Exercise: Music Box¶
In this exercise we will design and fabricate a simple music box and fabricate it using laser-cut plywood and standard components.
The overall objective is using mechanism to couple user inputs to a sound-producing process. The technical objectives are creating reliable mechanical freedoms and transmitting movement.
The solution could be as simple as a knob-driven striker which rotates to create a percussive sound, or could include more complex freedoms like a cam driving multipe elements. A traditional music box is essentially a complex cam (the cylinder) moved by a gear train or clockwork, driving the individual tone teeth of the “comb”.
Please choose a design goal in keeping with your existing design and CAD skills. If you are a novice, then please keep your priorities centered on creating a simple structure built from several parts. If you have more experience, please choose a scope that includes more elaborate construction.
Objectives¶
The overall objective of this exercise is to design and fabricate a freestanding device which conveys a user gesture through mechanism to a sound-producing process with one or more degrees of freedom.
The goals of this exercise are that you should be able to:
Design and fabricate an object which can create sound.
Design a structure to support the sound element while allowing one or two degrees of freedom.
Use bearing components to implement low-friction joints.
Design a motion transmission to manually actuate the device via mechanism.
Design a multi-part assembly including joinery.
Laser-cut parts, assemble, test, and iterate.
Kinematic Design¶
There are two main considerations: the movement of the user input affordances and the movements required to produce sound.
A robust solution for input is to implement a single revolute joint which allows a lever, dial, or crank to rotate around an axis. An important decision is placing that axis, both in terms of direction and where it is positioned relative to the sound elements. Linear or translational joints are also possible but trickier to implement robustly.
The sound producing movement is closely constrained by the sound producing process; it may require reduction to a smaller movement, additional passive freedom, or compliance to trigger the sound. E.g, a piano action includes a linkage will allows the hammer to strike the strings but bounce back to allow them to vibrate.
Motion Transmission¶
There are several ways to consider transmitting movement.
Linkages. Four-bar linkages can convey motion, translate rotation into reciprocation or vice versa, and change motion scale.
Tension elements. Strings or cables can provide linear motion over long distances. Gravity or springs can provide counterforce to keep the lines in tension.
Gears. Rotary motion can be magnified or reduced and transmitted between parallel shafts via gears.
Cams. Revolving elements with complex shapes can encode trajectories and transfer them to linkages or push rods.
Deliverables¶
Live in-class demo of your music box.
A short report posted to the shared drive including:
a short text statement reviewing your intent and outcomes
one or more photos
a brief video
your SolidWorks files