Wheeled Vehicle

Wheeled Vehicle is a physics based build event in which students must construct a vehicle powered only by a non-metallic elastic solid device. The participants must be able to adjust the vehicle to travel a specified distance around an obstacle as chosen by the event supervisor as fast and as accurately as possible.

Event Description
Prior to the event, competitors must design, build, and test a vehicle which is only powered by a non-metallic, elastic material that can store potential energy. This potential energy is stored (for example stretching a rubber band) and then released to make the vehicle move from the kinetic energy. The main object of this event is to avoid an obstacle and stop at or as near as possible to the specified distance while moving as fast as possible.

At the competition, the event supervisor will announce a track distance between 9 and 12 meters after impound is complete. The exact distance will be in different intervals for different levels of competition (see below). Competitors will be given a total time of 8 minutes to set up their vehicle and perform two runs. The vehicle must be triggered by actuating a release mechanism with a pencil supplied by the event supervisor.

Basic Construction Parameters

 * The vehicle should be designed to travel between 9 and 12 meters.
 * All energy used to propel the vehicle must be stored in a non-metallic, elastic device.
 * All wheels must fit in a ready to run configuration in a 25.0 cm x 60.0 cm space (no height restriction).
 * The vehicle must have a 1/4 inch wooden dowel attached to the front of the vehicle. This dowel serves as a measurement point for distance to the line, and also a method to trigger the photogate system (if used by the event supervisor).
 * The vehicle must be started by a vertically-actuated trigger.

The calibration intervals are: Regionals and Invitationals: 1.00 meter (100 cm) States: 0.50 meters (50 cm) Nationals: 0.10 meters (10 cm)

Designs
The three main parts of a design will be the energy mechanism, the turning mechanism, and the braking system.

Body design is also important- consider what type of car is most suitable whether it be a lightweight, easy-to-move car, or perhaps something in the middle that won't do a wheelie as easily, or maybe something ridiculously heavy, powered by a very strong elastic solid. Most teams choose to go as light as possible. Try to find ways to shave down weight wherever possible.

Elastic Energy Mechanisms
Some of the popular energy mechanisms are:


 * rubber bands
 * fishing poles
 * carbon fiber poles
 * bungee cords

These can be harnessed in many ways, such as a string wrapped around an axle, and the elastic unwrapping the string. Another popular method is to simply wrap the rubber band around the axle, hold it in place, and have it unwind during the course of the run to spin the wheels.

Braking Mechanism
A braking system is needed to stop accurately. Here are some things to think about:
 * It needs to be accurate.
 * It can be adjusted to whatever distance is announced at the competition.
 * Somewhat simple is better, so that there's not a whole lot of room for error.
 * It has to be very reliable, so it will work (near) perfectly every time.

Braking systems are built differently by each team to accommodate their vehicle. There are several systems that can easily be adapted into a device. (Scrambler, Mousetrap Vehicle, and many other SO events include similar braking concepts.)

With this planned out, you know what you need and you can start designing a mechanism. There are many different kinds of mechanisms online. However, you can also come up with your own braking device.

Threaded Rod and Nut
One of the mechanisms commonly used on a vehicle is the threaded rod and nut design, also known as a Scrambler Brake. It has been used by many competitors in multiple vehicle events and is usually very reliable. The details of how you build it and how you implement it are up to you, but the general idea is the same. First off, a threaded rod, a nut (preferably a wingnut) and something to hold the nut are needed. It is important to know how many revolutions of the wheel it will take for the vehicle to reach 12 meters. This can be done by using the formula for the circumference of a circle, which in this case is the wheel: C=pi*diameter(of the wheel). After figuring that out (in cm), divide 1200 by the circumference and you will know a number of revolutions of the wheel you will need to reach the maximum distance. With some extra calculations, depending on the thread count of your rod, this will tell you how long an axle needs to be and thus how narrow a car can be made.

First, start by looking at the blue line which in this case is our axle (which is the threaded rod). The red line represents the wing nut, the green circles represent the wheels, and the green line is the rod that holds the wing nut in place. As the wheels and axle spin, the wingnut will move down towards the chassis between the wheel and the inner assembly. Eventually, this nut will hit the chassis and lock up the axle, preventing the car from traveling more. In order to use this system for calibration, all you would have to do is start the nut on the chassis and then wind it out to the distance you need thinking about how much distance you get per turn of the wheel. You can easily figure this out using the formula above. As many might have figured out, there is one minor flaw in doing this: you cannot turn the wing nut until you move that green rod in the diagram to make it removable.

Turning Mechanism
For the turning mechanism, there are a few options. Some will probably work better than others.
 * One strategy was to go over the can, but a FAQ was recently posted on the official Science Olympiad website disallowing this.
 * Another option is to have the vehicle naturally turn one direction, the aim it the opposite way.
 * This would involve having one of the axles placed at an angle, and then starting the vehicle at an angle that allows it to start out to the side of the can and gradually return to the center.
 * A more complicated option would be to use an Ackermann steering system, but this is usually reserved for teams at the highest levels of competition.

Competition
Goggles are required for the competition. Also, any tools or computing device needed to assist in calculating distance/time are permitted. However, note that the rules prohibit the use of any electronic devices except calculators (e.g. laser pointers are not allowed). The vehicle must be impounded before competition starts, and the event supervisor may not announce the target distance until the last vehicle is impounded. The competition will be on a relatively smooth, level track (often a corridor or gym). For the two runs, there will be a total of 8 minutes of preparation time. However, once time expires, you will not be able to continue to conduct a second (or first) run. Vehicles are to be triggered only when the event supervisor has indicated one may do so. Do not chase after the vehicle; this will result in a Competition Violation. Wait until an event supervisor signals that the vehicle can be retrieved.

Helpful Links

 * ScienceGuyOrg Blogspot