I created this robot with my friend, Peter, for the Trinity Fire-Fighting Robotics Competition. This competition brings together many teams from the area (New England) as well as teams from overseas. The competition is divided into several divisions - middle school, high school, expert (anyone), and walking (also anyone). We chose the walking division. Naturally, our building material of choice was Lego bricks. In the competition the robot must navigate through a maze autonomously (without human control), locate a candle, which could be in one of 4 rooms, and extinguish it.

Mechanical
There are several mechanical challenges that arise in building a walking robot:

  • Balance
  • Torque (motor strength)
  • Leg rigidity
  • Turning

We overcame the issue of balance by using six legs (hence the name Fire Ant) so that at least 3 legs would be in contact with the ground at any given time, and allowing all the legs to be controlled by a single drive chain. To get enough torque, we used 4 motors in parallel, geared down, and also a complex leg design. The most common leg design found in simple walking robots moves legs in a cycloidal path.

Our design gave the robot an extra forward lurch at the end of each cycle. This means it would not be good at walking backward, but is faster when walking forward than a simple design. To handle turning we had a seventh leg which came down in the center of the robot, lifted the robot up, then pivoted. This was, of course, slower than a normal step of the robot, but most of the time was spent going straight, so this wasn't a huge concern.

Electrical
Aside from our motors, all electrical components were non-Lego. We used a Basic Stamp microcontroller to control the robot, Sharp IR sensors to detect walls, and a pyroelectric sensor to detect the flame. A few days before the competition we realised our ADC was flaky and had no time to get a replacement. Instead we attempted to modify our code to componsate for the occasional miss read, but it wasn't perfect. With any reading there is a certain probability it will be wrong, so there is a chance that several readings in a row will also be wrong. The more readings we consider the less likely this will occur, but there is a limitation on how fast we can make readings, and they will become less accurate when the robot is moving.

The Competition
The day of the competition arrived. Our robot was fantastic mechanically, but without reliable sensor readings we were mostly blind. Even so, we were the only team in the walking division to successfully enter a room, (two of three runs) though never the room with the candle. By the method of scoring, we received a bonus for entering the room, however another team received a bonus for starting by sound, (instead of pressing a button on the robot) and thus placed higher than us. We were still happy with second place and walked away with a plaque and a $200 prize. 

 

Image credit: Cycloid from Wikipedia Commons, by Matthew Conroy; local copy, original.