System Description
The design of the Earth Wheel can be divided into 3 main components:
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Frame
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Slow Strikers
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Rapid Strikers
Frame
The frame is used to mount the instruments and the rapid striker. It consists of:
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Inner and outer steel upper rings connected by 8 steel bars
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Inner and outerl steel lower rings connected by 4 steel bars
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4 vertical supports connecting the upper and lower portions of the frame
As can be seen in the above figure, the purpose of the frame is to support the instruments, slow strikers and rapid striker.
Slow Strikers
The slow strikers are used to strike the majority of the percussive instruments within the Earth Wheel. The striker is a 6 bar linkage which works on magnetic and spring forces. As the input link is pushed by the rotating actuating bar, the output bar is pulled up, as seen in the figure. The striker arm is pulled up as well by magnet force. As the striker arm is pulled back a torsional spring is compressed. Once the spring force is greater than the magnetic force the spring snaps the striker arm down against the instrument.
Rapid Strikers
The rapid striker is a second type of striker used to strike an instrument multiple times per revolution of the rail ring. As can be seen in the figure, a spring pushes a friction wheel is pushed against an extension plate which goes around the perimeter of the wheel. As the wheel and extension plates rotate they cause the friction wheel to rotate as well. Attached to the friction wheel is a set of cranks which, when rotated, result in the rapid striking of the instrument. The rapid striker is capable of striking an instrument approximately 18 times per reveolution.