开云体育

OK, it happened again.? This time, that PHD2 checkbox was clicked.
All I did was GOTO (under stellarium) a nearby star to center in the field of view for focusing.
Then the mount started running away with no STOP button.
I ran over and shut off the mount.
Then warm restart.
Reconnect under Stellarium.
The mount knew where it's new position was, so therefore I don't blame an uncontrolled motor.
Manually slew back to original position.
Plate solve.? Yup, the reported position was correct.? However, the DEC axis didn't move, only the RA, during the runaway.

Peter,

If I am understanding what you are doing here you now have 3 bearings with less play replacing the looser original 2. Each of the new bearings has less freedom for the shaft to rock up and down or back and forth, or any direction. Therefore each bearing needs to be more perfectly centered on axis to allow free shaft rotation. The present bearing seats may not have that level of alignment precision, one could be off center from the rest, or perhaps tilted at an angle. Therefore when you are locking down the clutches, you are further pulling in any axially play. Now you could have a situation where the shaft is being pressed in from the sides by the needles being at different distances from shaft axis center and you are creating pinch points. I agree with Alan that you should be testing shaft rotation by hand with no worm engaged to see if you can still rotate with normal forces, and not binding up under pressure. You might be reducing shaft play, but don't have enough tolerance left for normal shaft rotation.

Just thinking out loud. You would need to test torque values to confirm what your adjustments/modifications are actually doing.

Best regards.

On Sat, Jul 17, 2021 at 04:36 PM, <pcboreland@...> wrote:

I think I may have discovered something interesting regarding why it is so difficult to both reduce and get a consistent backlash value for Dec.

After changing out the needle bearings, and adding a third, I noticed how stiff the worm gear was to turn after I had tightened the clutch. When I later measured my backlash I had actually gone from 2500ms to close to 4000ms, even though a visual inspection of the mesh seemed good. Actually, I set the mesh with the clutch undone, using finger feel to sense if the alignment was good (no high-low spots) and little to no blacklash. The loading placed on thrust bearings seem to be were the problem resides. I ordered new clutch plates and just received new thrust bearings from McMaster- Carr. I'm concerned by the stiffness and I think this means considerable pressure has to build up before there is any rotational movement in the worm. This pressure (force) has the created in the gearbox and coupler. This is both bad for the gearbox and means a large backlash.?

Peter

This is totally expected.
Remember I said there were three concentric parts of the DEC axis:
a) the saddle and 1.25" shaft
b) the assembly that holds the ring gear (which I have never taken apart, so I don't know much about it)
c) the black outer anodized body

Part b) rides on it's own set of bearings that you don't see.? When everything is put together, tightening the clutch knob pulls a) downwards against c).? The clutch pad itself pushes b) downwards relative to c).? Well, c) holds the worm and b) holds the ring gear, so you'd expect the ring gear to move down a LITTLE bit, depending on what the bearing preload characteristics are.?

With that said what's important for low backlash is that the axis still turns freely when the clutch is engaged.? To test the b) bearings, remove the worm (or push it out of the way), loosen the clutch knob all the way, push down hard on the saddle dovetail with your palm, and see if the axis still rotates freely.? All bearings should rotate with minimal friction, and even the innermost needle bearings because they aren't loaded by the weight of the scope and counterweights.

Next, with the worm still out of the way,? Pull UP hard on the dovetail and try to rotate it.? Now you are testing the needle thrust bearing that is part of the clutch knob assembly.? BTW, did you rearrange the spacers so that there is a thick spacer between the wavy washer and the thrust bearing?? Because that would be pretty dumb to have the wavy washer pushing against the bearing surface.? (There should be a set of rollers and two thin plates for the bearing assembly, and a correct orientation)

Next, start to tighten the clutch knob and see if the friction increases.? On my G8 DEC axis, it increased a little bit, but on the G11 it is still fairly free to turn even with moderate clutch pressure.

Finally, with the worm still out of the way, load up the counterweights and a sacrificial scope ;) to see if the DEC spins freely with the clutch tightened somewhat.? NOW you are testing out the inner needle bearings with a realistic radial load.

With all that said, adjust the worm pressure / spacing with the clutch engaged the "usual" amount.? Also, yes, too tight worm mesh can increase backlash.? Also, too much axis friction can increase backlash.

On Sat, Jul 17, 2021 at 12:49 AM, "Guilherme Vênere wrote:

Alan

?

How do you have your mount limits configured? Did you use the default limit or MI-250 or did you customized them?

?

I had the same issue as yours and it fixed for me after I changed the mount limits from the default?

?

Guilherme?

Eastern position: 100
Western position:112
Western Goto Limit 2:18

Alan,

This really sounds like the issue I has 3 years ago when the Beta ware was created. I had runaway slews when GoTo commands were sent from SGPro. At that time I recall sending my Gemini logs to Rene G. in Europe who interpreted and wrote the work around. This may be a communication issue between apps. Why the same fix does not work for you might involve some code analysis, which not in my skill set. You might see if you can get HGM to involve the appropriate parties and what they might need from you to proceed. Or if there is a second Windows machine you can use to operate the mount, you may want start fresh. I have had cameras that would not operate on my laptop, only to work fine from a new dedicated desktop. Each had the same software packages but only the latter would work. Hope you find a solution.

