AP-1100 Guiding Questions


Horia
 

My AP-1100 (August 2021, no encoders) shows, most of the time, slightly worse guiding in Dec than in RA. A typical example (one 300sec frame) looks like this:

 

 

The blue curve is the RA and the red one is the Dec. The gray area on the left is the settling time after a dither. For a better view:

https://www.dropbox.com/s/2c2e5qfil3x2qzb/OneFrame.jpg?dl=0

 

The guiding parameters:

  • Guiding scale: 1.05 arc-sec / pix
  • Exposure: 2000msec
  • Time lapse: 500msec
  • Guide Speed: 15 arc-sec / sec (both RA and Dec)
  • Min move RA: 0.3pix, Aggression: 0.75
  • Min move Dec: 0.4pix, Aggression: 0.8

 

And the resulting rms values are:

I am imaging at 0,9 arcsec/pix and the difference between RA and Dec values can be clearly seen as a small elongation in N/S direction.

 

I have the feeling that the Dec axis have somehow more play compared to the RA. I have adjusted the backstop more than once without seeing an improvement.

 

Is this normal behavior for the Ap-1100?

The system is balanced as close to perfect as I could do it. Should I unbalance the Dec axis to be backside heavy?

Is there something else I should do?

 

Kind regards,

Horia

 

 


Luca Marinelli
 

Horia,

What does your Dec drift look like if you turn guiding off? Most of your guiding corrections appear to be in one direction, which could indicate poor polar alignment. 

Best,

Luca

On Dec 8, 2021, at 5:24 AM, Horia via groups.io <ATM@...> wrote:



My AP-1100 (August 2021, no encoders) shows, most of the time, slightly worse guiding in Dec than in RA. A typical example (one 300sec frame) looks like this:

 

<image001.png>

 

The blue curve is the RA and the red one is the Dec. The gray area on the left is the settling time after a dither. For a better view:

https://www.dropbox.com/s/2c2e5qfil3x2qzb/OneFrame.jpg?dl=0

 

The guiding parameters:

  • Guiding scale: 1.05 arc-sec / pix
  • Exposure: 2000msec
  • Time lapse: 500msec
  • Guide Speed: 15 arc-sec / sec (both RA and Dec)
  • Min move RA: 0.3pix, Aggression: 0.75
  • Min move Dec: 0.4pix, Aggression: 0.8

 

And the resulting rms values are:

<image003.png>

I am imaging at 0,9 arcsec/pix and the difference between RA and Dec values can be clearly seen as a small elongation in N/S direction.

 

I have the feeling that the Dec axis have somehow more play compared to the RA. I have adjusted the backstop more than once without seeing an improvement.

 

Is this normal behavior for the Ap-1100?

The system is balanced as close to perfect as I could do it. Should I unbalance the Dec axis to be backside heavy?

Is there something else I should do?

 

Kind regards,

Horia

 

 


ap@CaptivePhotons.com
 

Horia wrote:

  • My AP-1100 (August 2021, no encoders) shows, most of the time, slightly worse guiding in Dec than in RA. A typical example (one 300sec frame) looks like this:

There are a couple things you might do to isolate the issue:

  1. Run guiding assistant for a reasonably long time, like 10 minutes, with tracking corrections off (in the model).  This should yield a DEC result that is only from seeing and external factors, so in perfect seeing it's a flat line that drifts with polar alignment.  Seeing should be similar on RA and DEC so you can by eye eliminate seeing, and see what is left in DEC, notably are there still big excursions.  When done let it measure backlash also, which I would expect to be negligible.

 

  1. If you do see sharp spikes remaining, my guess would be wind or some external source.  That can cause different reaction in RA and DEC depending on wind direction and equipment shape.  If that's a possibility, go stand by the mount for a bit, and just see if the wind was calm, then look back at the data.  While there, look closely if anything might be dragging, touching unexpectedly (even a cable just tugging). Even if using thru-mount cables, give each a little tug at each end (pulling toward the mount) and make sure there is plenty of slack (not hanging loose, just not tight), as RA rotation might be tunning slightly on a taught cable.  And if you find nothing, AP might be able to help based on the GA run.

Linwood


 

Hello Horia

You would need to provide your  guidelogs to really know what is going on. Screen captures are interesting, but don't tell the whole story

If this is a new (to you) mount, i highly recommend you run a baseline guiding by following these steps (this is what we use in the PHD user forums) and then provide your guidelogs.


As someone else pointed out, your corrections are in one direction, which usually indicates polar misalignment, but i also see some axis bleed which could mean you have orthogonality issues in your calibration. Looking at a baseline guidelog will clarify what is going on

Brian

On Wed, Dec 8, 2021 at 2:24 AM Horia <ATM@...> wrote:

My AP-1100 (August 2021, no encoders) shows, most of the time, slightly worse guiding in Dec than in RA. A typical example (one 300sec frame) looks like this:

 

 

The blue curve is the RA and the red one is the Dec. The gray area on the left is the settling time after a dither. For a better view:

https://www.dropbox.com/s/2c2e5qfil3x2qzb/OneFrame.jpg?dl=0

 

The guiding parameters:

  • Guiding scale: 1.05 arc-sec / pix
  • Exposure: 2000msec
  • Time lapse: 500msec
  • Guide Speed: 15 arc-sec / sec (both RA and Dec)
  • Min move RA: 0.3pix, Aggression: 0.75
  • Min move Dec: 0.4pix, Aggression: 0.8

 

And the resulting rms values are:

I am imaging at 0,9 arcsec/pix and the difference between RA and Dec values can be clearly seen as a small elongation in N/S direction.

