Page 268 - Making things move_ DIY mechanisms for inventors, hobbyists, and artists

246 Making Things Move

3. Make a hole in the bottom of each of the cardboard pieces on the sides and
put a pen or marker in each hole.

4. Hold the center paper fastener and see how you can draw symmetrical (but
mirrored!) patterns by moving the cardboard pantograph around.

5. Try replacing some of the paper fasteners with pens to draw more lines, or
changing the length of some of the strips to make the patterns asymmetrical.

Ratchet and Pawl FIGURE 8-9 Ratchet and pawl

A ratchet-and-pawl system creates a stepped
motion and can be used as a locking mechanism
(see Figure 8-9). A ratchet is a wheel with notches
2
cut into it, similar in shape to a gear. A pawl pushes
against the notches and allows the ratchet to be
driven in steps. A second pawl (detent) can stop the
wheel from slipping backward. A ratchet-and-pawl
system can also be used as a clutch to allow a shaft
to rotate in only one direction.

Motion Conversion Options
Most of the time, the easiest motion to create as an input for a mechanism is rotary
motion, either from an electric motor or a hand crank. There are many ways to change
this rotary motion to linear, intermittent, reciprocating, oscillating, or irregular motion.
Sometimes you can convert between these motions as well—for example, between
oscillating and linear. You can also use the simple mechanisms described in this chapter
to transform a motion without changing its type. For example, you can change a slow
to a fast rotary motion, magnify linear movement, or change the axis of motion.

Table 8-1 shows some ways to convert between the following different types of motion:

• Rotary Motion in a circle (the most common input motion).
• Oscillating Back-and-forth motion around a pivot point, like a pendulum
in an old clock (this type of input is easy to achieve with a standard hobby
servo motor).
• Linear Straight-line movement.