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Monday, January 19, 2009

Building the Formula Hybrid Car

The chassis team leader putting the 4130 steel frame on the jig

This is the 1st post on building the Formula Hybrid car, there will be more if I am not busy building the car to write about building the car. The only reason I have time right now is because I managed to get myself sick by working all day every day instead of sleeping. Hopefully tomorrow I will be back in the machine shop, making the motor mount on the mill.

CNC (robotic) milling a block of aluminum to make the motor mounting plate
The team has spent nearly 6 months designing thing son paper, and just two weeks ago we made the first cut of metal. Since this is a hybrid car, and none of us had any experience with hybrid drivetrains, the motor and control tea started working on this last January when the construction of the 2008 car was just beginning. Now 1 day shy of 1 year later, we got our hybrid drivetrain to run this morning, Hurray! The design team is composed of 7 teams:

-Suspension, brakes, wheels, and tires
-Chassis, cockpit, and body
-Motor and Controls
-Batteries and High Voltage
-Low Voltage and Data aquisition

The engine is mostly stock (if Nascar is "stock" than so is this) so there is not too much work to do there. Our car will also have onboard engine, motor, temperature, and battery monitoring sensors as well as wheel speed sensors, GPS data logging, 3-axis accelerometers and suspension travel measurements. The software we use plots all of these on a GPS acquired map of the course, and allows us to tune the cars suspension, engine, and motor.

A 3D model of the front suspension and steering allows us to test for structural integrity based on spring compression, tire friction and roll stiffness during high g corners.

The teams are 2-3 people, except chassis which has 4 (and needs 7). There is an 8th team, called the "architecture team" that decided how our hybrid car would be put together. I am on the motor and controls team and the architecture teams. We are the hybrid part of the hybrid car. I am the only mechanical engineer on the electrical side of the design. There are really two architectures of a hybrid car- series and parallel. A series car is essentially an electric car that has a gas powered electric generator. It is efficient because the engine can always spin at its optimum speed, but heavy because it must have big batteries and a generator. Most Formula Hybrid cars, including every winner, has been this design. A parallel hybrid car is like a regular car, except that the electric motor is much smaller, and only helps out the gas engine when it is not powerful enough. The motor and batteries can be much smaller and lighter to achieve the same power. Decreasing weight is a great goal for a racecar, and the reason we chose this method. The drawback is reduced fuel economy. We don't care about fuel economy because we are racing against the clock, not the gas tank. Lighter is faster, and that's what really matters (in racing, not highway driving). This method is more complex to pull off in terms of electronics and many times more difficult to design around. The engineer must balance the weight of the motor and batteries and motor against the power gains to select just the right size and configuration.

The Yamaha WR 250 engine, still in the bike for early tuning, with titanium exhaust

Our design will use a 250cc Yamaha dirt bike engine. It's small, but can put out plenty of power for its size. It will also have a very nice titanium muffler kit and an autoclutch. The electric motor we are using is actually an industrial forklift motor. We will be using two boxes full of powerdrill battery packs to power the motor. To recharge the batteries we are going to use the drill companies chargers plugged into our car. We will carry about 30lbs of batteries compared to nearly 300lbs that other teams have used. Also, we modify the battery packs to get nearly 5x more power out of them. A very fancy electric part called a GFI senses if there is a short circuit or someone touching the wires, and automatically shuts down the batteries to prevent injury.

One of the welders uses tungsten-inert-gas welding to put together the frame

The team is working steadily, and we hope to get done in about 10 weeks. That's a tight schedule. Most teams spend a few months designing and a year building, not the reverse. However, no matter how well constructed your car is, you can't win with a bad design.

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