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This issue is part of what the Belleville disc springs resolves by taking up all backlash axially. the worm axels are sized as they are for the real world and ease of maintenance and replacement. These bearings are consumables and as such are replaced as they get dirty and noisy. For visual users none of this makes any difference at all as you can barely even measure a difference in PE using PHD2. But it is there if you want to "fix" it.? ? ?

--

Chip Louie Chief Daydreamer Imagination Hardware?

? ?Astropheric Weather Forecast - South Pasadena, CA?

Brett,

I'm sure you have solved this problem already, so this is for others with similar issue if stuck Allen key screw. I've found a driver works the best. You can buy driver hex key sets easily online. The hammer action does the trick without stripping the key hole.

Peter.

So, specifically here is what I would like to correct (it's not stopping me imaging right now, but I am tweaking software and balance each time etc)

This was over a single 15 min sub, so it isolates the data very well

The spikes down to -2.5 worry me Anything within 1" area which is most of the graph, I am not worried about

I noticed anecdotally it might have happened more often when the counterweight approached horizontal last time, so I moved my weight down a bit (East) but that seemed to have no impact. It's not a very big weight though

After two weeks of wonderful and badly needed monsoon clouds/rain over Tucson (heresy I know), I finally got a chance to test this simple hack when a part of the sky cleared near zenith. It turns out it worked very nicely with the guiding and motor loads. My DEC backlash is down 75% and RA guiding RMS is <1" in poor seeing. I decided to change the position of the DEC band to be in the same 45° position as the RA. This should give a bit more stability along the worm axis.

BTW - the reason you don't put a band on the block near the motor is due to that hole not having the adjustment clearance of the outer block.

Here are few pictures that I took to document the procedure (note high-tech labeling on the band from the local produce section of the grocery store).

This is an interesting read on what looks like a significant issue
/g/Losmandy_users/topic/g11_fix_source_for/21183709?p=,,,20,0,0,0::recentpostdate%2Fsticky,,,20,1,40,21183709
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On Fri, Jul 9, 2021 at 10:11 PM, John Kmetz wrote:

Each new worm new has a surface profile on the tooth faces right off the CNC machine, just as the rings gears do. Some have tried to use polishing compounds in the contact zone and other methods to wear things down a bit, but I don't think this was entirely successful. Letting the mount run over time is the best way to break in the gears as the surfaces will smooth down and mesh better over time.?

I have new worms running in both axis. I have no expedience to know how things change as they wear or how long that takes. To what extent are the one PHD2 tracking spikes a function of the worm surface? Does tracking improve or get worse as they wear in? Since I have a few worn worms I thought I might lightly buff one while spinning in an electric drill. I have to assume a polished worm has less friction/stiction.?

Another question I have is what effect do the needle bears have on the system. Do they have a frequency profile? I do have some axis movement. My rig is rather old, and I suspect these have never been renewed. However, it looks like a difficult job, not to be taken on lightly.?

Peter

On Fri, Jul 9, 2021 at 06:10 AM, Michael Herman wrote:

Alan Fang has that GM811 version and he is also investigating its behavior (or he is happy and his system is stable and in use).?

?

?

Alan, while visiting his parents in southern California, stopped by the humble Losmandy building and swapped out his G8 DEC axis for a G11.? They were very nice to give me a credit towards purchase of the new axis.? So now I am a G11 owner.
In the end, I had the G8 axis (while using a 40 lbs 10" F4 Newtonian) working "ok, but not trouble free".? Which means that on a day with good seeing, I could crank out many good frames in a row, but will occasionally have to cancel a frame before completion due to excessive DEC movement 30 seconds after a dither move, etc.? Given that it has a "resolution" of 1.x arc-sec, I would consider that it is good only up to 1000mm focal length and about 40 lbs.? The g11 has a worm wheel twice as big, so I expect all errors to be half as much, and a much better baseline to work from.

