Date   

Re: New Version of Explore Stars for Windows Available Now - Alignment Star Issue Fixed

jdm5@...
 

I think I will have to do a completely fresh install since when I attempt to update explorestars to the latest version from MS Store, my only choice is to run the installed version.


Re: ExploreStars DB Installer Testing

jdm5@...
 

Worked fine on my win 10 laptop. 


Re: Dec Worm Adjustment

W. Christopher Moses
 

Another great night of guiding...best I've ever had, actually.  Except for some gusts, the Total RMS was almost always below 0.5". 


Re: Dec Worm Adjustment

W. Christopher Moses
 

I uploaded the guide log to the Mount Related section.  Unfortunately, I was only able to get about 40m data before clouds rolled in.


New file uploaded to ESPMC-Eight

ESPMC-Eight@...
 

Hello,

This email message is a notification to let you know that
a file has been uploaded to the Files area of the ESPMC-Eight
group.

File : /Mount Related Files/Chris_PHD2_GuideLog_2018-08-03_001607.txt
Uploaded by : Chris_Moses <chris_moses@yahoo.com>
Description : Guiding after adjusting dec worm gear

You can access this file at the URL:
https://groups.yahoo.com/neo/groups/ESPMC-Eight/files/Mount%20Related%20Files/Chris_PHD2_GuideLog_2018-08-03_001607.txt

To learn more about file sharing for your group, please visit:
https://help.yahoo.com/kb/index?page=content&y=PROD_GRPS&locale=en_US&id=SLN15398

Regards,

Chris_Moses <chris_moses@yahoo.com>


Re: Dec Worm Adjustment

W. Christopher Moses
 

Hi,
My PA was very good, but I've done equally good PA before and have never seen it so low unguided.  My guided dec performance was even better.  I'll have to check my notes, but my total RMS was 0.45"-0.55".  That is really good for me.


Re: Dec Worm Adjustment

Jeremy Parker
 

Hi Chris,

Of that 0.51", was there any drift component? When you think about it, if you have good polar alignment, the DEC should not have to 'guide' much at all, because there isn't PE to deal with. If there wasn't a breeze or other small physical movement of the mount, I would also get better unguided DEC performance than guided. So I wonder if your guided DEC performance has also improved? My guided DEC performance seemed to degrade because of backlash, and overshoot, until I backed off on DEC aggressiveness in PHD. So if backlash is reduced, I would imagine that your guided DEC performance should also improve.

Jeremy


Periodic Error Worm/Wheel Mechanical Model Spreadsheet

hubbell_jerry@...
 

I have place the spreadsheet I created to model the periodic error of the mechanical worm/wheel system in the Mount Related file folder. There are 2 sheets, the first sheet model the worm and the second sheet models 200 minutes of the combined worm/wheel system. I had to limit the amount of time in the second sheet (12000 seconds) because the full 24 hours of the data was > 30 Mb and Yahoo did not allow a file that large to be uploaded. I have not provided any explanation of the equations, but there are column headers that describe the value. 

You can set the mechanical error (inches) for offset and run-out and the period. 

Give it a try.

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.


Dec Worm Adjustment

W. Christopher Moses
 

For no particular reason, I decided to adjust my dec and see if it had any effect.  It did.


All I did was use some feeler gauges and make the right side a tad bit tighter.  I then spun it around all the way by hand to make sure it wasn't too tight.


When I did a guiding assistant tonight, the dec was 0.51" for about 10 minutes.  That's unguided!  For me, that is a giant improvement.


Keep in mind that my guided performance was just fine before, so this was really just tinkering for the sake of tinkering.


Re: Determining Rate Offset Value

hubbell_jerry@...
 

I will find the spreadsheet and post it in the files section once I review it. It's been a while since I worked on it

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.


Re: Determining Rate Offset Value

reg dunkley
 

Jerry

I found your explanation most helpful. Thanks for a great post.

