Page 65 - Robots Androids and Animatrons : 12 Incredible Projects You Can Build

Switch
Nitinol Wire
+
Battery Actuator
–

AC Ohmic Heating
4.2 DC power to nitinol wire

for an extended period of time can damage the wire due to uneven
ohmic heating. Proportional control and steady-state contraction of
the material (without damage) can be achieved using a pulse-width
modulation (PWM) circuit to supply the electric current.
Some robotists have used nitinol wire to create a motorless hexapod
walking robot. While the robot can walk, it does so exceedingly
slowly due to the time required for cycling (heating and cooling) of
the nitinol material. The hexapod walker robot is truly a flyweight
(a few ounces at most) robot, neither structurally strong nor power-
44 ful enough to carry its own power supply.
While nitinol may be impractical for use in a hexapod walker, it is
appropriate for many other robotic applications. To learn more
about the capabilities of this remarkable material, let’s look at a
few commercial products that utilize the contractile ability of the
material. Figure 4.3 shows a mechanical butterfly. Nitinol wire
adds movement to the wings. The butterfly may be connected to a
solar engine (see Chap. 3) for power to create an interesting robotic
application.
Figure 4.4 shows a rocker ball demonstration device. The nitinol ac-
tuator operates about 20,000 cycles per day and will last for years.
Nitinol wire loops can be used to produce rotary motion. Figure
4.5 illustrates a simple heat engine. The nitinol loop is guided by a
groove in each wheel. The smaller wheel is made of brass for good
heat conduction. When the smaller wheel is placed in hot water,
the wheels begin to spin. The heat engine can also function using
solar energy. Focusing sunlight from a 3″ magnifying glass onto
the brass wheel will also activate the engine.
Nitinol can also be used to physically close mechanical push-but-
ton switches, as an actuator in production of lightweight air
valves, and in many other linear-motion applications.

Team LRN
Chapter four