I don't see how changing the worm gears can make the situation worse, but might just fix the problem. The documentation is straight forward enough and more than a few guys have done this in Australia without issue and have fixed PEC problems in doing so. If a different worm fixes the backlash problem that will be great. If it doesn't then I agree there really isn't much more I can do or try. The mount will go back to the factory!
Peter
You've got nothing to lose at this point. I changed my worm (single not both) over in less than an hour. It worked fine after I played with the tensioning rods and get them set correctly. They are 2.25 to 2.5 turns out from fully screwed in. You test afterwards and if too tight the mount will stall. If too loose you get the dreaded slipping crunching gears - ouch! It took about 20 minutes to get it right.
You've got nothing to lose at this point. I changed my worm (single not both) over in less than an hour. It worked fine after I played with the tensioning rods and get them set correctly. They are 2.25 to 2.5 turns out from fully screwed in. You test afterwards and if too tight the mount will stall. If too loose you get the dreaded slipping crunching gears - ouch! It took about 20 minutes to get it right.
Greg.
"New" worm is in. Now just waiting for dark with fingers crossed!
I'm sorry to report that I have identical results following the RA worm change. I find this almost impossible to believe because the two worms are really different. The "new" RA worm has much greater uncorreced PE than the original (7.1 arcsec vs 2.3). Nontheless, I ran PEMpro and quickly was able to reduce the "new" worm to +.9 -1.5 arcsec. Not a great result but I just wanted to smooth out the unguided tracking so that I could distinguish it from drift.
I tried numerous times on both sides of the meridian, and with east heavy balance. I always get the exact same result. Perfect tracking after a west slew, and at least 5 arcsec or more of drift after an easterly slew. When I balanced the scope east heavy the results were by far the worst of the night with 8-10 arcsec drift.
At this pojnt I am perplexed. Perhaps this is "normal?" I suppose no worm can be perfect in backlash, but is 5 arcsec too much for an MX? I've posted the question at SB. It takes about 1 min all up for the drift to stop after a slew (so no longer a full worm cycle, but this improved also with my original worm after I adjusted the 1/4-20s). I can no longer feel or see any free motion in RA compared to what I found earlier in the thread and led to adjusting the 1/4-20s, so things are better.
If I chase this any further it seems I have few options. 1. I can assume that I still have a worm problem as both worms came from an early batch and this new worm is actually just out of spec. I can ask SB to swap out this worm. 2. My methodology is crook and PEMpro is giving a false sense about what is actually happening. I don't know why this would be, but I've posted the question to Ray Garalak. 3. TSX is causing this? Can't see how or why with Protrack off, pointing corrections off, but I suppose I could try running the mount without TSX at all, slew with the hand controller and collect logs using CCDSoft. (I don't want to do this experiment.)
Just a few days left before my trip. I hope SB responds with something to try, or an offer of a worm exchange.
A friend loaned me yet another worm which I tested last night. No change. So, that is 3 different RA worms and I get identical drift after a slew to east, but no drift after a slew to west.
This time I took photos. 1 min exposures after east or west slew at .63 arcsec. PEC on, Protrack off. If I slew east, wait 1 min, then I get good tracking.
Some have suggested that I'm seeing telescope sag or camera sag, but I fail to see how that is possible. The geometry of imaging on the meridian at 0 dec would mean gravity would be acting on the y axis. All the motion I see is in RA.
Software Bisque has not responded to any of my posts since sometime last week. That alone is very frustrating!
Having tried 3 different worms would suggest (to me at least) that your drift is not worm related. Do you still have that 'slop' in the RA axis?.
May I ask the MX fraternity for a consensus on what direction you lift the RA Worm Assembly before tightening the 1/4-20 bolts. When I held/lifted it towards the worm gear I got the 'slop'. Holding/lifting it parallel to the Cam Stop pin fixed the 'slop'. My thoughts are that the latter allows the worm to self-centre in bottom of the worm wheel teeth and the Spring Plungers then hold it there with a specific pressure. I may have missed it, of course, but I couldn't find an unambiguous reference to the direction.
Having tried 3 different worms would suggest (to me at least) that your drift is not worm related. Do you still have that 'slop' in the RA axis?.
