In the early 1980s, my college-aged brother designed a simple motor-plus-battery car that raced along a string between our carport post and the street-side power pole. For years now, we've been improving on his basic design, with the initial goal of keeping it really simple: one battery-driven motor, optional flashing lights, and repurposed materials whenever possible. The primary racing objective was speed and stability. The car ran at full speed until it found the end of the string -- then you had to be there to catch it or be prepared to repair it before the next time trial.
We talked about making the car smarter so that it could stop and reverse directions, and came up with lots of schemes and circuits to make it possible, but for many years were more focused on the high-speed "Gump" mode of operation. Run Forrest, run!
The first version was made from a reclaimed motor with a pulley already attached, a spent 9v battery, and a short length of fence wire to use as the chassis and string guides -- zero cost. Using fence wire as the chassis framework allowed for many design variants from sleek and compact to exceptionally stable stretch versions. The wire bends easily and can be formed into whatever the designer wants, as long as they think about center-of-gravity, balance, traction, stability, and connecting a simple electrical circuit. One challenge along the way was to create both the chassis and guides from a single length of wire, front-to-back with only bends, no cutting or brazing.
In spite of the seemingly endless options that come to mind, we continue to be inspired by the original design and, to this day, enjoy reclaiming old motors, turning our own custom pulleys, and devising faster, more stable cars based upon the idea that was hatched up in Grandpa's basement workshop.
We hope you are inspired to take on the challenge to build a better, faster, and smarter string car!