 

I have the feeling that the Dec axis have somehow more play compared to the RA. I have adjusted the backstop more than once without seeing an improvement.

 

Is this normal behavior for the Ap-1100?

The system is balanced as close to perfect as I could do it. Should I unbalance the Dec axis to be backside heavy?

Is there something else I should do?

 

Kind regards,

Horia

 

 



--
Brian 



Brian Valente


Roland Christen
 

Your Dec guiding shows static friction which can be caused two ways. 1) it will occur if your Dec axis is unbalanced. 2) it will occur if you force the worm into mesh too tightly by not leaving a small amount of clearance in the backstop adjustment.

Static friction:
Generally people assume that the Dec axis must be tightly into mesh, so they force the mesh by adjusting the backstop very tightly. The assumption is that the tighter the mesh, the lower will be the backlash. This is counter-intuitive. Actually with a spring loaded gearbox you want only the spring to push the worm into mesh, never the backstop. The backstop should be adjusted a bit back to allow the worm to ride up and down into the high and low spots along the worm wheel. The backstop should never be set so that there is no clearance at all between the worm and worm wheel.

With proper adjustment of the backstop you should be able to gently press on the back of the motor box and feel the worm lift up out of full mesh. Not heavy pressure, but just 1 finger pressure. This is not complete disengagement, but just slight disengagement where the teeth are still near contact. You can tell if the worm is slightly out if you then gently push on the telescope in the Dec direction and can feel the free play. Very gently, as in just 1 finger pressure on the back of the scope. Then, as you let go of the back of the gearbox you should feel the axis play pretty much go away.

Dec Play:
If the Dec has actual play, even with the worm fully in mesh, then it may be that the end play nut on the worm is loose. That's an easy fix. The end play nut is on one side of the motor box under the circular cover that has 2 holes in it for a spanner wrench (if you don't have a spanner, you can use a needle nosed pliers). Older mounts may have a knurled cover which can be removed without using a spanner. Remove the cover to expose the end of the worm. You will see the stainless steel nut with 2 holes. Use the spanner to tighten this nut. Once fully tight, the Dec play should be gone.

Never use the backstop to try to tighten the Dec play. Doing so will make things worse - it will cause excess static friction that will prevent the Dec axis from moving smoothly at the sub-arc second level.

Roland Christen
Astro-Physics Inc.

-----Original Message-----
From: Horia <ATM@...>
To: main@ap-gto.groups.io
Sent: Wed, Dec 8, 2021 4:24 am
Subject: [ap-gto] AP-1100 Guiding Questions

My AP-1100 (August 2021, no encoders) shows, most of the time, slightly worse guiding in Dec than in RA. A typical example (one 300sec frame) looks like this:
 
 
The blue curve is the RA and the red one is the Dec. The gray area on the left is the settling time after a dither. For a better view:
 
The guiding parameters:
  • Guiding scale: 1.05 arc-sec / pix
  • Exposure: 2000msec
  • Time lapse: 500msec
  • Guide Speed: 15 arc-sec / sec (both RA and Dec)
  • Min move RA: 0.3pix, Aggression: 0.75
  • Min move Dec: 0.4pix, Aggression: 0.8
 
And the resulting rms values are:
I am imaging at 0,9 arcsec/pix and the difference between RA and Dec values can be clearly seen as a small elongation in N/S direction.
 
I have the feeling that the Dec axis have somehow more play compared to the RA. I have adjusted the backstop more than once without seeing an improvement.
 
Is this normal behavior for the Ap-1100?
The system is balanced as close to perfect as I could do it. Should I unbalance the Dec axis to be backside heavy?
Is there something else I should do?
 
Kind regards,
Horia
 
 

--
Roland Christen
Astro-Physics


Horia
 

Thanks everybody for your support.

 

This is a new (both to me and to the world) mount. It left Astro-Physics end of August 2021.

 

For the moment the wether is as bad as bad goes and it looks like it will stay that way for the coming weeks so that I can only present older data.

 

@Roland

>> Your Dec guiding shows static friction which can be caused two ways.

>> 1) it will occur if your Dec axis is unbalanced.

>> 2) it will occur if you force the worm into mesh too tightly by not leaving

>> a small amount of clearance in the backstop adjustment.

 

I must have a closer look at this, especially the meshing. Both axes are well balanced: I can disengage the Dec worm and put the telescope in whatever position from horizontal to vertical and it will stay there.

 

Re. Play in Dec, I have measured it using the guiding assistant from PHD2 at different moments in time and generally got very small but inconsistent values for the backlash: from about 100msec up to about 400msec. I do not know how to interpret the variance. Maybe it is actually due to stiction (i.e. static friction) in Dec.

