AER201: Engineering design

Second year design (AER201) is widely considered the defining course of Engineering Science, referred to as: “The Robot”. In this class, students in teams of three are presented with a challenge which requires the design of an autonomous robot. In 2015, my class was presented with the challenge of playing a real-time game of connect-4. The playing area was split into two halves with a dvidier and a makeshift connect-4 board in the middle. Ping-pong balls were placed in hoppers at specific locations on each half of the game board, and robots were tasked with collecting balls from the hoppers one at a time and placing them in the game board.

The Design

My team’s principle objective was creating a robust solution resistant to catastrophic failure, and easily repaired in the worst case. This lead my team to value reliability, modularity, simplicity, and low cost throughout the design process. This lead to the design of our robot, Sagan, a name chosen due to it’s revolving arm which ressembles the of a planet around a star.

Sagan docking with a hopper during development.

Mechanically, Sagan minimizes the number of sensors and actuators required to acheive the goal without requiring complex controllers, emphasizing simplicity and reliability. This is acheived through intelligent structural design, making the desired configuration the lowest energy state. In ball collection, two guides mounted on the front of the disk guide the robot into a hopper, passively correcting for small errors in navigation. The ball elvation system is another example, as the ball is scooped out of a well, and falls into the holding tube as the arm swings by. Sagan’s navigation system embodies the same values, with the three-wheel design allowing it to main contact with the game board at all times, reducing the potential of the robot becoming stuck or losing traction, potentialy throwing off estimates of distance. The use of an IR sensor array in concert with optical wheel encoders to measure distance travelled provides a mechanism for error checking and reduces positional errors.

To increase repairability, Sagan’s electrical system is entirely modular, connecting together through 4 and 6-pin connectors. This allowed the entire system to be rapidly disassembled and individual components repaired. This allowed the team to quickly perform critical repairs when a battery leak occured during a live demo. To reduce the risk of sensor or processor errors due to voltage variations, the sensors were driven through a high efficiency switching voltage regulator, and the microprocessor was driven by it’s own lithium ion battery pack.

The Results

It is often said that no plan survives contact with the enemy. In this case the enemy was the game board, as Sagan had difficulty navigating accurately along the black lines painted on the board in the days leading up to the competition, frequently getting off track before even collecting a ball, and rarely making it to the board to deposit one. Miraculously however, with some 11th hour adjustments, we were able to get navigation working on competition day, depositing three balls in the board over the course of 3 rounds. This allowed us to advance to the elimination round, landing us in the top 8 teams in our section, before being eliminated.

Reflection

Having only tinkered with a pair of old headphones before this, AER201 was my first hands-on electronics project. I had already taken a workshop on soldering and using protoboards, but in this project I was able to design, lay out, and assemble an electronics system to interface between the mechanical elements and the robot’s control system. This afforded me the chance to apply the theoretical knowledge gained in previous circuits courses, but also to apply design to an electrical system in addition to a mechanical one.