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Hi there,
New to Losmandy - just received my first one today, an 811G and just doing some indoor tests after I assembled it.
I've noticed there seems to be quite a bit backlash in the DEC. I did tighten the clutch but still I can move the DEC by turning the counterweight shaft, and can even hear a sound when it moves, sounds like it is bouncing between gear teeth...
I understand this particular 'issue' has been reported probably too many times but still I'm a bit concerned - is this backlash normal, or I need to do some adjustments myself?
Thanks a bunch!
Yue
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I have a G11G and it has Dec backlash.? I have had it 9 months and have not adjusted anything.? I balance the scope so it is a bit camera heavy.? Sometimes, depending on where in the sky I am pointing at, after a dither it takes sometime to clear the backlash.? I think its a known issue and in gear box, not the worm.? Before calibrating PHD2 I move the Dec axis north.? After calibration I run the guiding assistant and it gives me a backlash of 1300ms or so.?
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We got a very good explanation of this from Brian Valente maybe 18 months ago (I'm not sure).? Basically, you are feeling the effect of the spring-loaded worm.? It has some flexibility and is normal.
The other thing that will happen, when you are calibrating PHD2, is that the backlash will seem very large when calibrating, but actually, small corrections are made effectively.? Tell PHD2 to compensate for backlash in dec.? The effect of this particular mechanism seems to be that backlash seems to be large for large, sudden movements, but not for small ones.
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Thank you both and glad to hear that is normal! I'll go find that post by Brian? :-)
I'll be imaging with this 811G whenever the skies are clear next time. and thanks for those PHD2 tips!
Yue
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It should have been correctly adjusted during assembly.
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Jim W
Phoenix, AZ. USA
Losmandy G11G w/ L6, NINA 3.0 / ASTAP, ASI2600MC Pro, ASI533MM Pro,?Sky-Watcher Scopes, Canon L Lenses.
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On Wed, Dec 27, 2023 at 09:08 PM, Jim Waters wrote:
It should have been correctly adjusted during assembly.
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Jim W
Phoenix, AZ. USA
Losmandy G11G w/ L6, NINA 3.0 / ASTAP, ASI2600MC Pro, ASI533MM Pro,?Sky-Watcher Scopes, Canon L Lenses.
I¡¯m sure it was just like mine. But then it was boxed and shipped. No telling how many times it was dropped hard in shipping. Scott made this video for a reason. I had the same thing when I got mine. The adjustment is simple. Greg Morris
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Much like collimation on a reflector telescope, SLW adjustments should be something every owner should be comfortable with. Like Jim W. Said, being a new mount it should be pretty close to adjusted so the adjustments will likely be very small if at all. If one owns this mount for many years one will adjust the worm many times.?
my personal advice when adjusting either of the spring loaded worms is to take off the OTA and any weights. Ideally, like in the video, when you adjust the RA Spring Loaded Worm, remove the DEC axis (or make sure it is balanced and empty).
the last thing you want to experience is a worm gear chattering across the ring gear as the spring tension is reduced, thereby deforming your precision brass ring gear¡ forever. It isn¡¯t rocket surgery, just watch the video, follow along, and go slow the first few times.?
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On Wed, Dec 27, 2023 at 02:48 PM, <darkairmouse@...> wrote:
New to Losmandy - just received my first one today, an 811G and just doing some indoor tests after I assembled it.
I've noticed there seems to be quite a bit backlash in the DEC. I did tighten the clutch but still I can move the DEC by turning the counterweight shaft, and can even hear a sound when it moves, sounds like it is bouncing between gear teeth...
I understand this particular 'issue' has been reported probably too many times but still I'm a bit concerned - is this backlash normal, or I need to do some adjustments myself?
Yue, Since you just received your mount, I'd recommend trying to use it first before making any adjustments. There will always be a little play in both axes. If it was set any tighter you could start stalling the motors. Try it in the field, see how it guides, and then see if you're satisfied. Redoing the worms takes some practice and I would not change anything until you find something functionally wrong. Chances are it was set well in the factory and will work as expected under the night's sky. Good luck! John ? -- _____________________________________________________________________________________________________________________________________________________________________________ Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit 100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics Zenithstar 61 APO; PHD2, Sequence Generator Pro and PixInsight user
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The DEC backlash I have is not exactly as what's showing in that video - my DEC axis can only move left-right, that is, if I hold the saddle plate and move it left-right; if I move the saddle plate forward-backward or up-down the DEC stays, nothing moves.?
