Page 304 - Amphibionics : Build Your Own Biologically Inspired Robot

Amphibionics 07 3/24/03 9:13 AM Page 283
Chapter 7 / Turtletron: Build Your Own Robotic Turtle
Turtletron employs what is called the
Differential drive system.
differential drive system. It is one of the least complicated loco-
motion systems from a construction and programming standpoint.
The differential drive scheme consists of two wheels on a common
axis, with each wheel driven independently. This arrangement
allows the robot to drive straight, to turn in place, and to move in
an arc.
In order to ensure balance, some additional support beside the two
drive wheels must be provided to prevent the robot from tipping
over. This is usually done by arranging one or two caster wheels
in a diamond or triangle pattern. Turtletron uses the diamond pat-
tern, as illustrated in Figure 7.9. One of the problems with using
this configuration is that when the caster wheels are attached
rigidly to the robot body, undulations in terrain can leave the robot
supported only by the casters. The drive wheels may lose contact
with the surface and become unable to move the robot. To improve
on this design, a suspension system could be added that would
allow the casters to move up and down relative to the drive
wheels.

Electronics
To simplify the design and construction of Turtletron, the main
controller board and remote control that were built for the croco-
dile robot in the last chapter will be used. The circuits are identi-
cal, except that the software of the PIC 16F84 will be changed.
This robot will also include an ultrasonic range finder for room
mapping and obstacle avoidance, along with a linear shaft
encoder to keep track of distance. The main controller schematic
is shown in Figure 7.12. If you did not build the crocodile robot,
or would like to build a separate circuit board for Turtletron, fol-
low the instructions in Chapter 6. The parts needed to complete
the electronics are listed in Table 7.2.

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