Logged a ticket directly with Losmandy to get to the bottom of these issues. I dont think a 1"-3" re-occurring RA variance (+/-) is expected, so I must have set something up wrong.

Will report back with what I learn

Hello, Does anyone know if the following replacement/upgrade parts for the G-11 will fit on the old Celestron branded G-11? ?

G-11 SPDV saddle plate
CKS (or CKS B) clutch knobs
Polemaster adapter for G-11

Thanks

Hi Jean-Philippe,

Yes, you can set Gemini location and time from the GPS connected to your PC. In Gemini.NET driver, bring up the GPS window and connect to the GPS. You should see data being received from the GPS and latitude, longitude - and time updated. Click OK to close the GPS window when you see the new data there. You can then send the location and time to Gemini by pressing Set Now buttons under Site and Time in Gemini Settings window.

Regards,

? ? -Paul

For those interested in cage guided needle bearings, how they work and their relative advantage over the Torrington full compliment needle bearings used by Losmandy, I found this manufacturer article very informative (nice graphics):?Their design intrinsically keeps the rollers parallel with the shaft.?

Peter:

I have a few guiding runs but none long enough to get a meaningful FFT.? Weather has been dreadful but hopefully in the next few days I can grab a few unguided worm period's worth.? If the 80s still lingers, I can live with that since even the 32s in the Losmandys can be handled reasonably well with 1 - 1.5s guide exposures and keeping the aggression low-ish.? I'm seeing things <9.6s, but will be more illustrative once I have some data to share.

Keith??

Peter,

These are some interesting mods you are undertaking. I'm sure you will let us know if they are successful. With regard to the needle bearings, I imagine there needs to be some level of play with regard to needle movement. If the needles were perfectly rigid within the cage, both bearings on the shaft would need to be more perfectly parallel as seated inside the mount or there would be more significant wear on the shaft. The needles in both bearings and the main shaft would all need to be well aligned axially or you could be riding high on one end of a needle, and low on the other. So less play in needle bearing means more precise machining of the bearing seats in the housing. But if you can gain less shaft wiggle with the new bearings mentioned that would be great if the seat tolerances allow.

And yes I have done the Bellville washer mods on both RA and Dec. I tried a number of ways to tighten down the blocks as per Michael's instructions. I found if I used a C-clamp on the blocks before tightening down, I could flex down the Bellville washers to gain that axial tension. But if I clamped too hard, the worm was too difficult to turn and the motor stalled. Even after the mod, I still had some wiggle if I rocked the counterweight shaft back and forth, but yes much less than beforehand.

My feeling is still the worm machining and then polishing is a fine art, yet to be perfected here. Since mount performance relies heavily on worm profile, if there was a simple solution HGM would already be doing that. If you have the skills to gain a better outcome, please share when you have it down. Just adjusting the blocks the first time took 5 or 6 nights out for me. Make an adjustment, assemble rig, guide at night, check results, then tear all down again if not right.?

Best of success,

John

Keth,

Do you have any FFT graphs you could share?

If you have a large 9.6s error then the pinion gear bore hole is likely off center. The 80s error is very interesting, and possible confirmation it comes from this design of the gearbox. I have this issue with both the 80:1 and 125:1 gearboxes I use. I've previously mentioned not really liking the 25:1 gearbox. It seemed to have a lot of play in the output gear. For the Dec axis why not stay with?the stock gearbox. The issue here is backlash. The frequency response is really not important. I've started a separate thread discussion on the backlash issue. ?The good news about the 80s error it can be removed with a PEC curve. But have you read the thread on increasing the number of steps either via the gearbox ratio or the encoder for much improved RA performance? I have virtually no high frequency noise. The 125:1 gearbox uses the same pinion gear the 25:1 gearbox. My Ra is guiding at around 0.6 arc-sec rms with not sudden jumps. I just have that 80s error. I also changed the coupler to a one piece rigid one. I just posted how one can do this for under $10. You can find details here?/g/Losmandy_users/message/72710

Peter

I thought I'd report back on my efforts on the 25:1 McLennan gearbox mod to give another data point, and the results are ... not good.? To recap, the reason for trying these are that both replacement Losmandy gearboxes I received have significant 32s PE, about 1.5" peak to peak (older G11, OPW, not spring-loaded or tucked).

When I previously attempted the mod a few years back, I was using some donated McLennans (i.e. old and well-used) but with new pinions enlarged on a lathe at my work.? The high-frequency noisy tracking I saw at that time I attributed to the worn gearbox bushings, and went back to Losmandys.

