Posted by Lenord on August 12, 2002, 10:03 am For CCD work, the last I heard was that the gears exhibited too much PE. The testing was on a 24" gear IIRC. Andy had an experimental fix for that, but I am unsure as to the results. Backlash is easily compensated for in the software. The compensation is in arc minutes with 5 decimal places after that, for a precise correction. Lenord
Hi Herb,
I'll ask the end user of the gear to see what is up and report back.
--Previous Message--
: Thanks and yes I was planning on using Andy's
: gears. Is there a problem with them and
: CCD? (hope not)
: I was thinking about the backlash the spur
: gear would introduce? It may be better to
: go with a bigger worm gear instead, you
: think?
: Herb
: --Previous Message--
: Hi Herb,
: Somewhat correct. Back when that was written,
: Mel had 10 microsteps per revolution in
: his software. He now has 40. If you do the
: math: : gear ratio X microsteps per
: revolution X
: stepper microsteps per revolution= XXXXX
: and then
: XXXX divided into 1296000 you get the
: resolution of your system in arc seconds.
: Mel recommends .5 arc seconds per microstep
: minimum for visual use. For CCD work, some
: get into the .0XXXXX arc seconds per ms.
: Your 720:1 ratio on the RA, with a 400
: step stepper, would yield .1125 arc
: seconds per ms, plenty good for CCD work
: from what I am told. The Dec. on a fork
: mount at 480 might require some added spur
: gearing to the worm shaft to get excellent
: images. Not on a GEM though....
: As far as moving that kind of weight around,
: you can do that wiht the 720 and quite
: possible with the 480:1 Dec. If it were me
: though, I'd add in some spur gears to the
: worm shaft on the Dec. to get a good
: ratio. You can purchase good steel spur
: gears for cheap these days. A couple of
: bushings and a couple of set screws and
: you are in business.
: Are you going to try using Andy's gears for
: CCD work ?
: HTH
: Lenord
:
: --Previous Message--
: Lenord. I was wondering about the gear
: ratios.
: On Mels site he talks about having 1200:1
: to 2400:1 ratios. Is this because the
: stepper motors he was using were 1.8 deg
: per step @ 200 steps per revolution and
: The ones you are using are .9 deg. per
: step @ 400 steps per revolution?
: My fork mount weighs in at about 150+lbs.
: There's a lot of mass swinging around and
: slew rates are not a great factor since I
: won't be swinging from east to west or
: north to south. More than likely I'll be
: moving around in small portions of the
: sky. The initial slew will be the only
: major move I make per night and there's
: always something to do while waiting.
: I have a 720:1 ratio (22") on the RA.
: Should I worry about reducing this further
: or will this be adequate for good tracking
: and CCD?
: For Dec. I was wanting to keep the gear size
: somewhat smaller since it sits at the side
: of the fork and will be more succeptible
: to bumping. A 480:1 (15") would be a
: good size but would I want to reduce this
: somewhat to match more closely the RA
: gearing?
: What are your thoughts on all of this?
: Herb
: P.S. I will get with you about making up what
: I need to have a complete GoTo drive from
: gear train on in 2 to 3 weeks (wallet
: permitting).
:
: --Previous Message--
: Herb,
: Send a message to Andy Saulietis. His e-mail
: address is: iss@pvtnetworks.net
: He can fabricate gears/worms/clutches for you
: and will have an idea for you.
: Take Care
: Lenord Stage
:
:
: --Previous Message--
: I'm attempting to finish a fork mounted
: 16" Newtonian and need some help. I
: have 1" of shaft for RA and can't
: figure out how to get a worm gear and
: clutch system in such a short space. The
: shaft is 2" dia. for RA and 1.5"
: for Dec. The Dec shaft has 2.5" of
: shaft and isn't a problem.
: I should probably have something made for me
: rather than spend money on something that
: will end up in the (bad idea) extra parts
: box.
:
: : : : :
:
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