For clarity, I want to show the facts here - I don't want to make assertions about a person, their experience or other qualities as that is not the issue here.
The advert did lead me to understand the condition was good enough to assemble the mount, perform a few tweaks and then use it without maintenance.
Here and here are videos of the DEC operating without load. On testing the mount, when I used it to slew this sounded like metal grinding on metal. This may have 'disappeared' under full load, but in my experience if an issue is present, putting a full load on what I suspect to be a failing component would make me negligent and risk the equipment and the mount.
On manually testing the worm, it did not move smoothly but bumped and halted regularly - this was while disengaged from both the motor and the DEC gear.
When I removed the worm block and inspected the bearings, I found them worn and in one case missing a raceway entirely and with dried grease. Here is the photo of those bearings, here is a photo of the replacement bearings and here is a comparison shot.
I have since replaced those bearing, re-greased the DEC gear and worm block, re-seated it and adjusted it under load (evidenced here). Here is what it sounds like now. There are no bumps when I manually test the worm drive and no grinding noises when it slews (please excuse the frogs, it's night time).
This leads me to believe that the issue was worn bearings and that this was present when I took ownership of the mount.
As to periodic error - when I get a chance and have correctly polar aligned the mount, I will post the results here. It's cloudy tonight and I'm going away with my family for the weekend, but I'm eager to get this working to specification so will persist.
1. The buyer asked me as seller to assist with the motors, when they didn't work. I told him what to do and they then worked. Astronomy 101 stuff. why was this even asked ?
2. He then asked questions about gearing, and again I assisted with guidance. Then I heard nothing further. I repeat then heard nothing further ?
Then I get a couple of calls from people I know on IIS asking whether this guy knows enough to run this unit. I cannot answer this, ask him.
This thread is the usual tangents going off all over the place without being intimately involved. With one side of the story and totally inadequate actual detail.
Great stuff guys - shooting first without asking any questions
Seriously guys, this stuff is premier gear and needs care, and attention to detail, to get operational. I get a little of this from time to time when people buy gear and due to the learning curve of this level of gear have issues.
Sad, but don't bag people when you aren't involved. Poor behaviour from some of you. Particularly a PM received today from someone that knows who he is, and doesn't know me whatsoever, his language was appalling, get a set of manners mate
To the others that rang me to support, thanks guys, appreciate your caring
Quote:
Originally Posted by baileys2611
For clarity, I want to show the facts here - I don't want to make assertions about a person, their experience or other qualities as that is not the issue here.
The advert did lead me to understand the condition was good enough to assemble the mount, perform a few tweaks and then use it without maintenance.
Here and here are videos of the DEC operating without load. On testing the mount, when I used it to slew this sounded like metal grinding on metal. This may have 'disappeared' under full load, but in my experience if an issue is present, putting a full load on what I suspect to be a failing component would make me negligent and risk the equipment and the mount.
On manually testing the worm, it did not move smoothly but bumped and halted regularly - this was while disengaged from both the motor and the DEC gear.
When I removed the worm block and inspected the bearings, I found them worn and in one case missing a raceway entirely and with dried grease. Here is the photo of those bearings, here is a photo of the replacement bearings and here is a comparison shot.
I have since replaced those bearing, re-greased the DEC gear and worm block, re-seated it and adjusted it under load (evidenced here). Here is what it sounds like now. There are no bumps when I manually test the worm drive and no grinding noises when it slews (please excuse the frogs, it's night time).
This leads me to believe that the issue was worn bearings and that this was present when I took ownership of the mount.
As to periodic error - when I get a chance and have correctly polar aligned the mount, I will post the results here. It's cloudy tonight and I'm going away with my family for the weekend, but I'm eager to get this working to specification so will persist.
Perfect reply Simon, and thank you for not sinking to the level of personal retorts.
There was a mechanical issue with the mount as received. You amply demonstrated your mechanical aptitude that was called into question in not only diagnosing it but potentially fixing it.