David,

You may be going over some well worn paths to better worm performance which sound familiar. Searching through the forum might provide more insight. If you had a deep nick in the worm, like the outer edge of a tooth, you would probably see a sharp spike every 240 seconds, or every time the worm goes round once and hits the bad spot. If you weren't seeing this effect, the nick was probably not that significant. The worm and ring gears don't ride on the points, but a bit further in on the teeth faces. If you try to polish the worm by hand, you most likely will not be able to evenly remove metal from just the right spots and you could knock it out of round, creating further errors. Each new worm new has a surface profile on the tooth faces right off the CNC machine, just as the rings gears do. Some have tried to use polishing compounds in the contact zone and other methods to wear things down a bit, but I don't think this was entirely successful. Letting the mount run over time is the best way to break in the gears as the surfaces will smooth down and mesh better over time.?

If one worm is doing less than desirable guiding, swapping with the Dec worm is a quick test for possible improvement. The Dec worm has less effect on motion as it rocks back and forth to make corrections while guiding, and really only spins completely around while slewing, and wears more slowly. The RA worm is constantly turning and therefore creates most of the periodic errors. Once you have things apart, you may want to try the Bellville washer modification to reduce the 76 second error. But now you are talking about disassembly and modifications which are not under warrantee.? But it sounds like you may have gone that far already.

Hope you get to where you want to be.

John

On Fri, Jul 9, 2021 at 04:57 PM, <pcboreland@...> wrote:

On Fri, Jul 9, 2021 at 08:06 AM, Nick Ambrose wrote:

I do see fairly often, RA going to +/- 1.5-2" deviations (usually it is well inside +/-1" on my graph

Nike,

It's those transients (or just one) that I've found are the real problem with loosing what would be great frames shooting long exposures. I'm working hard to eliminate them with success! You know nice perfectly round stars with a little brother or sister just of to the right.?

You may already have said already, but what is image scale is your guiding system??

Peter

Right now I have a very forgiving 2.2 arc sec/pxl, so in theory any blip I suppose under (approx) 1.1" deviation would expect not to cause any issues ? I am pretty happy with my images but I can't help but think these must have some kind of an impact

Peter,
Have no Idea what the RA blips are, maybe the worm nick?? I'm thinking the DEC blips might be a bearing glitch like the RA's 76 second error. They seem to be evenly spaced. Will have to time them.
Never noticed the worm nick till adjusting it. Spinning the gears while adjusting the bolt next to the spring, the worm stuck a little bit in the same spot. Took off to clean, re-grease and examined the worm, found the nick.
?

On Fri, Jul 9, 2021 at 09:51 AM, David Malanick wrote:

Have a new RA worm on order because I noticed a nick right in the center of the worm that was causing a slight binding when meshed.
Under a magnifying glass I used 2500 grit sandpaper to fix a bulge caused by it but it's still noticeable.?
Then I looked through the magnifying glass and saw it was a little rough, along with the whole worm.
Took some ultra fine automotive final mirror polish on a buffing wheel and polished the worm all around for a few seconds.
Will replace that repaired worm with the new one when it comes and check the results.
The nick in the worm seems to be guided out by PEC.
I'm wondering if polishing the worm had any affect in getting the results I'm seeing?

David,

Buffing the worm sounds like an really interesting idea. Also, I've found that nicks are so easily created just installing the worm. Brass is so soft. I'm at about 0.65 arcsec without PEC. I too know I can do better, Those little Ra wonderings in your tracking curve, what do you attribute them too?

Peter

Peter

On Fri, Jul 9, 2021 at 08:06 AM, Nick Ambrose wrote:

I do see fairly often, RA going to +/- 1.5-2" deviations (usually it is well inside +/-1" on my graph

Nike,

It's those transients (or just one) that I've found are the real problem with loosing what would be great frames shooting long exposures. I'm working hard to eliminate them with success! You know nice perfectly round stars with a little brother or sister just of to the right.?

You may already have said already, but what is image scale is your guiding system??

