Re: Needle bearings and axial play, is this a significant performance problem and how difficult is it to fix?
On Thu, Jul 15, 2021 at 01:28 PM, Robert Hancey wrote:
Bob H. here, though I have one of the newer G211g and have yet to try my hand at astrophotography and new to commenting in this forum ( so please forgive any ignorance on my part). Comments seem to be about a variation that is 2-3 digits beyond the decimal and and the mount was designed (previous comment) to be a visual tool, is this subject the equilivent to "beating a dead horse ", as i am having a hard time understanding this line of thought, and I am nowhere even close to being an expert on my mount, and no way is this comment of mine to be considered to a negative to the topic starter, just wondering. Respectfully submitted.? ?
The G11 can be excellent for astrophotography when tuned and used properly.? This is not about 2-3 digits beyond the decimal of something, it is about real issues for minimizing tracking errors to a few pixels.? One of my favorite G11 AP galleries is here,?, to get an idea of what can be achieved.
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Re: Needle bearings and axial play, is this a significant performance problem and how difficult is it to fix?
Hi Robert,
This endeavor (astronomy and astrophotography) runs the gamut...from novice to expert and from visual observer to dedicated astro photographer.
And the equipment also runs a gamut from lightweight 60 mm wide field scope to heavy 16 inch f/10 SCTs...or even larger scopes.??
Add to that heavy or light cameras, filter wheels, piggyback telescopes...?
So: we all have different equipment needs.? And all the mounts are not identical...there were changes along the decades these mounts have been on the market.? It can be like comparing car models of different years.??
However this forum is for those who are not getting satisfaction from their particular unit, and those folks are sharing their experience, reporting what they see or hear (sometimes a noise seems incorrect) and asking for suggestions to try.??
So if you are in the group of happy folks, just ignore these deeper dives.? Use your mount and enjoy it.? If you are thinking of diving deeper yourself, these discussions might offer some things to think about.
There are far more expensive and far more sophisticated mounts on the market.? These mounts are not expected to match that higher cost class, but sometimes owners can get to an amazing performance level by some personal efforts.? This forum is also for those who want to see how far their mount can be pushed toward the high end.
Stay well and enjoy your new mount!
Michael
On Thu, Jul 15, 2021, 10:28 AM Robert Hancey < rdhx@...> wrote: Bob H. here, though I have one of the newer G211g and have yet to try my hand at astrophotography and new to commenting in this forum ( so please forgive any ignorance on my part). Comments seem to be about a variation that is 2-3 digits beyond the decimal and and the mount was designed (previous comment) to be a visual tool, is this subject the equilivent to "beating a dead horse ", as i am having a hard time understanding this line of thought, and I am nowhere even close to being an expert on my mount, and no way is this comment of mine to be considered to a negative to the topic starter, just wondering. Respectfully submitted.? ?
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Re: Needle bearings and axial play, is this a significant performance problem and how difficult is it to fix?
Bob H. here, though I have one of the newer G211g and have yet to try my hand at astrophotography and new to commenting in this forum ( so please forgive any ignorance on my part). Comments seem to be about a variation that is 2-3 digits beyond the decimal and and the mount was designed (previous comment) to be a visual tool, is this subject the equilivent to "beating a dead horse ", as i am having a hard time understanding this line of thought, and I am nowhere even close to being an expert on my mount, and no way is this comment of mine to be considered to a negative to the topic starter, just wondering. Respectfully submitted.? ?
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Re: 1st time buyer: Recommended knobs other than CKS?
For me, the knobs that allow you to secure the mount to the tripod with no wrench are invaluable as I have to set up each night.
However, I have noticed they loosen up a bit during the evening (maybe due to the cold ?) so need to crank them down pretty tight
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Re: 1st time buyer: Recommended knobs other than CKS?
Any accessory that replaces using a wrench in the dark with a knob is a good choice, in my opinion. Happy shopping!
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Re: Needle bearings and axial play, is this a significant performance problem and how difficult is it to fix?
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Re: Needle bearings and axial play, is this a significant performance problem and how difficult is it to fix?
Peter,
800 msec is for the gearbox only, with the 6.5 sec worm backlash the total is 7.3 sec; ?completely unguidable.
Assuming the gearbox backlash is fairly constant with temperature, the TVC could be set to at least correct that backlash, but the worm is the major contributor to my backlash and it varies with temperature, so TVC is not an effective solution.
I don¡¯t see how the coupler would introduce significant backlash, relative to the other contributors.
Before you start replacing components, you may want to measure the backlash of each individual component, as I have done, hence my suggestion that you measure the backlash of your gearbox and worm separately.
Eric
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Re: Needle bearings and axial play, is this a significant performance problem and how difficult is it to fix?
