Thanks Brian,

Here is a logfile. Some of the data is during guiding, and some from guiding assistant

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Thank you both. Great info Michael, I'll definitely be checking all these areas

Brian: I did go through that document but I also tried a lot of other things so my PHD logfiles are not clean. I will need to redo this

I did some guiding, and I was around 1.0 total RMS and surprisingly DEC was really low (around 0.5) and my understanding of a bad PA is that it would likely show in DEC more than RA.

At some point I may need to look at my guiding equipment. I have 6.45 arc seconds/pixel on the guider as I got a small setup to keep the weight down for the skyguider

I also tried a couple of test subs and I was able to get 5 and 10 min subs with reasonable FWHM and eccentricity (although not hugely better than 180s with my Skyguider, but much longer subs)

I'm sure it is something silly I am doing and not anything wrong with the mount

I'm also going to do the Sharpcap PA twice, with different rotation directions - I am suspecting something was off here but I dont know what as I have been using it for a year on the star tracker

I'll be able to try it tonight or tomorrow and report back

Thanks so much for all the help

Peter, Guilherme

Have either?of you tried Edward's or my settings?

------------------------
Jim W
Phoenix, AZ. USA

Losmandy GM811G, NINA 1.11, ASI2600MC Pro, Sky-Watcher Scopes

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Michael,

Thanks for this info. I assume the grease is for the worm? Your rig looks quite heavy. How much weight are you sporting? I have a 12" truss Newtonian that I want to mount in the fall. It seems from looking at your setup my G11 should be able to handle it? I estimate the weight of the gear will be around 65 - 70lbs.

I'll defiantly give the loose hanging weight a go. One thing to note, with the worm blocks removed you have very free rotation so easy to get a precise balance.?

Thanks for all the support guys,
??
Peter

Vishal,

I also recommend going for the G11 with your 130mm refractor.? I originally purchased a GM811G to carry a small 85mm refractor, then bought a G11 dec when I upsized to a 130mm refractor.

I found dec backlash easier to control with the larger worm wheel on the G11 dec axis.? The longer saddle clamp on the G11 is also nice to use with when mounting longer scopes.

I can feel the weight difference between the two if I'm carrying either mount in one arm (the 811 is definitely "easier"), although I can't think of a time when this has mattered.

Thanks,
Dwight

开云体育

Hi Greg -

I'd love to see a few images of what you've done to? the mount.? If I understand your description, you're basically just using the small rubber bands as some flexible shim material to keep the worm meshed?? That certainly is minimalist. Have you run into any issues where the pressure is causing extra load on the motors due to worm friction?? I'm interested to hear how it works out for you during imaging.

Good luck, and please keep us posted,
-Tony

Alan,

I will try a rigid one piece coupler. My RA has the OPW. I've found it's possible to feel it the gearbox is aligned or not with the coupler by rotating worm with your fingers. The nice thing about the Mclennan gearboxes is they have a metal plate.??I have removed the motor cover as is is really cosmetic, so will then be able to use a hex head screw to tighten down the motor box more sensitively to hopefully get a good alignment. My planned testing on this issue is as follows.

1. Install a new worm undamaged by the use of the Oldham coupler set screws. Use a dial caliper to measure any wobble in the worm for a baseline measurement.

2. Install the gearbox using two different clamp style couplers from Ruland. I have already posted the part number of one and will get the part number for a rigid coupler if there is one with the correct O.D. Repeat the dial measurement.

3. Run an imaging session and get new FFT data.

The reason for these tests is mostly to better understand to magnitude of errors caused by different elements in the drive chain. I've already demonstrated how much better the FFT looks with the 125:1 gearbox in terms of higher frequency components. I'll be testing the 50:1 and 80:1 gearboxes in near future too.?

Currently, there is an 80s and a 240s error as show early in the FFT plot I posted. These have a corrected magnitude of 0.35 arcsec using the hysteresis PHD2 algorithm. I've not found the Predictive PEC algorithm works. These numbers change depending on which site of the meridian I'm on. Usually, after the flip the 240s goes away completely, but since my current project is the Cygnes Wall no flip has been needed so the error is a problem for the resolution I'm at.