 

@Brian

This is a guide log from October. It contains just one Calibration run and mostly one free run (no guiding):

https://www.dropbox.com/s/76wykxui20u5x70/PHD2_GuideLog_2021-10-19_192830.txt?dl=0

 

and this is the corresponding Graphic:

https://www.dropbox.com/s/h2037p58uxspi8g/G-Assistent.jpg?dl=0

 

@Linwood

For the guiding assistant pls. see above.

 

Re. wires: I use through the mount cabling:

  • One cable for the Dec motor
  • One cable for Power (13.8V) – ultra flexible silicon cable
  • One USB cable

The USB/ Power distribution box is mounted directly on the saddle and there are no dangling wires:

 

 

 

 

For a closer look:

https://www.dropbox.com/s/awmm1bavhve5dn4/Cables.jpg?dl=0

 

@Luca

For polar alignment pls. see above. I do not think the spikes in Dec are due to it.

 

Kind Regards,

Horia

 


ap@CaptivePhotons.com
 

Horia wrote:

 

  • The USB/ Power distribution box is mounted directly on the saddle and there are no dangling wires:

That's a cool setup, I did something similar with a Pegasus Pocket Powerbox under my saddle.

 

I doubt this is the issue, but for clarity I am talking about the wires that go through the mount.  Those wires will not snag in the conventional sense, but do need enough slack that they smoothly turns inside the axis as the axis turns.  If it is tight, as it turns, it will stick and release a bit on insides of the axis.  So all I was suggesting is make sure where it comes out from the mount on the saddle and on the bottom if you tug a bit on it with your fingers there's just a bit of slack.


If it was that I would expect it to be less frequent than your spikes, but just mentioning it.

 

Unrelated: In looking at the calibration, both axis are a bit more off the lines than mine.  I have encoders, so that might be the reason, I have no other experience as have not tried turning them off.   Below is my last calibration run.  

 

I'm clueless what it would suggest if yours is abnormal; it is not backlash since it is on RA also.   I'll let someone smarter comment more fully on the guide logs, but the RA axis drift looks larger than I would have expected (which could be calibration especially since it is similar to DEC), but again I could be jaded by encoders. 

 

 


 

Linwood i'm not sure what you are referring to but the angle of the measurements vs the plot lines are not important 

Part of calibration's purpose is to measure that angle offset and then it's used for guiding later. Orthogonality between the red and blue lines is important

Your calibration looks excellent here

On Wed, Dec 8, 2021 at 12:37 PM ap@... <ap@...> wrote:

Horia wrote:

 

  • The USB/ Power distribution box is mounted directly on the saddle and there are no dangling wires:

That's a cool setup, I did something similar with a Pegasus Pocket Powerbox under my saddle.

 

I doubt this is the issue, but for clarity I am talking about the wires that go through the mount.  Those wires will not snag in the conventional sense, but do need enough slack that they smoothly turns inside the axis as the axis turns.  If it is tight, as it turns, it will stick and release a bit on insides of the axis.  So all I was suggesting is make sure where it comes out from the mount on the saddle and on the bottom if you tug a bit on it with your fingers there's just a bit of slack.


If it was that I would expect it to be less frequent than your spikes, but just mentioning it.

 

Unrelated: In looking at the calibration, both axis are a bit more off the lines than mine.  I have encoders, so that might be the reason, I have no other experience as have not tried turning them off.   Below is my last calibration run.  

 

I'm clueless what it would suggest if yours is abnormal; it is not backlash since it is on RA also.   I'll let someone smarter comment more fully on the guide logs, but the RA axis drift looks larger than I would have expected (which could be calibration especially since it is similar to DEC), but again I could be jaded by encoders. 

 

 



--
Brian 



Brian Valente


ap@CaptivePhotons.com
 

Brian Valente wrote:

 

  • Linwood i'm not sure what you are referring to but the angle of the measurements vs the plot lines are not important 

 

I was referring to how far his calibration points were off the lines, not that the axes were not space aligned.


Worsel
 

FYI

The RA and Dec lines on the calibration graph do not need to align with the graph axes.  PHD2 can account for that.  What IS important is the the RA and Dec lines are close to orthogonal.   Horia's graph looks good. PHD2 would have alerted you if the orthogonality error was high.

See https://openphdguiding.org/man/Tools.htm#Calibration_Details

It did take 18 steps to complete a calibration.  PHD2 recommendation is 8-14 steps.  If you use the built-in calculator (Guiding Tab - Advanced), it will determine the exposure time needed to achieve just 12 steps.  18 steps is not terrible...it just takes longer to complete a calibration.  Too few steps is not desirable and will raise an alert.

Bryan


ap@CaptivePhotons.com
 

Just to be clear -- again -- I was not suggesting that the calibration axes needed to align with the RA/DEC, only that the data points were a bit further off the calibration axes than I was used to seeing.  If they are good, great.  Sorry for the confusion.

