Battery Buggy

Overview
Battery Buggy is an event that requires participants to design and build a moving, battery-powered vehicle capable of traveling a certain distance and stopping as close to that distance as possible. These devices need to meet many parameters, such as size, total power used, types of power used (has to be electric!), and safety restrictions. The "buggy" must be designed with an adjustable mechanism of some sort to allow for different distances to be traveled. Battery Buggy was a real event for a few years back around the turn of the century, but has since only seen life as a rare trial event.

Ways to Build
Chassis material is up to your own discretion (common choices are wood, plastic, or metal), but choose a rigid material that you can connect into a tight, square frame. The closer the frame is to having 90 degree joints and the less bending occurs during travel, the straighter the vehicle will travel. Ensuring that your wheels and axles are uniform, straight, and identical is also important. Here are some examples

Braking systems
There are multiple ways to brake a Battery Buggy. The easiest way is to use a basic wing nut brake, which is depicted in the image below



This does not, however, remove power from the drive motor, which you want to do to prevent the motor from stalling as this can melt wires and burn up motors. To do that, you need to have the wingnut hit (and lock against) a momentary switch. If the motor is in a Normally Closed circuit (as it is in the diagram below), when the wingnut pressed the switch, the motor will be turned off. You can also wire the circuit by adding the wire that runs between NO and the (-) side of the motor so that it acts as an eddy current brake and resists further rotation. These measures should provide an immediate and effective braking system that can be reliably calibrated.



At the Competition
At competitions, the event coordinators select a "target distance" within a pre-determined range (it was five to ten meters when I did the event), and your device must be capable of getting as close as possible to this "target distance" while maintaining a straight line of motion (no side-to-side deviation). The possible distances are rather spaced at regional competition (0.5 meter intervals when I did it) but shrink gradually as you move on to nationals (0.01 meter intervals when I did it). Participants place their buggy at the starting line, and announce to the judges that their run is about to commence, at which point they let the buggy run. Teams aren't allowed to touch their buggy from that point until it stops moving. Two runs are given, with the score of the better run being used for ranking. Obviously, the closer you are to the "target distance," the more points you will receive. However, teams also score points by telling the judges how long it will take for their buggy to travel the "target distance", and the closer teams are to this time, the more points they will receive. Because of the nature of this event, a great deal of testing is required before competition. Teams must practice traveling the various intervals while recording the time it takes to travel such distances, and also test on many different surfaces (carpet, hardwood, tile flooring, etc.).

Misc
There are many ways of creating an adjustable system, including but not limited to through the use of a threaded rod/nut combination, the use of a limit switch, or simply charging rechargeable batteries to an ideal voltage. Innovation was slowing to a halt, however, so the event was removed in favor of Robo-Billiards back in the 2002-2003 season.

Links
Electric Vehicle pics

EV thread
 * Note Electric Vehicle was a C event in 2008 and 2009, it is similar to Baterry Buggy