By Chris Savage
GPS
FIGURE 1.
Big Trak (circa 1980).
Navigation
Part 1
In the 80s when I first started
building robots, I found there were
roughly three ways I could program
my bot for autonomous navigation
depending on the sensors. The first
option was basic roaming where the
robot would simply move in a given
direction until a sensor detected
something in its path, at which point
the robot would choose a new path
(based on where the object was
detected). The second option was to
use beacons or a line to guide the
robot from one point to another.
54 SERVO 03.2010
Finally, a third method known as dead reckoning was
demonstrated to me via a plastic toy tank created by Milton
Bradley in 1979 (see Figure 1). This six-wheeled toy tank
known as “Big Trak” was probably the most advanced toy I
had seen in awhile. It used an internal optical wheel
encoder to determine how far it moved and could execute
commands telling it how far to go in a direction, how much
to turn, and even to stop for periods of time.
Wide Open Spaces
In a living room or kitchen environment, the Big Trak
could be placed in a fixed spot at a fixed angle and expect
to navigate using dead reckoning with fairly good
repeatability. However, the playing field opened up for
vehicles that can move faster and farther such as radio
controlled boats, planes, and even larger robots. In these
situations, dead reckoning really isn’t that useful. To
complicate things even more, most typical sensors don’t
have the range to handle avoidance at the speeds these
vehicles move at. Lines become useless and beacons
