Handouts

First Time Coaches' Corner

Here are some general tips for Robofest 2005. You may find many of your students are already facile with the details of these points. I would appreciate your help in showing them the larger picture. This competition is an opportunity to learn good habits in design. Robots built quickly as a series of ad-hoc solutions usually do not work consistently. If you have students in the advanced division you might find helpful material in Henry Petroski's To Engineer is Human: The Role of Failure in Successful Design and Professor Petroski's aphorism, "The purpose of design is to obviate failure." For many students this will be their first exposure to testing and "getting the bugs out."

To Do lists for students preparing for competition day:
Before competition day

1. Invite your parents!
2. Go through your code and mark each place with comments where a value will need to be adjusted on the day of the competition. For example, the amount of turn required at the start for Robot 1 or the difference between pointing directly at a light and pointing 90 degrees away from a light at the end of the path for Robot 2. If you find there are more than 4 or 5 things that might need changing during the competition day, now is the time to try and improve your program.
3. Print out several copies of your code.
4. Save a backup copy of your code on a floppy disk or USB drive.
5. Buy fresh batteries and a roll of clear duct tape and be sure and locate the chargers for your laptops and a power strip to plug them into.
6. Find a cardboard box to cover each robot for programming.
7. Use tape labels with your team name and number on everything. Remember there will be 100 or more pieces of stuff like boxes and cords that look just like yours.
8. Practice getting your team introductions done in just 1 minute. Writng them down will help. For those teams doing an exhibition, you also need a well rehearsed 2 minute introduction to what your robots are going to do (so the total introduction is about 3 minutes).
9. Make sure Dr. Chung has your team pictures and pictures of your robots, well before the day of your competition.
10. Decide which team members will do what in the game area.
11. Re-read the game rules and write down a game plan of what to do when, not if, things go wrong.
12. Pack up everything.

1. Be on time.
2. Start the day with fresh batteries. Then...
3. Take your readings to adjust your light sensors etc. to the course.
4. Have fun!

Planning, sketching a robot design and outlining the robots' task in English pseudocode, is often the difference between a team that succeeds and one that does not.

Bracing and locking, to prevent a robot from falling apart during the competition, is the second prerequisite of a winning robot design. Understand the four types of Lego pegs

1. The 2 unit long black peg fits tightly for bracing. For locking a stack of bricks and beams with a perpendicular beam, remember the Lego horizontal unit is 5/6 of the vertical unit. In the picture of Robot 1 below notice that the 6 holes of the vertical locking beam cross 4 stacked beams + 3 stacked plates or 5 stacked beam units. 1 brick or beam is as high as 3 plates. This geometry means that the holes will only line up for effective locking when the height spanned is a multiple of 5 plates.
2. For bracing the 3 unit black peg is used in making long beams (like those of the chute on Robot 2, but stronger, with a brace beam on both sides of the joint) and at the corners of the 3-4-5 triangle that braces the tower of Robot 1.
3. The grey peg is used like an axle or hinge point, and sometimes can be used if you are short on black pegs.
4. The beige peg is 1 1/2 units and is needed in both robots for locking structures to the holes on the side of the yellow RCX brick. In robot 2, two beige pegs are used to lock an axle to a beam by fitting the short side of the pegs in a medium pulley.

For holding your robot together, or for holding several sub assemblies together that are being tested separately, and when pegs won't quite work, use duct tape and household silicon glue. Vinyl electrical tape may peel off under tension. Super glue or plastic model glue prevents you from reusing your Lego pieces for the next competition.

Keep it simple. Robot 1 needs to deliver a ball a mere 2 inches from its nose. In the example below this is done by simply dropping the ball. While Robot 1 travels, the ball is supported on arms held up by a cam resting on a small sliding platform. When the bar extending out from the platform strikes the back of Robot 2, the slider is pushed out from under the cam, and the arms drop. The ball drops into a chute on Robot 2 and the weight of the ball depresses a touch switch which starts Robot 2. When Robot 2 reaches its destination, its motor tips the chute toward the basket... only 4 inches from the robot's downward pointing light sensor.

Construction ideas for Robot 1:

	Side view of a ball dropping robot. Robot 1 has to be taller than Robot 2 so the ball can drop down. A triangular brace and a vertical locking beam holding the tower to the yellow RCX brick, help stabilize Robot 1.
Closeup of the cam that supports the arms	Closeup of the retaining pegs that keep the sliding platform in place
As an alternative to the cam and sliding platform shown above, consider a ratchet and pawl mechanism. The idea is the same. When the projecting arm hits the back of Robot 2, the arms holding the ball are released. In the pictures below, the edge of a short beam digs into the teeth of the gear so that it cannot turn clockwise. Pushing the bar lifts the beam so the gear rotates freely. Some tape on the stack of bricks that form the support for the "pawl" beam would make this more sturdy.

Construction ideas for Robot 2:

A side view of the second robot and closeups of some of its construction. Note George Miller's idea of using the bevel gears to mount the motor sideways. This makes the design more compact and easier to adjust the lever position by hand prior to the start. Notice the connection between chute and lever arm is by elastic band. Otherwise a lever that travels too far would tend to pry apart your robot. The substitution of 20 inches of aluminum wire for Lego axles and tubing in construction of the chute is not necessary. I ran short of axles because of other, unrelated experiments. I am sure you, like George, can come up with even better designs!
Mounting the motor, using one of the 1 X 2 motor mount plates. Notice the front of the yellow RCX brick top is 1 plate lower than the back.
The worm gear is mounted below the 24 tooth gear. That 24 tooth gear shares an axle with the lever arm beam which controls the tilting of the ball chute. The lever arm beam is fixed to that axle using 2 beige pegs in a medium pulley. The 24 tooth gear's axle is perpendicular to, and 2 beams + 2 plates above the axle of the worm gear.
The chute for the ball hinges on green 1 X 2 axle bricks. At the start of the course, the front of the chute is propped up by the white circular plate. As the weight of ball depresses the back end of chute the left beam pinches the touch sensor closed. At the end of the course, the front of the chute is pulled down by the small black elastic band. The grey 1 X plates on top of the chute beams are to keep the ball up off the touch sensor's black wiring brick.

Revised April 1, 2005