However, I decide to follow that video and make the adjustments. With that screw backed off and the one with spring pushed in (till it stops), I can't turn the gear (too tight) but I can still move the DEC; from here I can adjust the 2 screws (per that video) to make the gear easily tuned by just 2 fingers, but the DEC backlash (if it is really a backlash) is still there.? Then I did a test, this time I pushed the spring screw little further in till the DEC 'backlash) disappears, and the gear became very tight and I can't make it turn at all, no matter how hard I push the other screw in (I thought I was going to damage the thread), I had to back off the spring screw (and adjust the other one) to make the gear turn; then the backlash reappears...
So, my case is that either I have a (seemingly) smooth turning DEC (gear) with a backlash, or I have no backlash but can't turn the gear... LOL
I'll go with the backlash for now :-) knowing all this is just dry-run, the moment of truth would be when I take it out tracking/guiding/imaging. Will post the result here.
Thanks again for all the good information here, really appreciated!!
Yue
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Ok just found this video:??and wondering if the "..worm floating between the blocks.." at 1:14 is what happens here.
Yue
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Here's a picture showing the gap and that screw on the cover - looks offset a bit.
Yue
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On Thu, Dec 28, 2023 at 01:27 AM, <darkairmouse@...> wrote:
Ok just found this video:??and wondering if the "..worm floating between the blocks.." at 1:14 is what happens here.
Hi Yue, The blocks should be compressed towards each other as much as possible during the tightening process as to avoid the 76s error where the ball bearings can be slightly out of their races inside. Since you already started adjusting, all you can do now is try to duplicate what is seen in the video. Note that the adjustments are being done with the motor removed as you are checking tension between the outer spur gears. You can adjust with the motor still on but there will be more turning force required. Power must be off, or the motor will not turn. Wish I had seen your thread earlier - I never made any adjustments until after 3 years of use.? CS, John ? -- _____________________________________________________________________________________________________________________________________________________________________________ Losmandy G11G2 on pier; refurbed Losmandy G11 with OnStep controller; SkyShed design roll-off observatory; ZWO ASI2600MM-P; ZWO ASI071MC; Sky-Watcher Esprit 100 ED with field flattener; Celestron C925 Edge HD with 0.7XFR, William Optics Zenithstar 61 APO; PHD2, Sequence Generator Pro and PixInsight user
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Ha! I think that's it! Followed the 2nd video adjusted the blocks and the spring screw, that backlash is now gone and the gear turns even smoother!
Adjusting this mount is MUCH easier than adjust my Skywatcher(s)!! A great design I can see now.
Thanks for all the helps and tips, guys!
This mount gonna kick a......
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Hi John,?
Yes I did remove the (DEC) motor to make the adjusts as shown in that 2nd video. The reason why I started to question if that was a 'backlash' is the movement was quite large (well, within the context), even compares to my skywatchers that was large.
Whether what I've done is indeed a fix or a big mistake - wait until a clear night. To be continued LOL!?
Yue
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On 12/27/2023 10:54 PM, Ryan Noonan via groups.io wrote:
Much like collimation on a reflector telescope, SLW adjustments should be something every owner should be comfortable with. Like Jim W. Said, being a new mount it should be pretty close to adjusted so the adjustments will likely be very small if at all. If one owns this mount for many years one will adjust the worm many times.
Not necessarily.? When my GM811 was new it had very significant DEC backlash very much like the OP was describing.? You could see the DEC axis rotate back and forth when you gently torqued the DEC axis by hand.? I went several rounds with Brian, who basically said "just take it out under the stars and see how it does".? That did not make sense.... backlash is backlash and while an unbalanced load might bias the gears so the backlash is minimal, this will change drastically with pointing direction. In the end I took matters into my own hands and did the worm adjustment procedure per Scott's video.? This improved things quite a bit but I could never get below about 2500mS as measured by reversing DEC at guide speed and observing when the scope actually started to move.? It was also very inconsistent.... one night the backlash reported by PHD2 would be very low (like a couple hundred mS) and the next night it would be back around 2500mS. The backlash also had a tendency to slowly increase beyond 2500mS over a period of days to weeks.? Repeating the worm adjustment procedure would bring it down again (but still never below 2500mS). But this is a pain because it requires partial disassembly of the DEC assembly to allow rotating the worm manually. After MUCH experimentation and head scratching, I discovered that on my mount, on both the RA and DEC axes the hole in the baseplate where the left worm block pivots was oversized (or perhaps the worm post was undersized).? This allowed the entire worm assembly to move laterally enough to feel it if I laid my finger in the "V" between the gearbox plate and the worm cover and torqued the axis.? ANY movement here translates directly into additional backlash that cannot be adjusted out. This contributor to the backlash is not adjustable but IS fixable. However, it requires a fairly simple (and reversible) modification and I believe that is off topic for this mail list? the last thing you want to experience is a worm gear chattering across the ring gear as the spring tension is reduced, thereby deforming your precision brass ring gear¡ forever. It isn¡¯t rocket surgery, just watch the video, follow along, and go slow the first few times.
