a little late for me to get in with the due date around the corner, but what *I* would do is make a trike, have the front wheel made out of a yo-yo, and attach the yoyo's string through the pulleys. Wrapping 95% of the "traveling" string around the yoyo should give a clean separation as the weight falls.
Further I'd have the car get "pulled forward" by the string via a pulley in the launch mechanism.
Let us know how it went and what you learned
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Sometimes a Hypography Forum Administrator
"With a big enough engine, even a brick will fly." -Law of Aerospace
