I am now going to attempt to explain how to understand and build electric motor-driven animations. First off, I am not an engineer, just a fellow who has an understanding of mechanics. Secondly, this is NOT an article on servos, pneumatics or hydraulics, just good old electric motors. So, if this is what you're interested in , kick back and let's get started.
The basic problem with using electric motors is all their movement is rotational (goes around in a circle). Unless all your characters move in circles, we have to transfer that rotational motion into linear motion (going in a straight line). Here are some ways to do just that.
If you have ever seen a steam locomotive, you have seen this action. A piston pushes a linkage.
The linkage transfers the movement to a wheel, rotating the wheel. We will be using this action in
reverse. (See fig. 1) Use the motor to rotate a wheel. This will move the linkage, which pushes the
piston back and forth. The diameter of the wheel determines the length of back and forth motion
of the piston. This is the type of mechanism used for the electric chair animation. Simple, yet
effective.
Another application of the same principle is the "Flying Crank Ghost", which utilizes a right angle (crank) shaft with ropes and pulleys substituting for the linkages and pistons.
The animations seen at Christmas use the following type of mechanism. (See fig. 2) A slow RPM
motor is connected to a long shaft with a squared "U" bend in it. On either side of the shaft at the
"U" bend, are two levered shafts encircling the "U" with rounded rectangular hole. The width of
the hole is slightly larger than the diameter of the shaft, while the length of the hole is longer than
the diameter of the full rotation of the "U" in the motor shaft. Combined with the pivot point, this
allows these levers to go back and forth while the shaft rotates. Take this type of mechanism,
increase the RPMs, set the motor shaft parallel to the ground, and you have a flapping wing
mechanism. Add more than one "U" in the shaft, offset from each other by several degrees, and
you have the leg mechanisms for a spider or other crawly insect. Make this mechanism spin at
about 120 RPMs, add coiled springs to the ends of the levers, and you have thrashing tentacles.
"But", you say, "this is just back and forth movement. It doesn't look real. How do I get a more
random, lifelike look to my animations?" One of the answers to this question is to use cams. A
cam is an irregular or offset wheel. The linkage/lever rides along the outside of the cam utilizing a
a pin/roller, with a spring or gravity holding the linkage in place. The illustration in fig. 3 shows a
simple coffin lid lifter. This will give the appearance of someone trying to lift up the coffin lid with
a random looking movement. A simple lifelike animation.
These are just some simple animations that can be achieved by the use of electric motors an some knowledge of transference of motion. Utilizing these concepts, more complex animations can be designed and built.