1. The buyer asked me as seller to assist with the motors, when they didn't work. I told him what to do and they then worked. Astronomy 101 stuff. why was this even asked ?
2. He then asked questions about gearing, and again I assisted with guidance. Then I heard nothing further. I repeat then heard nothing further ?
Then I get a couple of calls from people I know on IIS asking whether this guy knows enough to run this unit. I cannot answer this, ask him.
This thread is the usual tangents going off all over the place without being intimately involved. With one side of the story and totally inadequate actual detail.
Great stuff guys - shooting first without asking any questions
Seriously guys, this stuff is premier gear and needs care, and attention to detail, to get operational. I get a little of this from time to time when people buy gear and due to the learning curve of this level of gear have issues.
Sad, but don't bag people when you aren't involved. Poor behaviour from some of you. Particularly a PM received today from someone that knows who he is, and doesn't know me whatsoever, his language was appalling, get a set of manners mate
To the others that rang me to support, thanks guys, appreciate your caring
Quote:
Originally Posted by baileys2611
For clarity, I want to show the facts here - I don't want to make assertions about a person, their experience or other qualities as that is not the issue here.
The advert did lead me to understand the condition was good enough to assemble the mount, perform a few tweaks and then use it without maintenance.
Here and here are videos of the DEC operating without load. On testing the mount, when I used it to slew this sounded like metal grinding on metal. This may have 'disappeared' under full load, but in my experience if an issue is present, putting a full load on what I suspect to be a failing component would make me negligent and risk the equipment and the mount.
On manually testing the worm, it did not move smoothly but bumped and halted regularly - this was while disengaged from both the motor and the DEC gear.
When I removed the worm block and inspected the bearings, I found them worn and in one case missing a raceway entirely and with dried grease. Here is the photo of those bearings, here is a photo of the replacement bearings and here is a comparison shot.
I have since replaced those bearing, re-greased the DEC gear and worm block, re-seated it and adjusted it under load (evidenced here). Here is what it sounds like now. There are no bumps when I manually test the worm drive and no grinding noises when it slews (please excuse the frogs, it's night time).
This leads me to believe that the issue was worn bearings and that this was present when I took ownership of the mount.
As to periodic error - when I get a chance and have correctly polar aligned the mount, I will post the results here. It's cloudy tonight and I'm going away with my family for the weekend, but I'm eager to get this working to specification so will persist.
Yes two versions that are worlds apart.
One by the purchaser who has ample skills to troubleshoot and repair, without disparaging anyone in the process.
The other by the seller who attempts to make the buyer appear inexperienced or incompetent ....backed up by bedtime stories of "mystical skills" required to master the use of premier grade equipment.
In my experience people pay for premier grade equipment for the extra features, reliability, expecting it to work as advertised so they don't have to fiddle endlessly to get it working properly.......especially when it's advertised in Excellent Condition which the buyer photos and videos show that it clearly wasn't.
I had a LOL moment yesterday evening. Still testing the mount and getting it PE correction-ready.
Removing and re-adding my scope to the mount seems to have taken it's toll on the knob for tightening up the front most saddle-clamp...but, in another show of mechanical application I've come up with a tool to use in place of the affected knob.
To the original question - I would expect used high quaity gear to work exceptionally well and be pretty bullet proof. I would expect a seller to state in advance if there are real problems with the gear being sold. I expect any high end mount has a non trivial learning curve to reach peak performance - not to do routine actions.
Grinding noises on first use sound like a major whoopsie that the seller and buyer should both know about before making the purchase decision. If the seller is unaware of these - or states they never happened for him - that's one thing. If they knew but didn't disclose that is another.
These mounts have a killer reputation at the price point, especially for robustness. If it's more than normal wear and tear I would ask what has this thing carried to be making the noises you have observed?
Hopefully the buyer and seller can come together on this and reach a great final result.
