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76sec error on new OPW-11
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I purchased the one piece worm from Losmandy hoping to get rid of some of my errors. |
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Jim can you share your guidelogs or PE analysis data files? On Tue, Aug 3, 2021 at 3:31 PM Jim Pollard <jlpollard10@...> wrote:
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Brian? Brian Valente portfolio |
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I suspect that you've got things too tight so there is binding going on. i suggest you loosen the connections at the coupler, the gear reduction mounts, housing and the bearing blocks so there is some play everywhere. You could do this work with the DEC axis pulled but then there is no pressure on the worm gear to keep it flat against it's thrust bearing. I suggest you leave the DEC axis installed but adjust the lattitude adjuster so that DEC axis is as horizontal as possible. Adjust the tripod legs to help that too. Run with the clutch relaxed so you can run the RA? motor without the dec axis moving. Put something in the way in case the DEC axis grabs and starts turning unexpectedly. Be safe.? Put an index mark on the worm gear and worm so you can visualize the rotation. You may notice that the worm gear may show some smoothing or wear on some section. Since this is a new worm, you may want to rotate the worm gear so the 'used' side is away from the worm. This will give your 2 fresh unworn surfaces to work with and avoids any uneven wear on the worm gear from the stainless steel worm.? The last two things to adjust are the transfer gears/gear reduction and the coupler.? I secure the transfer/reduction gear housing first being sure that the gears have a little float . Then run with the clutcand no tension on them and the shaft into the coupler goes in straight and is lined up with the worm so the coupler is all loose and straight. A lot can be told by the sound of the gear system and motor.? Listen for any uneven sounds, ticking or other periodic changes when running at full slew speed. If, before you started this process your made an index mark on the worm gear run the system with the clutch disengaged until the mark returns to it's starting point. If it all sounds smooth, reassemble and test. Be sure you clear any stored PEC data. You must fully initialize the system check and set all parameters and then do another shutdown and and additonal cold start. |
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On Tue, Aug 3, 2021 at 03:31 PM, Jim Pollard wrote:
I purchased the one piece worm from Losmandy hoping to get rid of some of my errors.Jim, As you know this is a bearing problem. Try this arrangement with just the one spring washer.? Also I found that these bearings were much better than the stock bearings:? Also, I just ordered these ceramic bearings to tryout:? Please report back you findings if you decid3ed to make these changes. Peter |
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This drawing has an error probably because you saw Michael Herman's drawing and don't understand how this is supposed to work.?
The bearing's outer shell is the part that is pressed by the spring disc NOT the inner race which carries the worm! By orienting the spring disc to contact the inner bearing shell or possibly worse the bearing dist cover you are creating pressure and drag where it should not be and potentially leaving the problem of unloaded bearing balls in the bearing unchanged.? This drawing needs to be replaced with the correct orientation not just an edited text.? Please believe me on this point as was adding Belleville spring discs to HEQ5 and EQ6 mounts before the GOTO computers were standard to solve this issue and the impact of thermal changes. Bearing induced PE is not unique to Losmandy mounts but it is more obvious because there is no threaded cap to retain the bearings which can e used to preload the worm bearings.? -- Chip Louie Chief Daydreamer Imagination Hardware? ? ?Astropheric Weather Forecast - South Pasadena, CA? |
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On Wed, Aug 4, 2021 at 07:13 AM, Keith wrote:
The washer in the drawing is backwards (should be contacting the outer race).Keith, This arrangement produced the lowest PE for me and I think I tried all possible arrangements .? My thoughts as to why this is, is? it is equalizing the pressure why the worm being driven into the bearing.? However my guided PE at 80s is still way too high at 0.7 arc-sec while guiding at Latitude 30 degrees. Michael Herman has suggest that I? try full ceramic bearings. They are expensive so I have opted to buy them in from China at $12 each. Will only use on the Ra axis. Peter |
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On Wed, Aug 4, 2021 at 08:15 AM, Chip Louie wrote:
This drawing has an error probably because you saw Michael Herman's drawing and don't understand how this is supposed to work.? Chip, OK, since I have gotten several push backs on this, and since I have quite a few guide logs that show a consistence error, I will reverse the washer and report back. I truly hope you guys are right! Peter
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Peter:
Keith |
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On Wed, Aug 4, 2021 at 09:41 AM, Keith wrote:
Peter:Keith, Thanks for this input. You could be entirely right about the 80s error. I too have speculated about this and the McLennan gearboxes. Although its pretty constant in magnitude between the 25:1 and 125:1 models. There are reports of the 76s error moving to 80s with the OPW drive, but there are? reports of people a new mount and OPW with a sizable 76s error. Interestingly I do not have this error. I'm moving in an entirely different direction going with onstep and using servos with high resolution optical encoders to direct drive the worm. No more gears. Of coarse when this is built I will know one way or the other where this 80s error originates. Peter |