Reg ... new to the game

On Thursday, August 2, 2018, 9:39:59 AM PDT, hubbell_jerry@... [ESPMC-Eight] wrote:


 

Hi Jeremy,


After thinking about what you are saying, I think what you mean is that the effective radius of the worm/wheel contact point changes based on the adjustment, and you are correct. The linear rate would change along the circumference of the contact point, but the angular rate is always constant as the motor's angular rate is constant. There should be virtually zero long term angular rate changes in the tracking rate due to the mechanical contact point having a different radius. Basically, if the worm turns exactly 360 turns in 24 hours, and there are 360 teeth in the wheel, then it doesn't matter how tightly the gear is meshed (or how loose) it will still turn the same 360 degrees over 24 hours.

What this leads me to believe is that the impact of wheel run-out causing binding issues is not the cause of the short term PE, it is the non-linearity of the gear teeth and how the contact point between worm and the wheel changes over time due to a worm defect. This changing radius between the worm and wheel contact point is what causes the PE. 

The only way to get a long term drift in RA rate is if the contact point radius changed in radius over the long term so that a wheel where the radius was increasing like a spiral would cause a decreasing instantaneous rate.Think about a spiral shaped wheel driven by the worm. 

There are 3 different defects that cause a PE or a changing contact point radius: the wheel being oblong, the wheel center shaft hole being offset from the true center, and the worm being bent causing run-out in the worm. The only one of these three that cause the substantial portion of the primary PE is the worm defect. The worm has a 4 minute period. The other 2 defects related to the Wheel would manifest as a long term drift with a period of 24 hours. Just as in the worm PE, the wheel PE is sinusoidal in shape and is not a constant drift rate. Depending on where on the sine curve you are on the wheel PE is may appear to be a long term linear drift over 2-3 hours.

An oblong wheel would cause the drift over 6 hours to move in one direction and then reverse direction and move the other way over the next 12 hours, and then finally reverse direction again over the final 6 hours of the period.  This is why when you record a PPEC curve it is not effective over the entire 24 hour period. We really only need to have it effective over a 6-8 hour period, but the larger the wheel defect in terms of offset and how oblong it is, the less effective PPEC becomes because it only corrects for the worm PE. 

The key in tuning your mount is to be able to set the orientation of the RA axis so that when the mount is pointed at the meridian the mesh is either at it's tightest or at it's loosest, not where it is at the average mesh distance. This will cause the long term drift to increase (or decrease) as you approach the meridian at the slowest rate, and then after crossing the meridian to decrease (or increase) as you track past the meridian.

There is one kink in this in that a meridian flip is performed causing the mount to slew to a different position on the wheel. This will be 180 degrees from the previous position which should be okay if the bulk of the long term drift was due to the wheel being oblong. If the drift in RA is due to the wheel being shifted off center, then this will cause a much larger change in the rate after the meridian flip.

I hope this clarifies what I think is going on. I had worked on a spreadsheet before showing the different components of PE combining the 3 different defects together calculating a theoretical PE curve based on specific run-out measurements. This worm/wheel model can help to understand the behavior of the mount and where to adjust the mesh and where to tighten the clutches in terms of worm/wheel contact point along the circumference of the wheel.

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.


---In ESPMC-Eight@..., wrote :

Hi Jerry,

I appreciate your analysis and agree that the PE, whether from the worm or the follower gear, should return to zero as oscillations normally do. The error in RA rate is due to the point of contact between the worm and follower moving in/out compared to a perfect circle, effectively creating a lever arm with a slightly varying length which is rotating the RA axis at slightly different angular rates.

So then the looseness or tightness of the worm mesh should just represent a static RA rate error, because the worm is physically being moved farther or closer to the RA axis of rotation when the mesh adjustment is made. The point of contact should move just like PE, but it is not periodic, it is a static error. Therefore I believe that the RA Rate Offset is the way we can compensate for having a looser or tighter worm mesh. This would explain why I needed to tweak it to three different values for three different worm configurations I tried, each with their own mesh adjustments.

Besides, atmospheric refraction shouldn’t come much into play when pointing at the equator and southern meridian, like in a calibration, or when imaging up near the zenith.

Let me know if this makes sense or if you disagree.