Yes, I agree that those things are important and thank you to all who are providing advice on this, I appreciate it very much.
However, rather than discuss the commercial aspects - the mechanical ones are more important to me, I can fix those, the commercial ones are painful to all involved, I'm not a fan of pain.
That being said I think I've made progress on the mechanics. A long update is below but for those that don't want the long read I have a question on Gemini servo motor gearboxes for the good people here: Should the shaft be able to shift in and out a little bit? This is from me using my finger to gently push on the end of the shaft coming from the gearbox and it has play in it, not sideways at all, just in and out by about 2 or 3mm (really need to get some calipers!). I'm guessing that this is ok but is that normal?
Long update:
It's hard to find bearings that are high quality in Australia. I realised after a little research that bearings ain't bearings. The ones I purchased were pretty cheap and apparently not high quality. My fault for not understanding and researching that in the first place so I'll correct that. Having realised that, I scoured local suppliers for high quality bearings, something closer to ABE7 or ABEC9 (P4 or P2). ABEC 3 is about as close as you get here 'in the sticks'. So I have some coming from Boca in America (ABEC7, ceramic balls, stainless steel housing).
Also, I noticed that the Oldham couplers and the plastic in-between them is yellowing with age so I ordered some replacements from Bintel which are designed to fit Losmandy mounts. I'm guessing that they will fit but will need to do a close comparison when I remove the worm drives and motors just to make sure. I probably should invest in a Vernier caliper I think...
I'm going to re-do the bearings *again*, replace the Oldham couplers and then re-jig it all for the last time.
Polar alignment is problematic. I've used many programs including TheSyX's Tpoint polar alignment report and they all seem to differ. I'm putting that down to potential mechanical inaccuracies in the mount at the moment. The best test I managed to complete so far is using PEMPro and their equivalent of a drift alignment. They tell me I'm good to go but TPoint tells me I'm 2 arc minutes out in RA and about 7 arc minutes out in DEC. I'm not going to fuss around with that right now until I've got the mechanics of the mount to where I think they are most accurate.
However, I did a test the other night using an autoguider and the results are promising. I'm getting between 0.9 and 1.7 pixel shifts between 4-second exposures on the autoguider (no idea what that means yet in terms of arc-seconds) and took a set of pictures of the Trifid Nebula (just to test if I could) using an SBIG ST-8300C. Here's the result which is promising. The stars are a little eggy. I expect to iron out the mechanical errors with more precision in the bearings and replacing the oldham couplers.
Quick update: After some good nights lately I think I've managed to get the DEC axis to within +- 4 arc second error before PEC (using PEMPro to measure, GSO RC 10" and an sbig st-8300c). I think that's pretty good for now.
RA is another story completely which seems to vary wildly between +-5 to +-20 with each separate measurement, it's not consistent which is frustrating. Time for some fiddling on that axis now. DEC only took 2 months to get to within original specification, RA probably won't take as long.
I'm glad you are making some progress with your mount!
I've never heard of using PEMPro to measure error in declination. Might you explain what you have done here? Since the declination axis typically doesn't move, except for guiding corrections, how can there be meaningful PE? Sure, if the axis were always rotating it would matter, but that isn't the case.
I personally wouldn't have any concerns about T-Point not agreeing with PREMPro's drift alignment. You wouldn't actually expect them to agree! T-Point is taking all sorts of things into account such as refraction, and specific mechanical issues with the OTA and mount that can be modeled. I have found T-Point to be somewhat sensitive to polar alignment wrt where and how many points are collected. I have obtained best results only when the points are spread equally on both sides of the meridian. I have been told specifically that this should not matter very much but my experience has been otherwise.
Yes, you are right. I'm making an assumption here based on a selection in PEMPro.
When you are measuring the RA error (the tab where it shows a graph) by default it shows the Y axis error, there's a drop-down box just below the graph, a bit to the left that allows you to select the X axis also. You can do that without affecting the measurements (i.e. it doesn't stop the process). When you select X it changes the graph. I'm assuming that the X axis graph is measuring movement of the centroid in the opposite direction.