And it may have been mine that had WAY too many points, as I may have changed things.  I posted it to show how close the points were to the calibration axes. 

This is the OP's calibration graph just for reference in case I confused things by posting a different one: 

I will go crawl back into my cave waiting for clear skies now.  :) 


Roland Christen
 


Play in Dec, I have measured it using the guiding assistant from PHD2 at different moments in time and generally got very small but inconsistent values for the backlash: from about 100msec up to about 400msec. I do not know how to interpret the variance. Maybe it is actually due to stiction (i.e. static friction) in Dec.
Stiction will show up in the backlash graph. During reversal the star actually moves further away from the zero line instead of heading towards the commanded zero point. The image below shows a Chinese import mount during reversal. The reversing command should send the next star position downward as the white dots show. Instead the star continues in the wrong direction, then doesn't move until several more commands are sent (green arrow). The Guiding Assistant doesn't know the difference between backlash and retrograde motion and subsequent non-movement of the axis, so it calls the delay backlash. The fact is, most of it is not backlash at all, and users attempt to fix it by tightening the mesh even more causes even more problems.

This particular graph is really really bad, some 100 times worse than anything you might encounter with an 1100. The pulse size of the movement shown below is 1799msec, which results in each step being a 27 arc sec command at 1x guide rate. for a precision mount like the 1100, I would not use anywhere near that size step for a backlash test. If you are looking for stiction at the arc sec level, the size of the step should be no greater than 300msec. For even finer resolution I would use 133msec steps. That would give you a resolution of 2 arc sec in axis motion. If you have any stiction, you will see it with those step sizes.

Roland



-----Original Message-----
From: Horia <ATM@...>
To: main@ap-gto.groups.io
Sent: Wed, Dec 8, 2021 1:39 pm
Subject: Re: [ap-gto] AP-1100 Guiding Questions

Thanks everybody for your support.
 
This is a new (both to me and to the world) mount. It left Astro-Physics end of August 2021.
 
For the moment the wether is as bad as bad goes and it looks like it will stay that way for the coming weeks so that I can only present older data.
 
@Roland
>> Your Dec guiding shows static friction which can be caused two ways.
>> 1) it will occur if your Dec axis is unbalanced.
>> 2) it will occur if you force the worm into mesh too tightly by not leaving
>> a small amount of clearance in the backstop adjustment.
 
I must have a closer look at this, especially the meshing. Both axes are well balanced: I can disengage the Dec worm and put the telescope in whatever position from horizontal to vertical and it will stay there.
 
Re. Play in Dec, I have measured it using the guiding assistant from PHD2 at different moments in time and generally got very small but inconsistent values for the backlash: from about 100msec up to about 400msec. I do not know how to interpret the variance. Maybe it is actually due to stiction (i.e. static friction) in Dec.
 
@Brian
This is a guide log from October. It contains just one Calibration run and mostly one free run (no guiding):
 
and this is the corresponding Graphic:
 
@Linwood
For the guiding assistant pls. see above.
 
Re. wires: I use through the mount cabling:
  • One cable for the Dec motor
  • One cable for Power (13.8V) – ultra flexible silicon cable
  • One USB cable
The USB/ Power distribution box is mounted directly on the saddle and there are no dangling wires:
 
 
 
 
For a closer look:
 
@Luca
For polar alignment pls. see above. I do not think the spikes in Dec are due to it.
 
Kind Regards,
Horia
 

--
Roland Christen
Astro-Physics


Roland Christen
 

Another way you can determine if your backstop is set too tight and you have stiction, you can do this:

Turn the locking lever on the gearbox back (counterclockwise) by just a few degrees (not 180 for full unlock). What this does is to artificially move the backstop enough to reduce the pressure of the worm teeth on the worm wheel. Then see if the Dec guiding improves. You can also do a calibration and backlash test using 300msec pulses and see if the graphs look cleaner and more like the ideal.

We always adjust the backstop here at the factory, and use almost no pressure when setting it. Depending on how much vibration occurs during shipping, this setting may either loosen up or tighten. It's something you should be aware of if you want the mount operating at its best. Adjusting this is in the manual.

Roland

-----Original Message-----
From: chris1011@...
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Wed, Dec 8, 2021 3:24 pm
Subject: Re: [ap-gto] AP-1100 Guiding Questions


Play in Dec, I have measured it using the guiding assistant from PHD2 at different moments in time and generally got very small but inconsistent values for the backlash: from about 100msec up to about 400msec. I do not know how to interpret the variance. Maybe it is actually due to stiction (i.e. static friction) in Dec.
Stiction will show up in the backlash graph. During reversal the star actually moves further away from the zero line instead of heading towards the commanded zero point. The image below shows a Chinese import mount during reversal. The reversing command should send the next star position downward as the white dots show. Instead the star continues in the wrong direction, then doesn't move until several more commands are sent (green arrow). The Guiding Assistant doesn't know the difference between backlash and retrograde motion and subsequent non-movement of the axis, so it calls the delay backlash. The fact is, most of it is not backlash at all, and users attempt to fix it by tightening the mesh even more causes even more problems.

