Throughout the entire development of Kraftmouse, our team experimented with many different designs. The three main design prototypes, in the order in which they were developed, included: a two light sensor design, a two touch sensor design and a one light sensor design in conjunction with infrared based Barrier Detection System (BDS).

Two Light Sensor Design

Initially in the design process, a two light sensor design seemed the most obvious solution for our problem of navigating Kraftmouse out of the corridor system. By using two light sensors positioned on the front of Kraftmouse at 45 and 135 degrees, we postulated a plan to exit the corridor by simply reading light intensity levels off the surrounding walls. The theory behind this was that as Kraftmouse got closer to a wall, the light being transmitted by the light sensor would be reflected off the white walls thus producing a light intensity level corresponding to a bright light level. The motor speed on that side of Kraftmouse would have a speed proportional to the intensity of the light recieved in reflection. Kraftmouse therefore turn away from the closest wall, towards open space and ultimately to a new home.

Unfortunately, as the lab progressed, so did the environment of the corridor. More specifically the wall color. From a once white, very reflective shade, the walls of the corridor were changed to an extremely absorbing dark black shade in which our light reflection system would not work. It seemed that with the black walls, an insufficient amount of light was being reflected back to the light sensor ultimately resulting in collisions and corner traps.

Two Touch Sensor System

Our second design prototype was a design comprising of a two touch sensor system very similar to the original light sensor design. This system worked very well at getting out of the corridor environment. We then shifted focus on task two; new home detection using varying light intensities. But in solving the problem of Task 2, the actual searching for a new home depending on the signal received from the transmitting RCX unit, we ended up in revamping the two-touch sensor to a new design; an infrared system.

Barrier Detection System

This system evolved because of how we approached solving Task 2. Although ultimately it was not actually used in that portion of the task. In order to solve Task 2 we postulated that with a system to detect whether there was a building immediately infront of Kraftmouse its light intensity level could be read and a decision on whether to enter or not could be made.

The BDS system was adapted from sonar and radar system's used by many Lego enthusiasts on the Internet. The basic function of these systems are quite simple and Kraftmouse's implementation was very effective - in ideal conditions it can detect obstructions more than a meter away and it adapts very easily to changing light levels. When the RCX sends an IR message it uses a series of IR pulses. Although these pulses may seem insignificant to the human eye, they are in fact quite blinding to the RCX's light sensor. Consider a situation where a barrier is placed infront of the IR transimiter that will reflect the IR light back at Kraftmouse's eye. If a series of light level samples are taken over a relatively long period some will contain bright readings while others would be dark. 200 miliseconds was more than sufficient. Remove the barrier and there will be no light reflected back. A nice trick for detecting buildings, barriers and other mousely concerns.

By developing this technology for KraftMouse, our team quickly realized that the the two touch sensor design used to exit the corridor system was redundant and were removed from the mouse. Ultimately allowing KraftMouse to actually look more like a mouse.

Free Wheel Design to a Skid Plate

Another hardware design modification done to Kraftmouse was that the initial design for the propulsion mechanism consisted of two motors and a pivoting two wheel support at the front, essentially a tricycle design with the power to the two rear wheels. Through many trials, it was concluded that the free rotating wheel supporting the front of Kraftmouse was confounding its turning efforts. Causing Kraftmouse to behave extremely unpredictably and also resulted in many situations where Kraftmouse would get stuck against a wall and despite its best efforts to turn around. Thus we improved this tricycle free-pivoting wheel system by using a stabilizing peg on the front end with a skid-plate at the bottom of the skid plate, a design adapted from Pathfinder I.