Expressway

During Christmas, 2004, I was reading about the new Parallax QTI Line Sensor and the instructions for it's use. Over the years, there have been several individuals use the Fairchild QRD1114 with some success. I had purchased several to play with several years ago, but hadn't taken the time. After reading the instructions, I thought that I could do it better. The old Wall Following modified Parallax BOEBot was still intact, so it was used as the base for Expressway. The results can be seen in the videos of the 2005 NEIRG competition.

The NEIRG line following contest consists of white floor tile with black electrical tape line. There can be 45 degree turns, 90 degree turns, or 135 degree turns. There is no minimum radius for any turns. The path may cross itself (at 90 degrees) and there is a two inch black square at the end. Competitors are not allowed to see the layout before their run. Each competitor gets one chance to complete the course and stop at the end. The timer runs from the time the robot initially starts until it stops at the end. If the robot needs correction, it can be picked up, but must be restarted at the beginning. Points are awarded for each tile successfully navigated and bonus points are awarded for stopping at the end. In the case of a points tie, the winner is determined by elapse time.

In the first video, Expressway completed the course but failed to stop at the end. With the clock still running, Expressway was restarted (second video), completed the course, and eventually stopped at the end. That was good enough for third place in the event.

The sensor package consists of six QRD1114s. The middle four keep Expressway on the line and the two outside sensors determine which way Expressway turns when it runs off of the line. The IR LEDs are on all of the time and the QRD1114 outputs are tied directly to BS2SX pins 0, 1, 2, and 3. The program is simple. There is just a branch on INA (INA is a four bit number that is the input status of pins 0 through 3). When no line is sensed, Expressway turns in the direction indicated by the last line sensed by the outside sensors. With this arrangement, Expressway could travel about 24 inches per second and recheck the line every 0.2 inches.

Expressway came together so fast that there was still two months to go before the contest. What to do? How about a song and dance at the end. "Camptown Races" seemed like an appropriate tune. A small amplifier and speaker were hidden under the BOEBot and a brief dance routine in step with the music was added. Note that the BS2SX both generated the tones for Camptown Races as well as controlled the motor. It was all a lot of fun.

So what is there to do for the next event. Could I get a robot to complete the course in less that 10 seconds? That would be a challenge.