For a practical demo, I used PEMPro to measure error, then tightened up the worm block by tiny amounts until the error in X was literally below +- 1 arc-second and the Y error was within +- 4.
Using relays on my autoguider, I was getting 0.5 pixel movements in the star centroid during autoguiding, pointing at the Cats Paw nebula while measuring this. Pointing east is not as accurate, getting around 1.5 pixel movement which I have a few ideas on how to reduce (slight imbalance for example might work there).
Re T-Point, yes I've read somewhere that it takes a lot of modelling parameters into account. Problem is, which measure to use? One saving grace is that they both seem to agree on vertical measurements - i.e. raising or lowering the mount to point to the SCP works well (nothwithstanding mechanical things like tightening up the mount moving the axis by a fair amount and coming up with techniques to counter that). They differ a lot in recommendations to move the mount horizontally. I've also read that it does not matter so much if you are autoguiding because small errors in polar alignment can be corrected through autoguiding corrections - cannot remember where I read that but it does sound reasonable.
Last edited by baileys2611; 24-07-2017 at 09:48 AM.
I've got no clear idea of what you are measuring in declination. It would seem to me that since dec isn't moving it would just be a measurement based on seeing. Anyway, what matters is whether you can guide reliably in dec...i.e., little backlash or stiction.
FWIW, because my location prevents much viewing to the East, I never could get a repeatable or reliable T-Point polar alignment. I use PEMpro to drift align and then I build a model with T-Point and completely ignore the T-Point polar alignment recommendations. I end up with great pointing, working Protrack, and have no trouble guiding. This all got discussed more than a few times on the Software Bisque Forum and the author of T-Point stated that extremely accurate polar alignment was not necessary in that Protrack would compensate, and he said that a drift alignment was an acceptable method to get reasonably close. The bottom line is the fact that there is no polar alignment that is best or works in all situations. There are alignments that minimise drift, others that minimise field rotation, etc, etc. I personally think that if you can drift align in PEMpro to the point where after say 7 minutes you are within 30 sec of aligned it is good to go.
Gday Peter/Simon
Just to clarify, did you get a good calibrate with PEMPro???
If not, and the camera is not perfectly aligned, the X and Y axes can cross contaminate each other
ie RA PEC will show up in the "DEC" trace.
In normal operation with PEMPro, the DEC axis data ( as noted ) should be a relatively straight line, with only "seeing" ripples on it.
Yes, realised that after my first few attempts. Made sure that the X axis was smooth (seeing aside) and am fiddling with the RA worm drive to reduce error. It's a pretty good process
After a few months of fiddling and testing, I'm not getting much better results so I'm guessing I've hit the limit of my abilities to fine tune or the mount is about as far as it will go. I'm quite pleased with the DEC, very little movement in that direction and when I trained PEC it was only moving tiny amounts (Canberra's seeing is not so good).
The RA on the other hand flops about a bit. I've tried tightening the worm against the RA gear but I'm at the point where if I tighten the worm against the gear any more, I get errors from the controller (too tight). So, attached is what a typical evening looks like while tracking now.
Stars are not pin-point but then for a mount that was 1/4 to 1/5 of my previous mount and 1/4 the price of a Mesu (mmmm.....Mesuuu), it's ok.
Although the G11 is a different mount, getting the right amount of play between the worm and wheel is an art, and you also need to do it at the tightest part of the wheel. Again, with the G11 I get the best performance when the RA has some play in it, your mount will do its own thing.
Assuming your polar alignment is good and your guide camera is correctly resolved into ra and dec, there should be very little correction in dec. Since you've got similar amounts of error in both you might well be looking at the seeing. It might be worth guiding no faster than once every 4 seconds and seeing how that looks.
Cheers
Andrew.
