Re: ATM 5 hour straight bolt guide curve

[The Silent Observer <silent1@ix.netcom.com>]

doug kniffen wrote:
> 
> What kind of curve is it??? Hyperbolic is a fairly good
> guess, but it also seems to be a section of one of those elliptic curves.

Actually, a hyperbola is a conic section.  This curve, however, is (I
think) a catenary, not a hyperbola.  It reaches horizontal at one limit,
and vertical at the other, but unlike a hyperbola, where those limits
are at infinity, this curve has the limits at a distinct distance --
horizontally, the length of the moving board from the vertical, and
vertically at the point where you've rotated 90 degrees from the
horizontal (the six hour point).  A curve that doesn't approach the axes
asymptotically can't be a hyperbola, nor a trig function -- that leaves
catenaries as the most likely family of curves to include your guide
surface.

Another possible issue here -- you made the board length equal to six
hours of screw thread, but as you draw up the board, you raise the lower
end; when the thread has advanced six hours, you won't be at 90 degrees,
which means you must be introducing more errors somewhere else (or, more
likely, you have to start well above horizontal because the guide curve
interferes with the upper board).  Either that or (I haven't carried out
the plotting) you might see the curve inflect back downward, which
introduces another complication in terms of which edge of the moving
board rides the curve.

Finally, if the board wears as the mount runs (and it will -- but how
fast?) you'd see you correction deteriorate over many uses of the mount,
especially if you don't always let it run 5-6 hours at a time.

-- 
Some of their knowledge is corrupt, and inaccurate, being gleaned from
all manner of sources.  But like us, they are wizards too.
                                                    -- Jaldis the Blind

Donald Qualls, aka The Silent Observer           NAR # 70141-SR Insured
Rocket Pages                http://silent1.home.netcom.com/launches.htm
Telescope Pages            http://silent1.home.netcom.com/astronomy.htm

Opinions expressed are my own -- take them for what they're worth
and don't expect them to be perfect.