them. The results are much
smoother and less noisy stacked images.


On Fri, Mar 19, 2010 at 10:17 AM, Howard <howard@astro-> wrote:

Good Morning Stefano!

Are you using guiding software that employs the ASCOM driver? If so,
are you using the old driver from the ASCOM website - v. 4.1.25 - or are
you using our new driver - v. 4.99.58 - available here:

http://www.gralak. com/apdriver

The reason I ask is that the old driver had a default backlash setting
that could be overriding whatever you might have set with the keypad. I
can't count the number of times this has been an issue, and it almost
always presents itself as oscillations when guiding. Let's first verify
that the backlash setting really and truly is at zero!

I would not loosen what sounds like an excellent gear mesh. Think of
it this way: If your car's right front wheel is out of alignment and is
pulling the car to the right, you can correct this by lowering the tire
pressure in the left front tire until the car tracks in a straight line.
You may have made your car go straight, but this probably isn't the best
solution. You will find that your 900GTO has enough mechanical
precision that the gear mesh can be adjusted to a level where backlash
is of little significance. Most of our most experienced AP family
members find that they simply don't need to use backlash compensation.

Mag. 7 skies!

Howard Hedlund

Astro-Physics, Inc.


____________ _________ _________ __

From: ap-gto@yahoogroups. com [mailto:ap-gto@yahoogroups. com] On Behalf
Of Stefano Cancelli
Sent: Friday, March 19, 2010 8:33 AM
To: ap-gto@yahoogroups. com
Subject: Re: [ap-gto] AP900GTO - DEC stiffness

Thanks, Rolando. I found the pdf's on the site that show the clutch
replacement procedure and the special extraction tool. This pretty much
answers my question as it appears its not an uncommon problem and one
is easily remedied. I wasnt' sure if the stiffness was coming from the
clutches not being disengaged fully or if it was some other mechanical
binding problem from the axis itself.

Another imaging session last night and still the occasional ping pong
dithering guider move between exposures. Once it settles however, it
make dec correction happily for long exposures without oscillation. I'm
wondering if perhaps the worm mesh in DEC might be a little too tight as
there doesn't seem to be any backlash whatsover in DEC. I know it might
counterproductive to think a tiny bit of backlash is a good thing, but
fairly easy to handle.


On Fri, Mar 19, 2010 at 4:06 AM, <chris1011@aol. com
<mailto:chris1011% <chris1011%2540aol. com>> > wrote:

In a message dated 3/18/2010 6:30:03 P.M. Central Daylight Time,
scancelli@trebleste <mailto:scancelli% 40treblestef. com<scancelli% 2540treblestef. com>>

This kind of behaviour seems like stiction to me and I'm wondering if
DEC stiffness is contributing to this.
Howard can answer you about the clutches being stiff and how to remedy
that. However, be assured that this has nothing to do with your
Whether the clutches are loose or fully locked has no effect
whatsoever on


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