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2015 West Michigan Coaches’ Clinic

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1 2015 West Michigan Coaches’ Clinic

2 Event Description Construct a vehicle, powered by the energy of a falling mass, to transport an egg across a track as quickly and as accurately as possible. This event has been around with many variations in both divisions for many years. This is a construction event, students may build their vehicle and launcher from scratch, or from purchased components, or from kit parts (if any). Students will learn, and must describe, the physics and the mechanics involved in the design and function of their device. To compete effectively, students must build precisely, practice , calibrate, and record results exhaustively.

3 Egg Transport Device Parameters
The rules describe dimensional constraints in great detail. Students (and coaches) MUST know and follow the rules. Failing to follow the rules in detail will waste time and effort. The egg transport device (the vehicle) will be designed to launch from a launching device, and coast across the track to the terminal barrier. The vehicle must be capable of stopping on its own. The distance it runs before stopping must be adjustable and self-activating. Students must learn to set the distance accurately for each possible target distance at a given competition. The egg will be the foremost object on the vehicle. If the vehicle hits the wall, the egg must absorb the impact. No cushioning may be used to mitigate the impact effect. The vehicle should run a consistent and predictable path. Students will learn to aim the vehicle at the center of the terminal barrier by adjusting the launcher, the vehicle, or simply by repetition. Students will have limited time – 8 minutes – to set up and run two runs. This should also be practiced.

4 Launching Device The vehicle is launched from a stationary device which transfers the energy of a falling mass to kinetic energy of the vehicle. The rules contain the dimensional requirements of the device. When building the launcher, make sure it does not exceed the maximums. Allow for a margin of error in judges’ verification. The launcher can be “aimed” so that the vehicle’s initial direction will bring it accurately to the target on the terminal barrier. In general, the falling mass starts as high as possible and transfers energy to the vehicle as it falls. Energy can be directly transferred by pushing or pulling the vehicle, or energy can be transferred to springs, elastic bands, etc, and then to the vehicle. High impulse, such as an elastic release or an impact release, can yield high initial velocity.

5 The Track The track is variable in length, and the increment of variation gets smaller, and the number of possible target distances gets larger, with higher level tournaments. The distance over which the vehicle is timed is always the same. When the vehicle passes out of the timed zone, it can slow down without affecting the time score. Run score is measured from the tip of the egg to the center of the terminal barrier, so accuracy is essential. New this year, a bonus is available in the form of a can set near the left side of the track. Going around the can without going out of bounds can add a lot to the score, but is risky. Floor texture and cleanliness also has a drastic affect on the accuracy of the vehicle travel and stopping distance. Don’t be shy about using a Swiffer to clean the track or a tape measure to confirm the distance.

6 Competition: Teams will have 8 minutes to set up, adjust, and start two runs. The best scoring run will be used to score the event. Students should practice the time they need to set up. This is an impound event. Target distances will not be announced until after impound. Spare parts must also be impounded. Students must listen to the event supervisors and follow instructions. They can and should check the distance from the egg to the terminal barrier on the first run, to improve the setting for the second run. The judges are not required to tell them the distance. If the egg hits the wall, it is broken if it is leaking. If in doubt, check for leaking with a tissue.

7 Scoring: High score wins. The rules describe the distance score, the time score, the bonus score, and the various penalties. Be certain that the students understand how points are scored (or lost). Note that the distance score is equal to the inaccuracy of the run in centimeters, so one point = one cm. The time score is 10 x number of seconds. Therefore, one second of running time has the same effect as 10 cm. of distance from the target. Score may be better if the vehicle runs slower but more accurately. The distance score is a direct point-to-point measurement, so the scoring is the same for a vehicle which is 50 cm short vs. one which touches the wall and offline by 50 cm. However, it is much riskier to end close to the wall. Most vehicles skid when the brakes are applied, and the skidding makes stopping distance unpredictable. Find a way to get the vehicle to slow down after it passes the 8.5 m line. If the students try for the bonus, they must consider whether it is worth the risk, or if they could do as well by running straight to the target. Penalties are ALWAYS avoidable.

8 Building the Vehicle The egg transport vehicle can be made out of any convenient material. It must be made of materials and with tools that the students can do the construction. The vehicle should be reasonably light weight. Extra mass will take extra energy to accelerate, and the extra momentum will cause more skidding when stopping. However, the vehicle must have enough mass to have momentum to avoid slowing too much due to friction in the bearings or from the floor. The vehicle should be stiff enough to avoid wasting energy during launch, as the chassis can flex or wobble, or bounce like an inch-worm. Keep the profile as low as practical. Make the chassis as long as possible. It will run straighter. When the brakes engage, a shorter chassis may swerve or bounce up from the floor. Keep the vehicle width narrow. It will run straighter with a wide wheel spacing, but may run out of bounds or hit the bonus can.

9 Wheels and Brakes Wheels can be purchased, modified, or made from scratch. Wheels for RC cars and robots can be bought from hobby supply shops. CDs can be used if a tread, such as a rubber band ore balloon, is applied to the perimeter. Wheels can also be cut out of wood, plywood, Lexan, aluminum, etc., with a hole drill on a drill press. Small wheels are better than large wheels. Large wheel require more starting torque, have greater angular momentum when stopping, and have lower resolution when setting the vehicle for running distance. Make a circular index an glue it to the wheels to assist in counting rotations and setting a partial rotation to get the distance accurate. The most common braking system is the “traveling wing nut” system, in which a wing nut moves laterally on an axle as the wheels turn, until it locks against a fixed point on the shaft.

10 Launching, Aiming, Practicing
Several types of launchers can be built. Pulley system launchers are easy to build and accurate, but deliver energy to the vehicle gradually and often have a slower launch speed. Elastic systems can store the energy and provide faster acceleration, but may be harder to control. Impact systems, like a falling pendulum, can be hard to control and may break the egg. See the wiki section at for some graphics of various launching and braking systems. Provide an aiming or sighting system on the launcher to make the runs consistent. If a target is used on the track, remember to remove it before running. Practice of different type of floors, be aware of the way the vehicle runs when the texture is different. Get a vehicle built quickly and start practicing. If the students have more ideas as they practice, they can build another vehicle or modify the one they are using. It will take many, many trial runs to calibrate the distance and direction of the vehicle.

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