I'm not sure at all that you can make the assumption that the worm periods are the same for the MX and MX+. The motors and basic design are totally different. Just ask the question on the PEMpro forum to be absolutely sure. The fact that you have trouble doing PEC with TSX in the Southern Hemisphere is not an isolated event. I know there are a few who have done it successfully, but those of us that couldn't do it, as far as I know, have always had good success with PEMpro. This makes me suspect that possibly PEMpro is using the incorrect worm period.
Maybe you can check this yourself by looking at the worm period time in the Bisque TCS. Then compare the time to the plot in PEMPro. Are they exactly the same? Another comparison you could do is to compare the correction curve generated by TSX and PEMpro. They really should look about the same! Do they? If they look the "same" but one is shifted it would mean one (or both!) have the wrong phase.
i just trawled through the SB user manual and it appears that the MX and MX+ have identical worm periods. i also came across this piece which was reassuring
When the counterweight shaft is oriented “non-vertically” and one or more counterweights are on the
counterweight shaft, and the right ascension axis is in the Track position, the extreme lateral force placed
on the worm and gear forces them to separate. At this point, the right ascension axis rotates to a
“balanced” position, and you will hear a chattering noise caused by the teeth of the precision gear
bouncing past the teeth of the precision worm gear. Despite the gut wrenching feeling this sound brings on, damage to the worm and gear is usually minimal.
I also had that happen a few times (it took me a while to get used to the 3 way switch thingy) and it didn't affect the mount at all. It will slip mainly if your cam pin is not fully in. Cam pin not tight though I don't think affects the PE though.
I also had that happen a few times (it took me a while to get used to the 3 way switch thingy) and it didn't affect the mount at all. It will slip mainly if your cam pin is not fully in. Cam pin not tight though I don't think affects the PE though.
Greg.
yeah i have been super careful with the pins, seems like something that is really easy to mess up. i have nightmares about leaving it in the lock position when i leave. but that makes me a lot more comfortable and eliminates 1 possible cause.
the issue appears to be mechanical. i am going to grab some logs tonight and post them to SB.
i have decided that the only way i can get any decent images is to take 15 second subs and choose which ones are okay. i am currently keeping about 50% of the subs i take which is a time consuming task. even the images i am keeping are not great. i am using it with PEC turned off, with it on it is even worse. i am really hoping i can figure this out because this is not a workable solution, and can only really be done on bright objects.
yeah i have been super careful with the pins, seems like something that is really easy to mess up. i have nightmares about leaving it in the lock position when i leave. but that makes me a lot more comfortable and eliminates 1 possible cause.
the issue appears to be mechanical. i am going to grab some logs tonight and post them to SB.
+1
I think its mechanical also. Sounds like other PMX's - it needs a new worm.
Yes, that is totally unreasonable! Something about tracking is completely messed up.
It seems that SB isn't paying enough attention to your posts. Perhaps if you start a new thread, re-post the tracking data, and possibly ask that only SB respond that might help. When the threads get a bit long, or just end up further and further down the list of new posts they can get totally lost.
Yes, that is totally unreasonable! Somerthing about tracking is completely messed up.
It seems that SB isn't paying enough attention to your posts. Perhaps if you start a new thread, re-post the tracking data, and possibly ask that only SB respond that might help. When the threads get a bit long, or just end up further and further down the list of new posts they can get totally lost.
Peter
i will give them another day or so. Steve did respond and since then it has been the weekend. if i dont get a response tomorrow night then i will do that.
the strangest part of this is that i cant train the PE out at all. anyway it is becoming stupid. the subs i am taking are unusable, it is frustrating. the moon is good, the weather forecast is great but i cant get any good data
looking at this plot, taken while guiding, it looks like the main error in tracking is not perfectly aligned with the X axis. is this consistent with PE issues? or is there something else amiss?
looking at this plot, taken while guiding, it looks like the main error in tracking is not perfectly aligned with the X axis. is this consistent with PE issues? or is there something else amiss?
Aidan,
What you see on the guiding graph is totally depends on the guide camera PA. If the guide camera is PA=0, or PA=180 then RA=X and DEC=Y. If PA=90 (or 270) then of course RA =Y.
So, if your camera is PA=0 then your guiding graph is showing drift in both axis.
