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Last night my sequence failed at the end of the night and my mount didn't stop tracking and park. It was stalled on the hardstop for at least 2 hours clicking away. When I started my sequence tonight this is what the graph looked like.  |
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Worm or worm wheel is damaged.
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MaksPower: I have my doubt on that, I took it completely apart and there is no visble damage, the worm is hardened steel and I flipped the spur gear 180 degrees, same issue. Besides, neither can move when its on the mechancal hardstop. |
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1 arc sec equates to 1 micron at the radius of the worm wheel. The guide log indicates it now has a defect approx 6 microns. Defects that small cannot be seen. The mount will never track as it did before. You figure what that means. |
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Theres a worm screw and a spur gear. MaksPower: There's a worm screw and a spur gear. 2 different things. If the mount is completely stopped, and there was any damage (from what? ) the damage would be localized. If I moved that whole spur gear 180 degrees there is no longer any part of that gear in contact with the worm screw. The mount only rotates 180 degrees +- 10. It would still be localized to the damaged area. |
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The damage is to the worm as well as the gear. the clicking noise is the worm jumping over the teeth of the worm gear against the spring that pushes the worm against the gear. |
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MaksPower: Possible but it would still be localized to the area it was sitting on. I still find it very unlikely to have it damaged not moving. Worm screws move thousands of revolutions and are constantly expanding and contacting and wearing with minimal overall impact. |
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MaksPower: Have you taken apart the CQ350? the knob actually locks the worm in place. Once engaged they cannot move out of engagement. PXL_20240810_102419620.TS~3.mp4 |
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It’s spring-loaded. When it clicks the movement against the spring can be felt at the green knob. Replacing the stepping motor won’t achieve anything. |
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MaksPower: watch the video, the only springs is when you release the knob they disengage the worm. A cam keeps it locked in place. |
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MaksPower: I was reading your posts on CN, its pretty ridiculous that the stepper motor doesn't have some sort of control to stop it from trying to move when its stalled. I had thought the stepper was slipping but after making a long video It just continually works away fighting the gears, it didnt look like it was skipping but it was grinding away and there are flakes of metal. I never had the issue with the EQ8 even though it stalled many times in the cold when the tolerances changed but I also didn't leave it sitting there for 18 hours. With that said, this will likely be the last time I get a SW mount. |
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In that video clip there is something that is a really really bad sign - what are the bits of junk all over the worm wheel (see arrows), and how did they get in there ? Those gears are supposed to stay meticulously clean. I suspect there's the evidence for what actually happens. If those are metallic and end up in the teeth it's not surprising if guiding was unpredictably bad.  |
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MaksPower: All those fibers you see are just organic plant fibers. I am surrounded by farmland and my own poplar trees and it gets dusty year round from plowing and harvesting. Its not a concern. These mounts aren't as sealed as one thinks, the EQ8 is even worse, completely exposed spur gears. I have had 8 mounts and have never had an issue with one except this one time. |
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Matthew, in the CN thread at post #400 someone received advice from Skywatcher confirming the worm will jump over the teeth of the worm wheel. I am trying to decide how best to prevent this, as these are not cheap mounts. |
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Matthew Proulx:MaksPower: Do you have a link to that thread on CN? It's my understanding that steppers can tolerate being stalled, because the coils are always powered anyway. What's the period of the error spikes in your phd2 graph? You can use a tool like PECPrep for detailed analysis of periodic errors. |
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Victor Van Puyenbroeck:Matthew Proulx:MaksPower: *** This is the thread https://www.cloudynights.com/topic/862983-skywatcher-cq350-owners/page-17# The periodic error has become unmeasurable now, the RA is so sporadic it's all over the board. Skywatcher contacted me back and they say the mount is definitely damaged after stopping on the hard stop and have sent me a shipping label to have it sent to them for repair. Seems they know there's a fault in this system. I confirmed that the stepper motor just keeps turning by driving the worm gear against the spur gear like Makspower said. It doesn't jump any gears from the few minutes period I recorded but it definitely is smashing against them and causing metal wear, I removed many flakes built up around the worm. I would have thought the stepper would slip but it doesn't. |
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Very interesting to read the comments in that CN thread, thanks! Matthew Proulx:MaksPower: The worm does not appear to jump over the spur gear teeth in this video. In order to do that, the worm should first rotate a significant amount and I don't see that here. The clicks in that video are very fast, way faster than a worm revolution, could another part of the belt drive be damaged? |
