Dexter the MicroMouse

Our goal was not to build a championship caliber mouse but to build a solid performer capable of finding the shortest route to the center of the maze. The following are some of the factors that we took into consideration as we designed our mouse.

 

Computing Power:

Dexter uses a single Motorola 68HC11 to process all of the information and has 32K of battery-backed RAM to store both the program and data. We chose this processor because we were already familiar with it which would speed up development time and because so much information and support is readily available from the Internet.

 

Motors:

We chose to use stepper motors in our MicroMouse because they are easy to control. By varying the number and duration of the pulses, we would be able to control the speed and distance travelled without having to use wheel encoders as we would if we had gone with DC motors.

We also liked the maneuverability of the "wheelchair" configuration of the wheels. This allows the mouse to rotate in place and escape dead-ends.

 

Sensors:

Our mouse uses IR sensors to detect the presence of walls. The first version of Dexter had only three sensors on each side and we found that this was not enough. Sometimes, when coming out of a turn, he would stray too far to one side or the other and the sensors would miss the walls resulting in a crash. Adding more sensors corrected this and has the added advantage that we can map walls in the adjacent cells.

 

Chassis:

We wanted people to be able to handle and examine our mouse without disturbing all of the delicate components. It was for this reason that we chose an acrylic box as our chassis. We chose a box whose size would allow the mouse to easily maneuver within the cells, and we then sized the circuit boards to fit that case. The case in our MicroMouse is actually the robot's second case. The first one looked like swiss cheese from all of the holes we drilled into it as we moved parts around during development.