A DIY Mechanical Puppet Animator
This is very simple device that uses a simple mechanism to animate some small puppets to make them look like they are dancing.
The mechanism converts the rotary motion of a motor into a linear motion that oscillates with simple harmonic motion (SHM). This means if the velocity of the rod was plotted on a graph, it would look like a typical sine wave. It is just a simple push-pull type device that is used to move a long rod back and forth. The moving rod will be used to transfer the motion to two puppets, side by side.
The images below show the mechanisms used to transfer motion to the puppets. The wooden 'T' piece tilts left to right repeatedly. It is linked to the main rod by a short length of silicon tubing which stretches ant the end of each stroke. The stretching of the tubing at the end of the stroke means that the motion of the puppets is more rhythmic because they stop briefly before changing direction. This helps to randomize the movements of the freely swinging arms and legs.
The mechanism is installed in a custom wooden box. The puppets are suspended from the 'T' piece by nylon strings attached to the hands and feet, and the main body is suspended from a fixed point to carry the weight.
To reduce the noise output from the device, the mechanism is boxed in with foam lined walls, and the joints are greased to reduce friction. The strings pass through small holes in the lower section so that the puppets are suspended in an independent cavity.
The speed of the motion is controlled using a simple pulse width modulator circuit based on a 555 timer IC. When powered by 6V DC the speed can be varied between stationary and 'crazy' where the puppets are moving very erratically. This allow the device to be used for longer periods because if the battery level falls the speed controller can be turned up to accommodate it.
These dancers are also able to demonstrate resonance! When the speed is adjusted just right, it is possible to 'tune in' to a part of the puppet which makes the movement suddenly become erratic and more significant.