I finally may have figured out what has been wrong with my MX since day one. It's quite simple actually, but has taken me forever to get to this conclusion, no doubt due to the fact that I started off with this gear knowing essentially nothing. It's been reasonable for others, and for me, to assume that I simply have done something wrong. It's not an invalid assupmtion because I have made plenty of mistakes. But, underlying all of this is the fact that the mount just has not performed as advertised. Typical issues have been that no matter how well I am polar aligned, no matter how good my model, Protack simply has not worked reliably. Sometimes an unguided image might work only to have the next attempt completely fail. I don't mean just a little non-round, I mean totally smeared. And I've had guiding issues galore. Not just in guiding, but in even getting a guide star to show up in the center of a guiding graph once it has been selected!
In the process of using PEMpro to measure my PE I noticed in a very clear way what seems to be happening. If I slew to a star by moving the mount in a Westward direction I will get a beautifully straight line demonstrating perfect tracking in RA. However, if I slew to a star by moving the mount Eastward, all hell breaks loose and I will get drift of up to 10 arcsec over the next worm cycle. After 1 cycle the mount stabilizes and tracks beautifully, but not necessarily where one initiated the tracking. It might be 5+ arcsec away. This is pretty clearly demonstrated in the attached graphs from PEMpro. (PEC on, Protact off, +15 dec on meridian)
Does anyone reading this forum know what adjustment(s) might be off in my MX to cause this behavior? I've asked the question at SB but so far there is no response from the powers that be. The only things I've done to my mount are to replace the belts and adjust the cam-stop. The belt is not loose, and I believe not too tight either.
Nice to finally discover the root cause, I'll bet.
I had a similar experience last night when I re-adjusted the backlash on the RA of my G11, and suddenly the guiding settled down and I finally started to see round stars in my subs. I've still got to get to the bottom of my guide camera drop-outs and some odd autofocus results though.
Fun, this astro-imaging, isn't it?
Cheers,
Andrew.
Have you put any cables through the mount in addition to those from the manufacturer? I did and had some problems in one rotational direction. They seemed to be acting as a spring, winding up going, say, West and helping to drive the mount in the opposite direction. (I'm not sure which direction was which and the effect was small.) I didn't notice any guiding errors like you describe but I removed them anyway.
Have you put any cables through the mount in addition to those from the manufacturer? I did and had some problems in one rotational direction. They seemed to be acting as a spring, winding up going, say, West and helping to drive the mount in the opposite direction. (I'm not sure which direction was which and the effect was small.) I didn't notice any guiding errors like you describe but I removed them anyway.
Charles
Hi Charles,
That's an interesting thought. I've run several cables through my mount that I can check out further. In balance mode I cannot feel any resistance in RA, but who knows? I would be very sorry to lose through the mount cabling as it was a strong selling point and is a great feature!!
One of the big remote telescope hosting operators warns against running cables through the mount. He suggests it is not a good idea. Nothing but trouble in the long run. Hard won experience. Anecdotal evidence.
Through-the-mount cabling gave me some grief last year. My homemade dew heater cables were binding inside the mount, too taught and resulted in RA motor strain and odd noises...
Attached is a 15 minute test image of mine, unguided with Protrack and PEC ON. You'll get there...
Last edited by Logieberra; 28-10-2013 at 10:17 PM.
Some do some don't , have u a recent pic of your setup Logieberra so i can see the cabling ?
Never been able to get even 10 mins unguided looking like that on mine. Would like to see how it looks.
Thanks Marcus.
Last edited by Mighty_oz; 28-10-2013 at 10:32 PM.
Reason: spellchecking
Through-the-mount cabling gave me some grief last year. My homemade dew heater cables were binding inside the mount, too taught and resulted in RA motor strain and odd noises...
Attached is a 15 minute test image of mine, unguided with Protrack and PEC ON. You'll get there...
Sometimes I think I will NEVER get anywhere! Logan, are you saying that you do not run any cables through your mount? Or, did you just do a better job running cables?
I'm concerned that all the posts here are about cables. Couldn't it be something mechanical in the worm, or the way the worm is mounted? I don't know what the plungers do for example, and isn't there an adjusment that provides back/forth adjustment of the worm? Sure, the comments about cabling might be the cause and I certainly will investigate it as best I can.
If you physically apply varying pressures to your RA axis in both directions, Do you get physical movement showing up at the camera ?
ie are the stars moving in your images - could be done by looking at elliptical stars in a finished image or by blinking and seeing the movement between a sub with RA load and no load.
You would need to try both directions.
If you start back at the camera and work your way forward to just the OTA/Mount you may also discover where that movement may be coming from, including from within the mount if that is where it is.
You would expect to get some movement, the issue is if its actually backlash which would usually show up as movement with two fairly finite end stops or if its gradual based just on the strain which just gets larger as the load gets greater.
You would still get both of course if you have backlash.
If you are concerned about your cables you could check to make sure the cable loop around both axis is sufficiently large enough (as per the original loops) and that the cables are not bound up.
Adding too many extra cables could be a real issue.
Some silicon spray may help, but if its tight start by removing one cable.
I will assume that you have left all cables loose and not zip tied or interwound.
Debugging this needs to be done by a process of either introduction or elimination of all possible causes - otherwise you are just guessing.
