AP900GTO - DEC stiffness


Stef Cancelli
 

Hi Everyone, I'm new here and this is my first post after getting first
light last night with my AP900GTO I picked up from a friend. I am thrilled
with the performance of this mount. I've been using a Tak EM200 up till now
and I thought that thing tracked well but this AP900 is an order of
magnitude better.

I am however, having a problem with stiffness in DEC with the clutches
released and the dampening knob fully retracted. It makes it very difficult
to judge OTA balance in DEC as it will not move at all unless I manually
rotate it with a bit of effort. I'm not sure this is normal as I'm used to
mounts where the axis will spin freely and smoothly when the clutches are
disengaged.

The other problem I'm having that I think may be related to the DEC
stiffness is that while guiding, between exposures when the guider software
dithers the next exposure, DEC will oscillate for quite a few cycles before
settling down. I'm pretty experienced at tweaking guiding parameters and its
nothing I can correct by adjusting parameters. Backlash for DEC is set to 0
so that is not the problem. Guide speed and pulse durations seem accurate
since it makes dec correction perfectly once i get it to stop ping
ponging.However, sometimes to get it stop oscillating I need to bring
aggressiveness down to 0 so Maxim stops sending DEC corrections. After a few
seconds, I can turn on DEC guiding correction and all is fine for the
duration of the exposure.

This kind of behaviour seems like stiction to me and I'm wondering if the
DEC stiffness is contributing to this.

Any insights would be very welcomed. Thanks again and looking forward to
contributing to this group in the future.

Cheers,
Stef Cancelli


Roland Christen
 

In a message dated 3/18/2010 6:30:03 P.M. Central Daylight Time,
scancelli@... writes:

This kind of behaviour seems like stiction to me and I'm wondering if the
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 guiding.
Whether the clutches are loose or fully locked has no effect whatsoever on
guiding.

Rolando


Stef Cancelli
 

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 that
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 after
dithering guider move between exposures. Once it settles however, it will
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 seem
counterproductive to think a tiny bit of backlash is a good thing, but its
fairly easy to handle.

Cheers,
Stef.

On Fri, Mar 19, 2010 at 4:06 AM, <chris1011@...> wrote:



In a message dated 3/18/2010 6:30:03 P.M. Central Daylight Time,
scancelli@... writes:

This kind of behaviour seems like stiction to me and I'm wondering if the
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 guiding.
Whether the clutches are loose or fully locked has no effect whatsoever on
guiding.

Rolando






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Howard Hedlund
 

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.

815-282-1513

________________________________

From: ap-gto@... [mailto:ap-gto@...] On Behalf
Of Stefano Cancelli
Sent: Friday, March 19, 2010 8:33 AM
To: ap-gto@...
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
that
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
after
dithering guider move between exposures. Once it settles however, it
will
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
seem
counterproductive to think a tiny bit of backlash is a good thing, but
its
fairly easy to handle.

Cheers,
Stef.

On Fri, Mar 19, 2010 at 4:06 AM, <chris1011@...
<mailto:chris1011%40aol.com> > wrote:



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

This kind of behaviour seems like stiction to me and I'm wondering if
the
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
guiding.
Whether the clutches are loose or fully locked has no effect
whatsoever on
guiding.

Rolando






------------------------------------

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<http://groups.yahoo.com/group/ap-gtoYahoo> ! Groups Links




observe_m13
 

I'm not sure about the dithering aspect as I haven't done this. Is it actually moving the guidestar position slightly? I would guess that it has to in order to dither. If so, the spur gear on the end of the motor shaft might be just starting to loosen up slightly and a small set screw will have to be tightened on the shaft to hold the gear rigidly in position. I think there is some info of how to check for and fix this in the tech ref section on the AP website about this as well.
Rick.

--- In ap-gto@..., Stefano Cancelli <scancelli@...> wrote:

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 that
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 after
dithering guider move between exposures. Once it settles however, it will
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 seem
counterproductive to think a tiny bit of backlash is a good thing, but its
fairly easy to handle.

Cheers,
Stef.




On Fri, Mar 19, 2010 at 4:06 AM, <chris1011@...> wrote:



In a message dated 3/18/2010 6:30:03 P.M. Central Daylight Time,
scancelli@... writes:

This kind of behaviour seems like stiction to me and I'm wondering if the
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 guiding.
Whether the clutches are loose or fully locked has no effect whatsoever on
guiding.