JK

I think I may have discovered something interesting regarding why it is so difficult to both reduce and get a consistent backlash value for Dec.

First, while out in the field disassembling my mount for the umpteen time, I had a very close call. Focused on the work at hand, I did not notice a thunderstorm moving in over head. Once I became aware of the suituation, I closed the observatory roof and started heading back to the house, when I felt a strange sensation, followed by a crackly noise, and I immediately hit the group. Almost instantaneously I heard and felt the crack of lightning. Several minutes later fire engines arrive at my neighbors house less than 800 feet from where I was standing. I never thought of this as a dangerous hobby?

After changing out the needle bearings, and adding a third, I noticed how stiff the worm gear was to turn after I had tightened the clutch. When I later measured my backlash I had actually gone from 2500ms to close to 4000ms, even though a visual inspection of the mesh seemed good. Actually, I set the mesh with the clutch undone, using finger feel to sense if the alignment was good (no high-low spots) and little to no blacklash. The loading placed on thrust bearings seem to be were the problem resides. I ordered new clutch plates and just received new thrust bearings from McMaster- Carr. I'm concerned by the stiffness and I think this means considerable pressure has to build up before there is any rotational movement in the worm. This pressure (force) has the created in the gearbox and coupler. This is both bad for the gearbox and means a large backlash.?

I will post my findings with the new parts next week.

Peter

I used one of those cheap $3 mini laser pointers at the hardware store, designed to make a spot for harassing / entertaining your pets.? It's about 3/8" diameter and 2 inches long.
I used a binder clip on one of those transfer gears and just put the laser on the binder clip.
For the worm, you'd clamp onto the bare exposed portion (obviously not the helical part), or if there's not enough room, maybe use something narrower like clothespin, etc.

I doubt there is a hardware problem
Both motors slew when this happens
Stellarium keeps reporting the crosshair position as it goes flying off, so the mount is clearly "telling" it that it's doing so
I use a 15V regulated power supply

As of yesterday, I had the "stop guiding when mount slews" checkbox on in PHD and the problem hasn't happened since.
Maybe Gemini gets confused when it gets both a guiding pulse and goto command at the same time?

Show a screen shot of PHD with these oscillations, and I can tell you.
It could be "forwards-lash" from a too tight worm mesh.
Or axis stiction.

The way to tell if you are getting good guiding or not is to see if the mount responds to corrections.
Since you still left the corrections checkbox turned off, I don't know.

Change the y axis to +/-4” and it will look much smoother! Seriously though the RMS pixel values are only 1/3 or 1/5 of a pixel, so even if there are some variations in RA I don’t think it will affect the final image unless you are imaging at high focal length.

From the picture it appears that you're getting 0.28 rms. Is that right? The best I've seen is 0.38 and I have a gm811g with the lightweight tripod. I usually check my focal length setting when I see rms better than I expect. I calibrate at the south equitorial at the beginning of each night to get best results.

The onstep sounds like a great and satisfying project!?

I don't know what to tell you, but I had some spikes in Dec, and I tightened it up and they disappeared. I think that the clutches should be cleaned when they start slipping like this, or you can get the special ones from Michael that handle some grease.?

Sorry I'm struggling to download, upload and get a proper resolution.? Here's a link to a better version in an album, I hope this works.

/g/Losmandy_users/photo/266134/3266050?p=Created,,,20,2,0,0

BTW here's an image of M39 from 20 subs that I took while observing these oscillations, letting DSS select the best 50%.? I think this is a turning point for me.? It proves that Ekos on a Pi with a cheap and simple DIY OnStep controller with no gearbox and simple DIY SLWs performs fine.? Of course the hassle of putting it all together, which takes a major amount of testing time, to get there.? But for me it's part of the fun, and satisfying.

No Stop Button? Haven't heard that one before.

Perhaps a power issue. Is the supply yielding 15V and enough amps? Then you might be talking cables or electronics, as Paul mentioned. This might be a factory job or a Service Ticket.

If Stellarium is a cause, don't use it. I get to targets with SGPro's Framing and Mosaic Wizard, or use the Catalog Objects right in the Gemini app. Or enter the coordinates from another source like Astrobin or Telescopius.

Last night I was autoguiding and DEC started periodic oscillations every 100 seconds or so while RA was fine at 0.5" RMS.? After I loosened the RA and DEC clutches a bit (I like to have them real tight) the vibrations went away and DEC was normal again.? Is this a known phenomenon, and if yes is there an explanation for it?

BTW This is the first time I counterbalanced in RA and I saw the RA error RMS cut in less than half leading to a total RMS of 0.6 to 0.7, sometimes dipping below 0.5.? It is major feat for me, of course I knew this is what everyone does to reduce the RA error.? This is with Ekos and OnStep with a 12" Newt and OAG with DIY SLWs.? I'm finally coming to grips with this modified G11S so I'm looking forward to repeating this on a regular basis.? My goal is to be around 0.5" total RMS.