Build Your Own Combat Robot

48 Build Your Own Combat Robot
FIGURE 3-3
Variations of
Ackerman steering.
Ackerman steering is used in radio controlled (R/C) model race cars and in
most children’s toys. It requires two sets of commands for control. Quite often, a
model race car R/C system will have a small steering wheel on the hand-held transmitter
to control the steering direction and another joy stick to control the speed,
either forward or reverse. This type of steering has the capacity to be more precise
than differential steering in following a specific path. It also works best for higher
speeds, such as that of real cars of all types and model race cars. Its major disadvantage
is its inability to “turn on a dime,” or spin about its axis. This type of
steering has a turning radius that can be only so small; it’s limited by the front-rear
wheel separation and angle that the front wheels can turn.
Differential Steering
Differential steering, sometimes called “tank-type” steering, is not to be confused
with tank treads. The similarity is in the way an operator can separately control
the speeds of the left and right wheels to cause a directional change in the motion
of the robot. Figure 3-4 illustrates how controlling the speed and direction of both
wheels with differential steering can result in all types of directional motion for the
robot. Note that each of the two separately driven side wheels has its own motor,
and no motor is required to turn any wheels to steer.
With differential steering, spinning on the robot’s axis is accomplished by moving
one wheel in one direction and the other in the opposite direction. A sharp turn
is accomplished by stopping one wheel while moving the other forward or backward,
and the result is a turn about the axis of the stopped wheel. Shallower turns
are accomplished by moving one wheel at a slower speed than the other wheel,