Rolando


[Non-text portions of this message have been removed]



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[Non-text portions of this message have been removed]


tomb1818 <tomb1818@...>
 

Hi Howard,
Does the precision apply to mounts like the 600? I have a small amount of backlash and was wondering if it would be useful to adjust it out( 2 mm at the end of the counterweight shaft.
Thanks

--- In ap-gto@..., "Howard" <howard@...> 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.

815-282-1513

________________________________

From: ap-gto@... [mailto:ap-gto@...] On Behalf
Of Stefano Cancelli
Sent: Friday, March 19, 2010 8:33 AM
To: ap-gto@...
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
that
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
after
dithering guider move between exposures. Once it settles however, it
will
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
seem
counterproductive to think a tiny bit of backlash is a good thing, but
its
fairly easy to handle.

Cheers,
Stef.

On Fri, Mar 19, 2010 at 4:06 AM, <chris1011@...
<mailto:chris1011%40aol.com> > wrote:



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

This kind of behaviour seems like stiction to me and I'm wondering if
the
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
guiding.
Whether the clutches are loose or fully locked has no effect
whatsoever on
guiding.

Rolando


[Non-text portions of this message have been removed]



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[Non-text portions of this message have been removed]





[Non-text portions of this message have been removed]


Stef Cancelli
 

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.

Cheers,
Stef.

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

815-282-1513

________________________________

From: ap-gto@... [mailto:ap-gto@...] On Behalf
Of Stefano Cancelli
Sent: Friday, March 19, 2010 8:33 AM
To: ap-gto@...
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
that
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
after
dithering guider move between exposures. Once it settles however, it
will
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
seem
counterproductive to think a tiny bit of backlash is a good thing, but
its
fairly easy to handle.

Cheers,
Stef.

On Fri, Mar 19, 2010 at 4:06 AM, <chris1011@...
<mailto:chris1011%40aol.com <chris1011%2540aol.com>> > wrote:



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

This kind of behaviour seems like stiction to me and I'm wondering if
the
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
guiding.
Whether the clutches are loose or fully locked has no effect
whatsoever on
guiding.

Rolando






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see http://groups.yahoo.com/group/ap-gtoYahoo
<http://groups.yahoo.com/group/ap-gtoYahoo> ! Groups Links













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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.
 
Chris

--- 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.

Cheers,
Stef.

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

815-282-1513

____________ _________ _________ __

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
that
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
after
dithering guider move between exposures. Once it settles however, it
will
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
seem
counterproductive to think a tiny bit of backlash is a good thing, but
its
fairly easy to handle.

Cheers,
Stef.

On Fri, Mar 19, 2010 at 4:06 AM, <chris1011@aol. com
<mailto:chris1011% 40aol.com <chris1011%2540aol. com>> > wrote:



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

This kind of behaviour seems like stiction to me and I'm wondering if
the
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
guiding.
Whether the clutches are loose or fully locked has no effect
whatsoever on
guiding.

Rolando






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[Non-text portions of this message have been removed]


Roland Christen
 

In a message dated 3/22/2010 10:36:28 AM Central Daylight Time,
scancelli@... writes:


Ok.. .this is interesting. So even at longer FL with under arcsec
resolution
of the main camera? I'm shooting at 1800 mm and .78asp. I was under the
impression that smaller, more gentle nudges were better.
Yes, 1x is best because it minimizes the effects of Dec backlash. I have
shot with 5500mm focal length and still use 1x for guiding.

Rolando


Roland Christen
 

In a message dated 3/22/2010 10:36:28 AM Central Daylight Time,
scancelli@... writes:


Another imaging session last night and still the occasional ping pong
after
dithering guider move between exposures. Once it settles however, it
will
make dec correction happily for long exposures without oscillation.
Just one more thought about this oscillation. In almost all cases,
oscillation is the result of improper calibration, which results in loop gain larger
than 100%. During calibration procedure, the mount is asked to move in RA
and Dec for a certain number of seconds so that the guiding software can
figure out how many seconds it takes to move a certain number of pixels (Pixels
per second). Because of inevitable delay in reversing Dec (RA does not have
this delay), there is always an undercount of the time it takes to move a
certain distance. Normally that delay is on the order of 0.5 seconds, but if
the geartrain in Dec is not fully meshed, it could be as long as 2 seconds at
1x, 4 seconds at 0.5x and 8 seconds at 0.25x! So you can see that if you
try to calibrate at 0.5x or even at 0.25x, you will undercount the time.

Now on top of that, if you calibrate for only 5 seconds, you will never get
any movement in the reverse direction in Dec, and the resulting parameter
numbers in your guiding software will be way off (too low by an order of
magnitude).

