ATM Barn door/Scotch/Haig mount timing idea

[Andrew Grisdale <roadwarrior@techieguy.com>]

Hello all,

I don't know if this a new idea, but I just thought of it myself....

I have nearly finished a simple barn door style mount, for some first attempts at astro 
photography, and put in this feature to help me turn it at the right speed. First I made 
a non moving bearing for my handle, I wanted to do that anyway for simplicity of fitting 
a motor drive later, basically it means having 2 large washers fixed with nuts, spaced by 
one nut, to the end of my threaded rod, and 3 holes drilled into them around the outside, 
and having the handle drive it with 3 rods sliding in those holes. Having done that, I 
had my idea, and have put a 30 tooth gear from a toy, on the handle spindle, and a simple 
fixed ratchet, a bit of plastic from a pop bottle,  so every 1/30 turn, it clicks. Now I 
can use a cheap quartz/analogue watch tucked into the side of my hat and dangling by my 
ear, that has an audible tick each second (when the hand moves) and turn the handle one 
click every two seconds for accurate movement. One could use an old but similar watch 
strap and some elastic to make a headband for the watch if desired. I specified a cheap 
watch since these are noisier and also some more expensive watches and stop watches have 
4 ticks per second from the balance wheel and escapement which is hard to keep track of. 
This is a tangent style design mount by the way, not the chord style with pivoted 
bearings. I guess one could figure how to do something similar on any. 

Hope someone finds that useful,

Andrew G.

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