May I ask the MX fraternity for a consensus on what direction you lift the RA Worm Assembly before tightening the 1/4-20 bolts. When I held/lifted it towards the worm gear I got the 'slop'. Holding/lifting it parallel to the Cam Stop pin fixed the 'slop'. My thoughts are that the latter allows the worm to self-centre in bottom of the worm wheel teeth and the Spring Plungers then hold it there with a specific pressure. I may have missed it, of course, but I couldn't find an unambiguous reference to the direction.
Charles
Hi Charles,
No, no slop at all in RA. Sorry, I just can't quite follow your other question about "lifting up." I think it's pretty clear that if you press "down" you disengage the worm, so I've just lifted up in the opposite direction. No slop at all so I think it must be correct.
Yes, I agree, it cannot be the worm if 3 worms give the identical results. I now have a theory that perhaps the motor is taking longer than it should to reverse direction, a bit like a car trying to accelerate in too high a gear. I thought I might test this by slewing west and then turning RA off. Then turn RA on and see if there is drift similar to reversing direction after an east slew where the motor must momentarily stop to change direction. Perhaps the momentum of the east slew is contributing to the lag. Who knows, but I can at least try this test and see. I think one fact from a previous test lends some evidence that this might be correct. When I loaded the mount heavy on the east side (pointing west) the drift error nearly doubled. A lagging motor might do that. I should try loading it heavy to the west to see if it accelerates faster and reduces drift.
One other thought passed through; assuming you use TSX, then by using its Closed Loop Slew to go to a target, you get very accurate pointing and could have used enough time to avoid the drift problem. CLS uses 2 slews, each followed by an image + download + imagelink. Sorry if I've talked a lot of nonsense but I've just about finished!
One other thought passed through; assuming you use TSX, then by using its Closed Loop Slew to go to a target, you get very accurate pointing and could have used enough time to avoid the drift problem. CLS uses 2 slews, each followed by an image + download + imagelink. Sorry if I've talked a lot of nonsense but I've just about finished!
Charles
No, please don't apologise! It's a fine idea. Right now though I want to find out the root of the problem. I'm sure there are work arounds but I don't see others needing to do that and I didn't buy a mount of this quality to have these issues. Pretty soon though I''m going to give up!
Tonight I tried a few things. I stopped the motor, then started it up and took an immediate photo. There was no trailing. Then I tried changing settings in the Bisque TCS. I found that if I reduced the acceleration/decelleration setting to 300 (a very low values with very slow slew speed) there was a clear improvement in drift. Usually I see 5+ arcsec in the first min. At this setting the drift averaged about 2-3 arcsec. I don't know what that might mean but I'm sure it is a clue that to someone at SB might ring a bell. I also disconnected TSX and ran the mount only from the hand control. I get round stars if I slew west, and trails if I slew east.
What scope and camera are you using on the mount? What focuser does it have?
Greg.
Hi Greg,
It's a Feathertouch on a TEC140 + Moravian G2-8300. But, before you start telling me about flexure the geometry isn't correct for this be be flexure. Observing at 0 dec on the meridian puts the force of gravity on the Y axis (dec) and there is o movement I can see there. All the trailing is in RA both in the photographs and in the PEMpro graphs.
A friend has repeated my tests with his MX/refractor combination and has had similar results! He gets good tracking after west slews, and trailing following east slews! I expect he will be posting his results in my thread at SB very soon.
Also, I have determined that the trailing is sensitive to the acceleration/deceleration parameters in the TCS. Putting the value to minimum decreases the problem to zero if slews are confined to 2 degrees or less. Anything on the order of 5 degrees slew produces the drift after an east slew. Interestingly I have been told that Astrophysics mounts compensate for backlash by making a second small slew that is adjustable. I can find no such setting in TSX.
Meanwhile, SB has not responded to any of my posts on their forum for more than a week! I'm starting to think they don't like what I'm showing and maybe they don't know what to do about it. It's not just in my mount. I'm fairly positive about this.
Just curious, I am not implying its flexure but its not mentioned in your posts what you exact setup is so it leaves it open. Do you have a photo of your setup.