Chip,
That's very interesting. I have posted here quite a bit about the caged bearings, but actually I might prefer the full compliment ones. They seem smoother. The thing is the shaft, at least mine, is 5 thou under size. The bearings are sloppy. The shaft touches the bears on just the top or bottom surface. That's a problems. ?Bearins are designed to be pressed in and the inner diameter reduces a little. These are only a very light press. Finger light. Makes them easily to change but they do no perform to spec. The 1.5" bore needs to be a few thou undersized to correctly compress the bearings I think.
Peter
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Re: Needle bearings and axial play, is this a significant performance problem and how difficult is it to fix?
On Wed, Jul 14, 2021 at 07:24 AM, Cyclone wrote:
Peter,
The backlash on my original Losmandy gearbox is 800 msec. With the gearbox installed on the motor and half the coupling on the output shaft, I took two pictures of the coupling on the output shaft, at each end of the backlash, measured the rotation angle difference in Photoshop and calculated the 800 msec at 0.5x guide rate. I did the same taking pictures of the other half of the coupling on the worm and calculated 6.5 sec. I don¡¯t have the spring loaded worm and the backlash is required due to tight spots around the Dec axis).
If I read your post correctly, it seems you have not identified the sources of backlash; you could try the method I described above.
Eric
Eric, So I'm focused on three things. The needle bearings. I've changed these out and added a third, but I will have more to say on that later. I have not touched my worm setup since last reading to get a comparitive measurement. Second, I will change the coupler to a rigid one and measure again, as the worn assembly can remain untouched. Third, I will follow some of the steps Allen has suggested.? I would die for 800ms! I should note that I set TVC to 0 based on something I read somewhere. Before that l had better backlash measurements. So forth, measure again with TVC set to 10. The problem is that so much of what we read here is antidotal. We need hard data that shows a progression of hopefully improving measurement to see what is significant. It's wonderful that we have to do all this work to get our mounts to perform! Pete
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Re: Needle bearings and axial play, is this a significant performance problem and how difficult is it to fix?
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Sounds like mine.?? Maybe a half octave higher pitch but same decibel level.
On Wed, Jul 14, 2021, at 12:14 PM, "Guilherme V¨ºnere wrote:
I had the same doubts as Alan when i first?got my G811G last month. I compared the noise with my OnStep GM8 which is completely silent and was worried I had installed the motors wrong. Brian told me the noise was normal and after some time it got a little better (still a bit noisy but acceptable)
Here's what i heard on the first night?
Guilherme
On Wed, Jul 14, 2021 at 8:39 AM John Kmetz < jjkmetz54@...> wrote: [Edited Message Follows]
The two transfer gears appear to have a dark grey lube on them.
The grease does darken over time, even if using clear Superlube. Metal fines and aluminum oxide from the gears starts to taint the color. This is normal.
And the newer gearboxes you can dissemble to clean and lube, or check for wear. My originals were riveted and could only be drilled out. Now they have Allen head screws which you can easily take out. If you stick your finger into the gearbox hole and hold down of the first gear that contacts the pinion gear, then rock the output shaft/spur gear, you can see how much play there is.
The only time I had any screeching sound though, was when I had the worm and ring pressed together too tightly. Worm tension has an effect.
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I had the same doubts as Alan when i first?got my G811G last month. I compared the noise with my OnStep GM8 which is completely silent and was worried I had installed the motors wrong. Brian told me the noise was normal and after some time it got a little better (still a bit noisy but acceptable)
Here's what i heard on the first night?
Guilherme
On Wed, Jul 14, 2021 at 8:39 AM John Kmetz < jjkmetz54@...> wrote: [Edited Message Follows]
The two transfer gears appear to have a dark grey lube on them.
The grease does darken over time, even if using clear Superlube. Metal fines and aluminum oxide from the gears starts to taint the color. This is normal.
And the newer gearboxes you can dissemble to clean and lube, or check for wear. My originals were riveted and could only be drilled out. Now they have Allen head screws which you can easily take out. If you stick your finger into the gearbox hole and hold down of the first gear that contacts the pinion gear, then rock the output shaft/spur gear, you can see how much play there is.
The only time I had any screeching sound though, was when I had the worm and ring pressed together too tightly. Worm tension has an effect.
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Re: Needle bearings and axial play, is this a significant performance problem and how difficult is it to fix?
My 2005 vintage G11 has caged needle bearings supporting the RA and DEC axles. I have rebuilt several G11 mounts for friends and club members and some may have been newer than mine but almost all had caged bearings on the axle shafts. I wonder if there was some substitution in production over the years. Scott often slipstreams updated parts and newer designs into production without noting or documenting the changes.
?
--
Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astropheric Weather Forecast - South Pasadena, CA?
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The two transfer gears appear to have a dark grey lube on them.
The grease does darken over time, even if using clear Superlube. Metal fines and aluminum oxide from the gears starts to taint the color. This is normal.
