Page 260 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

238 Making Things Move

or hundreds of years, engineers and designers have been coming up with ways to
Fconvert rotary motion into useful work. You already know how to choose a motor
and attach something to it, but maybe the output you’re looking for isn’t a simple
rotary motion.

In this chapter, we’ll explore how to convert rotary motion into more complicated
motions by combining simple machines. First, we’ll go over some general mechanisms
you can use, and then we’ll cover the basic types of motion and ways to convert
between them. Finally, we’ll look at some examples of combining simple machines to
create kinetic sculpture and mechanical toys. Whether you combine simple machines
for work or for fun, the applications are limited only by your imagination and, I suppose,
some pesky laws of physics.

Mechanisms for Converting Motion

Rotary motion—the most common input motion—can be converted into more
complicated motions through systems of cams and followers, cranks, linkages,
and ratchets. All complicated machines, mechanisms, and robots are made up of
combinations of simple machines like these. They help us convert rotary motion into
linear, up and down, oscillating, or intermittent output motion. Cornell University
keeps a library of examples that can be accessed online as the Kinematic Models
for Design Digital Library (http://kmoddl.library.cornell.edu). The work of Cabaret
Mechanical Theatre (www.cabaret.co.uk) and Flying Pig (www.flying-pig.co.uk)
highlight more whimsical examples.
This is a great time to start taking things apart, if you haven’t already. Many toys,
appliances, and other everyday devices have built-in mechanisms that you can
use—either directly in your projects or as inspiration for their design.

Do you have an old printer that doesn’t work? Then you probably have two stepper
motors that turn rotary motion into the linear motion of the print head with a system
of timing belts, pulleys, steel shafts, and bushings. Do you have an old Hokey Pokey
Elmo? You will find many treasures inside, including motors and linkages. Scavenging
parts from consumer products that benefit from economies of scale to keep prices
down is a great alternative to buying components piece by piece, which is always
more expensive. You can also use these parts to do some 3D sketching of your ideas
before committing to more permanent designs and materials.