141 replies to this topic

[DAVIDG]

Tim

   The electronics are the same as the LX200 Classic SCT and were designed to work on at least 12 volts and around 500ma. A 9 volt  rechargeable battery typically has a full charge voltage of 7.2 to 8.4 volts so your down 4 to 5 volts from the design voltage. That can be the reason why motor stalls with a small mechanical load. 

 

                   - Dave 

Edited by DAVIDG, 14 January 2025 - 11:29 AM.

[deSitter]

it runs okay until I put the gear cover on.  I cleaned the shaft on the end of the slo mo knob, and that helped a little, but it still stalls if I try to put the cover all the way on.

 

Man, what a pathetic POS!

 

-Tim.

Sounds like the cover is impinging on the worm tension bar. As mentioned, there is a thin aluminum plate that is designed to flex under influence of a set screw, for setting the backlash and worm tension. If something presses on that bar and deforms it, it will bind the worm and seize the motor. That's probably a big part of the problem. Run it with the cover off. The links above show how to tune it up. It's a tight fit under there, make sure the wires are routed away from trouble.

 

-drl

[tim53]

Sounds like the cover is impinging on the worm tension bar. As mentioned, there is a thin aluminum plate that is designed to flex under influence of a set screw, for setting the backlash and worm tension. If something presses on that bar and deforms it, it will bind the worm and seize the motor. That's probably a big part of the problem. Run it with the cover off. The links above show how to tune it up. It's a tight fit under there, make sure the wires are routed away from trouble.

 

-drl

I'm still not outside yet.  It's cold out there (57F!).  But looking up that thread, I think my problem is here:  

You can see two of the 4 screws holding the gearbox to the worm block toward the top of the picture.  The black thing between the screws is a rubber o-ring that gets squished depending on how tight the screws are.  I put them on tight, because they were tight coming off.  But that might have been due to some locktite on the threads.  I've got a ton of Harbor Freight o-rings I bought (during one of their rare "blowout sales" ).  So I could put a new o-ring in there.  But I find that kind of a strange way to adjust tension (end play, really).  Maybe what I should do instead of mess with that is adjust the end play on the other end of the worm and see if that loosens it up.  Like I said, the motor runs fine so long as I don't screw the cover (thin aluminum plate on the left under the slo mo knob).  I thought the problem was that the spur gear on the worm and on the knob were dragging against one another where they overlap, but maybe that wasn't the problem.

 

-Tim.

Edited by tim53, 14 January 2025 - 12:26 PM.

[deSitter]

I'm still not outside yet.  It's cold out there (57F!).  But looking up that thread, I think my problem is here:  

You can see two of the 4 screws holding the gearbox to the worm block toward the top of the picture.  The black thing between the screws is a rubber o-ring that gets squished depending on how tight the screws are.  I put them on tight, because they were tight coming off.  But that might have been due to some locktite on the threads.  I've got a ton of Harbor Freight o-rings I bought (during one of their rare "blowout sales" ).  So I could put a new o-ring in there.  But I find that kind of a strange way to adjust tension.  Maybe what I should do instead of mess with that is adjust the end play on the other end of the worm and see if that loosens it up.  Like I said, the motor runs fine so long as I don't screw the cover (thin aluminum plate on the left under the slo mo knob).  I thought the problem was that the spur gear on the worm and on the knob were dragging against one another where they overlap, but maybe that wasn't the problem.

 

-Tim.

Getting there!

 

The O-ring is just for allowing some slack in the alignment of the worm block with the gear shaft. Now, Imagine a block of aluminum. Now put it on the table saw and slice a gash halfway across it, so that only 1/16" of aluminum remained holding the 2 parts together - cut in half other than a 1/16" remainder. You can now take the block in your hands and bend one half relative to the other a slight amount, along the channel you just cut - 100ths of an inch back and forth. That's the basis of the mechanism for removing backlash! It's actually fiendishly ingenious. Of course if you bend it back and forth vigorously, it will break along the channel - but that's not what happens. You get it close when you install it, and then a couple of set screws are used to bend it just enough to take up backlash but not bind. It's a very fiddly adjustment but it only has to be done once.

 

So I'm thinking a trapped wire or the like is pushing on the part that bends, and is forcing it against the worm, so that it binds.

 

-drl

[DAVIDG]

 Tim,

  Can you post a picture of this cover that causes the motor to bind ?  I noticed that the gap with the O ring in it is not uniform. The top is bit wider then the bottom and it does look like that is causing the gear on the worm to rub against the gear on the slow motion shaft. 