Fast forward to now, where I bought 2 new McLennans with all the tapping etc going very smoothly.? The first attempt was to install the old pinions (bored out to 1/8" on the lathe).? Result: same high-frequency noisy tracking, on both pinions, and both gearboxes (despite feeling buttery smooth by hand, at least compared to the Losmandy/Johnson Electric ones).? So I thought, maybe the lathe chuck damaged the teeth (though on visual inspection they looked just fine).? Therefore I took the fresh pinions that came with the gearboxes, and carefully drilled them out ("holding" the pinions in a cavity in a piece of cedar just undersized to the pinion OD).? Result: same high-frequency noisy tracking (period less than the motor rotation period, so not due to a poorly drilled bore), and a pretty significant 80s PE (though much more concerned with the high-frequency jumps).

So, before I abandon this as a negative result, has anyone else seen this when trying this mod?? It appears that this goes swimmingly for everyone else who reports, just not me.? Not sure what I can be doing wrong here (e.g. playing with the motor to gearbox mesh doesn't improve things).? Barring any enlightenment, I may just to back to my original Losmandys (not the replacement ones).

Keith

Mark,

So you took the easy why out hey! :) The problem you describe may be attributable to the design of the needle bearings. The stock bearings are full complement Torrington. They do not necessarily stay parallel to each other, and perhaps this created the climbing effect.? I'm going over to caged needle bearings which keeps everything parallel.??

Peter

Michael,

I actually have an older mount. There is no wiggle and the left hand bearing block mount hole. I did the spring loaded worm mods myself. For me the jury is out as to whether a SLW is better or worse for guiding. I think it might be worse. It might be better to lap in the worm so no high spots and lock the sucker down. The nice thing about using higher ratio gear boxes is you have more torque. With the 25:1 ratio box I could stall out very easily. Not so the 80:1 and 125:1 boxes. Never stalled in fact. A lot of worm pressure and eventually it will wear in. I'm going to help it along a bit by lapping the worm to the gear wheel. The Hysteresis problem you mentioned on the new mounts maybe what is ailing someone else on this forum with high Dec backlash. My advice for what it is worth is to lock down the Dec axis. I'm not sure what spring loading buys you in tracking performance.?

The interesting thing to me is allan137 says a sloppy needle bearing and shaft assembly should have no effect on backlash. He has got me thinking, but I'm now committed to replacing them since I have removed them all. I have not touched my worm at all since my last backlash test, so will run the numbers again once re-assembled.?

If this is not the problem than the only left is the coupler. I found this great <$10 rigid coupler solution that will actually fit inside the worm housing. First the 1/4" x 1/4"? coupling:

3/4" long for Dec



1" long for Ra



Now you need a bushing. For the Losmandy motors you will need 3/16" ID and 1/4' OD. You will have to look this up (tubing bought from Lowes will suffice), but for the replacement gearboxes with a 4mm shaft this is what you need??.

Peter

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I think your math is pretty close now. ?But the seeing is also a consideration. ?For exposures longer than a few seconds, most of the time seeing is going to make tracking accuracy below 1/4-1/2 arcsec irrelevant. ?

Thanks Les ! In the full mosaic I will crop a lot less vertically since there is a lot of nebula in the lower portion of the image on the other side but I liked this closer crop for this portion.?

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Nice! ?It looks like the equipment is working well for you, and I really like the composition.

Stepping away from all the technical chat for just a moment here :)

I bought the mount to make images and here is my first. It's just the beginning of the final image which will be a 2-panel mosaic of the Veil.
This is only 4 hours, so the data is still quite noisy. The goal is to collect about 10-12 hours per panel

Sorry about the bandwidth but to correct myself once more, the RMS of the pixels in the last paragraph is really the size of the image of a point source in pixels (I used a factor 2 between them because the RMS goes in 2 directions).?

Sorry again, I'm just trying to define for myself what is a reasonable goal and when I should start using my mono camera.? I am not nearly at that goal, and my images show it.? HTH.

On Mon, Jul 12, 2021 at 11:44 AM, Brian Valente wrote:

>>> ?Pixels per arcsecond is therefore 3.6.? However this is an MC so the resolution is cut in half leading to 7.2 arc seconds per pixel.? For 1 arc second total RMS (keep in mind this is plus or minus which is a factor 2), a point source gets smeared out over 14.4 pixels.?

?

i think your first part is backwards, but your second part is accurate

?