If this were my mount I would start by eliminating T-point from the polar axis alignment equation. Since you want to collect PE data at DEC=0 why not use PEMpro to drift align the mount? This would establish excellent PA and essentially very little drift right at DEC=0. This will facilitate your PE collection and you can then try guiding knowing that your PA is pretty accurate for that region of the sky. It just eliminates one of many variables. Personally I have had trouble with T-Point and PA because I cannot see eqidistant E and W from the meridian when collecting data. Because of that I actually refer to use PEMpro to set my polar alignment. Then I build a very large model and ignore T-Points PA recommendations. This has worked quite well for me!
Here are other important easy mechanical tests for hysteresis and for backlash. Find a bright star and put the camera in focus mode. Bring up the cross hair. Now use the jog control and slew the scope 1 or 2 arc-sec? Does the star move in short slews in both RA and DEC? More importantly does the star re-center when you reverse the jog? If not, this is backlash. The next test involves putting the star in the center of the FOV/crosshairs and gently pushing on the mount in RA, and then DEC. Of course the star will move away from being centered but the essential part is when you remove pressure the star must exactly re-center. If it doesn't this is hysteresis. Dan Bisque told me my MX should not fail these tests. Do these tests because they could be very important!
EDIT: One more test while you are at it!!! Use PEMPro for this test as if you are collecting PE data. You have probably noticed that when the plots are completely horizontal that means the star is not drifting in RA. If the plots move at an angle (to horizontal) then that is drift in RA. Slew the mount West about a degree or two and immediately start collecting data. You should get a pretty straight line. Now, slew the mount East and immediately collect data. Is the line still straight (better hope so!) or not? If not, how long until it becomes level? (By the way, to do this test turn off Protrack and be sure to have drift aligned first so you know it's not polar alignment causing the drift!) Hopefully your mount passes this test. Some don't and it's a major problem as slewing East can cause bad drift for up to one worm cycle...meaning you essentially cannot guide for 3-4 minutes after an eastern slew.
Very good advice. Eliminate TPoint recommendations with drift alignment as drift alignment at the end of the day is what you are trying to do -eliminate drift.
I have had Tpoint tell me my PA was spot on only to see significant drift using PHD2 drift (very similar to Pempro drift). Once adjusted I got rounder stars so TPoint was off. I had used accurate polar alignment which seemed to give an odd result as TPoint said I was very close yet the accurate polar alignment had me doing some fairly large adjustments.
I do want to clarify something that might be taken from a casual read of my post. I am not at all saying that drift alignment is somehow superior to T-Point alignment. The reality is that there is no such thing as perfect PA. It really depends on where one is imaging, whether field rotation is a factor, etc, etc. The atmosphere through refraction will modify alignment and will be different depending on the altitude, etc, etc. So at best PA is a big compromise. The only reason I drift align is because of my limited visibility to the East. The only reason I've recommended that Aidan drift align is that at Dec=0 he will not have much drift, if any. That will certainly not be true at different sky locations! If I can digress, PA reminds me quite a lot of the musical term "equal temperament"....a basic compromise in pitch where every interval save an octave is "equally" out of tune..... a system where there is no difference, for example, between d# and e flat. It's a wonderful compromise that allows keyboard instruments to play completely out of tune all the time but "equally." Fortunately our ears adapt and put it right. I think PA is sort of like that; we try to put the PA where things are kind of equally good (or bad, you choose) over most of the sky we might care to image in. T-Point can do this job brilliantly as long as the data points are carefully selected. My experience says this means collect points equally on both sides of the meridian. I'm not sure Patrick Wallace agrees with me on this last point but it is my experience for what that is worth!
What you see on the guiding graph is totally depends on the guide camera PA. If the guide camera is PA=0, or PA=180 then RA=X and DEC=Y. If PA=90 (or 270) then of course RA =Y.
So, if your camera is PA=0 then your guiding graph is showing drift in both axis.
If this were my mount I would start by eliminating T-point from the polar axis alignment equation. Since you want to collect PE data at DEC=0 why not use PEMpro to drift align the mount? This would establish excellent PA and essentially very little drift right at DEC=0. This will facilitate your PE collection and you can then try guiding knowing that your PA is pretty accurate for that region of the sky. It just eliminates one of many variables. Personally I have had trouble with T-Point and PA because I cannot see eqidistant E and W from the meridian when collecting data. Because of that I actually refer to use PEMpro to set my polar alignment. Then I build a very large model and ignore T-Points PA recommendations. This has worked quite well for me!