 

                - Dave 

[tim53]

I'll take a pic when I go out to work on it in a while.  

 

I don't remember any flexible thin aluminum plate. The gear cover (on the left) is about 1/8" thick and attached to the box (the thicker part on the right, above) with 4 screws at the corners, with 2 alignment pins next to 2 of the screws on opposite corners.  When I had the motor running with the 9 volt battery, it ran freely when the cover was off, but about aligned with the pin holes.  As I moved the cover into place, the motor stalled before getting the cover on, which is why I was suspecting that the spur gears were dragging.  But I haven't tried to run it on 12 volts yet.

[DAVIDG]

 Tim

   What is going on with this area ? It looks like a plate is broke or bent and causing the shaft of the slow motion gear to be out of alignment ? 

 

                     - Dave 

 

[tim53]

HI Dave:

 

that pic is from another thread, so it's not mine.  There isn't anything in there between the gears on the right and the cover on the left.  The large gear on the center left, and the small gear to the right of it are both on the shaft with the slow motion knob (far left).  the shaft goes into a bushing on the gearbox on the right.

[tim53]

I'll go out and take a few pics of mine.

[tim53]

Okay, here we go, from cover all the way off, to partlly on, to on.

 

 

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[DAVIDG]

 Hi Tim

  It looks to me that the large white gear on the slow motion shaft is jamming up against the other gear that drives the worm  I think by tightening  the screws that hold the worm assembly on, the O ring is compressed too much and now there is no clearance between the gears.

   It also looks like the sensors for the encoder wheel are blocked with grease. If so they need to be cleaned out so the encoder will work. It also looks like the encoder wheel is bent so it needs to be straighten and make sure all the slots are clear. 

 

              - Dave 

[tim53]

I think you may be right about the comoressed o-ring. When I get back out there, I’ll check that. 
 

the encoder ring is not well shown in my images. I’ll take more pics when I go out. I don’t think it was clogged with grease, but I’ll make sure. It’s really thin and delicate. I’ll try to be careful with it. 

[tim53]

Today the motor turns a turn or so then stops. This with no load whatsoever. 
 

the encoder wheel is clean. It’s painted black and the discoloration in this pic is dark stuff behind it. The openings are clear. 

[tim53]

Pic too big to load. 
 

[tim53]

Put it all back together and plugged it in. No joy. 
 

im done. 

[CHASLX200]

Put it all back together and plugged it in. No joy. 
 

im done. 

It's no Unitron for sure, Wonder any of that stuff worked for long. Just super cheap built with plastic gears dears,

[deSitter]

Put it all back together and plugged it in. No joy. 
 

im done. 

If you want to send me all the boards I'll see what I can do.

 

-drl

[tim53]

I suppose I could think about that. The motor is really weak, though. I could stop it with very light touch on the encoder disk while it was running by itself with no load whatsoever. It’s hard to believe it could drive that mount. 
 

im looking at a couple onstep conversions I’ve seen with a search. Would prefer a turn key kit of course, but I could make motor brackets and worm blocks as needed. 

[starman876]

I thought there were kits out there that were ugly and play.  Maybe I am thinking about the fork mounts.   

[deSitter]

I suppose I could think about that. The motor is really weak, though. I could stop it with very light touch on the encoder disk while it was running by itself with no load whatsoever. It’s hard to believe it could drive that mount. 
 

im looking at a couple onstep conversions I’ve seen with a search. Would prefer a turn key kit of course, but I could make motor brackets and worm blocks as needed. 

 

One last thing to try before concluding the problem is electronic (bad transistor for example) - take the motor completely out of circuit by snipping the blue wire and then try to power it directly with 12v. It should spin vigorously and be impossible to stall by grabbing the shaft. If not, the motor is bad. Use a 1A 12v power supply of some sort (the 12v power brick itself is fine for this). Cut the plug off the brick (it needs to die anyway) and expose the wires, then touch to the terminals of the motor.

 

If the motor is bad, then it's dirty/worn brushes or a dirty stator, or the winding is partially shorted so that not enough of the turns in the armature winding are involved. The current meter on the mount is there for a reason. DC motors are actually very rugged but they don't respond well to getting very hot. If the scope is way out of balance, a lot of current will be drawn through the winding to work against gravity. The winding can actually burn up, or, it can partially short, so that insufficient winding path remains to create the strong magnetic field that the permanent magnets work against. That is fixed by rewinding the motor.

