I made a skeleton that dances when someone is close
I wanted to rig a sort of puppet so that it dances on its own.
I made a skeleton out of polymer clay, with a wire armature so that the limbs would be strong, and so that I could use wire to join the different pieces of the skeleton together so that they would all dangle from each other, and so that there was not much resistance or friction occurring, which allows it to move more fluidly and without as much restriction
After I made the form, I attached a string to the head, which controls the height of the skeleton, and one to each limb for individual arm and leg control.
In order to move them, I would string the string through the cardboard backing(visually separating the skeleton from the mechanisms) and use a servo motor to wind up the string and shorten it, causing the limb/head to rise or fall. I realized that since the servos only rotate up to 180 degrees, there was not enough circumference being used to wrap up a large enough amount of thread to really make a difference or let the skeleton dance, so I attached sticks to the servo,s and tied the string to the end of them. This makes it so that the circumference that the knot is traveling is substantial enough to change the length of the thread sufficiently, and is less problematic(in terms of tangling) than winding up the cord.
Once I rigged the body up, I added the speaker, which plays a tune while the skeleton dances, and hooked up a sensor that detects when someone is nearby. When the sensor is triggered, the skeleton dances by moving his limbs a semi-random amount.