Here are other important easy mechanical tests for hysteresis and for backlash. Find a bright star and put the camera in focus mode. Bring up the cross hair. Now use the jog control and slew the scope 1 or 2 arc-sec? Does the star move in short slews in both RA and DEC? More importantly does the star re-center when you reverse the jog? If not, this is backlash. The next test involves putting the star in the center of the FOV/crosshairs and gently pushing on the mount in RA, and then DEC. Of course the star will move away from being centered but the essential part is when you remove pressure the star must exactly re-center. If it doesn't this is hysteresis. Dan Bisque told me my MX should not fail these tests. Do these tests because they could be very important!
EDIT: One more test while you are at it!!! Use PEMPro for this test as if you are collecting PE data. You have probably noticed that when the plots are completely horizontal that means the star is not drifting in RA. If the plots move at an angle (to horizontal) then that is drift in RA. Slew the mount West about a degree or two and immediately start collecting data. You should get a pretty straight line. Now, slew the mount East and immediately collect data. Is the line still straight (better hope so!) or not? If not, how long until it becomes level? (By the way, to do this test turn off Protrack and be sure to have drift aligned first so you know it's not polar alignment causing the drift!) Hopefully your mount passes this test. Some don't and it's a major problem as slewing East can cause bad drift for up to one worm cycle...meaning you essentially cannot guide for 3-4 minutes after an eastern slew.
Good luck!
Peter
Hi Peter,
i ran an autoguider calibration, the results of which are on the left of the image i posted. my understanding, and correct me if i am wrong, is that there are 2 axis, the camera axis and the RA/Dec axis. the RA axis with respect to the camera is outlined on the left, the movement of the star in relation to the camera is outlined on the right. have i missed something? judging by that, it looks like there is movement in both axis but primarily in the RA.
i did run a polar alignment with PemPro a few days ago and it was bang on, within an arc minute. the strange thing about that test is that it started to drift, telling me i was quite a bit off the alignment and then it eventually came back to give me a good polar alignment score ... i guess that is consistent with my graphs but makes no sense as there should be periodic error in the dec axis
i will give those 2 tests a go and see how they fair. thanks for the trouble shooting tips, i have exhausted my knowledge a long time ago.
that is what i thought too. the close i image to 0 degrees dec the better. i got some decent images last night right on 0 dec. however, i wanted to test the out so last night i imaged NGC 6872 Iwhich is what these tracking logs are from, but i let it go from midnight to 5 am. i was watching the angle that the stars egged, if it was PA then you would expect that the angle would change over the course of the night but it didnt, it stayed exactly the same, not sure if i can explain that one
I'm in China as of today for the next 10 days so sorry for the delay in answering. Firstly, make your life easy and change your guide camera PA so that X=PA. That will make things so much easier to ID.
If you drift aligned near DEC=0 I wouldn't expect to have great tracking getting closer to the pole. In fact guiding near the pole can be very difficult!
But, something might be learned from your statement. After drift aligning you say "it started drifting, then was good" can you explain further? I take it that you drift aligned one night, started up later (or slewed?) and then you saw drift for a while which then got much better. If so this is exactly what I was proposing you test for where I said "edit" in a previous post. My MX did this and it was an unfixable mechanical error! It's quite rare for sure but when it's there it is a pretty serious. Were you testing in the same area of the sky you drift aligned in? If not then you would expect to see some drift.
As for an interpretation of your guiding graph I think this pretty tricky given your guide camera PA. Both axis contribution will blend together. The length of the angled drift shows that guiding just isn't happening over time. The back and forth excursions seem to show either horrid seeing, PE, or over correction, or all. It might be interesting to just look at a guide graph with corrections turned off. If the camera is a PA=0 the y axis excursions will represent "seeing" jumps given that Y isn't moving (no dec corrections). X will show seeing + any errors in RA (such as PE or crud on the worm/gear combination). This assumes that you drift aligned and testing in the same sky region.
Why guiding isn't fixing these issues (even a lot of PE) is a mystery. If you have backlash or hysteresis guiding is very difficult and you shouldn't see anything significant in a mount like the MX+. Do the tests to rule these issues in or out. Do all 3 tests at DEC=0 where you have drift aligned.