Peter

Sorry, the pics did not upload in order.
RMS Error in Px
.44"? jumped to .49"
.41"? jumped to .52"
Last picture guiding at .40" a goal I think is possible.
Seeing was average, checked and I was just on the edge of the jet stream.
Focal length is at 805mm with an OAG.
Know I'm just getting picky now but I am amazed at what this mount is capable of.?
I was between 2 garages, on grass with tripod legs almost fully extended to see over them, to get PA and then slew to DEC 0 for PHD2 GA run and a PEMPro run.

Have a new RA worm on order because I noticed a nick right in the center of the worm that was causing a slight binding when meshed.
Under a magnifying glass I used 2500 grit sandpaper to fix a bulge caused by it but it's still noticeable.?
Then I looked through the magnifying glass and saw it was a little rough, along with the whole worm.
Took some ultra fine automotive final mirror polish on a buffing wheel and polished the worm all around for a few seconds.
Will replace that repaired worm with the new one when it comes and check the results.
The nick in the worm seems to be guided out by PEC.
I'm wondering if polishing the worm had any affect in getting the results I'm seeing?

Might have to order a few worms and run some experiments.

I thought of the too!?
With a wider angle - that should be fine.
Thanks

--

Well I have done a bit of tweaking myself and believe I'm almost there.
I rebuilt my laptop from scratch so I didn't have time to fix a auto focus problem. So not in focus for last nights test.
After mount tweaks I ran PEMPro for 7.5 worm cycles.? Have to purchase, well worth the $150.
Guiding great, just a couple of hiccups to find.
You can see pic 1 then in pick 2 a little anomaly. Same with pic 3 then a little blip in pic 4.
Pic 5 would be my goal.

Does anyone know what would be?the selection in the Gemini II GoTo menus for the the center of Rho Ophiuchi complex?
Would you advise just going to the RA and DEC coordinates?
Thanks,
Tom

On Fri, Jul 9, 2021 at 06:10 AM, Michael Herman wrote:

Peter,

?

You have initiated many good experiments that have not been described earlier.? Like your alternative gearboxes over 50:1.? So you are pioneering new ground.? We all benefit from your research.?

?

If you have the tucked motors and spring loaded worm systems then your mount is past my versions of G11 and GM8.? Alan Fang has that GM811 version and he is also investigating its behavior (or he is happy and his system is stable and in use).?

?

?I think this is the end result of all our systems: when we image reliably with good results we stop, lock everything down, and just drive the mount.? It's like a cake recipe.? The work goes into the recipe then the recipe is "frozen".??

?

One last thought: having the R4 spring in place only works if the bearing above it can slide in and out by the spring force.? If the bearing gets stuck, the spring can't level the (far) bearing. What about the bearing nearest the gearbox? I've never fiddled with that one.? Could that one have a tight spot in its race?? Would undersizing that and lubing that do any improvement?? ?I don't think that area has been tried or considered.

?

I'm still awaiting some bearings with ceramic balls to arrive.? Hugo in Tehachapi told me he got some amazingly smooth tracking from full ceramic bearings (they were like $50 each) but I thought there would be no way to undersize their OD, so I kept the idea of using stainless steel bearing parts.? Maybe those ceramics he got are so perfect they don't need undersizing.? Anyway ... more experiments have been tried with further progress.??

?

Each of us uses different scopes, different cameras... as well as different latitudes, making our comparisons somewhat fuzzy.? We can compare our unguided PE peak to peak and RMS values.? We can show our exposure subs and final images.??

?

On other topics: The delta variant of Covid is being seen here in the US and is now in many places the dominant strain. Hospitalizations are going up, though still under ICU capacity (except in parts of Missouri?). And the initial vaccines are starting to wear off.? And the use of masks is waning too.??

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Stay well, all...

?

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Michael

?