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Victor Van Puyenbroeck: Watch the drive gear, it's clearly moving slowly but surely, it will keep applying pressure until no more metal can flex and then something will have to give. Whether it's grinding the gear, skipping a gear or slipping the stepper. I watched for 10 minutes at a different point and it did not stop moving, when I released the RA knob it was under a large amount of tension. Damage will be done wherever something can no longer give. When I first made this post I was under the impression that the stepper simply didn't have enough power to keep driving without slipping first. Well that was wrong and the seem to have ample power to do serious damage. We will see what skywatcher says when it comes back and whether they actually fix it or not. |
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I had the CQ 350 PRO the very first day mount came out. I'm the first to buy it in France. I use it for a long time now and tested many things cause there was no support or tutorial about CQ at this time. There are 2 things to know about CQ 350 PRO :
About the worm gear and wheel : until you have not had a clear night with stable sky (when you can obtain a 0,37" RMS for night) you don't know if they are damaged. But from my experience, those parts are almost undestructible. And I'm gonna explain why : They steel made, not copper alloy. One night, I had "jumps" in guiding. With regularity in the cycle. So, I made more tests. It appeared that my worm gear and wheel were a little bit too tight. And with the mount opened, I observed the phenomenon in the goal to fix it. And this is not the worm and wheel who were "jumping". In case of too much load/torque, the stepper motor is "jumping". And it makes the same noise. So, how did I solved the issue? Re tuning the play by giving a little bit more lose. The next night, over 240 x 60s sub, 2 had guiding issues instead of 35% to trough...just saying... Try to re tune your wg/w because in case of end strop blocking, the play moves. And needs a fine tuning. Are the stepper motor damaged? I believe they are not. My advice is : your guiding at 0,65" RMS is still good but depends on the reference : the guiding star and the atmosphere's stability. And we know CQ is sensitive to atmosphere's stability. And when you have (real) discussion with EQ8R (or RH) owners, they have the same kind of problem and result due to turbulence/stability. My 2 cents, |
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Watch the drive gear, it's clearly moving slowly but surely, it will keep applying pressure until no more metal can flex and then something will have to give. Whether it's grinding the gear, skipping a gear or slipping the stepper. I watched for 10 minutes at a different point and it did not stop moving, when I released the RA knob it was under a large amount of tension. Damage will be done wherever something can no longer give. When I first made this post I was under the impression that the stepper simply didn't have enough power to keep driving without slipping first. Well that was wrong and the seem to have ample power to do serious damage. We will see what skywatcher says when it comes back and whether they actually fix it or not. Just re-tune the play between worm gear and wheel for a good start. A first tuning without payload, then a second one like "in situation", with tube and all equipment. Sometimes there are differences between under payload and no payload. With payload, you will ba able to fine tune your mount. Then in PHD2, you redo a PEC calibration on a star and let trun for 15/20 minutes. You should recover a good guiding, then. |
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Philippe Germon:Watch the drive gear, it's clearly moving slowly but surely, it will keep applying pressure until no more metal can flex and then something will have to give. Whether it's grinding the gear, skipping a gear or slipping the stepper. I watched for 10 minutes at a different point and it did not stop moving, when I released the RA knob it was under a large amount of tension. Damage will be done wherever something can no longer give. When I first made this post I was under the impression that the stepper simply didn't have enough power to keep driving without slipping first. Well that was wrong and the seem to have ample power to do serious damage. We will see what skywatcher says when it comes back and whether they actually fix it or not. *** This is not a case of bad guiding or needing to be re-tuned. I have 4 eq6 mounts and an eq8 mount and have tuned them all. I adjusted the worm and gear mesh. Guiding went from .3" on both axis to 4" spikes on the RA the same day the mount was locked up on the hard stop. That's no f*****g coincidence. Even after taking everything apart and cleaning it and adjusting gear mesh it didn't change one bit. It also loses tracking claiming there might be snags. Nah it's fuckered somewhere. It's on its way to skywatcher already, let them deal with it. I'm done thinking about it. |
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Philippe Germon: In a typical spring loaded worm gear design, the worm, reduction gears, and motor are all part of one floating assembly. Based on what I've read on CN and in this thread, this worm gear assembly can be moved up or down by a cam attached to the locking knob shaft in the CQ350 design. This allows the user to engage/disengage the worm. How did you tune the worm gear/worm wheel? It looks like there are 2 main spring adjustment screws and 2 distance locking screws on the plate between the locking cam and worm gear block https://philhart.smugmug.com/Astro-Equipment/Sky-Watcher-CQ350/i-zMDHWKC |
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Victor Van Puyenbroeck:Philippe Germon: *** There's 4 Allen screws(2 push, 2 pull) that allow you to adjust the worm up and down inside the assembly, independent of the cam. You should run the mount both ways while doing it, it doesn't take much to grind gears. |
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There are more than 4 allen screws. There are also 2 allen end stop screws for the lower (wg/w ON) position 2 allen end stop screws for the upper position (OFF/disengaged) and 1 allen screws for blocking and maintaining the floattng assembly - how could I say? - tighly. You have to tune it in the end. if those 2 last screws are not adjusted, then the floating assembly is floating when gears are engaged. Then the mount can't guide cause the floating assembly is…floating. So, there is no precision. Adjustting the play is made of 9 screws. |