Thanks,
Jeremy


Re: Determining Rate Offset Value

Jeremy Parker
 

Hi Jerry,

I see that the oblong wheel could manifest as what might look like an RA rate offset error, in that we're typically only using a small portion, like 6 hours worth of the wheel, for example. I also agree that if the wheels turns once around in 24 hours, there is no RA drift. But I think that assumes a perfect mesh adjustment. In other words, the motor is turning at a constant rate, but having a point of contact between the worm and wheel that is farther from the RA axis of rotation will cause something less than 360° of wheel rotation in 24 hours. It's only the one or two teeth making contact in the mesh that is determining the rate of RA rotation, so assuming a perfectly constant motor rotation rate, the errors should be due to:
  1. Any change in the radius from point of contact to center of rotation of the worm gear. (As in PE)
  2. Any change in the radius from point of contact to center of rotation of the wheel. (As in oblong wheel defects AND/OR static mesh adjustments)
I think I can prove this by measurement, next time I'm out. I have my mesh set and know what RA offset rate I need to prevent drift currently. If I put some locktite on the mesh adjustment screw (to insure it doesn't move) and then back the mesh way off, I should be able to see that I've introduced some additional RA drift error. So long as I'm tracking over the same portion of the sky during the comparison, I should be able then determine with PHD whether there is drift. Does this seem like a good thing to try?

I'd be interested to see your spreadsheet and would be interested if the point of contact could be factored into the calculations.

Thanks again,
Jeremy


Re: Determining Rate Offset Value

hubbell_jerry@...
 

Hi Jeremy,

After thinking about what you are saying, I think what you mean is that the effective radius of the worm/wheel contact point changes based on the adjustment, and you are correct. The linear rate would change along the circumference of the contact point, but the angular rate is always constant as the motor's angular rate is constant. There should be virtually zero long term angular rate changes in the tracking rate due to the mechanical contact point having a different radius. Basically, if the worm turns exactly 360 turns in 24 hours, and there are 360 teeth in the wheel, then it doesn't matter how tightly the gear is meshed (or how loose) it will still turn the same 360 degrees over 24 hours.

What this leads me to believe is that the impact of wheel run-out causing binding issues is not the cause of the short term PE, it is the non-linearity of the gear teeth and how the contact point between worm and the wheel changes over time due to a worm defect. This changing radius between the worm and wheel contact point is what causes the PE. 

The only way to get a long term drift in RA rate is if the contact point radius changed in radius over the long term so that a wheel where the radius was increasing like a spiral would cause a decreasing instantaneous rate.Think about a spiral shaped wheel driven by the worm. 

There are 3 different defects that cause a PE or a changing contact point radius: the wheel being oblong, the wheel center shaft hole being offset from the true center, and the worm being bent causing run-out in the worm. The only one of these three that cause the substantial portion of the primary PE is the worm defect. The worm has a 4 minute period. The other 2 defects related to the Wheel would manifest as a long term drift with a period of 24 hours. Just as in the worm PE, the wheel PE is sinusoidal in shape and is not a constant drift rate. Depending on where on the sine curve you are on the wheel PE is may appear to be a long term linear drift over 2-3 hours.

An oblong wheel would cause the drift over 6 hours to move in one direction and then reverse direction and move the other way over the next 12 hours, and then finally reverse direction again over the final 6 hours of the period.  This is why when you record a PPEC curve it is not effective over the entire 24 hour period. We really only need to have it effective over a 6-8 hour period, but the larger the wheel defect in terms of offset and how oblong it is, the less effective PPEC becomes because it only corrects for the worm PE. 

The key in tuning your mount is to be able to set the orientation of the RA axis so that when the mount is pointed at the meridian the mesh is either at it's tightest or at it's loosest, not where it is at the average mesh distance. This will cause the long term drift to increase (or decrease) as you approach the meridian at the slowest rate, and then after crossing the meridian to decrease (or increase) as you track past the meridian.

There is one kink in this in that a meridian flip is performed causing the mount to slew to a different position on the wheel. This will be 180 degrees from the previous position which should be okay if the bulk of the long term drift was due to the wheel being oblong. If the drift in RA is due to the wheel being shifted off center, then this will cause a much larger change in the rate after the meridian flip.

I hope this clarifies what I think is going on. I had worked on a spreadsheet before showing the different components of PE combining the 3 different defects together calculating a theoretical PE curve based on specific run-out measurements. This worm/wheel model can help to understand the behavior of the mount and where to adjust the mesh and where to tighten the clutches in terms of worm/wheel contact point along the circumference of the wheel.

