Or, you could do it my way...plain and simple.
Find a piece of flat, thin wood, like balsa, some Crazy Glue, two hammers, two roofing nails (any size), and a box of Co2 air gun cartrdges.
1. Glue the wood to the "floor" of the coaster car.
2. Glue two (2) Co2 cartridges, one on each side -left and right - of the wood, with the thinnest, puncturable part facing out of two holes in the back of the car.
3. Have one person on each side hit a nail into the back of each Co2 cartridge at the same time.
The End :).
(Don't worry about the Co2 cartridge exploding. I've performed this plenty of times(not a coaster model, but you get the drift), and it's never blown up on me)
Good luck :).
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"Johnny Rotten shot me with his BB-gun."
*** This post was edited by Intamin2k on 5/4/2001. ***