OBJECT TRACKING
C-BOT
If you would like an introduction into the world of
artificial vision systems, this is a good starting point. We
will build a mobile object tracking and following robot
by first constructing a very simple robot base and then
using the artificial vision camera developed at Carnegie Mellon University
(CMU) to be our eyes.
by JOHN IOVINE
The heart of the project is the CMU camera itself.
Some of its features are:
• 17 frames per second capture rate
• 80 x 143 pixel resolution
• Gather mean color and variance data
• High speed TTL serial port
• Find center of object
• Raw image dump
• Color detection
• Adjustable image properties
• Transfer of binary bitmap of the tracked pixels
• Ability to control one servomotor
FIGURE 2.
Plastic body
mechanical
diagram.
48 SERVO 05.2009
C-Bot will not use
all of the available
features on the CMU
camera, however, the
Windows software
bundled with the
available C-Bot kit
will allow you to
investigate more
FIGURE 1. CMU camera.
camera functions than
would be possible with just the PC. If you are building the
C-Bot from scratch, the PC software is available separately.
I will touch upon that software later.
The CMU camera (Figure 1) captures a target placed
in front of its lens. The PIC microcontroller we will be
using interrogates the camera to find the position of the
target within the camera’s Field Of View (FOV). Using this
information, we can determine movement in both the
horizontal and vertical axis, and if our target moves away
or gets closer to the camera. The PIC uses this target
position information to activate the servomotors to move
the mobile robot to follow the target. If the target object
gets too close, the robot will back away. If the target
object moves away, the robot follows it. The robot has an
up-down servomotor connected to the camera to follow
vertical movement.
Before we get into experimenting with the camera, we
need a base to mount it on. You can either construct the
chassis described here or use something you might already
have on-hand. A kit is available.
Simple Mobile Chassis
To begin, we’ll start with a plastic frame cut out of
1/8” thick clear acrylic plastic. Follow the diagram in
Figure 2. The chassis uses three pairs of 90 degree
servomotor brackets (shown in Figure 3) to hold the
servomotors to the chassis.
The right and left drive servomotors are continuous
rotation. You could use the Parallax CR servomotors, Hi Tec’s
new HSR-1425CR, or modified HS-425 servomotors. The
servomotor that rotates the CMU camera up and down