Just so you know Yuri did test the FT3545 focuser and found minor flex under certain loads. It has less flex when it is upside down (focusing knobs up). Not that it flexes much. I have not seen focuser flex on my TEC180 and Proline, MMOAG and filter wheel.
What autoguiding system do you use? A guide scope or the ONAG?
Do you use all screwed adapters or eyepiece holders and extension tubes?
I have no experience with an ONAG. Is it reliable? Have you used it on other scopes/mounts?
I take it you've double checked your connections and everything is seated properly, the pick off prism is firm and does not wiggle etc etc.
I have sometimes had issues guiding after a slew, usually assumed operator error. Once the weather improves I will see if this is present with my PMX.
Overall I have found my mount to be very stable, any failed subs have usually been caused by the guider getting a mind of its own, sometimes correcting backwards, yes calibration was correct and the guider functioned fine for a few worm cycles but it would suddenly send reverse corrections resulting in a drift on one axis. When this happens I just turn the damn thing off and get much better subs without the guider. I'm not saying you have a guider issue at all, just that I have found SB software to really bug out and randomly malfunction, not just the guider stuff. It wouldn't surprise me if there is underlying issues with what is driving the mount. Mechanical behaviours with motors etc could easily be compensated via software, tbh I would expect this and can understand why AP mounts compensate for it.
Just curious, I am not implying its flexure but its not mentioned in your posts what you exact setup is so it leaves it open. Do you have a photo of your setup.
I take it you've double checked your connections and everything is seated properly, the pick off prism is firm and does not wiggle etc etc.
Greg.
Hi Greg,
Sorry I jumped the gun on your question, but I thought I knew where it might be heading. Of course I'm not saying my system wouldn't have any flexure. Everything does for sure, and so would my adapters and focuser, etc. It's just that the way I'm doing the tests I don't believe it is possible for ordinary flexure to explain the consistent results of drift after a slew east. For all these tests I've completely eliminated the ONAG. The camera is fitted to a Baader Click Lock that is clamped into the 2" Feathertouch. No, not ideal & not screwed together, but flex in this would show up in declination since I've got X=RA. And, it sure would be odd that flex would only exist after a slew in a particular direction, wouldn't it? I'd reason that something loose would move in both directions. Here is a quick view of the business end (camera is not RA=X in this photo!):
I certainly cannot feel anything moving in this setup!
The issues I've dealt with mostly concern two problems that I've never been able to properly rectify. One is the issue of Protrack and unguided. My supermodels have told me that I've got excellent PA, and I've used large models with 100s of points, yet unguided is all over the place. One time it will seem good but the next run terrible. I think I now realize that this has been slew dependent. Usually I'd just slew to a different part of the sky and start an exposure. From what I've been demonstrating I now think that if I slewed west I would get a good result, but that if I'd slewed east, and not waited at least a full minute, I would get a lousy result. The mount would be drifting between 5-10 arcsec over that first min and Protrack has no way to deal with that at all. Same thing with guiding I believe. If I slewed west, took a guide camera photo, select star, etc, the star will show up reasonably centered on the guide graph. But if I've done an east slew, the mount is "running away" during that first minute while selecting a guide star and plotting the first point on the graph. Often the first point is completely off the guide graph. Of course, if I wait a minute+ everything will be fine! Unfortunately I didn't understand this and thought I must be picking the wrong aggression settings, etc. You see the guide star escaping and think you need a higher setting to get it back centered. Then of course the drift ends and the setting is too aggressive. It also explains an issue that has made me nuts. I might have perfect guiding established. I finish with one filter and slew away to refocus with a different filter, slew back to the target and not be able to reestablish guiding with settings that worked just minutes before....all because I probably slewed east returning to the target.
For sure one can live with this if its understood. But, it's far from ideal and I sure didn't plonk down $10k for a mount that needs to be pampered in this way. These issues have all come into focus and demand resolution when I upped my imaging scale to .63 from 1.14. Probably for most people using the MX and doing wide field, or imaging scales greater than 1 arcsec you wouldn't really see this issue as much, but it gets amplified at long focal lengths for sure.
If I'm correct about this I bet there is a software fix that could deal with this by adjust how slews are done. Perhaps the mount needs to apply the brakes sooner and/or more gradually, or overshoot the target and slew back (west) by a couple of degrees. It could all happen automatically and transparently.
