Executive Summary

A one-fifth scaled and self-contained prototype of a Segway, or two-wheeled self-balancing
cart, was designed and built with line following and mass transportation capabilities. A 0.975
kg, 6 inch tall with 6 inch wheel diameter design utilizing polycarbonate materials was
developed with the consideration of competition constraints. Final costs totaled to be $120.17.
For the purpose of aesthetics and identifying the Segway, handlebars were produced but were
not included in the final mass of the cart or attached during the actual competition. A control
system diagram, a system architecture diagram, and an electrical schematic were used to
organize and develop a control program in C language for the Segway. Three photoresistors
were used to detect a line while infrared sensors were mounted to detect the body’s angular
position from the floor. The final competition involved a series of tests where the carts balanced
with and without weight, followed straight and curves paths of standard black electrical tape
while carrying a 200 g mass. Each of the tests during the competition was performed

Design Description

Design Constraints

The Segway design had to be self contained and turned on and off by a switch.
Thus, the batteries, or power source, must be on the cart itself. The container that was
used as the mass in the competition had a 6 inch diameter base, so the cart had to be
designed with a top plate large enough to hold the container. The maximum distance
of the top plate from the floor had to be less than 6 inches. This height does not
include the vertical handlebar post which had to be removable and between the lengths
of 7 to 9 inches. The cart also had to be rigid enough to hold and balance a mass of up
to 2 kg. The two cart wheels had to have diameters between 0.5 and 6 inches. To test
the balance of the cart, it was necessary to enable a maximum free range of motion to
60 degrees in both directions of the wheel axle.
The cost of the finished cart could not exceed the specified budget of $200.00 and
the weight of the cart should not have exceeded 1 kg. The incentive to keep costs and
weight low was included into the final score estimate with the score improving as
those parameters were reduced. Another important component of calculating the final
score was the time to execute a motion from the start of the motion to the end. The
tape paths that the robot had to follow during the competition grew increasingly
complex to test the cart’s agility and success of design.

Test Results
Scilab Simulation

Using the Scilab software, a program was written to produce the graphical
simulation of the Segway’s motion in Figure 9. The program can be found in
Appendix D.

The cart followed the entire length of the tape path, 3 meters, during the final competition
while carrying the mass. After the competition, the Segway was also tested to see if it could
follow non-linear tape paths. Without a mass, the cart performed with excellence. It
followed any curved path where the lighting was not too dark or too bright.
It was theorized that a lower center of mass would help the Segway balance. This was
evident in competition when the carts with lower center of masses were more successful in
balancing the mass. The designed Segway did not use encoders, which did not hinder its
performance. The provided photoresistors were sufficient feedback systems for allowing the
carts to follow the lines.