RE: ATM gears and such

[Dominic-Luc Webb <dlwebb@canit.se>]

On Thu, 15 Jan 2004, Peter wrote:

>
> To all Gear Makers out there who did their own:
>
> I'd like to know how did your home made gears work out? Have you measured
> the periodic error and if yes what was it?
>
> Thanks,
>
> Peter


I made a gear that would be criticised by most that worked
out for my needs. I made a motorized tracking drive for 35
mm camera that fits to a common camera tripod using a 555
timer, Johnson counter, Darlington array and stepper motor.
The gear on the motor was the one I originally found attached
to the motor, from a printer. The gear turned a belt. I inverted
the belt so the teeth (square) faced outward. The belt slipped
over a plastic disk I turned on a wood lathe. This disk is
turned by the stepper and turned around a screw that pushes the
camera along. It is essentially a barndoor arragement the screws
onto a camera tripod.

I filed into the plastic a little bit to randomize periodic
errors. I use this with a roughly 25-80 mm lens and it worked
fine in terms of the gear. A bigger problem was that the
stepper has a strong kick to it and this creates vibration.
Turning the gear manually (I have marks to cue me how far to
turn the gear every 15 sec) for up to 15 minutes gave tight
star images. I am not real impressed with photographs yet
to scan them, but this is because of another problem... I
live near an airport and it is nearly impossible to image the
darkest part of the sky (straight above) without several
airplanes flying right in front of the camera. Please note I
wanted wide field photos, the 25 mm end of my macro.

The inverted belt seems to work OK with a decent stepper and
wide field photos using 35 mm camera. Sometimes, it is terrific
to just have something really small and portable I can stick
in the back of my bicycle. What I really need is warmer
weather.



Dominic-Luc Webb
Near Uppsala, Sweden