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I received my new GM811G and finally got out under the stars to start learning the mount and Gemini 2 system.? Before I got started, I noticed some movement in the DEC axis.? With minimum effort, i can wiggle the saddle, i.e. DEC axis.? I am working with PHD2 and got some messages about the DEC axis, don't remember exactly.? I ran the guiding assistant and I thought the numbers looked good, except for the DEC Backlash was highlighted.? Here are some of the values:
RA Peak? 0.44px(6.73arc-sec)
DEC Peak? 0.37px(5.61arc-sec)
RA Peak to Peak0.47px(7.13arc-sec)
RA Drift Rate-0.09px/min(-1.41arc-sec/min)
RA Max Drift Rate0.04px/sec(0.67arc-sec/sec)
Drift-limiting exposure2.4s
DEC Drift Rate -0.01px/min(-0.21arc-sec/min
DEC Backlash >=34970 +/-99ms(247.1 +/-0.7a....
Polar Alignment Error 0.9 arc-min
High-frequency Star Motion
RA, RMS 0.05px(0.80 arc-sec)
DEC, RMS 0.05px(0.75arc-sec)
Total, RMS? 0.07px(1.10arc-sec)
Should I address the looseness in the DEC axis?? I've watched the video how to adjust the spring-loaded worm gear.? Would that be the way to eliminate the looseness?
Thanks for any help, Steve
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Hey Steve,
From my experience and thanks to Brian's help I have learned that you shouldn't worry about DEC backlash measurement.
It is just a thing PHD2 can't handle with a spring loaded version. Besides latest version of PHD2 will measure and compensate it while guiding, the more you guide the better it gets.
Also the better your polar alignment and seeing conditions are, the less it has to correct DEC.
Your RMS error looks good!
Cheers,
Carl
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Hi Steve
i would not worry about it right now - chances are it's some movement from the spring-loaded worm
your best bet for PHD is to do a baseline guiding by following these steps here:
that will give you (and the folks who support PHD including me) a great foundation for performance and your mount's characteristics
Hey Steve,
From my experience and thanks to Brian's help I have learned that you shouldn't worry about DEC backlash measurement.
It is just a thing PHD2 can't handle with a spring loaded version. Besides latest version of PHD2 will measure and compensate it while guiding, the more you guide the better it gets.
Also the better your polar alignment and seeing conditions are, the less it has to correct DEC.
Your RMS error looks good!
Cheers,
Carl
-- Brian?
Brian Valente portfolio
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Steve
also FYI the spring-loaded worms do not register well with the backlash measurement in PHD. If you review your actual guiding results you'll see they are quite good (i'm assuming the 1.1 arcsec/pixel is from guiding). you can't get that with a backlash of nearly 34 seconds.
Bruce and Andy and I have discussed this ad nauseam?
If PHD only worked with losmandy mounts?i think they would remove that warning, but there are many other types of mounts for which this is a helpful bit of information.?
On Thu, Apr 23, 2020 at 12:51 PM Steve Elmore via <gizmo_s67= [email protected]> wrote: I received my new GM811G and finally got out under the stars to start learning the mount and Gemini 2 system.? Before I got started, I noticed some movement in the DEC axis.? With minimum effort, i can wiggle the saddle, i.e. DEC axis.? I am working with PHD2 and got some messages about the DEC axis, don't remember exactly.? I ran the guiding assistant and I thought the numbers looked good, except for the DEC Backlash was highlighted.? Here are some of the values:
RA Peak? 0.44px(6.73arc-sec)
DEC Peak? 0.37px(5.61arc-sec)
RA Peak to Peak0.47px(7.13arc-sec)
RA Drift Rate-0.09px/min(-1.41arc-sec/min)
RA Max Drift Rate0.04px/sec(0.67arc-sec/sec)
Drift-limiting exposure2.4s
DEC Drift Rate -0.01px/min(-0.21arc-sec/min
DEC Backlash >=34970 +/-99ms(247.1 +/-0.7a....
Polar Alignment Error 0.9 arc-min
High-frequency Star Motion
RA, RMS 0.05px(0.80 arc-sec)
DEC, RMS 0.05px(0.75arc-sec)
Total, RMS? 0.07px(1.10arc-sec)
Should I address the looseness in the DEC axis?? I've watched the video how to adjust the spring-loaded worm gear.? Would that be the way to eliminate the looseness?
Thanks for any help, Steve
-- Brian?
Brian Valente portfolio
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PHD2 gives me an odd graph with my GM811G HD set up.
But what tells it all is my imaging results. As long as I'm getting great guiding and tracking (and I am),
I don't really care what sort of hash PHD2 shows.
Don't get hung up on PHD2 graphs. They can vary like the weather.
Pay attention to your results. That's the Proof that's in the Pudding.
PHD2 is to latch onto a single star, then follow it. And it can do that well enough for Photographic results.
Especially with your new mount. Mine does.
--
SonnyE
(I suggest viewed in full screen)
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Thanks for the response.? Last night and again tonight, i've been working on Alignment and Guiding.? I do my initial alignment with Polemaster, then go to building a model.? I will move the star close to my alignment center with the hand controller, then go to guide speed to get it right on the center of my camera field of view.? E/W movement responds well, but the N/S response is very very slow.? It may take 20 to 30 seconds to start moving.? This is probable when I'm changing directions, which is the backlash.? Now as I'm trying to get PHD2 to guide, the calibration fails because the backlash clearing failed, star did not move enough.? I think I really have a backlash problem.? What can I do to fix it?
I just tried to run the Star-cross test with PHD2 and did not get a cross.? Just a line with the bright spot in the center of the line.
Steve
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Hi Steve
>>>E/W movement responds well, but the N/S response is very very slow.? It may take 20 to 30 seconds to start moving.?
use center for visually centering?the star, guiding rate is aggravatingly slow even in the best of conditions.
