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Air Powered Car Brainstorm

  1. Jan 18, 2005 #1
    I have a good idea for a linear actuated drive system for automobiles and engines in general. I need a recommendation for a linear actuator that has a stroke of up to 18 inches, can perform very fast cycles of actuation and retraction in a controlled fashion, around 25 to 50 Hz. Needs to provide 100 lbs up to 500 lbs force onto shaft. Should be adjustable/controllable in terms of amount of force and cycle rates. I am looking currently for a low cost actuator with theses properties. If it works, you will be the second person to own a fairly sporty airpowered car. Air/pneumatic or electromechanical actuator doesn't matter to me. Please help the world get off the Oil Industry stranglehold. Thanks.
     
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  3. Jan 18, 2005 #2

    Cliff_J

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    few quick thoughts:

    very fast, long throw, high force = very high pressure = dangerous and expensive

    Change the design requirements (power is power, larger piston on a shorter stroke with less revolutions/sec make much things easier) a little and you could reduce this dramatically.

    You still need an energy source, it has to come from somewhere. Without addressing that, if you use the electrical power grid to make pressurized air you are in effect buring coal and natural gas since that is where a majority of power comes from in the first place. Now the storage ability is compromised, unless the range of your car is just a few hundred feet.

    If you need an internal combustion engine running on gas/diesel to make the pressurized air on a constant basis as driving, you'd be much better off in the electrical realm than mechanical pressures.

    The easiest way to achieve some of your ideas - a steam car. Jay Leno has one that has 700 ft-lb of torque from its 2-cylinder air motor and its quite sporty according to what he has said in TV interviews. The long wait time for the boiler to reach temperature makes it impractical, but this would be very easy to build. But then you could burn wood which is at least renewable.

    Cliff
     
  4. Jan 19, 2005 #3

    FredGarvin

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    At 50 Hz, that's a piston speed of 900 in/sec. That's pretty damned fast. A Ø 2.00 in. piston would require at least 160 psi to give you the 500 Lbf requirement. If you go with a bigger piston you have to think about the inertia of the piston itself. What exactly are you going to use to provide an air source that will keep up with that kind of demand?

    You've given plenty of specifications and what it should be able to do, yet with no idea on where to get it or how to go about it. Where exactly is the brainstorming part coming in?
     
  5. Jan 19, 2005 #4
    Alright, Here's the idea

    I researched online that a Gas engine piston chamber generates about 600-800PSI at compressed/ignition/power stroke of 4 stroke process. If you have a bolt cutter compound lever jaw mechanism that can take 50Lbs of force and translate that into 4000 lbs cutting force. I was envisioning a compound lever similar to this configuration to take 50 lbs force applied over a lever area of 18 in stroke and apply ~3000 lbs force over a 2-5 inch levered piston/crankshaft setup for RPM of 1250 to 2500 or possibly very low around 300RPM. The torque converter and gear ratios would need to be dramatically different to make it driveable. Alternatively, a swash plate could be used instead of crankshaft. The electrical source could come from small wind turbine/solar panel roof mounted or in hood mounted to power the EM actuator or to operate compressor refill in a pneumatic actuator.
    Thoughts?
     
  6. Jan 19, 2005 #5

    brewnog

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    Urm no.

    If a roof mounted small wind turbine/solar panel could produce enough electricity to power a car, then currently our cars would be powered by small roof mounted wind turbines, or solar panels.

    Sorry!
     
  7. Jan 19, 2005 #6

    FredGarvin

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    I really don't understand how you will incorporate the lever idea into a slider/crank mechanism like you say. I need a picture.

    I think you'll also have to do some more research on the power required to compress the air at volumes and pressures required. Compare that to what a solar panel or wind turbine put out and I think you'll see you'll come up short.
     
  8. Jan 19, 2005 #7

    Cliff_J

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    urbsurfer - two things to factor in.

    First, power is power. You can use a lever, transmission, pulley or whatever to change force but that is not going to change the power. If a lever increases force it decreases the distance that force is applied over by the same amount. If a transmission increases torque it reduces RPM by the same amount. Same for pulleys, double the force and you get 1/2 the distance, triple one and you get 1/3 the other and so on.

    Second, conservation of energy is important. If the car is moving forward at 20 MPH then the apparent wind on a still day would be 20MPH to the wind turbine mounted on the hood, correct? But that wind turbine would add drag and try to slow the car down. If it was 100% efficient at "catching" the wind, 100% efficient at turning that into power, 100% efficient at delivering that power and putting it to the wheels it could counter-act that drag it creates. But you still have the drag of the car's shape going through the air and the rubber tires on the ground to factor in. Ever try to push a car? Those forces are a lot to overcome for a person much less a wind generator, it'd have to be a big one. :smile:

    Plus, 100% efficient is handy for a textbook to learn a concept, once in reality it becomes a constant area to have losses. If you think about it a little more this should become clear, even 98% efficiency means eventually the kinetic energy in the moving car will be used up by the air friction and tire friction. You need someway to put energy into the system. Currently the cheapest way is oil based fuels.