Peter

On Mon, Jun 28, 2021 at 12:00 AM, "Guilherme Vênere wrote:

?

The flip *did not occur*. NINA stopped after the second exposure, showing the flip interface, but said the flip was done already without the mount actually moving. Gemini was tracking fine and stopped just for a second while the supposed?flip happened

?

Hi Guilherme

You have described perfectly the experience I now have. It used to work with 1.10 HF3 version, then stopped with 1.11 as I recall and certainly with the nightly builds. Good luck with your test of the HF3 version. This problem needs to be run to ground,. I do not want to have to give up using NINA.

Peter

I'm just saying, that from a theoretical perspective, a one-piece coupler maintains a kind of symmetry where it's indifferent to whatever the shaft angle is, and thus it will rotate at a constant speed.? This is as opposed to the oldham coupler where the center plastic piece slides back and forth, and thus the "gear ratio" changes a little bit for different orientations.? Remember those Shimano Biopace elliptical chainrings?
Another nice thing about the ruland type couplings is that if the colinear alignment is off, it will be rather obvious since it won't fit.

With that being said, Michael is right that there are many different causes for the 240s error.? Maybe try purposely mis-aligning the oldham coupler and see if the problem gets worse.
I forgot what system you have, but is there some way to pre-align the worm and gear shafts before putting on the coupler?

I agree, get the g11

Hi David,

Took your PEMPro data and ran it through on my laptop. I just wanted to see what kind of value range you were seeing in the Y axis, and the drift up and down is not that bad. I would say your polar alignment and seeing conditions were decent. PE of +4.6/-2.5 is fairly tight, but the RMS of 3.25 makes the data a bit rough. Then I am getting a correction curve of 7.12 peak to peak with RMS 2.4. I would probably be satisfied with this curve myself and would use it to program the mount. If you have already have done this and are using PE checked, your guiding results should have changed a bit.

But the Frequency Spectrum is showing your 76 error is larger than the PE as you already presented. Just to illustrate, my last PEMPro run that I did is below. Note the largest error is from the worm period. But since your mount has spring loaded worms and mine does not, a curve from someone who has one like yours might be a better base for comparison. Maybe someone will jump in here with one of their curves.

If you program your mount with the curve generated, you'll compensate for the PE but the 76 second error will remain. This error probably won't be fixed by anything but a mechanical adjustment to the mount. If this error is affecting your photos, some physical action would be needed; PEMPro or PHD2 won't remedy as far as I know. Feedback from HGM as to what they recommend under your warrantee situation will be a big part of your solution.

Hope you find a positive outcome.

Regards,?

John

Just to be clear this was done inside and I only did 1 sub after meridian flip to ensure the sequence would continue.??

------------------------
Jim W
Phoenix, AZ. USA

Losmandy GM811G, NINA 1.11, ASI2600MC Pro, Sky-Watcher Scopes

On Sun, Jun 20, 2021 at 01:47 PM, Chip Louie wrote:

Marc,

The original idea behind changing gearboxes was to eliminate the stock plastic gearbox uncorrectable periodic errors caused by the choice of internal gear ratios. There is no measurable hence observable advantage to increasing the mechanical advantage of the gearboxes on a properly adjusted mount.?

A properly adjusted Losmandy mount with the classic 2-piece straight drivetrain should never have zero backlash in a warm room or it will bind and lag as the mount acclimates to a colder environment. In Losmandy mounts with the classic drivetrain backlash shrinks the backlash as air temps fall. This is well known but poorly understood and has led to a zillion different people trying to invent or find ways to overcome a "problem" that is largely caused by not understanding how the mount reacts to its environment. To reliably resolve the changing backlash issue for most people the best solution now comes as standard equipment on all new Losmandy mounts namely the OPW Gen II spring loaded worm carriers.? Being spring loaded allows the worms to consistently maintain minimal backlash hot or cold which is just not possible with the classic 2-piece bearing mounts.? ?