>>>Now as I'm trying to get PHD2 to guide, the calibration fails because the backlash clearing failed, star did not move enough.
I'm wondering if you got the 'little southern movement' advisory? if so, the calibration succeeded, but it gave you a heads up if your guiding in dec is problematic. A lot of people confuse this advisory with a calibration failure.?
my suggestion is you take this up at the PHD forums, since you are now describing guiding questions and using PHD software
I am a regular over there, and put together a doc on creating a baseline guiding, i recommend you follow those steps?and then post to PHD if you have any additional?questions
On Mon, Apr 27, 2020 at 8:40 PM Steve Elmore via <gizmo_s67= [email protected]> wrote: Thanks for the response.? Last night and again tonight, i've been working on Alignment and Guiding.? I do my initial alignment with Polemaster, then go to building a model.? I will move the star close to my alignment center with the hand controller, then go to guide speed to get it right on the center of my camera field of view.? E/W movement responds well, but the N/S response is very very slow.? It may take 20 to 30 seconds to start moving.? This is probable when I'm changing directions, which is the backlash.? Now as I'm trying to get PHD2 to guide, the calibration fails because the backlash clearing failed, star did not move enough.? I think I really have a backlash problem.? What can I do to fix it?
I just tried to run the Star-cross test with PHD2 and did not get a cross.? Just a line with the bright spot in the center of the line.
Steve
-- Brian?
Brian Valente portfolio
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Backlash can come from different things. The meshing too lose, the gearbox, the coupling or the end blocks. If you have a spring loaded worm then you can rule out meshing. Gearbox backlash is usually very minimal. Check your couplings that they are tight. The end blocks is the most likely. If the gear moves axially between them you need to unsecrew one, squeeze the worm between the two and secure it again.
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Before I start trying the Spring-Loaded Worm Gear Adjustment, I would like an opinion.? Is 1¡ã of movement (play) acceptable?? I see in the video they are adjusting the RA axis.? My problem is in the DEC axis.? But after the adjustment, there was no play in the axis.? I would thing that I should have the same in the DEC axis.? I'm incline to perform the Spring-Loaded Worm Adjustment.? I will fix the play I am experiencing in my DEC Axis.? How many people have had to make these adjustments?? I attached a movie, I hope it comes thru.
Steve
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It looks like it's moving a fair bit. You should be able to get zero backlash in DEC quite easily without seizing anywhere across the whole circumference of the spur gear. I usually clean the worm dry and grease the spur gear alone with a wooden lollipop stick. It has just the right shape to "paint" the grease in the groove. Then mesh the worm to the max so it cannot move at all. With the gearbox removed try to rotate the old ham coupler by hand and release the pressure by a minute amount until it moves, then keep going for a 360 turn forward repeating for each tight spot. When done do it in reverse. If you're lucky you could have zero backlash provided your spur gear is perfectly round which it should. RA you can have a bit of backlash because you load the worm East when tracking. DEC I recommend to get as close as you can to zero.
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I did the Spring-Loaded Worm Gear Adjustment and the Dec looseness/backlash is significantly better.? So, either it came loose from the factory or it was damaged during shipment.?? I will be working more on it as I get a chance with dark skies.
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Steve did you run a baseline guiding before you did this?
I'm a little concerned you are focusing on the visual inspection, and not the actual DEC performance
for example, in your first post you had these numbers:
RA Peak? 0.44px(6.73arc-sec)
DEC Peak? 0.37px(5.61arc-sec)
RA, RMS 0.05px(0.80 arc-sec)
DEC, RMS 0.05px(0.75arc-sec)
although they aren't super helpful, this little bit shows your DEC is performing better than your RA.?
the spring-loaded worm really is something unique and PHD doesn't always register it well.?
I highly suggest you get to a baseline guiding and that will tell you how your mount is actually performing
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Brian,
Those were before I made any adjustments.? Here are the screen shots from after the adjustments and drift alignment.? Which numbers are the important ones?
Steve
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Hi Steve
Is this setup correctly? according to your settings your guider resolution is 30.5"/pixel?
the guide and debug logs would help here
On Wed, May 13, 2020 at 1:35 PM Steve Elmore via <gizmo_s67= [email protected]> wrote: Brian,
Those were before I made any adjustments.? Here are the screen shots from after the adjustments and drift alignment.? Which numbers are the important ones?
Steve
-- Brian?
Brian Valente portfolio
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I had not noticed the guiding resolution.? I may have 2x2 binning.? The guide camera 648x486, 7.4¦Ìm with a 100mm lens.? No binning will bring it down to 15.2"/pixel.? I did just add a 200mm guide scope.? That will bring it down to 7.6"/pixel.? How low do I go?? The guide camera is old, so I might be able to justify a new one.?
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That seems artificially large. even with comparable systems i usually see around 4-5"/pix
it really depends on your guiding results and your imaging resolution.?
If you G811 is brand new, that backlash number is not correct. PHD does not read the spring loaded worms well.?
As i mentioned above and several times, we would really need to see the guidelogs, preferably from a baseline guiding.?
Steve is there a reason you aren't doing the baseline or uploading guidelogs??
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i'd love to help, but this is just poking around the edges until we get some real data here
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I tried four times to upload the files and they never show up.? I will try again.
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Hi Steve
It worked this time
and this is following the baseline guiding? I can look at these later and give you feedback
On Fri, May 15, 2020 at 8:56 PM Steve Elmore via <gizmo_s67= [email protected]> wrote: I tried four times to upload the files and they never show up.? I will try again.
-- Brian?
Brian Valente portfolio
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Yes, this is after baseline guiding.? Thanks for taking a look at it.
Steve
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Steve Elmore