This particular graph is really really bad, some 100 times worse than anything you might encounter with an 1100. The pulse size of the movement shown below is 1799msec, which results in each step being a 27 arc sec command at 1x guide rate. for a precision mount like the 1100, I would not use anywhere near that size step for a backlash test. If you are looking for stiction at the arc sec level, the size of the step should be no greater than 300msec. For even finer resolution I would use 133msec steps. That would give you a resolution of 2 arc sec in axis motion. If you have any stiction, you will see it with those step sizes.

Roland



-----Original Message-----
From: Horia <ATM@...>
To: main@ap-gto.groups.io
Sent: Wed, Dec 8, 2021 1:39 pm
Subject: Re: [ap-gto] AP-1100 Guiding Questions

Thanks everybody for your support.
 
This is a new (both to me and to the world) mount. It left Astro-Physics end of August 2021.
 
For the moment the wether is as bad as bad goes and it looks like it will stay that way for the coming weeks so that I can only present older data.
 
@Roland
>> Your Dec guiding shows static friction which can be caused two ways.
>> 1) it will occur if your Dec axis is unbalanced.
>> 2) it will occur if you force the worm into mesh too tightly by not leaving
>> a small amount of clearance in the backstop adjustment.
 
I must have a closer look at this, especially the meshing. Both axes are well balanced: I can disengage the Dec worm and put the telescope in whatever position from horizontal to vertical and it will stay there.
 
Re. Play in Dec, I have measured it using the guiding assistant from PHD2 at different moments in time and generally got very small but inconsistent values for the backlash: from about 100msec up to about 400msec. I do not know how to interpret the variance. Maybe it is actually due to stiction (i.e. static friction) in Dec.
 
@Brian
This is a guide log from October. It contains just one Calibration run and mostly one free run (no guiding):
 
and this is the corresponding Graphic:
 
@Linwood
For the guiding assistant pls. see above.
 
Re. wires: I use through the mount cabling:
  • One cable for the Dec motor
  • One cable for Power (13.8V) – ultra flexible silicon cable
  • One USB cable
The USB/ Power distribution box is mounted directly on the saddle and there are no dangling wires:
 
 
 
 
For a closer look:
 
@Luca
For polar alignment pls. see above. I do not think the spikes in Dec are due to it.
 
Kind Regards,
Horia
 

--
Roland Christen
Astro-Physics


Horia
 

Yesterday I managed to drive out to the mount and tried the following, as suggested by Roland:

 

>> With proper adjustment of the backstop you should be able to gently press

>> on the back of the motor box and feel the worm lift up out of full mesh.

>> Not heavy pressure, but just 1 finger pressure.

>> This is not complete disengagement, but just slight disengagement where

>> the teeth are still near contact. You can tell if the worm is slightly out if you

>> then gently push on the telescope in the Dec direction and can feel the free play.

>> Very gently, as in just 1 finger pressure on the back of the scope. Then, as

>> you let go of the back of the gearbox you should feel the axis play pretty much go away.

 

Tilting the motor box as described was possible but certainly not with a one finger gentle press. I had to apply a lot of pressure with the hand to get a very slight disengagement. I could feel the play by gently moving the scope.

 

After releasing the pressure on the motor box, the play disappears but not instantly. It needs one or two seconds for the worm to fall back in full engagement. It feels like something is slowing down the movement.  

 

Then I tried to readjust the backstop. I released the two screws holding the box lever and let the lever fall in place under its own weight, i.e. without applying any extra pressure with the finger. After tightening the two screws, the behavior of the motor box did not change.

 

One more observation - and I have no idea if this is relevant or not: when releasing the worm with the lever, for the first about 80 degrees of rotation the lever has no effect whatsoever on the motor box. Then something engages the box and it starts lifting. At the end of the 180 degrees, the worm is fully disengaged.

 

Kind regards,

Horia

 

 

Von: main@ap-gto.groups.io <main@ap-gto.groups.io> Im Auftrag von Roland Christen via groups.io
Gesendet: Mittwoch, 8. Dezember 2021 17:09
An: main@ap-gto.groups.io
Betreff: Re: [ap-gto] AP-1100 Guiding Questions

 

Your Dec guiding shows static friction which can be caused two ways. 1) it will occur if your Dec axis is unbalanced. 2) it will occur if you force the worm into mesh too tightly by not leaving a small amount of clearance in the backstop adjustment.

 

Static friction:

Generally people assume that the Dec axis must be tightly into mesh, so they force the mesh by adjusting the backstop very tightly. The assumption is that the tighter the mesh, the lower will be the backlash. This is counter-intuitive. Actually with a spring loaded gearbox you want only the spring to push the worm into mesh, never the backstop. The backstop should be adjusted a bit back to allow the worm to ride up and down into the high and low spots along the worm wheel. The backstop should never be set so that there is no clearance at all between the worm and worm wheel.

 

With proper adjustment of the backstop you should be able to gently press on the back of the motor box and feel the worm lift up out of full mesh. Not heavy pressure, but just 1 finger pressure. This is not complete disengagement, but just slight disengagement where the teeth are still near contact. You can tell if the worm is slightly out if you then gently push on the telescope in the Dec direction and can feel the free play. Very gently, as in just 1 finger pressure on the back of the scope. Then, as you let go of the back of the gearbox you should feel the axis play pretty much go away.

