Page 88 - Amphibionics : Build Your Own Biologically Inspired Robot

Amphibionics 04 3/24/03 8:23 AM Page 67
Chapter 4 / Frogbotic: Build Your Own Robotic Frog
reached the specified position and will continue to seek for it in
one direction or another. With identical resistors in the network,
if a pulse with a width of 150 ms is sent to the servo, it will
remain motionless. Since no two resistors are exactly the same,
you may have to experiment with the pulse width value needed
for the servo to remain motionless. It will probably be within the
range of 147–153 ms. Figure 4.18 illustrates how the modified
servo will behave when control signals between 100 and 200 ms
are applied. When a signal with a pulse width of 100 ms is
applied to the servo’s control line, the servo will move in a coun-
terclockwise direction at full speed. The servo speed can be con-
trolled by varying the pulse-width value, with 100 ms being the
fastest speed in the counterclockwise direction, and 149 ms
being the slowest. The same holds true for the servo rotating in

FIGURE 4.18
Pulse width values used
to control a modified
servo.

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