Exercise: Two-Hand Toy

In this exercise we will design a simple two-handed toy and fabricate it using laser-cut plywood and standard components. By including two affordances for human input, it can either be operated solo by one person or simultaneously by two.

The overall objective is using a mechanical transmission to couple user inputs to a playful mechanism. The technical objectives include creating reliable mechanical freedoms and transmitting movement.

A few suggestions for an approach:

  • making sound

  • animating a simple puppet

  • a simple game

  • a visual effect like a gobo or moire generator

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 playful mechanism with two or more degrees of freedom.

The goals of this exercise are that you should be able to:

  1. Design and fabricate an object with two human affordances.

  2. Design a structure to support the performative element.

  3. Design a motion transmission to manually actuate the device via mechanism.

  4. Design a multi-part assembly including joinery.

  5. 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 for the expressive elements.

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.

Motion Transmission

There are several ways to consider transmitting movement.

  1. Linkages. Four-bar linkages can convey motion, translate rotation into reciprocation or vice versa, and change motion scale.

  2. Tension elements. Strings or cables can provide linear motion over long distances. Gravity or springs can provide counterforce to keep the lines in tension.

  3. Gears. Rotary motion can be magnified or reduced and transmitted between parallel shafts via gears.

  4. Cams. Revolving elements with complex shapes can encode trajectories and transfer them to linkages or push rods.

Design Rules

Your device should:

  1. Use both shape and movement to inspire joy.

  2. Include two affordances (e.g. knobs, levers).

Please observe the following design rules:

  1. Use only 6 mm laser-cut plywood.

  2. No glue.

  3. Use clevis pins as pivots.

  4. Use cotter pins, shaft clamps, and washers if needed.

  5. No bearings or motors.

  6. No electronics.

You may optionally include one or more:

  1. dowel pins

  2. piece of string

  3. rubber band

  4. paper doll

  5. found object

If there is something else you wish to include within the spirit of the assignment, please ask. The point of these rules is to keep our focus on joyful movement and form and not get distracted by components.

Deliverables

  1. Live in-class demo of your device.

  2. A short report posted to a subfolder on the shared drive including:

    1. a short text statement reviewing your intent and outcomes in about a paragraph

    2. one or more photos

    3. a brief video (e.g no more than 30 seconds)

    4. A dimensioned drawing of the assembly and key parts. The purpose of the drawing is to convey the idea, the scale, and critical mechanical elements, not communicate a complete shop plan; it is acceptable to omit some minor parts.