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# Windmill vehicle? connecting magnets to a wheel and recharging the battery while using? What problems might I run into? Answered

I'm starting a project. and wanted to know the best way to tackle it. The wheel is the size of a cd not including the tire. I wanted the four wheels to generate power to make the battery's last longer. Any ideas would be helpful.

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## 6 Replies

Making the wheel motors turn motion into electricity is the exact opposite of making the wheel motors turn electricity into motion. You can do one or the other, but not both at the same time. How about this this: Most of the time, your vehicle is powered with a sail like a sailboat. The wheel motors are used as generators to charge the battery. (Taking energy away from the wheels and putting it into the battery would slow down the vehicle a bit, but maybe not enough to matter as long as the wind was good.) Then, when the wind dies, you can fold down the sail and use the wheel motors to continue driving the vehicle (albeit for shorter distances or much more slowly).

SYMMETRY (author)2009-03-07

What about a wind turbine type set-up where there is no real friction

NobodyInParticular (author)2009-03-07

If you take energy out of the wind to put it into the battery, it's blowing the vehicle forward that much less. And yes, a turbine's friction and turbulence would waste a large portion of your energy, so it goes into neither forward motion nor making electricity. That's why I suggested using a sail to power the vehicle. Rather than using a turbine and motors and wasting energy at both the electricity-generating and electricity-using steps, just use the wind directly; one step, less waste. Using electric motors on the wheels as generators is not especially efficient either, but probably more efficient than a small turbine. (And efficiency might not matter so much if you were trying to slow down the vehicle anyway.)

SYMMETRY (author)2009-03-08

Thanks for the reply I'm going to tinker a little more with the idea

shooterakqj (author)2009-04-09

I am thinking of the same thing that you are. I am also being told that this cannot be done because it would essentially be perpetual motion. I think if I used all moving parts on a car and transmitted that energy to charge a battery, then why couldn't that work. even if it weren't done magnetically a gearing system or flywheel system could be used so the energy loss wouldn't be as great and if I have multiple points of gain such as the wheels and the axles I could generate more than is being used.

kucloth (author)2009-04-23

Well.. anything that is moving on a vehicle is doing so because of an energy source causing it to move. Attempting to harness energy from a wheel, axle, etc, would only cause the energy source causing their motion to work harder. So, any energy that you gained from something like that would be lost somewhere else. (probably much more lost than could ever be gained) Energy is not free... Consider the thought of putting pinwheels on a moving car to generate electricity (like a bunch of little turbines) Any energy gained could not be equal to the energy lost due to the extra wind drag on the vehicle. Does that make sense? Like NobodyInparticular said, using a wind sail would work because the energy to propel the car (and generate electricity during it's motion) is external to the car, so it does not cost it anything. Although, trying to create electricity by use of an axel or wheel based generater would be like driving with your brakes on... The best way to use a generator on a car is to only turn it on when you are trying to slow down ( approaching a stop sign, going down a hill too fast, etc.) because the generator will act like a brake on the wheels. Sorry if that isn't clear...