Re: ATM [~OT] Roll film holder plans?

[Del Stanton <sd20@earthlink.net>]

Are you considering 120 roll film ?

My approach would be to use a small induction motor,
essentially stalled to maintain tension on the take-up
spool. This motor could be an inexpensive open frame shaded
pole motor run at reduced voltage - perhaps a small motor
would require some belt pulley arrangement to increase the
torque.  This motors, at full voltage, generate considerable
heat.  So you will have to evaluate how hot it runs at
stall, when you are unable to provide any fan cooling. 
Better - you could also just turn the motor on during the
film advance cycle.  If you do it that way provide a thermal
fuse so if the motor gets left on by some circuit mishap it
doesn't burn up.  Then a stepping motor to drive a pinch
roller to advance the film , pulling it across the picture
taking aperture.  That stepping motor would be programmed to
run a given number of steps.  A PIC microprocessor - or even
a Parallax Basic unit could do that nicely.  The thing is
you want to measure the motion of the film - not the
rotation of the take-up spool.  Then your frame spacing on
the film will be consistent.  

The Rollie Twin Lens Reflex Cameras use a small roller with
very fine, sharp teeth that runs against the film to
accurately measure the movement of the film.  You might be
able to find such a roller as a replacement part - then run
the take-up spool with a stepper that is controlled by a cam
driven by the metering roller (with suitable gear
reduction).  (Or count up the pulses from an inexpensive
rotary encoder - salvage the bits and pieces form a old
computer mouse.)

Good rollers could be salvaged from an old Polaroid roll
film or film pack camera - the mechanism that breaks the pod
and rolls the goop out ..... The assembly also provides the
squeeze needed to get consistent drive.

Arrange a leaf spring to provide some tension to the outer
diameter of the feed spool (the one the film came on).

Del Stanton    sd20@earthlink.net

matt@considine.net wrote:
> 
> Hi,
> 
> Does anyone know of 'net plans for a roll-film holder/camera body?  I'm
> looking for something that could be made by an amateur and would incorporate
> some sort of film advance mechanism.  The ATM relevance is that it would be
> used on a telescope to replace a heavier commercial camera body.  I guess
> the part I can't figure out myself is a simple, clean film tensioning and
> advance mechanism.  Anyone with any thoughts?
> 
> Regards,
> Matt
> Considine