Suggestions to Preston Briggs
This site was last updated on February 15, 2008.
Jeffrey Rein sent along the following example
of combat-flier's therapy.
The Bunker Buster
A friend of mine is a scoutmaster and said he was running a pinewood derby race with NO RULES, except no pyrotechnics. He was building an electric car. This sounded fun. I started to think a CO2 powered rocket car, but how to make it work? I won't go into all of the failures (lots), but when I tested the prototype and it ran out of my shop, across the patio, turned right, flipped and rolled 3 times and smacked into the side of my house. I thought: "Cool."
Dirty Dan Rutherford had these CO2 cartridge holders for his free-flight planes. They would puncture the 800-psi cartridge and stop the flow with a small ball in a seat. They held the 8-gram cartridge. When my friend, who is also a paint baller, showed me a 12-gram cartridge, I thought: small block or big block?
I wanted to run a big block, so I took two of the cartridge holders and cut and split them. Put the two together, now an inch longer and wrapped it with carbon fiber and CA. Now I got a Big Block.
To fire it I needed to push the little ball bearing back away from the seat to allow the gas to escape. I did this with a bellcrank and a piece of piano wire. To get the mechanical advantage, I put the wire as close to the mounting screw as possible and the spring as far out as necessary. This worked very well.
Now I needed a way to activate it. I built this mouse trap thing to the front bumper so that when I armed the car, the weight of the car would keep it from firing. When they race, they have nails on a lever and drop the lever to release the cars. When the nail drops, the bumper pops out which triggers the mouse trap, which then fires the bellcrank, and away it goes.
How did it do? Well, I won every race. In fact when I crossed the finish line, most of the cars were only about half way down the ramp. My target time was 2 seconds, but it was actually clocked at 1.3 seconds, so it exceeded all of my expectations. Sure is fun beating up on 10 and 12 year olds. My friend's electric car did well also, crossing the line at 2.4 seconds.
Well, it was also time for my kids to race as well. I asked my 6-year old boy what kind of car he wanted, and he said "a shark". I said "sharks are nice, but what kind of CAR do you want?" He repeated "A Shark. Come on Daddy, I know you can do it." How can I turn that down? He has confidence in me. So I built the shark. With some 1/16" and 1/64" plywood, 1/4" dowels, and some 5-minute epoxy with micro balloons I made it happen. He won three races, then lost to his sister. But he did get the trophy for best design.