motorized wheel vehicle. The vehicle only requires two motor controllers because each half of the vehicle should be controlled as one single unit.

Think of the wheels of your four-wheel drive vehicle working like the tracks of a tank in that all the wheels on one side work together at all times.

To go straight, all four motors are driven at the same speed and in the same direction. To create a slow, arching turn, both motors on one side of the robot are run faster than the motors on the other side. To cause the robot to spin, just run the motors on one side forward and the others in reverse.

Skid steer vehicles get their name from the fact that the wheels have to slide or skid when the vehicle turns. This skidding means that more power is needed to turn the vehicle than if a simple differential drive system (see Figure 2) were used with an additional caster wheel for balance.

The additional power needed to turn a skid steer vehicle

is the major drawback to this type of design. Once you understand the basic concept, you can build vehicles that use more than a four-wheel drive or even tracks, though more wheels mean more friction when turning.

Mounting Problems

The Four-Wheel Drive Rover 2 Robot Kit from Lynxmotion, Inc., was used as the base for my robot. The Rover uses four motors with a 50:1 gear reduction connected to a Dual H-Bridge Motor Controller. While the Four-Wheel Drive Rover 2 Robot Kit was a nice starting point for this robot, the disadvantage of using a vehicle with a center articulated chassis became apparent when I started attaching electronics.

The initial set of sensors consisted of three sonar sensors, three infrared (IR) sensors, and four whisker sensors. A sensor array was devised that used the three

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