Posted by Lenord on August 11, 2002, 11:58 pm 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 --Previous Message--
Hi Herb,
Lenord
: 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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