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 rigs etc.

Sources:

C and H Surplus Pasadena California

Herbach and Rademan www.herbach.com

© Copyright 1999-2004 Ron Dexter. All Rights Reserved.