The Project Alligator

Step 3 Mechanical Assembly (Jaw Movement)

I decided against the crank mechanism because it would have been more complex to stop the crank mechanism at the right spot. The jaws were to be moved by a wire mechanism. The wire was to be wound on a shaft connected to a motor. The motor gets started by the motion detection mechanism. When the jaws would have completely opened it trips a limit switch, which reverses the direction of the motor. The jaws would close because of the gravity. However, release of the wire would make it close in a controlled fashion. When the jaws would close completely, it would trip another limit switch to stop the motion or reverse the motor if the motion was being detected again. I found this great website specializing in the old surplus material. I bought about $50 worth of the material from http://www.surpluscenter.com .

A 17 RPM motor was perfect for the winding mechanism to open the jaw. I decided to use a 10lbs fishing line instead of wire. Connecting a shaft to the motor was a challenge. The motor had a small shaft with 5/16" in diameter. With some advice from the railroad newsgroup, I decided to drill a small hole on the motor shaft. For the long shaft, I used a hollow brass tube from the local hobby store, whose internal diameter was 5/16". I drilled a through hole on the hollow shaft. The hollow shaft was inserted on the motor shaft aligning the three holes. A split pin was inserted through these holes making t a permanent extension. I inserted a long 5/16" bolt (With its head cut) into the hollow tube to make it strong. Believe me; this simple 'thingamajig' took me more time than it should have. Designing the electrical circuit was fun and one of my strengths.