 

Dec Play:

If the Dec has actual play, even with the worm fully in mesh, then it may be that the end play nut on the worm is loose. That's an easy fix. The end play nut is on one side of the motor box under the circular cover that has 2 holes in it for a spanner wrench (if you don't have a spanner, you can use a needle nosed pliers). Older mounts may have a knurled cover which can be removed without using a spanner. Remove the cover to expose the end of the worm. You will see the stainless steel nut with 2 holes. Use the spanner to tighten this nut. Once fully tight, the Dec play should be gone.

 

Never use the backstop to try to tighten the Dec play. Doing so will make things worse - it will cause excess static friction that will prevent the Dec axis from moving smoothly at the sub-arc second level.

 

Roland Christen

Astro-Physics Inc.

 

-----Original Message-----
From: Horia <ATM@...>
To: main@ap-gto.groups.io
Sent: Wed, Dec 8, 2021 4:24 am
Subject: [ap-gto] AP-1100 Guiding Questions

My AP-1100 (August 2021, no encoders) shows, most of the time, slightly worse guiding in Dec than in RA. A typical example (one 300sec frame) looks like this:

 

 

The blue curve is the RA and the red one is the Dec. The gray area on the left is the settling time after a dither. For a better view:

 

The guiding parameters:

  • Guiding scale: 1.05 arc-sec / pix
  • Exposure: 2000msec
  • Time lapse: 500msec
  • Guide Speed: 15 arc-sec / sec (both RA and Dec)
  • Min move RA: 0.3pix, Aggression: 0.75
  • Min move Dec: 0.4pix, Aggression: 0.8

 

And the resulting rms values are:

I am imaging at 0,9 arcsec/pix and the difference between RA and Dec values can be clearly seen as a small elongation in N/S direction.

 

I have the feeling that the Dec axis have somehow more play compared to the RA. I have adjusted the backstop more than once without seeing an improvement.

 

Is this normal behavior for the Ap-1100?

The system is balanced as close to perfect as I could do it. Should I unbalance the Dec axis to be backside heavy?

Is there something else I should do?

 

Kind regards,

Horia

 

 


--
Roland Christen
Astro-Physics


Roland Christen
 

"After releasing the pressure on the motor box, the play disappears but not instantly." Yes, that's exactly how it should work. The spring system has a built-in dampening mechanism.

"when releasing the worm with the lever, for the first about 80 degrees of rotation the lever has no effect whatsoever on the motor box." Yes, that is correct, the springs keep the worm teeth in contact with the worm wheel teeth. That rotation of the lever moves the backstop far away from the mechanism. You can see that if you press on the back of the motor box and you will be able to move it completely out of mesh when you put pressure on the motor box. At a point beyond 90 degrees the lever internally begins rotating the motor box to where the worm begins to lift completely away from the worm wheel. That is how it works, and what you describe is perfectly ok.

"After tightening the two screws, the behavior of the motor box did not change." I don't know what this statement means. Can you elaborate? After tightening the screws the motor box should remain in place and the worm teeth should be in good contact with the worm wheel.

Roland Christen

-----Original Message-----
From: Horia <ATM@...>
To: main@ap-gto.groups.io
Sent: Fri, Dec 17, 2021 6:55 am
Subject: Re: [ap-gto] AP-1100 Guiding Questions

Yesterday I managed to drive out to the mount and tried the following, as suggested by Roland:
 
>> With proper adjustment of the backstop you should be able to gently press
>> on the back of the motor box and feel the worm lift up out of full mesh.
>> Not heavy pressure, but just 1 finger pressure.
>> This is not complete disengagement, but just slight disengagement where
>> the teeth are still near contact. You can tell if the worm is slightly out if you
>> then gently push on the telescope in the Dec direction and can feel the free play.
>> Very gently, as in just 1 finger pressure on the back of the scope. Then, as
>> you let go of the back of the gearbox you should feel the axis play pretty much go away.
 
Tilting the motor box as described was possible but certainly not with a one finger gentle press. I had to apply a lot of pressure with the hand to get a very slight disengagement. I could feel the play by gently moving the scope.
 
After releasing the pressure on the motor box, the play disappears but not instantly. It needs one or two seconds for the worm to fall back in full engagement. It feels like something is slowing down the movement.  
 
Then I tried to readjust the backstop. I released the two screws holding the box lever and let the lever fall in place under its own weight, i.e. without applying any extra pressure with the finger. After tightening the two screws, the behavior of the motor box did not change.
 
One more observation - and I have no idea if this is relevant or not: when releasing the worm with the lever, for the first about 80 degrees of rotation the lever has no effect whatsoever on the motor box. Then something engages the box and it starts lifting. At the end of the 180 degrees, the worm is fully disengaged.
 