If you have 7.2 arcsec per pixel?and you are guiding at 1/2 arcsecond, that is 1/14th of a pixel. What am I missing?

?

?

>>>For quality AP the goal should be 0.25 arc seconds total RMS.

?

Curious where you got this? That seems astonishingly low. Or maybe I don't understand what 'quality' means in this context

?

?

On my AP1600 in Chile where seeing can be as low as 0.4" that level of RMS is possible with absolute encoders, a large pointing model, guiding, and a little luck. But even then it's often higher.?

You have a point though the original was a typo (the first part says pixels per arc sec which is right then I continued with arc sec per pixel).

OK reset let me try again.? The example has?7518/4185 pixels per arc second, that's about 1.8.? Let's assume MM for now.? So a point source with an RMS of 1" will be spread out over 2" (because RMS is measured around the average so it goes in both directions), which is 3.6 pixels.? For an MC camera let's add 1 pixel so that's 4.6.?

Am I correct this time?? The numbers keep getting smaller fortunately, but 3.6 or 4.6 is certainly not sub-pixel.

You ask about 0.25 arc second and why.? Like I said on a good night I get 1" total RMS and the images are noticeably blurry.? Some people here claim they get 0.25" RMS so redoing the math we get 0.9 pixel RMS for mono, 1.9 pixel RMS for OSC.? That's where it pays off to do mono.? On a very good night of course.

Hello
I have discovered that under the gemini telescope set-up windows I can configure (port # and baud rate) a USB gps receiver and get data (tiem and position)
Is there a way to feed directly the position data to the mount?
It's of course possible to create a new location, but this is a little bit heavy since I'm regularly changing from one (random) location to another (more random even!)

clear skies!

On Mon, Jul 12, 2021 at 08:20 AM, Henk Aling wrote:

On Fri, Jul 9, 2021 at 12:27 AM, Brian Valente wrote:

Hi Nick

?

>>>Is there a way to analyze what kind of impact this actually has on images ??

yes - look at your images. You can also do quantitative analysis such as FWHM and Eccentricity.??

?

?Right now, you are guiding?sub-arcsecond, which is a fraction of a pixel difference in your final images, so I suspect any additional mechanical tweaking will result in literally no difference in your images.?

?

Guiding sub-arcsecond is not nearly sub-pixel in many cases.? For instance for my APS-C sized ASI2600MC and a 1380 mm FL Newt? I have norm([6249;4180])=7518 pixels on the diagonal for a FOV of?(28/1380)*(180/%pi)*3600=4185 arc seconds.? Pixels per arcsecond is therefore 3.6.? However this is an MC so the resolution is cut in half leading to 7.2 arc seconds per pixel.? For 1 arc second total RMS (keep in mind this is plus or minus which is a factor 2), a point source gets smeared out over 14.4 pixels.? For quality AP the goal should be 0.25 arc seconds total RMS.? For an MM cam that would be about 1.75 pixel.? When you say sub-pixel I presume you mean 0.5 pixel or so.? Unless I have an error in the math, I think you are overly optimistic by a factor 15 to 30 for many cases.

Wow, 0.25 seems really low (although a friend here is getting around that with his CEM70 right now, but not maxing out the payload)
I'd settle for 0.6-0.7 with no RA spikes quite happily right now though !

Guiding sub-arcsecond is not nearly sub-pixel in many cases.? For instance for my APS-C sized ASI2600MC and a 1380 mm FL Newt? I have norm([6249;4180])=7518 pixels on the diagonal for a FOV of?(28/1380)*(180/%pi)*3600=4185 arc seconds.? Pixels per arcsecond is therefore 3.6.? However this is an MC so the resolution is cut in half leading to 7.2 arc seconds per pixel.? For 1 arc second total RMS (keep in mind this is plus or minus which is a factor 2), a point source gets smeared out over 14.4 pixels.? For quality AP the goal should be 0.25 arc seconds total RMS.? For an MM cam that would be about 1.75 pixel.? When you say sub-pixel I presume you mean 0.5 pixel or so.? Unless I have an error in the math, I think you are overly optimistic by a factor 15 to 30 for many cases.

One correction, the difference between MC and MM is additive not multiplicative.? So for an MC camera we have the MM number plus 2 or so, which is about 9.2.? The difference between MM and MC will therefore also not show until say, 0.25 arc seconds total RMS.? Which is why I am still not using my MM camera because I am struggling to get 1" total RMS from my G11S (heavily customized with OnStep/DIY SLW, not standard Gemini).