Trajectory

Overview
"In this event you must make a device that is able to launch a pliable, hollow ball that is 3cm to 9cm. Your device must be powered by a non metallic elastic solid. The device you make must fit in an 80cm by 80cm cube. The launch area in which you place your device is a 1m by 1.5 m rectangle. You want the ball to hit a target between 2 and 8 meters. There are two targets at least 2 meters apart. Each target is either a 1m by 1m square or a 1m diameter circle. At the Regional level, targets are placed at 1 meter intervals. At the State level, targets are placed at 1/2 meter intervals. At the National level, targets are placed at 10 cm intervals. You must tell the judges which target you are going to try to hit and when you are going to fire. One of the targets is on the ground and the other one is up to one meter off of the ground, at 10 cm intervals. The goal is to be able to hit both targets and be accurate. When scoring, you want to get the least amount of points. Four graphs and tables must also be turned in, worth 100 points each. Your target score is the number of millimeters from the center of each target. Penalties are also given for not wearing safety goggles, being inside launch area during launch, the part of the device being outside of the 80cm x 80cm x 80cm cube before or after launch, and the device being outside of launch area. A 100 point penalty is added when any of those occurs."

Device
Design Stage - there are two types of ways for the ball to be propelled toward the target and the differences are important. you can push the ball or you can pull the ball, I prefer pulling the ball. I prefer a swinging arm style launching device however other configurations are available. A swinging arm style Catapult like this was used by the winning Trajectory team at Nationals in 2008.

The Pull Method


The pull method can be adapted in many ways. The push methood can be highly inaccurate and incredibly screwy (which means when you are testing which basically is experimentation, you have too many variables to deal with and you will lose your ability to have an dependent variable (the adjuster) to use). ALSO, even if you have the best machine in the world, you need a laser guide system to help you line up your device to the target and also investing time and energy to make a laser targeting system connected to your distance calibration system would be good ideas too!

The pull method is shown in various configs below.



The Push Method
In the interest of being fair I will give you an idea of how to make a good Push method device.



The picture is of a 2nd at states in Northern California device This device was accurate to + or - 5cm The main concept of the push method is to secure the elastic in two parallel in front of where the projectile starts and then putting the elastic behind the projectile so that it will "push" it towards the target. The way we did this to make this process more accurate is to use a tube and to take a piece of wood to push the ball, which was the same diameter as the tube, down the tube and towards the target. We had 4 different angles we could do this at and 10 power levels. We put about 50 pounds of bricks on the front and sides of the device so as to ensure the device didn't move around in the launch area in the process of firing.

The Teeter Totter
The teeter totter was my first choice when experimenting with gravity, however, i approached that category wrong and mine didn't work. my second was a catapult, it work reasonably well, however, my rubberized material to launch it was too stretchy and stretched out enough to the need to estimate the next launch was necessary but never reliable (although i got 9th at state last year like that). frames look like below. you need to keep in mind easy and cheep ways to adjust your device so it goes further or whatever so you can be exact on both shots. think about stuff that can be always accurate and you can't make a mistake on while setting. Things like this may be elongated stims that correspond to a ruler or something to set your device at. other ideas are... compasses, rulers, lasers, gear systems to set launch arms in place then can release at that point, etc.

Construction
Good solid construction out of wood, preferably 2x4 with glued and screwed connections and heavy bracing to keep the base on the ground when the forces change so drasticly in directions while launching. remember to leave a spot where you can sit on it or put a 5 gal bucket of sand or two to keep it down (the device will slide forward so put gippers on the bottom but not too many (the more the less friction they have)).



Test
Test it so it works in the parameters. Then test it in different temperature settings and also at different temps and different humidities and so on because the device can be affected by all or any one of those factors. do your main testing at 72-74 deg f. make sure you are on level ground and are exact.

you want to get it to the point where you can test it all weekend and nothing goes wrong, you are like going to win. That is optimal, however, it takes weeks to months of 2 hours a night after school testing, calibrating, recording, monitoring, and this is if you are lucky your machine isn't messing up or breaks one week before state like mine. good luck, in this even you will need it. more specific questions email me at monolithel@aol.com and for subject please place "traj questions" and pictures are always helpful. My name is Eric and i am a sophomore, don't be shy.

Tips

 * Make sure you use something that will not stretch out a lot over time. Or if you must use something that will change over time make sure you have a few sets to use and rotate them so they are all the same.
 * Make sure to put a ball(or whatever you are launching) in before you launch sometimes it can be easy to forget to reload it.

Files
[[Media:trajectorygraphs.xls|Graph Examples]]

Links
New York Coaches Conference