Kind regards,
Horia
 
 
Von: main@ap-gto.groups.io <main@ap-gto.groups.io> Im Auftrag von Roland Christen via groups.io
Gesendet: Mittwoch, 8. Dezember 2021 17:09
An: main@ap-gto.groups.io
Betreff: Re: [ap-gto] AP-1100 Guiding Questions
 
Your Dec guiding shows static friction which can be caused two ways. 1) it will occur if your Dec axis is unbalanced. 2) it will occur if you force the worm into mesh too tightly by not leaving a small amount of clearance in the backstop adjustment.
 
Static friction:
Generally people assume that the Dec axis must be tightly into mesh, so they force the mesh by adjusting the backstop very tightly. The assumption is that the tighter the mesh, the lower will be the backlash. This is counter-intuitive. Actually with a spring loaded gearbox you want only the spring to push the worm into mesh, never the backstop. The backstop should be adjusted a bit back to allow the worm to ride up and down into the high and low spots along the worm wheel. The backstop should never be set so that there is no clearance at all between the worm and worm wheel.
 
With proper adjustment of the backstop you should be able to gently press on the back of the motor box and feel the worm lift up out of full mesh. Not heavy pressure, but just 1 finger pressure. This is not complete disengagement, but just slight disengagement where the teeth are still near contact. You can tell if the worm is slightly out if you then gently push on the telescope in the Dec direction and can feel the free play. Very gently, as in just 1 finger pressure on the back of the scope. Then, as you let go of the back of the gearbox you should feel the axis play pretty much go away.
 
Dec Play:
If the Dec has actual play, even with the worm fully in mesh, then it may be that the end play nut on the worm is loose. That's an easy fix. The end play nut is on one side of the motor box under the circular cover that has 2 holes in it for a spanner wrench (if you don't have a spanner, you can use a needle nosed pliers). Older mounts may have a knurled cover which can be removed without using a spanner. Remove the cover to expose the end of the worm. You will see the stainless steel nut with 2 holes. Use the spanner to tighten this nut. Once fully tight, the Dec play should be gone.
 
Never use the backstop to try to tighten the Dec play. Doing so will make things worse - it will cause excess static friction that will prevent the Dec axis from moving smoothly at the sub-arc second level.
 
Roland Christen
Astro-Physics Inc.
 
-----Original Message-----
From: Horia <ATM@...>
To: main@ap-gto.groups.io
Sent: Wed, Dec 8, 2021 4:24 am
Subject: [ap-gto] AP-1100 Guiding Questions
My AP-1100 (August 2021, no encoders) shows, most of the time, slightly worse guiding in Dec than in RA. A typical example (one 300sec frame) looks like this:
 
 
The blue curve is the RA and the red one is the Dec. The gray area on the left is the settling time after a dither. For a better view:
 
The guiding parameters:
  • Guiding scale: 1.05 arc-sec / pix
  • Exposure: 2000msec
  • Time lapse: 500msec
  • Guide Speed: 15 arc-sec / sec (both RA and Dec)
  • Min move RA: 0.3pix, Aggression: 0.75
  • Min move Dec: 0.4pix, Aggression: 0.8
 
And the resulting rms values are:
I am imaging at 0,9 arcsec/pix and the difference between RA and Dec values can be clearly seen as a small elongation in N/S direction.
 
I have the feeling that the Dec axis have somehow more play compared to the RA. I have adjusted the backstop more than once without seeing an improvement.
 
Is this normal behavior for the Ap-1100?
The system is balanced as close to perfect as I could do it. Should I unbalance the Dec axis to be backside heavy?
Is there something else I should do?
 
Kind regards,
Horia
 
 

--
Roland Christen
Astro-Physics

--
Roland Christen
Astro-Physics


Roland Christen
 




-----Original Message-----
From: chris1011@...
To: main@ap-gto.groups.io <main@ap-gto.groups.io>
Sent: Fri, Dec 17, 2021 10:51 am
Subject: Re: [ap-gto] AP-1100 Guiding Questions

"After releasing the pressure on the motor box, the play disappears but not instantly." Yes, that's exactly how it should work. The spring system has a built-in dampening mechanism.

"when releasing the worm with the lever, for the first about 80 degrees of rotation the lever has no effect whatsoever on the motor box." Yes, that is correct, the springs keep the worm teeth in contact with the worm wheel teeth. That rotation of the lever moves the backstop far away from the mechanism. You can see that if you press on the back of the motor box and you will be able to move it completely out of mesh when you put pressure on the motor box. At a point beyond 90 degrees the lever internally begins rotating the motor box to where the worm begins to lift completely away from the worm wheel. That is how it works, and what you describe is perfectly ok.

"After tightening the two screws, the behavior of the motor box did not change." I don't know what this statement means. Can you elaborate? After tightening the screws the motor box should remain in place and the worm teeth should be in good contact with the worm wheel.

