Stepper Rattle

I love rattles because, with their loose mechanical properties, they are never exactly on the beat. They can produce natural rustling sounds or white noise to wash over rhythmic and harmonic sections of music. Rattles are an important part of many rituals, dances, and performances where the performer’s movements, the visual design of the instruments, and the sounds that they produce are all interconnected. I chose to continue in that combined media tradition by attaching a closed-circuit camera to the instrument for live performances in order to project its movements while it produces sound.

For over twenty years, I have worked really hard to make robotic instruments that could be programmed precisely with limited latency. The SR plays by a different set of rules and is completely off the (MIDI) grid. It moves in and out of timed tempos and exploits the complex behavior and sounds produced by a stepper motor.

Unlike most motors that have one coil, the stepper has at least four. Instead of a single supply of DC to one coil, it is controlled by circuitry that creates a sequence of pulses that turn specific coils on and off to create steps of very precise forward and reverse moments. It emits interesting tones as it is modulated by the circuitry. I realized the potential along with its ability to produce mechanical percussion.

The guts of the Stepper Rattle contain 3D printer driver circuits and a microcontroller. There are two outputs from two contact mics. One mic is attached directly to the motor picking up its synthesizer-like tones from its oscillating coils. One mic is mounted to the soundboard that the mallet beats upon. Each mic has a separate volume knob. A stepper can behave in many different ways depending on the pitch that you feed into its driver circuit. There is a knob that controls tempo (the range of its beater’s motion) and another that controls its overall pitch. The IR sensor tells its program to switch direction after it smacks the soundboard.

The pitch knob combined with a toggle and a tempo knob affects the steppers full range of behavior and allows the performer to quickly switch between modes from drone-rhythm to bleeps to very fast metal-like percussion to nervous squealing. I am still discovering new ways to manipulate its sounds and movements each time I perform with it.

Classification: Percussion, Electrophone