Mini Sumo Robot
Señor Lopez El Pesado
Team Fedora
(San Marin High School)
Lopez El Pesado Background


Construction Process

The Team

The Competition


This project is sponsored by San Francisco State University, School of Engineering - Robotic Competition. The challenge is to build, from the kit, a 2-wheel robot that can move in all directions. It has a photo cell that can sense different levels of light and react to it. The kit is provided by SFSU to participating teams. The robots will then participate in an elimination competition.


The kit generally consists of:

The PIC micro-controller needs a regulated 5V supply. The 5V regulator converts the 9V input into 5V. The 0.1µF capacitor is a decoupling capacitor which helps reduce noise in the power supply. It is likely that this capacitor is not necessary in this design because there shouldn't be much noise in the circuit, but it never hurts to be careful. The 100 Ohm resistor between the LED and the power supply limits the amount of current that the LED can draw to 50 mA.

The 40K resistor that is in series with the cadmium sulphide cell (CDS, photo resistor) creates a voltage driver. When the sensor is detecting a light-colored surface, its resistance will decrease which will cause a voltage decrease at the center of the driver. This voltage change is detected by the PIC's A/D convertor. The servos require a 1 to 2 millisecond pulse every 20 milliseconds or so. The length of the pulse would determine the position of the servo if the servos in this kit had not been modified for continuous rotation. Since they have been modified for continuous rotation, only pulse lengths of 1 and 2 milliseconds are used. The resistors between the servo headers and the PIC are there to prevent potential damage to the PIC in case the servos are connected to the robot backwards.

The software inside the robot waits for five seconds after the robot is turned on and then takes a reading of the amount of reflected light that the CDS sensor is receiving. This reading is set as "normal" surface. The robot will then start to drive forward. While it is driving, it constantly increments a counter called random, which helps determine the direction the robot will turn when it encounters a line.

To detect a line, the robot constantly compares the current amount of reflected light to the "normal" level. If the difference between the two is above a certain threshold then it has detected a line. The consequence of this strategy is that you won't need to calibrate the robot to each different surface and lighting condition. It will detect white lines on black surfaces, or black lines on white surfaces. When it detects a line, it looks at the "random" variable and uses it to determine which direction and how far to turn.

Construction Process

Señor Lopez El Pesado was built over several weekends, when student members had more time to get together in the garage of Farzad's house. First, most of the mechanical pieces were put together. Then electronic components were set in place, soldered to the printed circuit, then mounted on the chassis. Finally the testing phase began. Like many first time projects, our robot did not work on the first try. It turned out, due to lack of experience in soldering, that we had loose connections and even a short circuit on the board, which we identified and corrected. See Señor Lopez in action.

It is worth mentioning that the mounting instructions included in the kit did not completely match the kit's components. In some cases the instructions had to be analyzed and modified to match the kit's components. Also, to better protect Señor Lopez from damage, we have added a roll-cage on top. This simple wire-based structure will protect its printed circuit in the event of a rollover.

Team Fedora The Team

Teacher: Mr. Andre Sisneros (Physics teacher)

Student Members:

With special thanks to Farzad's younger brother, Farzin. His help in finding loose connections on the electronic circuit board has been instrumental.

The Competition

Twenty five teams signed up to build this Mini Sumo Robot. On the competition day (February 24, 2005) only 15 teams had their robots ready for battle. The competition began at 10 a.m. in the Jack Adams Hall of SFSU's Cesar Chavez Student Center. It lasted 2 hours. Our team managed to reach the semi-finals. At the end Señor Lopez ranked 4th among 15 competitors.

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