After a few months of fiddling and testing, I'm not getting much better results so I'm guessing I've hit the limit of my abilities to fine tune or the mount is about as far as it will go. I'm quite pleased with the DEC, very little movement in that direction and when I trained PEC it was only moving tiny amounts (Canberra's seeing is not so good).
The RA on the other hand flops about a bit. I've tried tightening the worm against the RA gear but I'm at the point where if I tighten the worm against the gear any more, I get errors from the controller (too tight). So, attached is what a typical evening looks like while tracking now.
Stars are not pin-point but then for a mount that was 1/4 to 1/5 of my previous mount and 1/4 the price of a Mesu (mmmm.....Mesuuu), it's ok.
Any suggestions for further improvements?
From where you started Simon, good to hear you have improvements
The average guide errors look to be around +/-0.5 pix..? What's the image scale for that graph in "/pix?
I know this story; I experienced it myself quite a few years ago with my PME. That was in perfect working ordertoo; except the worm gear had been changed out with a new one (nice), but it had not been fitted correctly (the grub screws were loose and that created slop in the pointing and guiding). It took some time to find the problem and fix it. It gave me the you know whats having to sort something that was in perfect working order. To be frank when someone sells a piece of kit and says it is perfect working order, that means it works as per design parameters. Grinding, poor tracking etc is not as per design parameters. It grinds my gears (yep pun intended) when people do this and I read about it here and on other sites. I don't know either of you involved really, but the evidence is certainly compelling here. Clearly the mount was not in perfect working order and it should not have been sold as being the case. Some transparency would have been the right thing to do.
Although the G11 is a different mount, getting the right amount of play between the worm and wheel is an art, and you also need to do it at the tightest part of the wheel. Again, with the G11 I get the best performance when the RA has some play in it, your mount will do its own thing.
Assuming your polar alignment is good and your guide camera is correctly resolved into ra and dec, there should be very little correction in dec. Since you've got similar amounts of error in both you might well be looking at the seeing. It might be worth guiding no faster than once every 4 seconds and seeing how that looks.
Cheers
Andrew.
Thanks Andrew - that an interesting idea! It would also improve the resolution of my guide stars. This was taken at 1 second intervals with corrections coming from the ST4 port on an SBIG ST-i directly to the Gemini (L4 of course, I've read that if it were anything earlier I would need some sort of optocoupler).
From where you started Simon, good to hear you have improvements
The average guide errors look to be around +/-0.5 pix..? What's the image scale for that graph in "/pix?
Mike
Thanks Mike. By the way, Ron Abbott from Land of Oz Observatory mentioned your name recently and said to say hi.
Re your question - Gah! Maths! Here goes:
SBIG ST-i is 7.4 microns, I'm using off-axis guiding so the scope focal length comes into it. The scope is 2032mm f/8 (I like it a lot!).
I was binning at 2x2 during this guiding.
Based on the formula here: I get a calculation of 1.5 arcseconds per pixel. So, the graph would show an average error of 0.7 arcseconds error in RA and 0.5 in Dec I think?
I know this story; I experienced it myself quite a few years ago with my PME. That was in perfect working ordertoo; except the worm gear had been changed out with a new one (nice), but it had not been fitted correctly (the grub screws were loose and that created slop in the pointing and guiding). It took some time to find the problem and fix it. It gave me the you know whats having to sort something that was in perfect working order. To be frank when someone sells a piece of kit and says it is perfect working order, that means it works as per design parameters. Grinding, poor tracking etc is not as per design parameters. It grinds my gears (yep pun intended) when people do this and I read about it here and on other sites. I don't know either of you involved really, but the evidence is certainly compelling here. Clearly the mount was not in perfect working order and it should not have been sold as being the case. Some transparency would have been the right thing to do.
Thanks Paul, agreed. The PMX I used to use was heavenly (ahaha). But on the bright side I think I've learned a lot from this exercise! Anyone else with an MI-250 that wants some tips, I'm good to offer them.
