Wind-Up Hybrids: Lessons from Toy Cars

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.

Brian Watt’s amazing rubber band car.

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.

For their first major design project, freshman mechanical engineers at Johns Hopkins had to think low-tech. No motors or batteries. Each vehicle could be powered only by two mousetraps and six rubber bands.

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.

Boberg Book Cover Image

Cover image from Evan Boberg’s “Common Sense Not Required.”

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.”

GM FX85 Team

General Motors FX85 leadership Team with a mock-up of the FX85 flywheel hybrid transmission.

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.

A flywheel hybrid made out of Lego.

Happy Holidays!


  • Bryce

    Thats cute. I don’t know if I want giant rubber bands or flywheels disintegrating my transmission or engine though.

  • Dan L

    There are two main difficulties with flywheels:
    1) They tend to explode. (But then so do gasoline tanks and lithium batteries)
    2) They “leak” energy in the form of heat caused by friction in the bearings. This effectively limits their usefulness to applications where the energy only needs to be stored for a few minutes.

  • AP

    In addition to Dan L’s flywheel comments, add
    3) Their speed decreases as their energy is used, so you need a CVT and a regular transmission to match the flywheel speed to the wheel speed.
    4) Their failures aren’t “slow,” like a leaking flaming gas tank: they’re more catastrophic.

    As far as springs go, their energy-density is low, even compared with batteries, so they have to be heavy and large: a lot of their energy goes into moving themselves. A freshman mechanical engineer could easily calculate the maximum possible range of a spring-powered car.

  • mdensch

    I would be interested in seeing more discussion about hydraulic hybrid technology. The physics behind it is, essentially, the same as that which is described here, but appears to be more viable, more durable and, according to its proponents, more efficient than electric hybrids.

    UPS is participating in testing of this and from what I understand, the results are quite promising.

  • sausageslaps

    i have had this idea for years, a high tension spring contained in a casing which releases energy under controlled conditions.

  • Danny

    It;s bizarre that a my kids toy car has help the lesson for for hybrids. Although we need to still need to overcome the problem with friction in the within the bearings.

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  • Anonymous

    lol

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  • DrBill

    Did you know that in the 1950′s the Swiss ran their Busses off Flywheel technology ?
    Don’t know why they stopped though. Probably because of the oil companies.

  • tapra1

    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.Tech Blog

  • fajar yulianto

    Its nice to read this. I’ve made a full scale prototype of a human powered vehicle with almost similar concept. But I use coiled spring instead rubber band. I found that adding a flywheel into the powertrain reduce the speed perfomance a little but increasing climbing ability significantly, and saving a lot of energy when pedalling. I planned to bring it into small mass production by the end of 2012.

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