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Alt Energy, Physics

Why not have real wind up cars?

Think about the implications of spring stored energy scaled up to real cars. Is it possible? An aspiring aerospace engineer blogging at Astrochara, shared with Truestrange a video of a mousetrap powered model car that will travel 60 feet. The plans are available so you can make one:

In my AP Physics class we were required to create a mousetrap car that was able to roll 45 feet in order to obtain a 100 test grade. I was quite excited by this challenge, and created a car that rolled a total of 60 feet on the first test run, only taking a total of 3 hours to build! Here, I will be instructing you how to build a successful mousetrap car.

Read more, instructions here:


Here is a video of this design in action.

A mousetrap car is a small vehicle whose only source of motive power is a mousetrap. Variations include the use of multiple traps, or very big rat traps, for added power.

Mousetrap cars are often used in physics or other physical science classes to help students build problem-solving skills, develop spatial awareness, learn to budget time, and practice cooperative behavior.


Damninteresting has an article on wind up cars:

Many hybrid cars use an interesting system called “regenerative braking” to recapture some of the energy which is wasted with conventional braking systems. On a typical car, each wheel has a rotor disk, and braking is accomplished by causing the brake pads to squeeze the rotor and create friction which slows the car, converting the forward momentum into waste heat. But a hybrid doesn’t use the brake pads at all unless you hit the brakes hard… Instead, the car’s momentum is used to crank its electric motors, which slows the car while recharging the onboard batteries.

This brilliantly simple system is part of why hybrid cars are so fuel efficient in stop-and-go traffic. But hybrids have their downsides… For one, a modern hybrid’s batteries only last 8-10 years on average, and they are extremely expensive to replace, on the order of $3000-7000. Battery disposal is also a sticky problem, since Nickel-Metal Hydride batteries contain hazardous chemicals. In addition, although hybrids save some weight by including a smaller gas engine, they add it all back by including the heavy electrical components: two electric motors and the batteries.

Could there be a way of usefully recapturing a car’s kinetic energy on deceleration without adding so much weight, and without the expense and environmental impact of batteries? What about a wind-up automobile?

… Ultimately, the real question is whether torsion energy storage is any more efficient than it’s electric hybrid cousin. Data indicates most electric hybrid regenerative braking systems work at less than 50% efficiency by the time the kinetic energy is converted into electricity, then put back into propelling the vehicle… but it is difficult to say what a torsion hybrid’s efficiency might be once friction is accounted for.


The energy efficiency of a vehicle is the ratio of the output energy to the input energy. A mousetrap is powered by a helical torsion spring. The stored energy in joules can be calculated. 

One estimate is roughly 1.2 joules with a 66% loss of energy to friction for another design. Link (pdf)

What are your thoughts on the feasibility of a torsion drive? 

About Xeno

E pluribus unum.


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