oh right, another thing is that it STILL takes about 15 seconds after a dither move for the axis to "settle down".? ? Whereby "settle down", I mean that guiding is reliable again without any sudden unexpected moves.? Maybe NINA or PHD makes the dither move too suddenly?? I know from adjusting the focus knob that it only takes about 3-4 seconds for the scope to stop vibrating.

Hello again,?
I thought that maybe there would be a lot to say, but there isn't.? The G11 DEC axis seems to work well over a fairly wide range of worm meshes.? Maybe because it has low friction even with a medium-tight clutch, and so it can rotate with minimal stiction, hysteresis, etc.? If the mesh is too tight, the backlash test will show an initial rise (just like I showed with the G8 axis), and the guiding will show characteristics of "forwards lash", where PHD will try to push the mount north, but instead it will move south even further before suddenly snapping back.

On the other hand, I made the mesh looser and looser until it was obviously rattling, and the PHD test and guiding were still good.? I think this is because my scope setup is "right side heavy", and so it always wants to rotate the DEC axis clockwise when viewed from above.? In this instance, only one side of the worm teeth are loaded, and you are pretty much running it like an "east heavy" RA axis.? Probably this method reduces worm to ring friction.

I did these tests with TVC = 10 and at large deflections there is almost no hysteresis, so maybe this value is at risk of being a little too high.? Usually these backlash values (as called out via a single number via guiding assistant) range from about 400-800ms, and turning off TVC adds another 7-800 ms.? It's a shame that PHD backlash test won't use smaller than 500ms steps, otherwise we could see better what happens at the initial turn-around point.? I think the ideal worm mesh will be what makes the backlash plot turn around as soon as possible, even if there is some backlash gap at larger displacements.

The only remaining problem is that even the lightest puff of wind will cause the axis to go off by 1-2 arc-sec.? Then again, I am using a BIG 12" F4 tube newtonian.? Perhaps if I increased the weight imbalance for more DEC preloading, that would make it "stiffer"?? I've also been slowly tightening the worm mesh to hopefully find the point where both sides of the worm teeth just start to engage.? Perhaps this is the "correct" worm mesh, and would require an infinitesimally light pressure if the worm were truly "spring-loaded".

开云体育

Thanks for the tip.

Thanks for the write up.? I did not know the ring gear sits on only a needle thrust bearing, and effectively a bushing sleeve.? I would have thought it used a bearing for radial constraint, but ok, whatever.
As long as it can spin with low friction.

I'll definitely look into PEMPro, Brian also mentioned the Oldham coupler misalignment so that's already someting I'm looking to fix. Hopefully that will get this to be good enough but if not, the Belleville washer upgrade doesn't seem too dificult from what I've read about it.?

The thread is probably 1" x 16tpi.? You can confirm by holding one of Losmandy's 3/8" x 16 tpi bolts up to it to check.

On Sun, Jul 25, 2021 at 02:35 PM, <pcboreland@...> wrote:

Paul,

I'm somewhat mystified why you set your TVC value to zero when imaging. And what do you mean calibration in both directions?

The purposed of TVC as I understand things is to nullify Dec backlash. Just as an autofocuser has a similar backlash correct facility. If your guide rate is say 1s, and your measured backlash greater than 1s and TVC = 0, then you are unable to make a Dec correction before the next pulse comes along. This will surely leave to over correction. If backlash is say 2s, then using TVC it's possible to zero out the backlash entirely I've found. However, PHD2 cannot issue pulses shorter than 20ms, so in practice I think it would be best to shoot for a backlash of 50ms. This value of 50ms though cannot be measured it seems by the guiding assistant, but has to be determined adaptively. I look at the value after about 1hr of guiding. In the guide log I posted the backlash was measure at below 20ms so I'll need to reduce the TVC value. My value of 70 is equivalent to 17.5 at the 0.56 arc-sec step rate. I am interested in seeing where I end up. One thing is clear I'm not touching my Dec worm from her on. It's locked down:)

Peter

Peter, there are some things that are too good to be true :) TVC is useful for visual, but more often than not results in sub-par guiding performance. The reasons are complex, but here are some, from my experience:

1. TVC/backlash is needed only when reversing DEC direction
2. Reversing DEC direction is a pretty complex mechanical operation. There's change in torque, change in speed, change in motor duty cycle to speed up and slow down, change in all between all the gears and slack in-between them. Remember, you're reversing the direction of your entire telescope and counterweights -- this is a hard process with a lot of variables. The heavier the scope, the harder this becomes.
3. With any amount of polar misalignment (even a tiny one), your DEC axis will be mostly lagging behind or getting ahead. If your guide corrections are not excessive, you'll very rarely need to reverse DEC corrections. You just need to keep correcting at the same rate and in the same direction 4. As been noted before, the amount of backlash varies with the physical OTA position and weight distribution. You're just as likely to undershoot (which is OK) as overshoot (not OK) with any specific TVC setting at different positions in the sky

If you ever try to guide with one of the DEC directions switched off (the one that's not needed for correcting for polar misalignment), you'll see why TVC is really not necessary. You mostly don't want to, and mostly, don't need to reverse DEC directions, at least not frequently. You also don't want to correct with a full aggressiveness of the guider to avoid overshoots. For all these reasons, I prefer to leave TVC at zero.