So, to make matters really bad, if you do 3 things wrong: use less than 1x
guide rate to calibrate and guide, have some significant de-mesh in the worm
gears, and calibrate for less than 10 seconds - then you will indeed end up
with bad parameter numbers and will likely see oscillations during guiding.


Therefore, you must do the opposite: use 1x guide rate to calibrate, make
sure you have good worm mesh, calibrate for at least 10 seconds time period.

Some other himts: if you are using MaximDL, make sure you are always using
Dec value = 0 - do not use any other Dec value to modify the guiding. Do
your calibration once, near the celestial equator and use that value everywhere
in the sky - don't worry, it will work perfectly even near the poles. Also,
please check your parameter numbers after calibration to make sure they
make sense. What is a parameter number? That is the number of pixels per second
in both RA and Dec that the guide program has calculated from your
calibration routine. These numbers should be nearly equal or at least close in value
for both RA and Dec when you calibrate near the celestial equator. If they
are quite different (by more than 10%) then that is a very good indication
that you have a bad calibration result.

An example of parameter numbers: if your pixel scale is 1 arc sec per
pixel, then the proper parmater numbers that shoudl show up each time you
calibrate will be 15 in RA and 15 in Dec. 15 is the number of arc seconds per
second that the mount moves at 1x sidereal rate. If your resultant parameter
numbers are 15 in RA and 7 in Dec, then you have a bad calibration (excessive
backlas due to poor mesh, or not enough cal time, etc). Bad calibration will
result in loop gain larger than 100%, which will result in oscillation or
hunting, as the mount is consistently given too large a correction signal for
the star's position error, and the guide star will seem to bobble back and
forth.

Good luck and good hunting, er, guiding.

Rolando


Howard Hedlund
 

Since the backlash you describe is in RA, it is not as critical to
remove it. The 600E mounts are a bit trickier to get a perfect gear
mesh, but they are still very high precision mounts. If you felt the
backlash in dec, I would say to go for it and try to remesh. As it is,
the question is "How much do you enjoy tinkering?"



Mag. 7 skies!



Howard Hedlund

Astro-Physics, Inc.

815-282-1513

________________________________

From: ap-gto@... [mailto:ap-gto@...] On Behalf
Of tomb1818
Sent: Sunday, March 21, 2010 4:39 PM
To: ap-gto@...
Subject: [ap-gto] Re: AP900GTO - DEC stiffness






Hi Howard,
Does the precision apply to mounts like the 600? I have a small amount
of backlash and was wondering if it would be useful to adjust it out( 2
mm at the end of the counterweight shaft.
Thanks

--- In ap-gto@... <mailto:ap-gto%40yahoogroups.com> ,
"Howard" <howard@...> 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 <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.

815-282-1513

________________________________

From: ap-gto@... <mailto:ap-gto%40yahoogroups.com>
[mailto:ap-gto@... <mailto:ap-gto%40yahoogroups.com> ] On
Behalf
Of Stefano Cancelli
Sent: Friday, March 19, 2010 8:33 AM
To: ap-gto@... <mailto:ap-gto%40yahoogroups.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
that
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
after
dithering guider move between exposures. Once it settles however, it
will
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
seem
counterproductive to think a tiny bit of backlash is a good thing, but
its
fairly easy to handle.

Cheers,
Stef.

On Fri, Mar 19, 2010 at 4:06 AM, <chris1011@...
<mailto:chris1011%40aol.com> > wrote:



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

This kind of behaviour seems like stiction to me and I'm wondering
if
the
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
guiding.
Whether the clutches are loose or fully locked has no effect
whatsoever on
guiding.

Rolando






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<http://groups.yahoo.com/group/ap-gtoYahoo> > ! Groups Links











Howard Hedlund
 

I will second this. Please calibrate and guide at 1x.



Mag. 7 skies!



Howard Hedlund

Astro-Physics, Inc.

815-282-1513

________________________________

From: ap-gto@... [mailto:ap-gto@...] On Behalf
Of chris provost
Sent: Sunday, March 21, 2010 8:57 PM
To: ap-gto@...
Subject: Re: [ap-gto] AP900GTO - DEC stiffness





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.

Chris

--- On Sun, 3/21/10, Stefano Cancelli <scancelli@...
<mailto:scancelli%40treblestef.com> > wrote:

From: Stefano Cancelli <scancelli@...
<mailto:scancelli%40treblestef.com> >
Subject: Re: [ap-gto] AP900GTO - DEC stiffness
To: ap-gto@... <mailto:ap-gto%40yahoogroups.com>
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.

Cheers,
Stef.

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

815-282-1513

____________ _________ _________ __

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
that
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
after
dithering guider move between exposures. Once it settles however, it
will
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
seem
counterproductive to think a tiny bit of backlash is a good thing, but
its
fairly easy to handle.

