Ajay Kapur & Jim Murphy
Kritaanjli is a robotic harmonium with 44 solenoid actuators and a variable-speed bellows pumping mechanism.
Kritaanjli consists of an aluminum framework which surrounds a harmonium. Attached to the framework assembly are three major subassemblies: the electronics enclosure, the bellows-pumping mechanism, and the keyboard actuation mechanism. T-bracket aluminum extrusions were chosen as the materials for Kritaanjli’s framework due to the ﬂexible modularity which they aﬀord: mounting subassemblies to the aluminum extrusions proved simple and eﬃcient. The electronics enclosure houses the microcontroller and daughterboards and is mounted directly on the frame to minimize distance of cable runs. To pump the harmonium’s bellows, a DC electric motor is connected by means of a crank mechanism ﬁrst to a crankshaft and then with a clamp directly to the rear of the bellows. The crank travels about the motor’s hub on a wheel with a diameter equal to the harmonium bellow displacement. To vary the harmonium’s output volume, the motor speed can be increased; additionally, harmonium motor speed must be increased to maintain a constant volume as more keys are depressed. Key presses are achieved through the use of linear DC solenoids arranged in an array above the harmonium’s keyboard. Each key has an accompanying dedicated solenoid. The solenoids are mounted on an aluminum bracket and are connected individually to a MOSFET driver board contained within the electronics enclosure.