Re: Sawtooth pattern in DEC
Thanks, Paul. Should I use a different backlash setting in PHD2?
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Re: Sawtooth pattern in DEC
Hi Arun,
Possibly backlash. It takes a while for DEC to reverse direction. When it does, you see the large jump resulting in a saw-tooth-like pattern.
Regards,
? ? ?-Paul
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Hello,
Attached is my guiding log from last night. I'm looking for some input on a sinusoidal or sawtooth pattern I'm seeing in DEC. Guiding in RA seems reasonable -0.54" RMS. The sawtooth pattern is not something I've seen before. Apart from double checking DEC balance, could there be other culprits? Typically, DEC is better for me than RA. If I had the same performance in DEC as in RA, I'd be where I want to be, so feels like I'm close, just need to solve this "special" cause. For example, if DEC had also been 0.54", I'd be at 0.75" RMS over a 4 hour period, which I'd consider good.
Info on my setup
Stellarvue SVX080T-3SV (80mm f/6)
OAG with ZWO ASI 290MM Mini (2.9 micron pixels)
Mount is a GM811G, main cam is a ZWO ASI1600MM Pro. Other accessories mounted are dew heater, motorized focuser. All cables are bundled into a cable organizer and secured at two points to the DEC axis to prevent drag.
Thanks,
Arun
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Re: Another night of Stellar Performance
SonnyE,
I'm not sure what you are saying here. Are you saying the PHD2 PE data people use to debug and refine their mount's tracking is not valid and the data cannot be compared between mounts???
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Chip Louie - Chief Daydreamer Imagination Hardware
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Re: Oldham Coupler replacement success?
Taylor,
There are other types of couplers out there but they all have their own advantages and disadvantages. The best results have been produced with Oldham couplers in good condition where the gearbox and worm shafts are well aligned. The main issue with doing this is that there have been multiple versions of the Losmandy mount drivetrains in use over the years. The best version drivetrain was the original OPW setup that carried the gearbox and worm on one platform so there were no changes in the alignment of the gearbox shaft and worm shaft while backlash was adjusted. This has been lost with the gen-2 OPWs but the OPWs are half the cost now. So the best advice is to simple get the shafts aligned as well as possible to minimize the very small angular velocity changes of a misaligned Oldham coupler.?
? ?
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Chip Louie - Chief Daydreamer Imagination Hardware
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Re: Oldham Coupler replacement success?
Anytime we would change out, or have to dismount a motor with a flexible coupling, we would have our machinist help with the final alignment.
Of course, these were typically pumps running at much higher speeds than ever found in a mounts drive train.
Introducing any different flexture into the tracking, such as a different coupling, can also introduce a different reaction, and cause unwanted results.
What is the cost of the linked bellows type couplers? There is probably some good reason why the Oldham Couplers were chosen by Scott.
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SonnyE
(I suggest viewed in full screen)
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Re: My backlash is larger than yours!
Sonny
Good results speak for themselves!
In my experience, the Gemini 2 has been as infallible as it can be. Much better than most.
It was just a strange thing to have happen. And I do believe it was before the Format and Repair of my mounts software.
As I said, I found it quite comical, and unexplainable.
After finding my way with the Gemini 2, I have accuracies most dream about.
But I do my modeling my way, and it works. I wind up with slews generally centered well enough to not need centering further.
I've been very impressed, and very pleased.
But, I don't necessarily do things
Most recently, PHD2 got wonky on me. Removing (uninstalling it) and installing a new copy fixed it and I think made PHD2 work even better than my past experiences with it.
Not mechanical issues, but software getting skewed.
--
SonnyE
(I suggest viewed in full screen)
-- Brian?
Brian Valente portfolio
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Re: My backlash is larger than yours!
In my experience, the Gemini 2 has been as infallible as it can be. Much better than most.
It was just a strange thing to have happen. And I do believe it was before the Format and Repair of my mounts software.
As I said, I found it quite comical, and unexplainable.
After finding my way with the Gemini 2, I have accuracies most dream about.
But I do my modeling my way, and it works. I wind up with slews generally centered well enough to not need centering further.
I've been very impressed, and very pleased.
But, I don't necessarily do things
Most recently, PHD2 got wonky on me. Removing (uninstalling it) and installing a new copy fixed it and I think made PHD2 work even better than my past experiences with it.
Not mechanical issues, but software getting skewed.
--
SonnyE
(I suggest viewed in full screen)
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Re: Oldham Coupler replacement success?
Taylor,
The only study I found was from Michael Sinescalchi. His website described trying a Ruland coupler.? It did not improve PE, maybe worsened it.? No knowledge of other types of coupler.?