Michael,

Thank you for your help this. There are still a number of issues needing to be locked down to achieve the level of performance one expects from expensive premium mounts (accuracy, no transients moves, very low noise for a clean accurate PEC curve). Through this path of discovery I have learned several important things that will greatly improve the performance of a mount like the G11 to get you in the range of around 0.6 arcsec or better plus or minus with a 35 to 40 lb payload (summertime). Here is my current summery of the important steps to take to improve mount performance:

1. Change the Ra coupler a one-piece rigid one to significantly reduce the 240s error. This unfortunately requires some engineering work.??Since it has a dia of 5/8" it will not rotate without the screws touching the sides in the OPW. I replaced the 4-40 screw with tapered ones, drilled out the coupler screw seating's to seat the tapered screws, and parred down the heads to as small as possible. They still will not clear the base plate so a hollow will need to be ground. I did this with a file. There maybe a 1/2" dia rigid coupler out there but I could not find one. My belief is if people have very large values it is due to misalignment of the worm and the motor drive shaft. The Oldham set screw coupler is the real problem here.?

2. Increase the number of steps per Dec worm revolution. Going to a 50:1 gearbox might be enough to overcome erratic PHD2 behavior in this axis. My suggestion however is not to change out the gearbox but rather the encoder as I originally planned to do before going off down the gearbox route. You have two choices 512 or 1024. I would opt for 1024. The nice thing about going this route is slewing speed should be preserved and you? not need to change the stock Losmandy gearbox.

3. Increase the number of steps for the Ra axis by 4x. I did this using a McLennan 125:1 gearbox (5x). This gearbox has really nice high frequency characteristics, and a large pinion gear (same as 25:1 McLennan gearbox), but the slew rate will have to be dropped down to 160 - 200. Again, I will in the future explore changing over to a 1024 encoder and use the McLennan 25:1 gearbox. This gearbox does not have the large 32s error component of the stock Losmandy gearbox. The other important thing is increasing the number of steps per worm revolution allows one to create a high resolution PEC curve. I've demonstrated that the Gemini II controller will accept a curve with 32000 steps, contrary to what was previously thought. Elimination of the higher frequency noise components does allow a very precise PEC curve to be created, which I've demonstrated to myself using PECPrep. However PEMPro is required in? order to sync and download a PEC curve.?

With that said, I want to reintegrate that the easiest way I think to to make these improvements is simply to change the encoders. I have not done this but will be doing this in the near future. I feel this is important to do for completeness. I have an 80s error problem as previously noted in earlier? (possibly from the gearbox), which should be removable via PEC. Just in case anyone is wondering, these mods have not caused me to loose any imaging time. As an engineer I want to explore the boundaries of what is possible with this mount. I will be loading it up with 70 - 75lb payload soon, and the way it performed previously would have forced me to give in up and lay out for a premium mount.

Work planned:

1. Take measurements with PEMPro generated PEC curve,
2. Take measurements with and without spring loading the Ra worm.
3. Find source of the 80s error.
4. Take measurements using higher res encoders with 25:1 gearbox so slew speeds are preserved.?

Peter

Also, usually I measure eccentricity on subs, but I just extracted a lightness of my 2x drizzled data that I ran background extraction on (the luminance portion as extracted by Pixinsight) and the eccentricity was 0.399 and to my eye, the image looks like it.

I don't think I could ask more than that

Thanks you both, Brian & John

In my opinion, my images look amazing (for my level of experience at least - I am far from an expert here)

My FWHM & Eccentricity are a bit higher than I'd like but I dont think this is anything to do with the mount. I used the "Carey" mask after auto-focus and unless I am mistaken, it was perfectly in focus, so any increase in FWHM above what I want is due to my gear and conditions

Similar on the eccentricity, it's in the low 0.5s which is good, but not 0.4s. I think this is the "duo-band" filter mostly as well as a little bit of sensor tilt I think I saw using the CCD tools.

My guiding RMS is fantastic, even for a less forgiving imaging train

These are the results from 4.5 hours of guiding the other day