And no, I never measure backlash from a guide log. There is too much noise in the data guiding for me to trust the results. Measure backlash directly, using a guider and a watch, or do a guider calibration or special tools that exist for this purpose.?

Regards,

? ? ?-Paul

On Sat, Jul 24, 2021 at 02:40 PM, Paul Kanevsky wrote:

On Sat, Jul 24, 2021 at 05:07 PM, <pcboreland@...> wrote:

Regarding TVC value, I think yo are right. I knocked it down from 90 to 70, but even so the min value selected was 20ms all said and done at the end of the session, which is as low PHD2 can go. You can see the Dec oscillating. I'll reduce it further, but at some point you have to go image something,??

I always leave TVC set at 0 when imaging. When I need to calibrate the auto-guider, I set the TVC value that results in about equal calibration in both directions. Then I turn off TVC for the rest of the session.?

Regards,

? ? ?-Paul

Paul,

I'm somewhat mystified why you set your TVC value to zero when imaging. And what do you mean calibration in both directions?

The purposed of TVC as I understand things is to nullify Dec backlash. Just as an autofocuser has a similar backlash correct facility. If your guide rate is say 1s, and your measured backlash greater than 1s and TVC = 0, then you are unable to make a Dec correction before the next pulse comes along. This will surely leave to over correction. If backlash is say 2s, then using TVC it's possible to zero out the backlash entirely I've found. However, PHD2 cannot issue pulses shorter than 20ms, so in practice I think it would be best to shoot for a backlash of 50ms. This value of 50ms though cannot be measured it seems by the guiding assistant, but has to be determined adaptively. I look at the value after about 1hr of guiding. In the guide log I posted the backlash was measure at below 20ms so I'll need to reduce the TVC value. My value of 70 is equivalent to 17.5 at the 0.56 arc-sec step rate. I am interested in seeing where I end up. One thing is clear I'm not touching my Dec worm from her on. It's locked down:)

Peter

Ken,

Polishing the male thread is a common trick used in auto garages where the bolt won't quite fit into the hole anymore. Often it the very tip where the damage is and if you can buff that out you should be able to get it started. When I built my pier I needed some custom bolts, so I cut down 3/4" threaded stainless rod and then ground, tapered and polished the ends to get the nuts to screw on. As Michael H. said, we don't know the thread pitch which HGM uses, so unless you have a thread gauge, you won't know which large tap and die set to use. It could even be a proprietary size the factory uses to discourage parts substitution.? A clean and polish, followed by some grease, should allow you to eventually thread in. Just go slow one step at a time, and if you feel resistance, back out and try again until you get the bad spot. A rotating brass brush might help with the inside threads. Stainless is fairly hard, so you probably won't take off metal too quickly with brass bristles.

Good luck.?

Jeff,

The best way to actually get this equipment sold is to split it up.

I'm interested in buying the tripod and @PCBorland is interested in the mount.?

You will end up money ahead to do it this way.? ?

I don't have a way to PM you so please send me an email at mikeby.miikeby at (the service is gmail)??

or you can reach me on Cloudy Nights.?

Michael..

Hi Ken,

If you found metal then there was some type of debris or cross threading. Since this part has close tolerance you need to clean out the debris from the mount as well as the threads on the counterweight bar. Be sure everything is completely dry and then lubricate the male threads with a very thin coat of bearing grease before attempting to thread it in. Never tighten it beyond the point where it is just snug. If you hit any roughness.. go in a 1/4 or 1/2 turn then back it out and clean off debris then try again. You may have to run the threads a few times and clean the male threads after each time. Once you can thread it in smoothly for future use use a bit of anti-sieze on the threads to prevent tempurature change from locking the two pieces together. If you don't have a rubber strap wrench, a leather belt will do the trick? loop the belt around the shaft and pinch the two ends where they meet then fold the belt over to the left or right and wrap the two ends around together.in the counter clockwise (loosen) direction. Then as you squeeze the belt and twist the belt will tighen against the shaft and give you some leverage and grip.?

Old trick.. works though.? Rubber bungee cords work too!!

If it continues to cause problems, you'll need to run the threads with a tap and dye to smooth the threads and cut them in a bit. I wouldn't polish the male thread edges down though. The problem is the threads aren't cut quite deep enough on one piece or the other so the fit is too tight. Impossible to know without a proving nut which side has the issue.?

You'll best call in for some support at that point. Could probably figure it out with a close inspection of the threads. If the top edges of the thread are a bit squared off and not sharp, that side isn't cut deep enough. However there could be other more subtle problems. In any case, fixing it should be easy but only if you have the right tools.

M

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Michael

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Vishal,

Your 120 and 60 second errors are integral of the 240s worm period so a PEMPro PEC correction curve might do so good to even these out. If the 120s error is very large and the Oldham couplers need some adjusting you might get some better alignment loosening the button head screws as seen in the following pic, and moving around the base plate a bit. But the 76 second error is non-integral and won't be helped by a PEC curve.