My view is the Oldham works fine, but you need to be sure the gearbox drive shaft and worm drive shaft are lined up, so the coupler only spins, not angles or center white part slides.??
All the best, Michael
On Tue, Jun 16, 2020, 1:43 PM taylor waber < taylorwab@...> wrote: Hi All,
Wondering if anyone has had any success with a replacement coupler for the Oldham coupler design, such as a bellows coupler that Real14 on CN
Would this reduce backlash or improve periodic error?
Or any thoughts/advice against replacing this? I have the GM811 w/ OPW and tucked motors (NOT spring loaded worm).?
Thanks?
-Taylor
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Oldham Coupler replacement success?
Hi All,
Wondering if anyone has had any success with a replacement coupler for the Oldham coupler design, such as a bellows coupler that Real14 on CN
Would this reduce backlash or improve periodic error?
Or any thoughts/advice against replacing this? I have the GM811 w/ OPW and tucked motors (NOT spring loaded worm).?
Thanks?
-Taylor
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Re: My backlash is larger than yours!
>>>
But a "Hard Boot" often solves any unusual stuff.
if that's the case with the situation you describe, it's possible that a bad alignment caused the model to get corrupted
I'm not saying the Gemini is infallible (as evidenced by the beta firmware), but things like 180 degrees off are common signs that a setting somewhere was not correct
If that happens again, maybe you can record exactly what happened in what order, and we can look more closely at it
On Tue, Jun 16, 2020 at 12:48 PM, Brian Valente wrote:
If the mount is pointing 180 degrees the wrong direction that almost certainly a date/time and/or location issue
After doing a fresh modeling build up and having successfully slewed around to a few other stars?
Nothing changed the settings, it just got weird.
So I shut down the Gemini 2, re-centered my telescope, and started over.
I was actually laughing at the antics.
But a "Hard Boot" often solves any unusual stuff.
?
--
SonnyE
(I suggest viewed in full screen)
-- Brian?
Brian Valente portfolio
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Re: My backlash is larger than yours!
On Tue, Jun 16, 2020 at 12:48 PM, Brian Valente wrote:
If the mount is pointing 180 degrees the wrong direction that almost certainly a date/time and/or location issue
After doing a fresh modeling build up and having successfully slewed around to a few other stars? Nothing changed the settings, it just got weird. So I shut down the Gemini 2, re-centered my telescope, and started over. I was actually laughing at the antics. But a "Hard Boot" often solves any unusual stuff. ? -- SonnyE (I suggest viewed in full screen)
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Re: My backlash is larger than yours!
On Tue, Jun 16, 2020 at 11:50 AM, Magnus Larsson wrote:
That is what the beta firmware is here to solve - when the mount looses all sense of directions! Have you tried it? It works very nicely on my mount, this far.
Best,
Magnus
Hi Magnus! What beta firmware might that be? I not long ago formatted my Gemini 2, and had to re-install everything. Maybe it was recently enough to have gotten the update? For me, the loss of intelligence in the software has not been a huge problem. But one I haven't forgotten, for sure. It was actually comical to me. I believe I simply shut down the mount and started over. It worked fine after, the "hard reboot". But was funny when my telescope was pointing SSE instead of NNW at the end of it's slewing. (And really glad I was in attendance at the time. Whew!) ? -- SonnyE (I suggest viewed in full screen)
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Re: My backlash is larger than yours!
>>>That is what the beta firmware is here to solve - when the mount looses all sense of directions! Have you tried it? It works very nicely on my mount, this far.
that is not accurate. the firmware update addresses certain situations where the movement in both ra and dec is very small and could result in a runaway condition.?
it is not a "loses all sense of direction" solution
If the mount is pointing 180 degrees the wrong direction that almost certainly a date/time and/or location issue
On Tue, Jun 16, 2020 at 11:51 AM Magnus Larsson < magnus@...> wrote:
Sonny,
That is what the beta firmware is here to solve - when the mount
looses all sense of directions! Have you tried it? It works very
nicely on my mount, this far.
Best,
Magnus
Den 2020-06-16 kl. 20:32, skrev Sonny
Edmonds:
Well, that sucks for you, I think.
My backlash is so minuscule, I often find myself dropping down to
guiding speed during my centering process. Because I sometimes
overshoot with the tiniest blips.
I've have had unexplainable times when my mount will decide to go
180¡ã to where I know the star is. Not often, but enough to make it
memorable. Pointing at the ground is not where it's at.