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Brian,
Here's the logs from the other night. Last night something happened with my NINA sequence and it's all screwed up. There's also a picture of one of the bearing blocks that came with the OPW from your shop. It looks like something shifted during the cut and there is a step on the journal that rides in the base plate. In your opinion, do you think this could lead to problems? The way it is now, only about half of the journal is in contact with the base at any one time. Jim P |
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Jim,
That's not right. It looks all chewed up. They are smooth and black on the bottom. The left hand one has no movement in it's hole. The right hand one can move a little in it's hole. They ought to replace these, or better yet take a look at the entire worm assembly, as there could be other manufacturing issues. What about the hole in the plate? Peter |
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Peter,
That's the right side journal that moves to adjust the backlash. I thought it was funny that it wouldn't be anodized but the cut is definitely not right. I purchased the OPW as a standalone. I already purchased the brass worm. This is on a 2006 (?) G-11 with straight in motors. I was in the machinist trade over 30 years and this looks like it overlooked somehow during QA. If I don't hear back from Brian I'll email Tanya tomorrow and show her the picture. Jim P |
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On Wed, Aug 4, 2021 at 03:05 AM, Michael Ben-Yehuda wrote:
Put an index mark on the worm gear and worm so you can visualize the rotation. You may notice that the worm gear may show some smoothing or wear on some section. Since this is a new worm, you may want to rotate the worm gear so the 'used' side is away from the worm. This will give your 2 fresh unworn surfaces to work with and avoids any uneven wear on the worm gear from the stainless steel worm.?Michael Ben-Yahuda, Respectfully, I now believe your assertions that we only use 50% of RA ring gear is not correct. This would only be the case if we never ever loosened the clutch to change the scope position. For instance if you were at zenith the ring would be about 90 degrees off CWD. And then if you had one of the cross-app communications errors, or some kind of power failure, you might have to break the clutch and rotate the telescope 90 degrees back to CWD, but the ring gear stays where it was. If you do a Cold Start (necessary if you have lost orientation) from CWD, the ring is still 90 degrees from the old CWD, but the Gemini now is starting from the new ring CWD rotation. If this happens twice in a row, the ring is now 180 degrees from the original CWD gear position. Or in other words once you break the clutch and do a CWD Cold Start you could be at any random point on the ring gear. There can be no good unworn side, or bad worn-down side, to switch back and forth from. Making this recommendation as a means to better guiding may be misleading. Regards, John K. |
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John, I would not suggest rotation of the RA ring gear as a matter of course... Any eccentricity or variation can change the PE . The recommendation for indexing is to get repeatability.? There is also an issue with slew limits which requires that the relationship between DEC axis and RA position be maintained. It's a matter of procedure to maintain CWD. If you want to use stored PEC then you need to maintain the relationship between CWD, worm gear and DEC axis orientation across the clutch.? |
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On Thu, Aug 5, 2021 at 05:14 AM, Michael Ben-Yehuda wrote:
If you want to use stored PEC then you need to maintain the relationship between CWD, worm gear and DEC axis orientation across the clutch.?Michael, Typically when using PEMPro, we use a hour or less of data to create a PEC curve which is then uploaded to the Gemini unit. Therefore we largely measure the behavior of the worm, and possibly some of the profile found on that section of ring gear. It would be nice to have data over the entire circumference of the ring gear, but that would take 24 hours of data, and some method of rotating through various sections of the ring. But how to maintain using the preferred best mating parts and only those parts is something I'm not sure the average user could do in practice. Since you can't see inside during operations, this may be difficult. But regardless of the random ring position which may be at CWD at a Cold Start, the PEC curve plays back with the same worm oscillations being repeated, and PE should be mostly negated for better guiding. Without PEMPro I can readily see the sawtooth pattern in PHD2 during guiding. I think we would all like to see better guiding performance without using a correction curve if possible |
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Well, I talked to Tanya at Losmandy and she said that's how all the blocks look.
Kind of hard to believe. I said something about the block not being anodized and she said that's how they come in. It sounds like the bearing blocks may be outsourced and they are received anodized and the right side one is modified. That's why it's not coated. |
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On Sat, Aug 7, 2021 at 06:56 PM, Jim Pollard wrote:
Well, I talked to Tanya at Losmandy and she said that's how all the blocks look.Such BS. I'll post some images tomorrow of blocks I just bought in. Peter |
Chip Louie