Page 28 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

Chapter 1 Introduction to Mechanisms and Machines 9

just past your elbow. Your bicep must work hard FIGURE 1-8 Your arm as a third
to lift even a small weight in your hand, but the class lever
weight can travel through a long distance since
it’s far from the pivot point at your elbow. A
triangular arm that allowed your bicep to attach
near your wrist would be more efficient, but it
would have a very limited range of motion.
Fishing rods and tweezers also work as third
class levers.

You can also combine levers into linkages, which
we’ll talk more about in Chapter 8. For now, take
a look at a project from some former students of
mine, shown in Figure 1-9. The two weights are
being balanced by a first, second,
and third class lever all at once. The
fulcrums of each are circled. Can FIGURE 1-9 Lever madness (credit: Lesley
you tell which one is which? (Go to Flanigan and Rob Faludi)
http://itp.nyu.edu/~laf333/itp_blog/
2007/03/lever_madness.html to
confirm your answer.)

2. Pulleys

A pulley, also known as a sheave,
block (as in block and tackle), or
drum, is basically a wheel with a
groove along the edge for a rope or
belt. It’s another simple machine we
can use to gain mechanical
advantage in a system. The two types of pulley systems are closed and open.
Closed Systems
I will call a pulley system on a fixed-length rope or belt that’s constantly tight a closed
system. A common example of this is the timing belt in a car, as shown in Figure 1-10.
Timing belts use pulleys with little teeth on them that mesh with matching teeth on