That is not possible if the worm spring bolt is properly tightened to Losmandy specs because it also acts as an out travel limiter.? I simply turn it in until it bottoms on the worm post and then back it off 1/2 turn.? That puts the spring compression pretty close to the 8mm figure I got from Brian and also prevents the worm from being forced out of engagement.? Note that before I discovered this, one night I pushed the tube with the clutches locked down tight and the RA worm skipped a couple teeth.? That one cost me $100 ;)? On the up side, the replacement worm has un-measurable 240 second periodic error. Paul G. -- Paul Goelz Rochester Hills, MI USA pgoelz@... www.pgoelz.com
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My own G11S had way more backlash than I liked.? One participant at the Kaibab Star party with a G11 that just had an RA extension installed that came fresh from Losmandy claimed that it was delivered with a large amount of backlash.? I'm not sure if it was caused by Losmandy because he was unaware that transporting a mount with the clutches tight (which he did) can cause that too.? I would not trust the backlash to remain unchanged during delivery transportation.? Unless you pick it up yourself, like I did.? At any rate, just learn to make the adjustments ASAP, which you will have to do routinely.? Thermal effects, non-perfect mechanics, carrying the mount and the SLW back-off screw setting can all cause this.? Counterweighting can mitigate the presence of backlash, which you will probably never be able to fully eliminate.
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On Thu, Dec 28, 2023 at 11:41 AM, HenkSB wrote:
that transporting a mount with the clutches tight (which he did) can cause that too.
Didn't know that, and I'm sure I would do the same if you haven't mentioned it!?
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On Wed, Dec 27, 2023 at 11:48 AM, <darkairmouse@...> wrote:
Hi there,
New to Losmandy - just received my first one today, an 811G and just doing some indoor tests after I assembled it.
I've noticed there seems to be quite a bit backlash in the DEC. I did tighten the clutch but still I can move the DEC by turning the counterweight shaft, and can even hear a sound when it moves, sounds like it is bouncing between gear teeth...
I understand this particular 'issue' has been reported probably too many times but still I'm a bit concerned - is this backlash normal, or I need to do some adjustments myself?
Thanks a bunch!
Yue
Hi Yue,? Welcome to the Losmandy club! Are you currently imaging and moving to Losmandy to continue imaging or are you a visual user??A lot of new Losmandy owners get all up on the tire about what appears to be backlash as new Losmandy owners. What most of us learn over time is what does it matter if something feels out of place but the results work well. Some of the backlash is due to the way the spring loaded one-piece worm mounts are implemented. It is the nature of the beast to exhibit some springiness on the axles when exerting external force on them. But AFAIK nobody pushes on their counterweight or scope tube while imaging and the observed springiness has little impact on measured guiding results.? That said the Losmandy drive system has some parts that tend to loosen and yours may have done so in shipping. The most common reported issue is worm bearing block shift. When this occurs the additional space allows some axial play between the worm shoulder and bearings. This is commonly reported as feeling like flipping from one worm face to the other when in fact it is the gap between the worm shoulder and bearing. The other commonly seen issue in this area is the small grub screws on the Oldham coupler loosen just enough to allow some rotational movement and this often manifests as backlash lag with a long period. Unfortunately both of these issues present in the same way and the only solution once you have checked the spring and worm lift are correctly set is partial disassembly to retorque the Oldham coupler grub screws (2 per coupler) and squeeze and torque the worm bearing block fasteners to minimize axial play.? But being both a new mount and a new user my suggestion is to set up your new mount and use it and learn how the Gemini 2 works and if imaging get you guide scope and camera setup and optimize the autoguiding software and then measure the unguided PE and guided PE error to see if you need to even touch the drive system or not. Then let us know how it works.? ? -- Chip Louie Chief Daydreamer Imagination Hardware?
? ?Astrospheric Weather Forecast - South Pasadena, CA?
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Greg
Ryan Noonan
Chip Louie