I do want to clarify something that might be taken from a casual read of my post. I am not at all saying that drift alignment is somehow superior to T-Point alignment. The reality is that there is no such thing as perfect PA. It really depends on where one is imaging, whether field rotation is a factor, etc, etc. The atmosphere through refraction will modify alignment and will be different depending on the altitude, etc, etc. So at best PA is a big compromise. The only reason I drift align is because of my limited visibility to the East. The only reason I've recommended that Aidan drift align is that at Dec=0 he will not have much drift, if any. That will certainly not be true at different sky locations! If I can digress, PA reminds me quite a lot of the musical term "equal temperament"....a basic compromise in pitch where every interval save an octave is "equally" out of tune..... a system where there is no difference, for example, between d# and e flat. It's a wonderful compromise that allows keyboard instruments to play completely out of tune all the time but "equally." Fortunately our ears adapt and put it right. I think PA is sort of like that; we try to put the PA where things are kind of equally good (or bad, you choose) over most of the sky we might care to image in. T-Point can do this job brilliantly as long as the data points are carefully selected. My experience says this means collect points equally on both sides of the meridian. I'm not sure Patrick Wallace agrees with me on this last point but it is my experience for what that is worth!
Peter
Great post Peter. Belongs as a sticky somewhere in a thread where people are learning about PA. Love the equal temperament analogy - very apt actually for explaining that perfect PA is a myth.
Aidan, hope you get to the bottom of your woes soon. Can only imagine how frustrating this is currently for a top of the line mount. This hobby really can be a torture chamber at times.....
I'm in China as of today for the next 10 days so sorry for the delay in answering. Firstly, make your life easy and change your guide camera PA so that X=PA. That will make things so much easier to ID.
If you drift aligned near DEC=0 I wouldn't expect to have great tracking getting closer to the pole. In fact guiding near the pole can be very difficult!
But, something might be learned from your statement. After drift aligning you say "it started drifting, then was good" can you explain further? I take it that you drift aligned one night, started up later (or slewed?) and then you saw drift for a while which then got much better. If so this is exactly what I was proposing you test for where I said "edit" in a previous post. My MX did this and it was an unfixable mechanical error! It's quite rare for sure but when it's there it is a pretty serious. Were you testing in the same area of the sky you drift aligned in? If not then you would expect to see some drift.
As for an interpretation of your guiding graph I think this pretty tricky given your guide camera PA. Both axis contribution will blend together. The length of the angled drift shows that guiding just isn't happening over time. The back and forth excursions seem to show either horrid seeing, PE, or over correction, or all. It might be interesting to just look at a guide graph with corrections turned off. If the camera is a PA=0 the y axis excursions will represent "seeing" jumps given that Y isn't moving (no dec corrections). X will show seeing + any errors in RA (such as PE or crud on the worm/gear combination). This assumes that you drift aligned and testing in the same sky region.
Why guiding isn't fixing these issues (even a lot of PE) is a mystery. If you have backlash or hysteresis guiding is very difficult and you shouldn't see anything significant in a mount like the MX+. Do the tests to rule these issues in or out. Do all 3 tests at DEC=0 where you have drift aligned.
Anyway, this is all I can think of at the moment.
Peter
Thanks Peter, i really appreciate you spending the time to help me work through these issues. have a lot of things to try to troubleshoot the issue now and i will give them a go, i have found that tracking is the best on Dec = 0 so i am going to spend the amazing weather i am getting to image a target on that line then work through my issues during the next full moon.
in response to your questions, i would have to physically change the guide camera to align with the X axis as it is an OAG. i have a rotator and have got it set up so that the main imaging camera is aligned with the RA axis. that has enabled me to diagnose the issue a little better. when i mentioned the drift alignment, what happened was that the plots PemPro was taking started to wonder off, telling me i had a huge polar alignment issue, but it slowly wondered back to the correct line, telling me that i didnt have a polar alignment issue. this was done in the same PA routine, i am not sure if i slew just prior to capturing that data.
i will run through all the tests at Dec = 0 and see what is what.
thanks again for your input, it has been valuable.
I understand your desire to image during a new moon and good weather. I don't blame you! And, I know your mount is remote. Next time you go out though I'd certainly rotate the guide camera so it is the same as the imaging camera. It will help you diagnose guiding issues. And to "push" on the mount obviously you need to be there. I can't think of how this test could be done remotely. It really seems as if something mechancally is wrong. When I'm back from China if you think I can help somehow don't hestitate to ask given we are both in Sydney.
