There was a really interesting robot contest held as part of a combined electrical engineering, computer science, and biology course at Case Western Reserve University. Over 500 students were endeared to science by Dr. Randall D. Beer, Dr. Hillel Chiel, and Dr. Richard F. Drushel (Beer, R.D., Chiel, H.J., Drushel, R.F., Autonomous Robotics to Teach Science and Engineering. Communications of the ACM 42, 6 (1999), 85-92.)
Step-by-step, students learn to build robots that hunt for plastic eggs and bring them to their team’s respective nest. The university provides identical buckets of LEGO parts for building drive trains and egg gathering appendages, as well as identical embedded motherboards and snap-in sensors. This allows students to quickly assemble, program, and test various robots, rather than consuming time trying to machine and solder from scratch.
Egg hunting robot.
In the contest, each colored egg is worth 1 point, whereas each black egg is worth -4 points. A mindless robot that gathers all 50 eggs at its nest would end up with zero points (40 colored eggs + 10 black eggs × -4). But, a smart robot that dropped all of the colored eggs in its nest and all of the black eggs in the opponents nest would end the game with the best score of 40 to -40.
As you can imagine, this method of scoring results in all sorts of creative strategies. Robots range from offensive (bring colored eggs home), to sneaky (plant black eggs in opponents nest), to defensive (block opponents from scoring or planting), to various combinations per team (two robots play per side simultaneously).
What I like about the contest is that it isn’t so advanced that few people are qualified to participate, nor is so simple that it would bore college students or intermediate builders. The contest is non-destructive, uses a variety of sensors, and doesn’t devolve into a single optimal solution.
In other articles, I describe how to paint plastic eggs and test them with infrared sensors. And, I discuss how to make a polarized light sensor for beacon navigation so that the robot can find its home nest and the opponent’s nest.
This article provides instructions on making a robot egg hunt arena. Of course, the playing field can be used for other contests as well. The instructions and photographs are useful in learning general construction and woodworking techniques.
The approximate dimensions of the Robotic Egg Hunt arena are shown below. Or, click here for the robotic egg hunt dimensions in PDF format.
Robotic egg hunt arena dimensions.
All walls are 1 foot high to reduce ambient light from the sides and to facilitate infrared reflective or touch sensors for wall avoidance.
The arena walls are flat black. The nest walls and floor are flat white, as opposed to the arena floor which is gray carpeted. The difference in floor reflectivity can be used by the robot to determine when it has entered a nest.
The beacons shine through windows in each nest that are 7 inches wide by 4 inches tall, centered vertically and horizontally on the rear wall of the nest. The window in one nest has vertically-polarizing film, whereas the other next has horizontally-polarizing film.
Robotic egg hunt nest window frame dimensions.
The beacons are 100 W halogen light sources that output 1400 lumens. Theoretically you can substitute a cooler light source (fluorescent or LED) as long as the wavelengths are compatible with the robot’s sensors.
Portable halogen work light. WorkForce #429 804.
I’m using a 250 W portable halogen work light with a 100 W replacement bulb.
Unlike precision metal stock, wood has very strange dimension conventions. They cut the wood like McDonald’s weighs a Quarter Pounder -- net before cooking.
You should bring a measuring tape with you when you go to the local hardware store or lumber yard to select wood for the arena walls. If the lumber says “1 × 12 × 72″, you’ll likely have “¾ × 11¼ × 72″. That’s what I ended up with and it is perfectly acceptable. But, it is important to understand that nominal (advertised) dimensions are not actual finished dimensions.
Choose wood that is flat, even, and has as few knots as possible. I saved a little money by buying lower grade wood, and it cost me significant time in correcting warpage and avoiding knots.
Engineered wood like particleboard or fiberboard is cheaper, more uniform, and usually available with white and black surfaces. However, engineered wood is heavy. If the arena is going to be hauled around a lot, you might want to select natural lower-density wood instead. I chose pine.
Now let’s take a closer look at how to make the window for the polarized beacon in the scoring nest.