Cheers,
Stef.

On Fri, Mar 19, 2010 at 4:06 AM, <chris1011@aol. com
<mailto:chris1011% 40aol.com <chris1011%2540aol. com>> > wrote:



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

This kind of behaviour seems like stiction to me and I'm wondering
if
the
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
guiding.
Whether the clutches are loose or fully locked has no effect
whatsoever on
guiding.

Rolando






------------ --------- --------- ------

To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups. yahoo.com/ group/ap- gtoYahoo
<http://groups. yahoo.com/ group/ap- gtoYahoo> ! Groups Links













------------ --------- --------- ------

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Roland Christen
 

In a message dated 3/22/2010 1:05:23 PM Central Daylight Time,
calypte@... writes:


WRT the above quoted statement -- OK, that's true for Maxim DL. What
about CCDSoft? Not an A-P mount, of course, but I've found little benefit to
setting the dec parameter to anything other than zero for autoguiding.
Always set the Dec to zero, otherwise you are courting potential
instability due to higher loop gain. You always want the loop gain to be 100% or
lower. Loop gain over 100% means that the correction signal sent to the mount
will be larger than the error it is trying to correct. That will cause the
mount to overshoot and begin limit cycling, hunting or oscillating.

Rolando


Stef Cancelli
 

Ok.. .this is interesting. So even at longer FL with under arcsec resolution
of the main camera? I'm shooting at 1800 mm and .78asp. I was under the
impression that smaller, more gentle nudges were better.

Cheers,
Stef.

On Mon, Mar 22, 2010 at 10:57 AM, Howard <howard@...> wrote:

I will second this. Please calibrate and guide at 1x.



Mag. 7 skies!



Howard Hedlund

Astro-Physics, Inc.

815-282-1513

________________________________

From: ap-gto@... [mailto:ap-gto@...] On Behalf
Of chris provost
Sent: Sunday, March 21, 2010 8:57 PM
To: ap-gto@...
Subject: Re: [ap-gto] AP900GTO - DEC stiffness





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.

Chris

--- On Sun, 3/21/10, Stefano Cancelli <scancelli@...
<mailto:scancelli%40treblestef.com <scancelli%2540treblestef.com>> >
wrote:

From: Stefano Cancelli <scancelli@...
<mailto:scancelli%40treblestef.com <scancelli%2540treblestef.com>> >
Subject: Re: [ap-gto] AP900GTO - DEC stiffness
To: ap-gto@... <mailto:ap-gto%40yahoogroups.com<ap-gto%2540yahoogroups.com>
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.

Cheers,
Stef.

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

815-282-1513

____________ _________ _________ __

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
that
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
after
dithering guider move between exposures. Once it settles however, it
will
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
seem
counterproductive to think a tiny bit of backlash is a good thing, but
its
fairly easy to handle.

Cheers,
Stef.

On Fri, Mar 19, 2010 at 4:06 AM, <chris1011@aol. com
<mailto:chris1011% <chris1011%25> 40aol.com <chris1011%2540aol. com>> >
wrote:



In a message dated 3/18/2010 6:30:03 P.M. Central Daylight Time,
> > scancelli@trebleste f.com <mailto:scancelli% <scancelli%25>40treblestef.
com<scancelli% 2540treblestef. com>>
writes:

This kind of behaviour seems like stiction to me and I'm wondering
if
the
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
guiding.
Whether the clutches are loose or fully locked has no effect
whatsoever on
guiding.

Rolando






------------ --------- --------- ------

To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups. yahoo.com/ group/ap- gtoYahoo
<http://groups. yahoo.com/ group/ap- gtoYahoo> ! Groups Links













------------ --------- --------- ------
>
To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups. yahoo.com/ group/ap- gtoYahoo! Groups Links















------------------------------------

To UNSUBSCRIBE, or for general information on the ap-gto list
see http://groups.yahoo.com/group/ap-gtoYahoo! Groups Links




CurtisC <calypte@...>
 

Some other himts: if you are using MaximDL, make sure you are always > using Dec value = 0 - do not use any other Dec value to modify the
guiding. Do your calibration once, near the celestial equator and use > that value everywhere in the sky - don't worry, it will work
perfectly even near the poles.
My new Mach1GTO is due here in two days. Looks like I have a lot to learn. I hope I get good results sooner than with my G-11! The people in the Losmandy group are upset over my parting comments yesterday.

