Ihave been reading SERVO
Magazine and Nuts & Volts for a few
years, but throughout this time I have not
been doing any robotics myself, so I decided that I
needed to start experiencing things first-hand. This
article describes my first venture into the world of robotics.
I have been an electronics
hobbyist since I was young and an
engineer for many years. Throughout
these years, I have been scavenging
parts from cast-off hardware and
from the trash at work, so I have a
reasonable supply of parts and
materials available in my scrap boxes. I
also have a laptop computer from my
work and a handheld GPS unit for
hiking. The project presented in this
article utilizes scrap box parts with a
few purchased items to build a GPS
guided autonomous robotic car.
developing a prototype vehicle that
can navigate around my yard and the
neighboring field to serve as a test
bed for these systems.
FIGURE1. (Above)
The completed car. Many trim pieces
originally installed on the car were
removed to provide flat mounting
surfaces for the various assemblies.
12V sealed lead acid battery. I took it
home to try out; it had one weak cell
but other than that, it performs very
well. So my total cost for the car and
the main power source was $5. Figure
1 shows a view of the car with all of
the components installed.
My ultimate goal is
to develop a robotic
lawn mower.
A robot that mows a lawn in a
controlled fashion requires developing
a precise navigation system, identifying
and tracking local objects, performing
obstacle avoidance, and perfecting
other systems. I wanted to start by
56 SERVO 04.2008
Finding The Platform
Looking at what is available for
hobby robots, I found that few of the
robot kits available are rugged enough
or large enough to bounce around in
the outdoors. I wanted a pre-built
test bed that did not require much
hardware development. Fortunately,
many people have purchased ride-on
cars for their children, and these toys
get cast off as the children get older
or as the batteries die. While these
cars have several drawbacks, they can
carry more weight than I needed and
are large enough and durable enough
for my purposes.
I was able to get a car from a
thrift store for $5 that had two weak
6V batteries and no charger. I went to
my local recycling station to discard an
old battery, and saw a new looking
Modifying The Wiring
For high/low speed control and
forward/reverse, these cars use simple
switches. I removed all of this original
wiring to convert the car to computer
control. I considered using a radio
control (RC) speed controller for the
drive motors, however, I have many
relays that I recovered from the
trash at work. The relays are easily
interfaced to control electronics using
transistors and resistors, and on/off
control is simple to implement in
software. The relay wiring and drive
