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Measuring RPM via Photo reflector
Computer
Interface
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Once the robot has found its way into a room, it must
then determine if the candle is present. As stated previously, the sensors
should be capable of locating the candle from the doorway of any given
room. To ensure that the robot can scan the entire room contents, it
first attempts to drive 12 inches into the room. If it encounters the
circle surrounding the candle or travels all 12 inches, it will begin
a counterclockwise sweep to "look" for the candle. If the
candle is present in the given room, the robot will move toward it (if
it is not already close enough) and blow it out. Figure 9 demonstrates
the Room subroutine and how the robot behaves once it has entered a
room. It should also be noted that if the candle has already been extinguished,
the robot will simply stop at the doorway and back up to the facing
wall.
Once the robot has processed all four rooms, it can then realign with a wall and follow that wall back to the starting point. Again, during the return trip, the robot does not enter the rooms looking for the candle. By performing the tasks listed in the above three flowcharts, the robot is able to enter the house, locate the candle, extinguish it, and navigate back to the beginning. A series of tests were perfomed on the robot to see how it would perform with the candle in various locations in the house. 24 fixed candle locations were chosen and a series of 24 trials were conducted. Out of the 24 trials, the robot was able to successfully extinguish the candle 21 times. At the time of the trials, program code was still under development, and thus the robot only completed its return (without touching any of the walls) on 13 of the 21 attempts. The time taken for the robot to reach the candle and extinguish it ranged from 14 seconds in the first room to 49 seconds in the fourth room. With a 55% reduction in time, the worst case scenerio would be approximately 27 seconds per trial. These results demonstrate that the robot can accomplish all desired tasks while performing reliably. Conclusion The annual fire fighting robot competition is an interesting event that challenges the contestants to design a small robot that is capable of finding and extinguishing a lit candle. A solid and reliable design for this competition has been constructed and tested with promising results. The two-wheel design allows the robot precision movement by using stepper motors while also keeping control simple. Proximity sensing is accomplished though the use of IR phototransistors. The devices work well in allowing the robot to determine how far it is from the walls in any given direction up to a distance of approximatley 6 inches. By modulating the IR emitters and passing the phototransistor output through a bandpass filter, the effects of ambient light can be greatly reduced. The two rechargable batteries (for the motors and logic circuits, respectively) have been tested under full load and are capable of supplying the robot with enough power to complete all three of its trials. By using a tone decoder to begin its trials, the robot will receive a 5% reduction in overall time. Furthermore, the program code written for the 68HC12 microcontroller is capable of moving the robot through the model house without touching any walls. It can enter each of the rooms, scan for the lit candle, and extinguish it if it is present. Once is has navigated the entire house and put out the candle, the robot will the navigate back to the starting position. At this point in time, though, the primary task left to be completed is continued development of program code. In certain portions of the house, the robot does not move efficiently (that is, it comes quite close to hitting the walls). As the program code improves, though, the robots performance improves. The existing code (see Appendix C) does, however, successfully accomplish all necessary tasks for competition. The existing robot chassis has evolved from an early prototype. Although the existing chassis serves its basic purpose of supporting the necessary hardware, the design can be improved. An improved chassis design could be lighter to create less torque on the stepper motors. This should result in a faster maximum speed and/or a longer battery usability. Also, an improved chassis could allow better placement of the circuitboards and wiring that is less disorderly. By developing software to write programs into the byte-erasable EEPROM on the 68HC12, the authors could more effectively utilize the available memory. This would allow the D-Bug12 software to be replaced and would free up most of the flash EEPROM space for additional code development. The software listed in Appendix C nearly fills the entire array of byte-erasable memory, and this has become a serious limitation. With more code space available, the robot would be able to perform more rigorous computations on the incoming sensor data. Specifically, a more stable control method could be implemented. Arena Floorplan
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