And the newer gearboxes you can dissemble to clean and lube, or check for wear. My originals were riveted and could only be drilled out. Now they have Allen head screws which you can easily take out. If you stick your finger into the gearbox hole and hold down of the first gear that contacts the pinion gear, then rock the output shaft/spur gear, you can see how much play there is.
The only time I had any screeching sound though, was when I had the worm and ring pressed together too tightly. Worm tension has an effect.
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Related question, which I hope isn't too far off this topic:
Has anyone who's adjusted the motors to reduce noise also measured before-and-after PE FFT charts?
I am curious whether the mechanical adjustments that reduce noise also reduce any periodic or non-periodic errors (dare I dream, the 32s error)? Or, the opposite: could it introduce/amplify any error?
I'm waiting for a clear, stable night to start testing my GM811G again, and am weighing which adjustments to make, and in what priority.? The noise is not an issue for me, but would be interested in adjusting the motor seating if it meant reduced error.
Hoping you engineers and master tinkerers could either opine theory or relay actual experience.
Thanks all,
Jason
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Re: How to determine mechanical CWD position?
Hi Alan,
There is a simple mechanical procedure to assure accurate CWD:
Tools:? a short "torpedo level".??
Procedure:
?Put your counterweight bar horizontal.? ?Level the counterweight bar with the torpedo level. ?Adjust your RA setting circle to a convenient position at the marked pointer, so you can rotate the axis by 90 degrees.? I use 6 or 12 or 18 or 24 o'clock.?? ?Rotate the RA back to CWD position and use the setting circle marks to get that to 90?degree angle from the horizontal. ( 6 hour difference of course) ? Now RA is set.
?For DEC you use the dovetail and the bubble level to again set the dovetail to be horizontal.?? ? Use the DEC setting circles to a convenient position so you can rotate by 90 degrees. ? Now rotate the dovetail by 90 degrees. ? DEC is now done.? You are at CWD.
? I add tiny triangular pieces of white Thermal Printer tape, like used in Brother labelmakers.? I put on white triangle pointers to mark places on the setting circle area, so I can assess the 90 degree position for either side of the mount.??
Have fun, (and beware of plates that can't be solved.)
On Wed, Jul 14, 2021, 6:41 AM Paul Kanevsky < yh@...> wrote: Other than doing the initial rough alignment on the pole, why would the accurate CWD position matter? If you follow up with any other type of polar alignment routine, the accuracy of the initial position will become irrelevant. I usually find the CWD by gravity in RA and by sight, sighting along the OTA towards the pole, in DEC.
Regards,
? ? -Paul
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Re: How to determine mechanical CWD position?
I'm curious what results you are getting with the Sharpcap PA process?? Precise CWD hasn't been required in any of the mounts or techniques i've used for polar alignment including Sharpcap
I've found Sharpcap's?plate solve approach accounts for any RA or DEC misalignment?
Polemaster has a similar mechanism in repeatedly asking to align the star pattern. I often mount the polemaster to the OTA which has very rough RA and DEC CWD and it polar aligns very well
Let's assume I think the mount is in CWD position, but the DEC axis is actually 3 degrees off.
When I start the polar alignment, I adjust the az knob so the pole is somewhat centered.? To make the telescope straight, now the az is off by 3 degrees.
After I rotate the RA axis 90 degrees, I find that I have to adjust the az back 3 degrees.
-- Brian?
Brian Valente portfolio
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Re: Needle bearings and axial play, is this a significant performance problem and how difficult is it to fix?
Peter,
The backlash on my original Losmandy gearbox is 800 msec. With the gearbox installed on the motor and half the coupling on the output shaft, I took two pictures of the coupling on the output shaft, at each end of the backlash, measured the rotation angle difference in Photoshop and calculated the 800 msec at 0.5x guide rate. I did the same taking pictures of the other half of the coupling on the worm and calculated 6.5 sec. I don¡¯t have the spring loaded worm and the backlash is required due to tight spots around the Dec axis).
If I read your post correctly, it seems you have not identified the sources of backlash; you could try the method I described above.
Eric
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Re: Needle bearings and axial play, is this a significant performance problem and how difficult is it to fix?
Where did u clip the laser, and was the worm "loaded normally"?
We'll have to see the PHD backlash graphs to figure out what is going on.
Dirty little secret : Start the guiding assistant, then click stop right away, then hold down the Ctrl key and left click on the "cancel" button.? It will start the backlash test right away and you don't have to wait two minutes.
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Re: Needle bearings and axial play, is this a significant performance problem and how difficult is it to fix?
Alen,
first what a great great piece you wrote on backlash. From the graphs you posted I might be too tight? Second, you mentioned going to I think guiding rate and counting. You say you counted 2a before any movement in the worm. When I do this test it moves immediately and a see no visible backlash, yet I still measure 2.5s in guiding assistant. What might be going on here?I looks like a possible clear night so I'm anxious to get this sorted.
Peter?
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Michael Herman
Chip Louie