Software

Designing KraftMouse is a one of kind system in programming. The beauty of Kraftmouse's design is that only one kind of input, light intensity, was used. This unique and simple design forced the KraftMouse team to do as much as possible with the control software to take advantage of only one input. So it became important for the control software to be flexible and powerful - more flexible and powerful than the standard Mindstorms graphical development environment.

LegOS

Truly the most powerful system available for the RCX is the embedded operating system kernel and cross compiler set called legOS. Developed by Lego enthusiast around the world, this system provides a full C compiler and rudimentary operating system kernel for the RCX as well as some tools to download programs onto the RCX unit via infrared. Briefly, this system supports an impressive set of features, including 32k RAM for programs and data as well as complete access to the 16MHz 8bit Hitachi CPU and all connected devices. More details of this wonderful tool are available at the project's homepage: http://www.noga.de/legOS/. Unfortunately getting a legOS based robot to communicate with a regular Mindstorms IR system is quite complex, so in the end this system was abandoned.

Not Quite C

Not Quite C (NQC) is a simple C-like language that provides access to many of Mindstorms more useful functions without breaking compatability with other Mindstorm robots. Unfortunately, it also has many of Mindstorms annoying drawbacks. Lego chose to implement its system as a program interpreter that runs as a program on the RCX. Without going into too much detail the results of this architecture discision is that Mindstorm programs have a limited size (6K) and can use only a few variables (16). Fortunately, this proved sufficient for KraftMouse's purposes. More information can be found at the NQC homepage: http://www.enteract.com/~dbaum/nqc/.

Two Light Sensor Design

As described in the hardware section, KraftMouse initially had a two light sensor design. The Valentino Braitenberg VEHICLES inspired the design. Essentially, four tasks were set up, with two global variables. Analogous to an organism with left and right eyes, left and right legs and left and right neurons. The eyes would set shared variables according to the measured intensities on their respective sides. The leg's would read these values and set the speed of their motors in proportion to these values. Certain thresholds were determined such that if both eyes read sufficiently bright levels KraftMouse would backup and spin to face right a predetermined amount.

Two Touch Sensor System

With the advent of less reflective walls the above two light sensor design was discarded and replaced with a two touch sensor system. At first the program was kept as close as possible with the light sensor program. When a touch sensor was touched the robot would reverse the corrisponding motor for a preset amount of time. In order to navigate around corners and ultimately escape the corridor, the left touch sensor would reverse the left leg longer than the right. This system proved very effective for navigating the corridor.

Barrier Detection System

When the IR based barrier detection system was developed, it was decided that in the interest of simplisty and elegance the touch sensors could be removed. This of course meant that the left right contrasting architecture would have to be replaced. In order to navigate the corridor a very simple locomotion algorithm was used.

Is there a barrier in front?
- Yes. Is there a barrier to the left?
  - Unknown. Turn left.
  - Yes. Turn right.
  - No. Turn left and advance.
- No. Go forward.

In order to increase the accuracy of the Barrier Detection System (BDS), KraftMouse was also updated to take single steps instead of continuously moving. After each step it would make its decisions and readings while stationary.

The development and refinement of the BDS system took a lot of time and it did not leave much time to make the house choosing algorithm due primarily to time constraints. As originally intended the BSD would detect whether a barrier or a building was in front of it. The original idea was that once the presence of a building was determined a light level reading could be made. Unfortunately this system only worked on the dim house, as the brightness of the bright house overloaded the BDS system.

However, due to the increased accuracy that NQC gave with its light level readings, the two houses could be isolated based on their respective light ranges. KraftMouse would sweep left until a light level was found within the range of the target house. In addition in order to avoid collision with the corridor structure while looking for the houses, the BDS system was used to backup KraftMouse whenever a barrier was detected in front of it.

Aside, a light calibration step was installed into our program. Before setting KraftMouse on its journey to find a new home, it was necessary to calibrate light levels for the dim house, the bright house as well as the "bonus" task of stopping in the corridor when an extremely bright light was shined on it. This was achieved by using NQC as well and triggering the calibration step with the use of a touch sensor, located on the rear of KraftMouse.