Li'le Rosie by Doug Oda

Li'l Rosie the Fire Fighting Robot 

Dimensions: 10 inches high, 8 inches in diameter 
Power: 8 "AA" cell batteries 
Locomotion: Two DC motors 
Brains: Siemens 80C515 microcontroller 
Fire detection: 1 EG&G Thermopiles with Fresnel lens 
Fire extinguisher: Balloon filled with CO2 

Liíl Rosie is a custom robot built to compete in the 1998 Fire Fighting Robot Contest. The task consist of 3 basic parts which are navigating a floorplan to search for a candle, identifying
the candle as a candle, and extinguishing the candle. 

Navigating a known floorplan is relatively easy. There are two drive wheels in Liíl Rose each of which is attached to a optical encoder wheel. One rotation of a drive wheel moves the
robot forward 2 inches and generates sixteen pulses to the microcontroller. The direction can be determined at any time by subtracting the pulses generated by one wheel from the other.
The differance is used to lookup a direction value in a lookup table. Any accumulated error can be corrected using the proximity sensors located around the front of the robot. The speed
is in controlled by pulsing voltage to the motors. The longer the "on" time of the pulse the greater the speed. The voltage generated by the motor during the "off" time of the pulse is
measured by the processor and is a indicator of how fast the motor is turning. The processor then uses this information to adjust the pulse on time for a constant motor speed (standard
PWM with back EMF speed control scheme). 

The problem if identifying a candle is solved using a thermopile and with an infrared frasnel lens to detect the heat generated by the candle. The lens and sensor are mounted on a turret
that makes a 180 degree sweep. The voltage generated by the amplifier/sensor circuit is read by the microcontroller and an increase of temperature in a particular spot is identified as a
candle. 

Extinguishing the candle is easy. A balloon protrudes 3 inches in front of the robot 8.5 inches off the floor. The robot simply drives straight at the candle until the balloon pops. The heat of
the candle pops the balloon when the balloon passes over the candle and the force of the CO2 escaping the balloon blows out the flame. The robot senses when the balloon is ruptured
by listening for the loud bang with the same microphone that is used for sensing the starting buzzer. 

The total cost of the robot is less than $100. Most electronic parts were given as samples with the remaining parts purchased from a local surplus warehouse. The big expences were the
optics, the optical proximity sensors (borrowed for the contest) and time. 

Email: Doug.Oda@StdReg.Com


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