The goal of this university assignment was to equip a two-wheeled roboter with behaviors which allows it to roam a disaster area and identify victims in need of rescue, and then move them into a specific area. The victims are represented by small cylinders placed in a 9 square meter big arena. The robot has to bring the cylinders into the rescue zone: a 40 cm x 40 cm big area with black surface and with an infrared-emitting beacon placed in the middle.
ConstructionThe robot chasis is based on the Boe-Bot Construction Kit from Parallax. The mechanics are controlled by 4 servos. Two continuous servos are used for the wheel movement. One servo was mounted between the two wheel servos to control the frontal claw for grabbing cylinders. The fourth servo was mounted at the front to turn the two sonar sensors.
The frontal construction of the robot is mainly for grabbing the cylinders. The upper part houses two push buttons at the front for obstacle detection and a light barrier which is interrupted, when there is an object between the two claws. The two lower parts are movable and are attached to a servo to be able to close them.
SensorsTo interact with the surrounding the robot is equipped with the following sensors:
- For detection if a cylinder is in the claw or not a light barrier is used. A focused LED shines on a photoresistor, which is build in a voltage divider to convert the change in resistance into a change of voltage. The additional resistor is chosen in the way that the voltage on the input pin is below 1,4V (boe bot threshold voltage) for the open light barrier and above 1,4V if the light barrier is closed.
- The floor sensor is basically build the same way as the light barrier, only that the LED is not shining directly on the photo resistor but instead the light is reflected from the floor. In this way it is possible to distinguish between white and black surfaces. The circuit for both sensors is shown in figure 2 on the left side.
- The IR sensors are used to detect the signal of the IR beacon, we installed two of them to be able to distinguish the direction of the IR Emitter.
- The sonar sensors are integrated circuits which only need a electric supply and deliver already a signal in the right level, therefore no additional circuits are needed.
- The whiskers are two push buttons in the front of the claw. They detect, if the robot hits an obstacle.
The BrainThe Basic Stamp Microcontroller has a lot of restrictions. With only 32 Bytes of RAM and a program size (EEPROM) of maximal 2 KBytes we could not implement all the features we wanted. For example it was quite impossible to implement odometry and even more difficult to save a map of the arena.
Therefore we decided to go for a set of simple behaviours, without remembering much of the sensory information we collected. The behaviour set consists of 9 states. And even with these few states, we reached the maximum size of the EEPROM.
You can differentiate between two general behaviour patterns: The first one (Searching Mode) is for finding the cylinders and moving in the arena. As soon as the robot grabs a cylinder, it changes to the second behaviour pattern (Returning Mode), which leads the robot back to the rescue zone. When it drops the cylinder (accidentally or on purpose) it goes back to the first pattern.
You can find a more detailed description of the construction and algorithms in our report: report.pdf