Peter, the plunger settings are critical, as is engagement of the worm via adjustment of the large bolts on either side of the worm. There are PDFs on the bisque site under Downloads.
As rally pointed out, I'd examine all possibilities.
Sorry for curt replies, I reply over mobile. Not easy.
Last edited by Logieberra; 02-11-2013 at 09:18 AM.
'if I rotate the scope to DEC +15 on the meridian, grab hold of the counter weight shaft and apply modest pressure I can clearly rock the RA axis enough to visually see the camera on the end of the scope move back and forth relative to the ground'
From the SB document, Replacing the Paramount MX Worm Block Assembly:
Centering the Worm Block
To ensure the worm teeth are as centered as can be on the gear teeth, ensure the 1⁄4-20’s are tightened while lifting up and engaging worm block. You will need two 3/16 allen wrenches.
1. Ensure 1⁄4-20 screws on rotate axis are loose.
2. Lift up on worm block, and engage worm teeth with one hand, and rotate the gear
back and forth with other to ensure teeth are sitting inside each other and not on
top of one another.
3. There are two ways to tighten the 1⁄4-20’s. One way is to have someone help you
by one person pulling up on worm block with both hands while the other person tightens 1⁄4-20’s simultaneously. The second way is to pull up with both hands, then while holding worm block in place with one hand (not letting go of both at once) and tighten the right side first which will keep worm block engaged. While holding that screw tight with the wrench, tighten the left side simultaneously.
4. Make sure the 1⁄4-20’s are nice and tight. They can then be tightened a little more while the worm isn’t engaged.
Worm 'centering' is via 3/16-inch bolts #3 and #4.
P.S. There is slop when in lock mode. That's normal and intended. I assume you're in tracking mode here when you see the RA slop?
Last edited by Logieberra; 30-10-2013 at 02:07 PM.
If you physically apply varying pressures to your RA axis in both directions, Do you get physical movement showing up at the camera ?
You would expect to get some movement, the issue is if its actually backlash
Rally
OK, I put the scope/mount to ca +15 DEC/meridian and applied some pressure back and forth to the counter weight shaft. In that position the counter weight shaft is horizontal. The RA axis moves and the camera swings quite a bit relative the ground. Pushing on the end of the scope in the declination direction produces close to zero motion. So, there is quite a big difference between the two axis.
I removed the cover of the RA axis. I would expect to see movement in that situation since the cover locks the worm down in tracking mode. I applied upward pressure to the worm gear housing which I think engages the worm and the ring gear. It takes a very large amount of pressure to diminish obvious movement of the worm gear assembly. I don't have any idea if this test is valid to determine anything.
I guess the RA movement might be indicative of something since it seems so much more than the dec axis, however there is also a lot more weight moment on the RA axis. Perhaps that is responsible for the movement. I'm not sure.
I'd head straight to the plungers on RA and adjust them. They are the simplest of mechanical adjustments on the MX.
From the SB document, Replacing the Paramount MX Worm Block Assembly:
Centering the Worm Block
To ensure the worm teeth are as centered as can be on the gear teeth, ensure the 1⁄4-20’s are tightened while lifting up and engaging worm block. You will need two 3/16 allen wrenches.
1. Ensure 1⁄4-20 screws on rotate axis are loose.
Logan,
Thanks very much for this!!
I've read the entire Worm Block Assembly document. Just to be completely certain (as the document doesn't identify the plungers) are they the 2 vertical screws on either side of the cam stop pin? And the 1/4-20 are the 2 hex nuts with the two allen wrenchs shown in the photo you attached?
Yes, the plungers are the 2 vertical (small grub) screws on either side of the cam stop pin, no's 5 and 6.
The two 1/4-20s are the hex/allen bolts that you tighten with two allen wrenchs on either side of the block, no's 3 and 4, for horizontal worm spacing.
Last edited by Logieberra; 30-10-2013 at 02:08 PM.
Thanks a lot for the video! I've now made the adjustments and I think the RA axis feels much better. Now, just a clear night to confirm all is well. The mount homes fine so I couldn't have messed it up too much, hopefully.
Re the plungers. They were not too far out. In fact they were 2.25 turns out. I'm not sure if that means the worm on the gear is shallow or a bit deep. I decided to leave them at 2.25 for the time being. The firmness came entirely from adjusting the 1/4-20s. I didn't have a helper but think it's right now.
I had previously changed my belts months and months ago from black to grey. And, now that I think of it, that might be the genesis of this issue for me. I followed Chris' Youtube video on removing the motor/worm, but comparing what he shows to the pdf on doing this maintenance I notice that he skips over the 1/4-20 adjustment in the process. That missing step may have tripped me up. I think it's odd that SB recommends the video - perhaps not realizing that step is missing. I think Chris has done a great job with his video, but perhaps I should point this out to them. Would you?
I may be incorrect but I think the plungers are just springs to hold the worm in the wheel. They don't adjust the depth of the worm in the wheel which is, I believe, your problem. The Bisque pdf, Adjusting the MX Cam stop, probably should have a reference to the plungers but assumes they are set correctly and I believe adjusting them will only give a different pressure holding the teeth engaged.
The Bisque pdf, Paramount Worm Block assembly, IMO, is the one that you need to follow as that adjusts the depth of the Worm in the Wheel.
