Each motor draws between 2 and 3 amps under normal load conditions. So, if

one motor controller were used, it would need to be able to drive up to 12 amps. In order

to save cost, two less powerful motor controllers are used. Each VNH3SP30 h-bridge

motor controller can drive 9 amps continuously. The figure above shows that the motor

controllers are stacked on top of each other to save space on the robot. The top controller

drives the two motors on the left side while the bottom controller drives the two motors

on the right side.

Three output pins of the microcontroller are required to control each motor. But,

since both motors on the same side never need to turn in opposite directions, the control

lines can be tied together so that 3 output pins can be used for each side (two motors).

See figure 6 for a diagram of the motor controller wiring.

Sonar Units

To avoid collisions, the robot employs 4 ultrasonic sensor units. These devices

use the properties of ultrasound to take measurements that can then be interpreted by the

microcontroller to decide if there is an object in front of it or not. The Maxbotix LV-EZ1

modules are used. They have a range of 0 to 21 feet in 1 inch increments.

As figure 7 shows, there are 4 units aimed outwards from the front of the robot.

The bottom two are angled parallel with the front panel while the top two are angled

slightly upward. This gives the robot a wide view of what is in front of it.

Each module is connected to one of the microcontroller’s ADC pins. The voltage

read on the pin is then converted to inches. The following code reads the input, then does

the conversion.

Human Detectors

There are two human detectors mounted on the top of the robot. These

sensors work by sensing the infrared radiation emitted from the human body. They have

a range of about 20 feet. They output data to the microcontroller in the form of a varying

voltage. So, each detector is connected to an ADC pin of the ATmega128.