The 76 second error is always the worm bearings and to minimize that you can try to squeeze the right worm block toward the left and get the balls riding better within the races, after loosening the block screws. Other than that you can try the Bellville washer modification as discussed here many times. Search for 76 second error in the forum and you should find a plethora of information.

Hi Brian,
Thanks for your response. Yes the fine copper wavy is there under the lock collar to keep some spring pressure against the polar scope. the collar and setscrew were loose when I bought the mount. I only discovered this today in what is really the first pass over what I've got.?

The problem is that the silver focus lock ring hits the RA axis shaft which becomes the stop rather than the lip on the edge of the polar scope against the back of the RA clutch.?

Installed a new 0.128" thrust bearing in place of the 0.030" bearing and the extra 0.098" was just enough that the scope seats against the clutch now. So I have a 0.10" and a 0.125" installed and its just to the point of OK. The roller assemblies were both? 5/64's .so I put in a new one.

Whatever the grease is on the axial bearings it might be too thick.? I cannot put a wavy ring in with the clutch pad as there is no grove for it.? I have a brass center there.

Not sure about the age of this mount.? It's got a Gem-1 ver 3 (last one) controller but for all I know it was an add on.??

I also found that the RA clutch is was feeling rough threading it on and off because at least one of the screws holding the handles was a bit too long. It was intruding on the internal threads and was catching the threads of the RA axis as the clutch was being threaded up the shaft. It's a knurled rather than scalloped? collar so perhaps that tells you something about the age. Quite annoyed at that. as with the other issues.15 mins with a sharp file and the screws are now fixed. and the threads have been run through to clean it all up.?

The last thing I found in today's venture into getting this mount ready to use was that the screws that lock down the altitude adjustment are also too long.? They hit each other before pressure is properly applied to lock down the altitude.adjustment.? It looks like the seller had added a couple of washers (they do not appear to be stainless,? but it still wasn't enough. I've yet to trim those screws down. That will be a task for tomorrow.?

What surprised me was that the Seller said the mount had been serviced in 2019. He lives 20 mins from Burbank so I can only imagine he brought it in to Losmandy for this. These kinds of things should have been caught and fixed.because they are pretty obvious but who knows. A lot can happen in a couple of years, even with a pandemic! . There's always something.? It would be interesting to see the service history. though if there is one.

Thanks for the info on the lubricant. I've used Superlube and Phil Wood's green #5 for roller bearings and a few other nore exotic things but not Arctic.

?

Attached are a couple of pics.?

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As a second note, I'm finding that the RA axis is a bit stiff. There is plenty of lubrication on the axial needle bearings. Perhaps too much. The lubricant is a whitish material with a tinge of red.?

I have to fully release the clutch to the point of loose thrust bearings to get the axis to swing CWD with no scope and only the counterweight bar. I'm not sure if it's the clutch dragging or that the lubricant is too stiff for the bearings or that the bearings are worn.? Suggestions welcome. What's the best lubricant for these axial bearing???

?

Thanks again..
M

Hello,?

I just bought a G11 and am working through it's issues. I know every mount has it's quirks, but some of these I didn't expect.

RA axis the polar scope locking collar was very loose. So I snug it up and make sure I can still rotate the scope but that there's no play.?
Then I tighten the RA clutch and discover that the polar scope can no longer be turned. It's pushing hard against it's locking collar. I had noticed that the scope
turned with the locking collar, which I did not expect. but this was something else.? Relaxing the clutch the polar scope frees up.? I remove the polar scope and tighten the clutch
again. This time i look at the polar scope and eventually discover that the silver focus lock collar is hitting against the RA axis shaft. The only solution is that there must be a spacer missing.?

I go ahead and pull apart the RA drive check the internal bearings and clean the clutch plate and surfaces to get rid of slippage. I discover that the two thrust washers are of different thickness. One is 0.10" and the other is 0.03" . I have no idea if this is correct.? ?The seller had given me a small box with some parts.? In there I find 2 thrust bearings and 2 thrust bearing roller assemblies. The thrust bearings measure 0.125". thick.

Can someone tell me what the thrust bearing thickness is supposed to be?? If I change the .030" bearing for the .125" bearing there may be just enough space for the polar scope to seat correctly.?

Thanks in advance..

Michael.

Ken,?

You may want to carefully inspect the threads on the bar, especially towards the end. Make sure there are no nicks or flat spots on the high points on the threads and that they taper into somewhat of a cone section at the very tip. If you see something you can carefully file out any metal debris inside the thread depressions. If it were me, I would probably wire brush the threads on a wire wheel to polish them down very slightly, after correcting the nicks. Start gently so you don't remove too much metal, and recheck fit.

But then you might have have debris inside the female portion you want to brush out, like Michael said. You could try a toothbrush first, then a brass bristle brush or a steel brush if that doesn't work. Then flush out with WD40 or some GumOut JetSpray carburetor cleaner, followed by compressed air, if you have that.

You probably got some dust or sand contamination in there, common for operations in the dark.

Good luck!?

?