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Richard Turner
member
Reged: 01/25/09
Posts: 58
Loc: NC
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I've tried to adjust as much of the dec. backlash out of my LXD 75 mount for purposes of guided deep space imaging. I snugged the worm to the worm gear to the point where I could feel no play when turning the worm by hand, but not so tight that binding would occur. This might be too tight for go-to's, but I was wondering if the tightening is the right way to go to help the PHD or Envisage handle the backlash?
I've tried Envisage and PHD with mixed results. Some 3-minute guided exposures show trailed stars at 650mm (5" Vixen reflector, f/5, guided with 50mm finder). Envisage seems to have trouble handling dec backlash. My polar alignment is not drift-align, but I do get alignment  close to the pole,(usually around 5-10 arc minutes). I try for good balance in dec., with slight east-heavy right ascention.
I was wondering if anyone could give me some tips that might improve my guiding.
Thanks,
Richard
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Richard Barton Turner
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EricJD
sage
Reged: 07/24/07
Posts: 424
Loc: Chesapeake VA
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If most of your 3 minute exposures are good then I'm afraid that you're not going to be able to get much more out of this mount unless you get it hypertuned. The mount just isn't of high enough quality, out of the box, to expect much more than this.
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Orion 120mm ST
LXD75
DSI Pro 3
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Eddgie
Carpal Tunnel
Reged: 02/01/06
Posts: 2701
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Did you also take out the play between the spur gears?
I find that these gear teeth are rather large (Celestron uses a bit finer teeth in it's design). Anyway, when you have a large spur gear, the teeth need a bit more clearence for wear purposes, HOWEVER in THIS application (telescope drive), I think it is safe to ignore potential wear issues. In a spur gear used on manufacturing line equipment, it will turn milliions of turns in its lifetime.
In your telescope? Not so much.. LOL.
Anyway, my advice is to remove all backlash from the spur gears if you have not already done so. Put a small amount of grease on the teeth just to get the tooth faces to slide a bit easier against one another.
Unless you are using the scope for hours and hours every nigth, and doing dozens and dozens of long slews every hour, just ignore any worry about wearing out these gears in your lifetime.
Regards.
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Celestron C14, CGE (Big Al)
Astro-Physics 6" f/8 (Buffy)
Televue 101 (No name, but I call it my Widescreen HD Space TV)
The night sky is my mistress. She seduces me away from all other lovers.
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yock1960
professor emeritus
Reged: 06/22/08
Posts: 976
Loc: SW Ohio, USA
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There is a guide over in the files section on LXD75Telescopes Yahoo! group, called guiding.pdf. It gives a strategy for trying to guide with PHD. It mainly deals with getting PHD to calibrate succesfully, so if that's not an issue, it may not be much help.
That being said, I'm guiding at F4 and imaging at F5.9 and some nights are better than others. I usually do some star repair on most of my images, again it varies. I see it as the price of using a < $1300 mount.
Do check the set screws on the spur gears! They are notorious for coming loose. They are very small and you just can't get them tight enough! I've even had them come loose after using thread locker!
Steve
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LXD75 GEM
Orion Starblast 4.5" Imaging Reflector
William Optics Zenithstar 66 SD APO
Meade DSI II OSC
Meade DSI III OSC
Orion Starshoot Autoguider
Televue Powermate 2.5x
Discovery 6" Dobsonian
Nikon Action Extreme 10x50's
Gallery
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Richard Turner
member
Reged: 01/25/09
Posts: 58
Loc: NC
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Thanks for the replies. I'm going to grease those spur gears, make sure they are tight on the shafts, and that they are snug against one another, as well as check for any slop in the worm or worm gear contacts. Then, I'll use quiet slew (it's much slower than regular slew) to keep the stress on the gears down some.
I think I will also adjust the RA agressiveness in PHD to try to get better east-west guiding.
Thanks,
Richard
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Richard Barton Turner
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rob0260
super member
Reged: 01/31/09
Posts: 116
Loc: Teulon, Mb., Canada
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I just bought some locktight and a set of metric allen keys to tighten the setscrews on the gears of my ldx75 but even the smallest allen key is too big for the setscrews. It's a 1.5mm. Does anyone know what size allen key I need to tighten the setscrews? This info would save me a lot of trial and error and running around. Thank you in advance.
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SN8, LXD75, ETX 80, 4 1/2 inch Newtonian, DSI-C, Meade series 4000 eyepiece set, Antares ub2s barlow, antares 5x barlow, 10x50 binoculars.
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BCB
Undercover Saboteur
Reged: 11/24/03
Posts: 5196
Loc: Look over your shoulder
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Needs a 1mm key.. OR if the holes a bit stripped/worn, a standard hex key, in .050 size works well too..
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Mark
Lost in thought. Please send search party!!!
Astro-Tech 111EDT
Orion 8" F5 Newt w/Moonlight CR-2 focuser
SVP mount w/Meade 497 Autostar GOTO mod
Treeline Observatory
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rob0260
super member
Reged: 01/31/09
Posts: 116
Loc: Teulon, Mb., Canada
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Thanks Mark. Now for a trip to the hardware store to get one. Regards, Rob.
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SN8, LXD75, ETX 80, 4 1/2 inch Newtonian, DSI-C, Meade series 4000 eyepiece set, Antares ub2s barlow, antares 5x barlow, 10x50 binoculars.
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