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Monday, January 19, 2009

Formula SAE Driving

Me driving the 2006 1st place Formula SAE car, converted to stock

The Formula Hybrid team has been busy 24/7 since just after the new year working on the new car. Just for a relaxing day, we took the old car out for a fun day of driving. Last semester a small handful of the team took the task to fix the 2006 Formula SAE car, which won the 1st place in the competition, and won the Road&Track magazine's Triathlon trophy. It previously had a supercharged single cylinder ATV engine , custom exhaust and intake, with an $5,000 aftermarket engine controller that mapped the ignition and injection timing by reading the manifold pressure, speed, and throttle position sensor. If that didn't make any sense don't worry, it was really cool, really powerful, and really unreliable (surprised?) We removed the siezed engine, and replaced it with a stock engine, stock exhaust, and a carburetor. After that we tore out the entire wiring harness and started over. After fixing the shifter and suspension, it was time to drive.

Suited up and ready to drive

I got the opportunity to drive the course first yesterday. It is a very tight autocross style course that limits your speed to less than 60mph, but can require turning at ~1g. Our practice "track" is actually a crappy old runway covered in dirt and grass, oh well. Driving one of these cars requires special safety equipment: a thick engine firewall, five-point safety harness, fireproof suit, gloves, and shoes, a helmet, and arm restraints. The arm restraints tether your arms to the car so you don't break them when the car flips. Rolling the car is pretty unlikely, because the roll center is only about 10.5" off the ground, nearly even with the center of the wheels. The car would have to lean nearly 90 degrees before it would roll over! This leads to very good cornering performance. We also took this opportunity to familiarize the car to potential drivers for the future. A few people we know through various connections who are not on the design team have Formula and Kart racing experience, and may be driving for us. Most of the design team members are engineers, not drivers. Our only experienced driver is about 6'4" and 300lbs, which means he just won't fit. At 6' even, and 170 lbs, I am at the very limit of what fits in the car. It was designed to fit only one driver, and he was much smaller (and faster) than me.

Patrick wondering why the clutch won't work, turns out the cable snapped

The clutch cable snapped after a dozen laps, but we brazed a new connection on the old one with a blowtorch, and got back to driving. I left early that day but a few hours and many laps later the differential threw a few bolts, resulting in some destruction and complete loss of fluid in the drivetrain. by evening the problem was diagnosed, a snapped bolt had punched a hole in the custom made differential case. By 4:00AM the drivetrain team had the parts out of the car and on the operating table. We will have to manufacture a new case for the differential and refill it with fluid, which is the best we could have hoped for. These racing differentials cost $2,700 apiece, plus a few more k for CNC machined mounts, bearings, and joints.

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