Wind-Up Hybrids: Lessons from Toy Cars

Published December 23, 2008

Frugal and simple are the keywords for this recession-era gift-giving season. This signals the resurgence of low-tech classic toys made of wood, tin and string, which can delight just as much or more than expensive electronic and plastic toys. One of the retro classic toys—the wind-up rubber band car—points the way to low-cost energy storage strategies for hybrid cars.

No, we’re not talking about Floridian Brian Watt’s adult-sized rubber band car, shown at last year’s MakerFaire. “This is taking rubber band and cardboard technology to the extreme,” said Watt. He admitted that his design was “experimental” but wondered: “Who knows how far it could go if you use more rubber bands?”

Freshman mechanical engineering students at Johns Hopkins University in Baltimore, picked up on that question when they were assigned their first major design project: To construct model cars that propel solely on energy from six rubber bands and two mousetraps. The cars were put to the test by racing one another on an 11-foot long S-curved slalom course. The project focused on principles such as potential and kinetic energy, friction, and material properties.

Real-World Wind-up Hybrids

Can the idea of rubber band power be scaled up to cars in the real world? That’s apparently exactly what Chrysler hybrid engineers were considering in the 1990s. Chrysler engineer Evan Boberg, in his tell-all book “Common Sense Not Required: Idiots Designing Cars & Hybrid Vehicles,” explained how Chrysler engineers connected huge rubber bands to a transmission. The rubber bands were wound up and released to propel the car. Unfortunately, according to Boberg, sometimes the rubber bands exploded causing a safety hazard.

A similar but far more effective—and apparently dangerous—strategy is the use of flywheels. Boberg wrote that one Chrysler technician sacrificed his life when a test flywheel disintegrated.

Almost every vehicle with a manual transmission is already fitted with a flywheel—a kind of high-speed spinning device—to smooth the flow of power from the engine and to provide a small store of energy to help prevent stalling on launch.

In a flywheel hybrid, the mechanical system recovers the kinetic energy of a vehicle during braking and transfers it to the flywheel rather than using an electric motor to store it in batteries as with current hybrids.

In the 1980s, General Motors Research investigated the potential of flywheel hybrids. A 44-person FX85 task force demonstrated the ability of its flywheel design to achieve 10 percent improvements in fuel economy, but abandoned the program based on “a considerable increase in complexity and cost.”

The idea of mechanical winding and spinning energy storage for hybrids persists. In 2007, a group of leading British companies announced its plans to develop flywheel hybrid system in accordance with new Formula One regulations. The idea is to store just enough energy for a burst of speed to pass the competition at exactly the right moment.

And at the 2008 Detroit Auto Show, AFS Trinity Power Corporation—a company that develops energy storage systems using batteries, flywheels and ultracapacitors—unveiled its Extreme Hybrid XH-150. In the vehicle, AFS Trinity applied its technology to a stock Saturn Vue Greenline Hybrid, to produce a small plug-in hybrid SUV capable of 150 miles to the gallon, according to the company.

There’s no reason to wait for AFS Trinity to roll out its technology. You can follow Rob Hangen’s lead, and build your own flywheel hybrid drivetrain…out of Lego. Batteries and rubber bands not included.

Happy Holidays!

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