Roland Christen

-----Original Message-----
From: Horia <ATM@...>
To: main@ap-gto.groups.io
Sent: Fri, Dec 17, 2021 6:55 am
Subject: Re: [ap-gto] AP-1100 Guiding Questions

Yesterday I managed to drive out to the mount and tried the following, as suggested by Roland:
 
>> With proper adjustment of the backstop you should be able to gently press
>> on the back of the motor box and feel the worm lift up out of full mesh.
>> Not heavy pressure, but just 1 finger pressure.
>> This is not complete disengagement, but just slight disengagement where
>> the teeth are still near contact. You can tell if the worm is slightly out if you
>> then gently push on the telescope in the Dec direction and can feel the free play.
>> Very gently, as in just 1 finger pressure on the back of the scope. Then, as
>> you let go of the back of the gearbox you should feel the axis play pretty much go away.
 
Tilting the motor box as described was possible but certainly not with a one finger gentle press. I had to apply a lot of pressure with the hand to get a very slight disengagement. I could feel the play by gently moving the scope.
 
After releasing the pressure on the motor box, the play disappears but not instantly. It needs one or two seconds for the worm to fall back in full engagement. It feels like something is slowing down the movement.  
 
Then I tried to readjust the backstop. I released the two screws holding the box lever and let the lever fall in place under its own weight, i.e. without applying any extra pressure with the finger. After tightening the two screws, the behavior of the motor box did not change.
 
One more observation - and I have no idea if this is relevant or not: when releasing the worm with the lever, for the first about 80 degrees of rotation the lever has no effect whatsoever on the motor box. Then something engages the box and it starts lifting. At the end of the 180 degrees, the worm is fully disengaged.
 
Kind regards,
Horia
 
 
Von: main@ap-gto.groups.io <main@ap-gto.groups.io> Im Auftrag von Roland Christen via groups.io
Gesendet: Mittwoch, 8. Dezember 2021 17:09
An: main@ap-gto.groups.io
Betreff: Re: [ap-gto] AP-1100 Guiding Questions
 
Your Dec guiding shows static friction which can be caused two ways. 1) it will occur if your Dec axis is unbalanced. 2) it will occur if you force the worm into mesh too tightly by not leaving a small amount of clearance in the backstop adjustment.
 
Static friction:
Generally people assume that the Dec axis must be tightly into mesh, so they force the mesh by adjusting the backstop very tightly. The assumption is that the tighter the mesh, the lower will be the backlash. This is counter-intuitive. Actually with a spring loaded gearbox you want only the spring to push the worm into mesh, never the backstop. The backstop should be adjusted a bit back to allow the worm to ride up and down into the high and low spots along the worm wheel. The backstop should never be set so that there is no clearance at all between the worm and worm wheel.
 
With proper adjustment of the backstop you should be able to gently press on the back of the motor box and feel the worm lift up out of full mesh. Not heavy pressure, but just 1 finger pressure. This is not complete disengagement, but just slight disengagement where the teeth are still near contact. You can tell if the worm is slightly out if you then gently push on the telescope in the Dec direction and can feel the free play. Very gently, as in just 1 finger pressure on the back of the scope. Then, as you let go of the back of the gearbox you should feel the axis play pretty much go away.
 
Dec Play:
If the Dec has actual play, even with the worm fully in mesh, then it may be that the end play nut on the worm is loose. That's an easy fix. The end play nut is on one side of the motor box under the circular cover that has 2 holes in it for a spanner wrench (if you don't have a spanner, you can use a needle nosed pliers). Older mounts may have a knurled cover which can be removed without using a spanner. Remove the cover to expose the end of the worm. You will see the stainless steel nut with 2 holes. Use the spanner to tighten this nut. Once fully tight, the Dec play should be gone.
 
Never use the backstop to try to tighten the Dec play. Doing so will make things worse - it will cause excess static friction that will prevent the Dec axis from moving smoothly at the sub-arc second level.
 
Roland Christen
Astro-Physics Inc.
 
-----Original Message-----
From: Horia <ATM@...>
To: main@ap-gto.groups.io
Sent: Wed, Dec 8, 2021 4:24 am
Subject: [ap-gto] AP-1100 Guiding Questions
My AP-1100 (August 2021, no encoders) shows, most of the time, slightly worse guiding in Dec than in RA. A typical example (one 300sec frame) looks like this:
 
 
The blue curve is the RA and the red one is the Dec. The gray area on the left is the settling time after a dither. For a better view:
 
The guiding parameters:
  • Guiding scale: 1.05 arc-sec / pix
  • Exposure: 2000msec
  • Time lapse: 500msec
  • Guide Speed: 15 arc-sec / sec (both RA and Dec)
  • Min move RA: 0.3pix, Aggression: 0.75
  • Min move Dec: 0.4pix, Aggression: 0.8
 
And the resulting rms values are:
I am imaging at 0,9 arcsec/pix and the difference between RA and Dec values can be clearly seen as a small elongation in N/S direction.
 
I have the feeling that the Dec axis have somehow more play compared to the RA. I have adjusted the backstop more than once without seeing an improvement.
 
Is this normal behavior for the Ap-1100?
The system is balanced as close to perfect as I could do it. Should I unbalance the Dec axis to be backside heavy?
Is there something else I should do?
 
Kind regards,
Horia
 
 

--
Roland Christen
Astro-Physics

--
Roland Christen
Astro-Physics