    Cliff
     
  9. Jan 20, 2005 #8
    little help

    hi im a 8th grader in atlanta and am currently doing research for a project about a wind/electric powered car

    i do not know much about the subject being in 8th grade but would like some ideas and information on the subject

    my idea is for something like a fan mounted infront of the radiator that turns a turbine... this along with the wheels would help generate atleast some electricity for the car to run on... this would reduce the amount of electricity needed from another source... this would be a mainly electric car like the hybrid's tht exist today but would atleast have a little more electricity to run on reducing the use of the combustion engine... please let me know what you think along with ideas and information on the subject :confused:

    thanks alot

    -Joe
     
  10. Jan 21, 2005 #9

    brewnog

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    Again, the amount of power you can get from such a system would be insignificant in comparison to the amount of power needed to run a car. Aside from that, you'd have to propel the car forwards somehow in order to provide 'wind' to spin your fan, which is commonly known as a perpetual motion machine.
     
  11. Jan 21, 2005 #10
    well my idea is to have the electric powered car... the electric power would get the car moving so that the fan turns... it would be solely electric but the axil and fan would power the turbine which would atleast generate some amount of electricity right? the electricity generated would help charge the batteries
     
  12. Jan 21, 2005 #11
    can sum one give me some information to make sumthing like this work??
     
  13. Jan 21, 2005 #12
    What would happen if you ran the car on nitrogen instaed of gas?
     
  14. Jan 21, 2005 #13

    Q_Goest

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    Hi UT. What everyone here is trying to tell you in so many words is that it is impossible to make this work.

    Let's assume we make a massive windmill on the front of this car, powerful enough to produce the energy needed to drive it. The problem is that the energy needed to drive the vehicle depends on how much energy it takes to drive the windmill. The windmill isn't making free energy, it needs to be forced through the air in order to make energy, and the energy it takes to force it through the air must come from the motors which drive it. And unfortunately, it will take more energy to drive it than the windmill makes. So there is never any chance of this device working. It is classified as a perpetual motion machine that creates energy.

    "How do you know this simply by hearing this small amount of information about the idea?" you might ask. It's actually pretty simple, you can draw a control volume around the object and know that the amount of energy going in must equal the amount coming out except that losses such as friction which converts useful energy to heat will result in less useful energy coming out of any given control volume. These kinds of ideas pop up all the time, and they are generally easy to spot. I'm sorry to say that such an idea won't work whatsoever, even to a very tiny degree. Any windmill on the front of a vehicle will require more energy to drive it than it produces because it produces a resistance to the air which needs even more energy to overcome than it will ever produce.

    Besides, I work for Ford, and we're presently in the process of patenting this idea now that you've mentioned it, so please cease and decist. <grin>
     
  15. Jan 21, 2005 #14

    Q_Goest

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    One other thought, you may notice a large number of hydraulic pumps used to drive actuators such as on heavy equipment, cranes, bulldozers, etc... but very very few air compressors used to drive actuators. That's because air heats up considerably when compressed which is energy being converted to heat which is lost. Hydraulic pumps don't have this massive loss. So very few companies make air driven machinery because it's inherently inefficient. Only small things like air tools in a garage can afford the huge inefficiencies inherent in air driven actuators.
     
  16. Jan 21, 2005 #15

    FredGarvin

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    Ran which part of the car on nitrogen? Why do you think that would be beneficial?
     
  17. Jan 21, 2005 #16

    Cliff_J

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    There is no such thing as a free lunch. Remember the acronym TINSTAAFL.

    UT, you probably have a skateboard park nearby right? Well take something that rolls (a skateboard, a basketball, a baseball, a golf ball - doesn't matter) and go up one of the half-pipes with the slopes that faces another.

    (for those who don't recognise the name half-pipe see link)
    http://www.thrillseekersunlimited.com/ESbmxskate.htm

    Now at the top of the half pipe release the rolling item and let it go. As it rolls down the first "hill" it picks up speed, correct?

    Now it goes up the other "hill" and looses the speed as it goes up. Then it goes down that "hill" and back towards the first.

    How many times does the object roll between the two hills? Maybe twice or three times? Friction used up the potential energy the object gained when you carried it up.

    No difference for fan-generators. To produce power, it takes in power and adds friction.

    A solar panel would help a little, it'll help slow the battery discharge unless the panel is incredibly big and mounted to an incredibly small and light car.

    You as a person can change this half-pipe behavior of rolling only a couple times before slowing to a stop. You can use your leg muscles to input energy to the system just like you can move back and forth on a swingset and go faster. That energy came from food, that food gathered its energy from the sun - its like indirect solar energy! Anyways, in the same manner the car engine needs to constantly add energy to a car converted from the energy stored in the fuel to keep the car moving down the road.

    TINSTAAFL
     
  18. Jan 21, 2005 #17
    I have to laugh at this thread. We are talking about wind powered cars and getting all complex with wind turbines and such. Has anyone considered a sail? LMAO!

    All of this talk about propellers in front of radiators and such are just complex schemes that can be boiled down to motor turning a generator that in turn powers the motor. Not going to go.
     
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