I have sometimes had issues guiding after a slew, usually assumed operator error. Once the weather improves I will see if this is present with my PMX.
Hi Chris,
I think it would be terrific if you could confirm or refute what I'm seeing!
My tests were all done at .63 arcsec using my imaging camera near 0 dec, near the meridian. However, day before yesterday I ran the same quick test over wide areas of the sky and got identical results.
I too believe that software could fix this. At the moment I think SB thinks I'm just a big pest. A few confirming responses my kick a potential fix into high gear so any input you could offer would be appreciated! Thus far I have one other person confirming this, and one person no longer with an MX but saying he had a similar issue. He dealt with it by waiting an entire worm cycle after slewing in order to get a good Protrack result.
It sounds like something mechanical that is either too loose or too tight.
So the problem is after an eastern slew it will not guide for a minute as it drifts a lot.
I notice the PME is designed to slew past the object and then come back to it. I seem to remember some AP mounts do that. Its probably a way to get all the slop in the gears out so the gears are fully in contact and enmeshed nicely for accurate tracking.
Perhaps SB don't know what to do next without the physical mount in their hands to check it over.
I'd be asking them to take it back and replace it with another unit and shipping at their expense at this point. Its probably something hard for us to see and know like a bad ball bearing or even shipping damage. Who knows if it a part got dropped in the factory and installed anyway??
It sounds like something mechanical that is either too loose or too tight.
So the problem is after an eastern slew it will not guide for a minute as it drifts a lot.
I notice the PME is designed to slew past the object and then come back to it. I seem to remember some AP mounts do that. Its probably a way to get all the slop in the gears out so the gears are fully in contact and enmeshed nicely for accurate tracking.
Perhaps SB don't know what to do next without the physical mount in their hands to check it over.
I'd be asking them to take it back and replace it with another unit and shipping at their expense at this point. Its probably something hard for us to see and know like a bad ball bearing or even shipping damage. Who knows if it a part got dropped in the factory and installed anyway??
Greg.
Greg, I agree with you 100%. But I cannot even get a reply to my posts now for nearly 2 weeks. I think I should be phoning SB on Tuesday and demanding some help. I leave for the USA on Wednesday and if they even read my posts they know this.
However, as others begin to confirm this it may be something in some MX mounts and not just in mine. The most recent post on the SB thread is from a friend in Australia showing possibly the same behavior with his MX.
Your comment about how the ME slews past and comes back is most interesting. I wonder why SB felt that this wasn't necessary in the MX? Perhaps they made an error in judgement on this.
Your comment about how the ME slews past and comes back is most interesting. I wonder why SB felt that this wasn't necessary in the MX? Perhaps they made an error in judgement on this.
Peter
Hi Peter,
I've a feeling that this is what the Closed Loop Slew does although I'm not sure if the first slew overshoots or falls short. The target is always visible in that cr@ppy Fits Window, and the second slew drops it dead centre.
I've a feeling that this is what the Closed Loop Slew does although I'm not sure if the first slew overshoots or falls short. The target is always visible in that cr@ppy Fits Window, and the second slew drops it dead centre.
Charles,
Thanks for pointing this out. Have I missed something basic? Is there a recommendation that the CLS should be used instead of just slewing to an object? Why would one use this type of slew? Is it just for centering an object if it isn't in the center after a slew?
It adds far more precision to your slews. I did a meridian flip followed by CLS and got with 2 pixels of my image. I mentioned it because of your comment about why this feature wasn't built into the MX. I felt it might give you time for your Drift problem to overcome what might be causing it. Search the SB site for Closed Loop Slew, there is a fair amount of traffic that might be informative. I use it all the time where I can.
It adds far more precision to your slews. I did a meridian flip followed by CLS and got with 2 pixels of my image. I mentioned it because of your comment about why this feature wasn't built into the MX. I felt it might give you time for your Drift problem to overcome what might be causing it. Search the SB site for Closed Loop Slew, there is a fair amount of traffic that might be informative. I use it all the time where I can.
Charles
Hi Charles,
Is CLS an option somewhere in the Sky X? Where is it located in the menus?