 

This mount is worth saving. It can carry a ton and the go-to function works very accurately.

 

(This all reminds me of working on Aurora Thunderjet HO cars )

 

-drl

[tim53]

I had the scope out last night to view Jupiter, on the manual Super Polaris mount.  As I said elsewhere, that scope is too much for a super Polaris.  Since Jupiter was near the zenith, I had a tough time aligning on it.  The finder is straight through, and I find myself unable to contort enough to look through the eyepiece, so I did the thing where I view the scope and Jupiter from the side, and move the axis I'm closest to until the OTA points in the direction of jupiter, then view along the other axis and repeat.  That usually got me close enough to get jupiter in or very near a wide field view in the 'afractor.  I quickly noticed a problem with focusing.  Jupiter seemed to slowly drift out of focus a couple times.  I had to tighten the tension knob to keep it from doing that.  Next thing I noticed was a slight flaring of the planet just outside focus, that didn't quite go away at focus.  By moving the focus knob back and forth, I was able to see that because the focuser drawtube is too loose in the focuser body, it's going off axis slightly when racking it in and out.  This actually took a while to confirm, as the scope shook for a good 5 seconds after each tough of the knob.

 

I need to replace that focuser, or fix it somehow so it stays concentric.  Considering I paid $300 for the scope and mount, I expect a focuser will more than double my investment.  Hopefully, it'll be worth it.  I'm also likely to invest in or make a Dovetail plate for the scope rings from the LXD600 before I fix the drive on the LXD600.  

 

Considering I was "retired" from JPL during the November layoffs, one might think I'd have time to do all this stuff I've been wanting to do with the hobby for the past 5 decades.  But my favorite saying has become "the trouble with retirement is you don't get a day off."

 

-Tim.

[deSitter]

I had the scope out last night to view Jupiter, on the manual Super Polaris mount.  As I said elsewhere, that scope is too much for a super Polaris.  Since Jupiter was near the zenith, I had a tough time aligning on it.  The finder is straight through, and I find myself unable to contort enough to look through the eyepiece, so I did the thing where I view the scope and Jupiter from the side, and move the axis I'm closest to until the OTA points in the direction of jupiter, then view along the other axis and repeat.  That usually got me close enough to get jupiter in or very near a wide field view in the 'afractor.  I quickly noticed a problem with focusing.  Jupiter seemed to slowly drift out of focus a couple times.  I had to tighten the tension knob to keep it from doing that.  Next thing I noticed was a slight flaring of the planet just outside focus, that didn't quite go away at focus.  By moving the focus knob back and forth, I was able to see that because the focuser drawtube is too loose in the focuser body, it's going off axis slightly when racking it in and out.  This actually took a while to confirm, as the scope shook for a good 5 seconds after each tough of the knob.

 

I need to replace that focuser, or fix it somehow so it stays concentric.  Considering I paid $300 for the scope and mount, I expect a focuser will more than double my investment.  Hopefully, it'll be worth it.  I'm also likely to invest in or make a Dovetail plate for the scope rings from the LXD600 before I fix the drive on the LXD600.  

 

Considering I was "retired" from JPL during the November layoffs, one might think I'd have time to do all this stuff I've been wanting to do with the hobby for the past 5 decades.  But my favorite saying has become "the trouble with retirement is you don't get a day off."

 

-Tim.

My 127ED has a Moonlite focuser that is perfectly integrated with the rear tube flange. Contact them - they may have some NOS in their inventory.

 

If you ditch the focuser, I might be interested in fixing it up.

 

-drl

[Jay_Reynolds_Freeman]

I used to own a 127ED OTA but I did not have Meade's mount -- I mounted it on a Losmandy G-11. I am posting because in case anyone is interested, some fellow observers and I once did an optical-performance shoot-out between several high-end refractors of 127 to 130 mm clear aperture, including my 127ED.

[deSitter]

I used to own a 127ED OTA but I did not have Meade's mount -- I mounted it on a Losmandy G-11. I am posting because in case anyone is interested, some fellow observers and I once did an optical-performance shoot-out between several high-end refractors of 127 to 130 mm clear aperture, including my 127ED.

That was a good read! My 127ED does 300x on Jupiter with ease. I prefer 200-250x. It is a real sleeper scope as your article shows.

 

-drl

[CHASLX200]

The optics were good on my 5" ED and had a yellow cast.