If you need to power through lags or tight spots on the worm and worm gear you need to set your backlash correctly for these spots under the conditions which they occur.?
?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astropheric Weather Forecast - South Pasadena, CA?

I agree with the clearance needed to account for thermal contraction with changes. There are areas on the transmission train that need to give like crumple zones. I'm still not sold on spring loading the worm meshing though. I need more time. . I'll get to that once I have sorted out my couplings between the gearbox and worm shaft.

On Sun, Jun 20, 2021 at 07:07 AM, <pcboreland@...> wrote:

There are a number of reasons to change out the gearbox from Losmandy. I have the original ones with plastic tabs, their modified version and the 25:1 McLennan. I built my observatory early January in subzero conditions using heat plankets to set the concrete pillar etc. Having an observatory has been a game changer for me with not a single imaging night missed this year. In those winter months my rms error was 0.8 down to 0.5 arcsec rms. This was with the stock gearbox and the one piece worm on the Ra and original worm on Dec. Even with these good tracking numbers my RA was always 30% worse than Dec. So room for improvement I feel. When you look at the FFT response the 32s error was quit high at 0.2 arcsec rms or higher. Very low 76s error and the is some 240s as might be expected. The high 32s error in my mind a definite feature of the Losmandy gearbox they use and is ultimately the limiting factor on performance, assume one knocks down the 76s error. PEC does a reasonable job knocking down the 80s and 240s errors for me.

If you go over to the McLennan gearbox, the 32s will go away due to a different internal gearing arrangement. But you may introduce a significant 9.3s error if you do not reamer out the pinion gear accurately enough to fit the 1/8th inch shaft of the high torque motor. This does not get quided out and a noticable sinewave will be seen in the tracking error graph. Further, I was not impressed with the build quality of the 25:1 ratio gearbox in that there was much play in output shaft relative to the bushings, potentially making worse the 80s and 240s error. You may well trade one set of problems for another.

If you are going to the trouble and expense of changing out the gearboxes, the other option might be to use either a 50:1 or 80:1 gearbox. Early indications are there is significant benefit to doing this in terms of significantly lowering the rms racking error. Presently, I have only experience with the 125:1 gearbox, but a PEC indexing limitation seem to preclude using this high a ratio. Moreover, rpm limitations will drastically reduce slew rates. In the past some have worried that reaming out the very small pinion gear to 1/8th inch might be a problem. I did not find this to be the case.?

In conclusion I would defiantly suggest going to the 50:1 gearbox, but the sweet may well be the 80:1 ratio.

Reaming works well. There isn't much material to remove and a reamer will always follow the original bore so it's very easy to do. Here's a couple of pics when I did mine last year. Close up of the motor shaft.

Hi Vishal,

With a few years of experience owning both a G11G and a GM8G IMO the GM811 is not the value you may think it is as there is little difference in cost but that limitation in payload is right on the edge of needing the 60 pound payload of the G11G. I bought the G11 first and the GM8 as a second mount visual only. As tiem went on I updated the 2005 vintage G11 to a full house G11G with all options available and the G11 which was no slouch but inconsistent became a reliably excellent imaging mount with low PE hot or cold and with no need to adjust as was always the case with the Losmandy original classic 2-piece drivetrain. The GM8 is a great workhorse mount and as a matter of fact I use it a lot more than the G11 because I am in a visual observing group which is always so much fun I forget that I'm an imager. I updated to the GM8 to a fully optioned GM8G and it remains a great mount but it is really not a great mount for longer imaging payloads even though it easily handles a heavy 10" LX200 SCT, C11 SCT and heavy bespoke Parallax/AT130 apo and TEC140 apos. Get the G11G for the extra few hundred dollar more, it is not a lot heavier but it is a lot more stable and will carry your 130mm apo for imaging perfectly and leave you room to move up to that big 160mm apo or RASA-11 with confidence that it will carry them for imaging without a mount change. Trust me.?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astropheric Weather Forecast - South Pasadena, CA?