Page 214 - Amphibionics : Build Your Own Biologically Inspired Robot

Amphibionics 06 3/24/03 9:02 AM Page 193
Chapter 6 / Crocobot: Build Your Own Robotic Crocodile
most commonly used way in which crocodiles move around on
land. It is usually slow, although it can be modified so that the
crocodile reaches speeds of 5 to 10 kilometers per hour when
required. Although the term “belly crawl” implies a certain style of
locomotion, in reality there are several variations on this gait suit-
ed to different situations, and only at very slow speeds does the
crocodile actually crawl, as the name suggests.
The high walk and gallop are unlike a reptilian gait. The crocodile
walks more like a mammal during the high walk. The gallop is very
spectacular to watch, and propels even large crocodiles away from
potential danger at very high speeds. The robotic crocodile in this
chapter will use a method of walking on four legs where the body
is raised completely above the ground.

Overview of the Crocobot Project

The robot crocodile that will be built and programmed in this
chapter is controlled remotely by a human operator via a wireless
data link. The robot and the remote control that will be built are
shown in Figure 6.2. The wireless data is transmitted from the
controller and received by the robot using RF modules built by a
company called Linx Technologies. The robot achieves locomotion
using four legs that are driven by a twin-motor gearbox. The
geared motors operate on voltages between 3 and 6 volts, making
them perfect for small walking robots. The motors are controlled
using the L298 dual full-bridge driver. The motor driver takes its
control signals from a PIC 16F84 microcontroller. The microcon-
troller will also be used to interpret the control commands sent
from the hand held remote control. The remote control uses a PIC
16C71 microcontroller featuring four analog to digital converters.
Two of the analog to digital converters will be used to monitor the
position of the control stick on the remote control device. This is
accomplished by reading the voltages produced by the poten-

193