WRT the above quoted statement -- OK, that's true for Maxim DL. What about CCDSoft? Not an A-P mount, of course, but I've found little benefit to setting the dec parameter to anything other than zero for autoguiding.


tomb1818 <tomb1818@...>
 

"if it aint broken don't touch it!"
As to precision, you are right. I get +/- 4 arcsec without pem.

I'm gonna leave it alone.
Thanks

--- In ap-gto@..., "Howard" <howard@...> wrote:

Since the backlash you describe is in RA, it is not as critical to
remove it. The 600E mounts are a bit trickier to get a perfect gear
mesh, but they are still very high precision mounts. If you felt the
backlash in dec, I would say to go for it and try to remesh. As it is,
the question is "How much do you enjoy tinkering?"



Mag. 7 skies!



Howard Hedlund

Astro-Physics, Inc.

815-282-1513

________________________________

From: ap-gto@... [mailto:ap-gto@...] On Behalf
Of tomb1818
Sent: Sunday, March 21, 2010 4:39 PM
To: ap-gto@...
Subject: [ap-gto] Re: AP900GTO - DEC stiffness






Hi Howard,
Does the precision apply to mounts like the 600? I have a small amount
of backlash and was wondering if it would be useful to adjust it out( 2
mm at the end of the counterweight shaft.
Thanks

--- In ap-gto@... <mailto:ap-gto%40yahoogroups.com> ,
"Howard" <howard@> 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 <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.

815-282-1513

________________________________

From: ap-gto@... <mailto:ap-gto%40yahoogroups.com>
[mailto:ap-gto@... <mailto:ap-gto%40yahoogroups.com> ] On
Behalf
Of Stefano Cancelli
Sent: Friday, March 19, 2010 8:33 AM
To: ap-gto@... <mailto:ap-gto%40yahoogroups.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
that
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
after
dithering guider move between exposures. Once it settles however, it
will
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
seem
counterproductive to think a tiny bit of backlash is a good thing, but
its
fairly easy to handle.

Cheers,
Stef.

On Fri, Mar 19, 2010 at 4:06 AM, <chris1011@
<mailto:chris1011%40aol.com> > wrote:



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

This kind of behaviour seems like stiction to me and I'm wondering
if
the
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
guiding.
Whether the clutches are loose or fully locked has no effect
whatsoever on
guiding.

Rolando


[Non-text portions of this message have been removed]



------------------------------------

To UNSUBSCRIBE, or for general information on the ap-gto list
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<http://groups.yahoo.com/group/ap-gtoYahoo>
<http://groups.yahoo.com/group/ap-gtoYahoo
<http://groups.yahoo.com/group/ap-gtoYahoo> > ! Groups Links



[Non-text portions of this message have been removed]





[Non-text portions of this message have been removed]




[Non-text portions of this message have been removed]


John Murphy
 

I also used to own a G11. For the price, it is a good mount and it is capable of producing good images. But you are right - it can take a long time to learn how to get the best out of it. It needs plenty of care and attention when setting up for imaging. Works best when everything is set up exactly right. But by the time I sold it, I had grown quite attached to it.

I bought my AP1200 a year ago. I got superb results straight out of the box. It just works. Does exactly what it is asked to do. And the tracking is awesome - much better than I expected. And being able to delay or advance the meridian flip by many hours has also been a major advantage to my long imaging runs.

I let MaximDL get the dec from the mount for calibration and guiding. This gives a constant loop gain for the whole sky (I usually set this gain to 0.6). Of course it is also best to calibrate the guider close to a dec of zero to reduce calibration errors. Works for me.

As to DEC and RA stiffness - this is a good thing - reduces the effect of gusts of wind. To balance the RA and DEC, I use a kitchen scale so I can read the force required in both directions. This is probably over kill - the mount does not seem to mind moderate balance errors (in either direction).

My final hint is to use a cable wrap around the dec cable. By making the cable thicker (about 2 cm diameter) it becomes impossible for it to catch on the clutch knobs.

John Murphy

--- In ap-gto@..., "CurtisC" <calypte@...> wrote:


Some other himts: if you are using MaximDL, make sure you are always > using Dec value = 0 - do not use any other Dec value to modify the
guiding. Do your calibration once, near the celestial equator and use > that value everywhere in the sky - don't worry, it will work
perfectly even near the poles.
My new Mach1GTO is due here in two days. Looks like I have a lot to learn. I hope I get good results sooner than with my G-11! The people in the Losmandy group are upset over my parting comments yesterday.

WRT the above quoted statement -- OK, that's true for Maxim DL. What about CCDSoft? Not an A-P mount, of course, but I've found little benefit to setting the dec parameter to anything other than zero for autoguiding.