I can't blame the mount though. Often it is the program in my
computer, drivers, or I think a square electron passing through...
8^(
When it does go bonkers like that, it does tend to wrap my bundle.
;^) Argh!
--
SonnyE
(I suggest viewed in full screen)
-- Brian?
Brian Valente portfolio
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Re: Another night of Stellar Performance
You are not quantifying things if all things are not identical.
And none of us have exactly the same things. So anybodies results are never the same as another.
On top of that, none has laboratory grade, certified and tested quantifiers. There will always be differences.
So Your results can never weigh against another's results.
They are your personal results, at your particular place and time, with your atmospheric differences.
Including how you stick out your tongue. (Left, Right, or Middle.)
That's why professional labs share samples with each other to test their results against each other.
And I sure don't see that in this group.
Including any considerations of repeat accuracy.
[edited by moderator]
--
SonnyE
(I suggest viewed in full screen)
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Re: My backlash is larger than yours!
Sonny,
That is what the beta firmware is here to solve - when the mount
looses all sense of directions! Have you tried it? It works very
nicely on my mount, this far.
Best,
Magnus
Den 2020-06-16 kl. 20:32, skrev Sonny
Edmonds:
toggle quoted message
Show quoted text
Well, that sucks for you, I think.
My backlash is so minuscule, I often find myself dropping down to
guiding speed during my centering process. Because I sometimes
overshoot with the tiniest blips.
I've have had unexplainable times when my mount will decide to go
180¡ã to where I know the star is. Not often, but enough to make it
memorable. Pointing at the ground is not where it's at.
I can't blame the mount though. Often it is the program in my
computer, drivers, or I think a square electron passing through...
8^(
When it does go bonkers like that, it does tend to wrap my bundle.
;^) Argh!
--
SonnyE
(I suggest viewed in full screen)
|
Re: My backlash is larger than yours!
Well, that sucks for you, I think.
My backlash is so minuscule, I often find myself dropping down to guiding speed during my centering process. Because I sometimes overshoot with the tiniest blips.
I've have had unexplainable times when my mount will decide to go 180¡ã to where I know the star is. Not often, but enough to make it memorable. Pointing at the ground is not where it's at.
I can't blame the mount though. Often it is the program in my computer, drivers, or I think a square electron passing through... 8^(
When it does go bonkers like that, it does tend to wrap my bundle. ;^) Argh!
--
SonnyE
(I suggest viewed in full screen)
|
Re: Another night of Stellar Performance
Under sampling images are certainly a great way to be able to ignore objective PE error numbers. The lost detail is not and cannot observed due to having huge circles of confusion and soft images that if you stand far enough back from look okay.?
The current DSO best practices seem to be a sample rate that is 2.5 times better than atmospheric. This is coming down from the best planetary imagers in the world using lucky imaging techniques which oversample at even higher rates and may be trending up.?
This requires objective knowledge about a mount's error rate. I learned this back in my studio days shooting cut sheet 4x5 macros from a 25 pound tripod that had to be reshot. I used a 400 pound camera stand for second session and the job was accepted.?
Just saying.?
--
Chip Louie - Chief Daydreamer Imagination Hardware
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Re: Another night of Stellar Performance
Different people have different approaches to this, which I respect. For me personally, quantifying things has been a big help. While there are many variables, several of them lend themselves to be quantified and doing this has helped me get more consistent results.
With respect to guiding - at the first cut, as long as guiding RMS is better than your image scale, you're better off worrying about other issues. Today, I image at 480mm with an ASI1600, which is 1.6"/pixel. If I get 1.1" RMS on a bad day, I still shouldn't be focusing on guiding - I won't really see the improvement in my images. But I am soon migrating to a 10" Newtonian which has a focal length of 1000 mm. That's an image scale of less than 0.8"/pixel, and I can pretty much guarantee that if I get 1.1" RMS guiding, I am going to, at best, lose resolution, and at worst, get egg shaped stars if guiding in one axis is worse than the other. That would make me sad, One approach for me is to buy a mount that costs 3x as much as my GM811G and be guaranteed of great results at that focal length, but the other is to see if I can improve the current equipment's results with some effort. Hence my interest in whether Richard's number is 0.3" RMS or 0.3 pixels. If I know that my mount is capable of consistently being guided to, say, 0.6-0.7" RMS, then that would justify me putting continued effort into improving guiding. Other imagers I work with do get these numbers from where I am, but they also use much more expensive mounts.
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Re: Another night of Stellar Performance
Yes, wanting to quantify things is a wacky idea.
Keith
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Paul Kanevsky
Chip Louie
Michael Herman