i have to build a vehicle that can transport a battery 7 meters in a straight line as fast as possible using the potential enerygy of no more than two kilograms falling from a maximum height of 80.0 cm. i want to build this brake: http://www.scioly.org/w/images/1/19/SC-brake2diag.gif [Broken] http://www.scioly.org/w/images/4/46/SC-brake2.gif [Broken] "This system is very popular among competitors. While only slightly more complicated than the string method, it is more consistent. The basic concept of this design is using a threaded rod for the axle, placing a nut (usually a wing nut is used) on the axle. As the wheels rotate the rotating motion is transferred in to horizontal motion of a wing nut moving it along the axle. When the wing nut reaches a barrier, it will no longer be able to move, and thus stops the axle from turning. The distance is set by setting how far the wing nut starts from the barrier and is usually measured in rotations of the wheels. While as described the system is still vulnerable to skid, it can be minimized by carefully choosing a material for the barrier that the wing nut engages during the stopping motion. By choosing something rubbery many teams achieved a gradual locking of the wheels, which effectively eliminated any skid inherent to the system. The wing nut also adds some friction to the axle, thus the car may not roll as smoothly or as far. " and i am absolutely desperate because i don't know how to build it! if someone could recommend the wood to make the car out of. i was thinking balsa wood since it's light. i bought a 1/4" diameter threaded rod and wingnut and rubber washers but i don't know how to put the thing together! i will be SO SO SO SO absolutely grateful to anyone that can give me any ideas or help! thanks so much!