cymbalic

cymbalicA study of the motion known as “spolling,” (spin + rolling) the motion a coin takes when spun on its edge. Based on the findings of mathematician and physicist Leonhard Euler, this project was an attempt to create a mechanism which convert rotary motion from two motors, to “spolling motion”. A cymbal is attached by sitar strings through a pulley system, then to the mechanized wooden disk. The observer activates the sculpture by spinning an a Euler disk on its’ concave plate.


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At the core of its design, four cams are used to manipulate a larger flat 16” disk. Two 1/2” metal rods, coupled to DC gearhead motors, each intersect a pair of cams. Each pair consists of two different sizes to make up for the offset in height of the intersecting rods. On the large disk suspended above, four equally spaced tuning pegs each hold a sitar string which then travels through a pulley, down to a cymbal. The sitar strings are fed through equally spaced holes in a cymbal which is mounted to the bottom metal frame, and then tied firmly. The intention is to have the cymbal take the motion of the Euler disk.

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circle2 = circle1 + 2offset 7 = 5 + 2(1)

The distance from the center of the circle at which the rod intersects determines the amplitude of the linear motion converted from by each cam. Each rod intersects the cam 7/8” from the center in order to prevent the larger disk from hitting the outer metal frame.

In order to enable an element of human interaction, the increasing frequency that the Euler disk produces when spun is programmed to control the speed of the motors. An Arduino Uno paired with a Polulu Dual VNH5019 Motor Driver Shield is used to operate the sculpture. To detect the frequency of the disk, Adafruit’s Electret Microphone Amplifier MAX4466 is placed under the concave mirrored platform. Since the Arduino analog read rate samples at about a quarter of audio rate, an alternative approach was taken in order achieve more reliable results. A threshold on the amplitude is set to initiate the start of the motors. The speed iterates faster as long as the amplitude remains above the threshold. As soon as the amplitude falls under the threshold, the motors come to a sudden stop. The electric microphone proves to be very sensitive, enough to create a sudden movement when the disk is touched. This way, the user immediately experiences the interaction.

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