Robot UN-PONG (2002)
- Susana Tricarico
- Jul 21, 2020
- 3 min read
With Ricardo E. Ramirez
This robot was created as final project for the class Smart Robotics Seminar in the Master in Industrial Automation. UN-PONG moves in an arena of 1.5m of diameter filled with white ping pongs. The robot wanders until it finds a red ping pong and traps it.
Design Requirements
The requirements given by the professor were:
Maximum dimensions: a cube of 25x25x25cm
Arena: 1.5m in diameter and 10cm height, constant illumination and flat surface
Detection and selection: Identify and collect a standard size red ping pong ball among an undetermined group of white ping pongs.
General Considerations
Behavior
The robot should wander in the arena, avoiding obstacles while doing so until it finds and traps a red ball. In case of a collision, the robot must react and change course. To achieve this, we defined a Behavior-based algorithm [1]. The behavior for picking-up the ball has the highest precedency given that after finding the red ball, no other behavior is necessary.
Wander: The robot was programmed to move in a straight line until an obstacle is detected, and then turn a certain angle. Because of mechanical characteristics, one of the motors is faster than the other. That resulted in a random behavior.
Obstacle Avoidance: If the robot detects an obstacle ahead, it will turn in the opposite direction to keep with the wandering behavior. If it backs up and detects an obstacle in the back, the robot turns right and goes forward.
Collision Reaction: If the robot detects a collision, depending on the side of the activated sensor, it turns in the opposite direction. If both collision sensors are activated, the robot backs up for 3 seconds and starts the wandering behavior again.
Pick-up Ball: When the robot detects a red ball in the lower tunnel, it activates the trap, stops wandering, beeps and turns on an indication LED.
Electronics and Smart Control
Power
A set of two batteries power the robot. One of them feeds the electronics and the other one feeds the actuators. Tests showed autonomy of more than 3 hours.
Sensors
Collision Reaction: two micro switches in the front, on the left and right sides are activated by an acrylic sheet when colliding with objects.
Obstacle Avoidance: the robot uses three photoelectric proximity sensors. The range goes between 2 and 60 cm. The sensors are located in the front left and right sides and in the back of the platform.
Ball detection: the sensor is a set photoresistor of 7mm in diameter connected to a comparator and while light. The photoresists must be calibrated in the detection environment.
Actuators
Traction: it is achieved through two 5V DC motoreducers with a current 250mA.
Ball pick-up: The trap is activated by a DC motor and a nut-bolt reduction linked to the trap.
Coding and decision-making: All sensors and actuators are connected to the CPU of a PIC 16F877. The following picture shows the block diagram.
Mechanics
Platform and cover: We selected the size of the platform to better fit the dimensions of the motoreductors, the available tires, and the required room to allow the ping pong balls go through the platform. The resulting diameter was 22cm. The material for the base was 4mm agglomerated wood. This wood was also used in the supports for the motors. The guides for the ping pong funnel and sensor supports are made of acrylic. Other support structures for electronics were made of PVC profiles. The entire design was projected in SolidEdge Software. The cuts were made with laser and manual tools. The cover was made of poster board.
Navigation and Shocks: We used plastic tires 65mm in diameter and covered with rubber from a RC Car. The tires were connected to the motoreductors by a system of pulley-band. The auxiliar support rests on two teflon legs with sphere feet.
Trap: It has the shape of a mouth to guide the balls to a tunnel where the photoresists and the light were located. After determining the red color of a ball, a C-Shaped acrylic leaf falls to trap the ball.
Flow Chart
Conclusion
Adding a variable gain, would result in an improvement to the color sensor. This will allow to avoid the noise produced by change in the environment light
Traction on the tires became critical in the turns and wandering behaviors
The navigation system provided a proper answer to the requirements
Batteries provided an excellent autonomy time thanks to the separation between actuator and electronics power
The architecture provided flexibility to implement changes
The distance to wall was very dependent on the sensor calibration
Published as RAMIREZ, R.E.; RUGE, S.C. UN-PONG, Robot móvil explorador. In: IEEE Latin American CAS Tour 2002, 2002. Memorias de IEEE Latin American CAS Tour 2002. Bogotá: Universidad de los Andes, 2002.
[1] ROLF, PFEIFER y SCHEIER, CHRISIAN. Evolutionary robotics –a research program for cognitive science: a tutorial. pags 69-98.
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