The JavaBot1 is a small line following robot designed to follow a black line drawn on a dry erase board. It is designed to follow very tight curves. The software still has lot’s of room for improvement but works well as is.
The JavaBot1 uses 2 Cirrus CS-70 servos that have been modified
for full rotation and have had their controller boards removed to
convert them from servos to gear motors.
Servos are a common motive power for small robots due to their
low cost, ready availability, standardized sizes and the fact that it
only requires 1 bit on your processor to control the motor.
We initially tried this approach but found that the speed control was
very minimal with a finer control needed for this application. The
servo controller boards were then removed and the wires soldered
to the motor terminals and case ground. The motors were then
controlled by an H-bridge circuit to allow direction and speed control
with only 2 processor bits per motor. This is implemented as one bit for
direction and another bit for power/speed control per motor.
In order to follow the line I/R reflective sensors were used to
detect if a line was present or not. The sensors chosen are the
QRB1114 from QT Optoelectronics and have a focal point of
about 1/4 inch. They are available from DIGI-KEY.
Most line followers use 2 or 3 sensors of this type to do their
detection. This works but does not give the ability to follow
lines with very tight turns. An array of seven sensors arranged
in an “inverted V ” patternare bolted under the front of the robot
The sensors are wired with all the receivers connected in parallel and
fed to an LM311 comparator to set the threshold trigger level with it’s
output fed to a processor bit. The transmitter LEDs are connected
to a 74HCT138 with a current limiting resistor to VCC. This allows
the entire array to use 4 bits for the sensors.
For more detail: Line following robot using PIC16F84