rhythm apparatus for the overhead projector

the apparatus consists of two analog robots, that are mounted into an aluminum frame. each of them is driven by a simple microcore circuit that generates a movement pattern by triggering motion on two motors. their motors are directly driven by the circuit, the currents that produce the rhythmic signals are the same currents that make the motors turn. through this direct coupling the circuit is very sensitive to feedback from the motors.  because the robots are mounted into the frame they do not move forward any more, but they swing two aluminum sticks back and forth.
the frame that holds the moving sticks is placed on an overhead projector so that the shadows and silhouettes are projected onto the screen. inside of the overhead projector are placed two solarpanels that provide the energy for the robots. sound is picked up from the structure by directly picking the electronic signals that drive the motors and by placing piezo-pickup microphones that are hit by the moving bars.

their are three ways to play with the apparatus.
the first is by modulating the amount of light which modifies the behavior of the circuit in multiple interesting ways. at very low levels of energy, the circuit may emit a pulse from time to time, but never enough to drive a motor. with a little bit more energy a mode switch happens and the circuit goes into a pattern also referred to as hypersaturation, the circuit oscillates at a very high frequency, to fast for the motors to move but of course audible: a high pitched tone. when gradually increasing the energy level at a critical moment a mode switch happens, the motors start to turn.
the second way to play is through direct physical interaction with the apparatus. because the motors provide feedback into the circuit, it is sensible to the load on the motors. when there is no load, the motors rotate freely without any oscillation. any obstacle may make them reverse, so putting your fingers brings the machine to swing back after hitting. Adding rubber bands between the bars makes them go back and forth.
the third way to play is to couple both machines, this can be done mechanically by putting a rubber band between the legs or electronically by connecting one output with an input of the other circuit. both coupling have the effect that the motion of both machines synchronizes, so that they reverse on the same beat.

here is a sound sample from a recent living room performance.

the rhythm apparatus for the overhead projector is based on previous work the rhythmusgeber which can be heard here: and seen here