Stretching a string between two trees is relatively simple. Here's a technique we use that is easy to set-up and remove, doesn't cause tree damage, and provides some end-of-string crash protection for the string car!
- Wrap a bungee cord around a tree or post and link the hooks together. Tie a loop in one end of the string and slip it into a miniature carabiner that's been clipped into the bungee cord. A short length of a swimming pool noodle with the string passing through the middle provides a cushion for the inevitable collision.
- Repeat the process on the other end of the string. Shorten the string a bit before tying the loop. The bungee will stretch and keep the string taut.
The string car will be more stable if it is balanced on the string. To balance the car, move the pulley on the motor shaft closer to or farther away from the motor. If moving the pulley doesn't balance the car, try bending the wire chassis to change the relative position of the battery and motor.
It's time to race! Flip the switch on, place the pulley on the string, and carefully release the car. It will quickly zip to the other end of the string where a friend can catch it. They will remove the car from the string, turn it around, and send it speeding back to you.
The fastest car will have the shortest lap time, so a stopwatch is needed for most single-string races. Placing two strings side-by-side provides a drag race track -- it'll be obvious who won the race!
Racing stripes on the battery box would be a nice touch. It's essential, however, to give your car a name like Speedy or The Zoominator. A fitting name will encourage it to perform at its best!