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.


---In ESPMC-Eight@..., <jrs1@...> wrote :

Hi Jerry,

I appreciate your analysis and agree that the PE, whether from the worm or the follower gear, should return to zero as oscillations normally do. The error in RA rate is due to the point of contact between the worm and follower moving in/out compared to a perfect circle, effectively creating a lever arm with a slightly varying length which is rotating the RA axis at slightly different angular rates.

So then the looseness or tightness of the worm mesh should just represent a static RA rate error, because the worm is physically being moved farther or closer to the RA axis of rotation when the mesh adjustment is made. The point of contact should move just like PE, but it is not periodic, it is a static error. Therefore I believe that the RA Rate Offset is the way we can compensate for having a looser or tighter worm mesh. This would explain why I needed to tweak it to three different values for three different worm configurations I tried, each with their own mesh adjustments.

Besides, atmospheric refraction shouldn’t come much into play when pointing at the equator and southern meridian, like in a calibration, or when imaging up near the zenith.

Let me know if this makes sense or if you disagree.

Thanks,
Jeremy


Re: Determining Rate Offset Value

Jeremy Parker
 

Hi Jerry,

I appreciate your analysis and agree that the PE, whether from the worm or the follower gear, should return to zero as oscillations normally do. The error in RA rate is due to the point of contact between the worm and follower moving in/out compared to a perfect circle, effectively creating a lever arm with a slightly varying length which is rotating the RA axis at slightly different angular rates.

So then the looseness or tightness of the worm mesh should just represent a static RA rate error, because the worm is physically being moved farther or closer to the RA axis of rotation when the mesh adjustment is made. The point of contact should move just like PE, but it is not periodic, it is a static error. Therefore I believe that the RA Rate Offset is the way we can compensate for having a looser or tighter worm mesh. This would explain why I needed to tweak it to three different values for three different worm configurations I tried, each with their own mesh adjustments.

Besides, atmospheric refraction shouldn’t come much into play when pointing at the equator and southern meridian, like in a calibration, or when imaging up near the zenith.

Let me know if this makes sense or if you disagree.

Thanks,
Jeremy


Re: New Version of Explore Stars for Windows Available Now - Alignment Star Issue Fixed

hubbell_jerry@...
 

The version number probably should be changed, but it wasn"t this time around. Dan will probably update that, but the version you installed has the fix.

Thanks for bringing that to our attention.

Jerry Hubbell
Director Electrical Engineering
Explore Scientific, LLC.


New file uploaded to ESPMC-Eight

ESPMC-Eight@...
 

Hello,

This email message is a notification to let you know that
a file has been uploaded to the Files area of the ESPMC-Eight
group.

File : /User Contributions/ascompad.ahk
Uploaded by : Chris_Moses <chris_moses@yahoo.com>
Description : AutoHotKey script to bring AscomPad to foreground using control-q. Should work for cuurent version and version 1.02

You can access this file at the URL:
https://groups.yahoo.com/neo/groups/ESPMC-Eight/files/User%20Contributions/ascompad.ahk

To learn more about file sharing for your group, please visit:
https://help.yahoo.com/kb/index?page=content&y=PROD_GRPS&locale=en_US&id=SLN15398

Regards,

Chris_Moses <chris_moses@yahoo.com>


Re: Determining Rate Offset Value

W. Christopher Moses
 

Very interesting.  Thanks for the feedback.


Re: UPDATE: Losmandy One-Piece Worm Block for ES G11 PMC-Eight Mount System

W. Christopher Moses
 

Have you seen the trick people do by wrapping a weighted cord around the RA axis?  Kind of a spring-loading hack.


Re: UPDATE: Losmandy One-Piece Worm Block for ES G11 PMC-Eight Mount System

W. Christopher Moses
 

Excellent


Re: New Version of Explore Stars for Windows Available Now - Alignment Star Issue Fixed

W. Christopher Moses
 

If you are doing a completely fresh install, please test out my DB installer.  There are instructions in the User Contributions section of the File section.

Thanks,
Chris

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