Home-Made Zoom Motors
Before the J 4, we made our own motors from surplus DC gear motors. The most
important part is a slip clutch to prevent too much torque on the zoom ring
against the internal stops at the wide and tele ends. These clutches are available
from Sterling Instrument. Clutches can also be built into the ring gear on the
lens. Globe and Pitman Motors are available from surplus and stock. A simple
reostat circuit will provide speed control but changing the voltage with taps
on the battery pack will give better control. A resistor that charges a capacitor
to full supply voltage will give the motor a little "kick" to get it started
smoothly. Adjust the capacitor size to give the right amount of kick. These
motors will accelerate and stop smoothly. An "X" wired DPDT switch works for
reversing. You will need a high wattage pot for speed control.
Why build your own when there are great controls out there? Cost or say you
need a 20-minute zoom. These motors will move other things too.
Model remote control motors, with transmitters and receivers will move props
C and H Surplus Pasadena California
Herbach and Rademan www.herbach.com
© Copyright 1999-2004 Ron Dexter. All Rights Reserved.