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Please help me understand why this won't work

  1. Feb 2, 2006 #1
    For a while I've had a concept for a vehicle that combines existing technologies, but like most of my concepts, it seems too good to be true. Can someone explain the physics which disallows it?

    The concept is for a vehicle which I've dubbed the Segway Rickshaw (link to my .pdf sketch is below). Basically it is a two wheeled vehicle that utilizes the balancing technolgy of the Segway along with the energy re-capture technology of hybrid cars to produce forward motion via gravity. The idea is that if you place a mass on wheels and balance it at an angle it will create forward motion. One of the key engineering obstacles is that the falling motion (produced by gravity) has to be reversed into forward motion to prevent the mass from falling. Have I lost you? Or, am I basically breaking all sorts of laws of physics?

    At any rate, I think it's at least a cool design and an opportunity for me to understand better forces I want to comprehend.

    Thanks,
    Robert

    http://www.geocities.com/rghusted/mypage.html
     
    Last edited: Feb 2, 2006
  2. jcsd
  3. Feb 2, 2006 #2
    You need to accerate the mass forward to prevent the machine from falling. This acceleration requires energy which won't be provided by the falling mass. Research "perpetual motion" and you'll see why this won't work.
     
  4. Feb 2, 2006 #3

    FredGarvin

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    Your link to the pdf file isn't working right now. I have a tendancy to agree with Dngrsone. It does sound like you are trying to get all of your motion solely from just the "falling" mass which is a no-go. There has to be some other form of energy input into the system.
     
  5. Feb 2, 2006 #4
    Eeek! You're right about the link. Yahoo now charges for sharing files Grrr. I'm working on a new link.

    Also, I'm not suggesting that power solely come from the falling mass. I guess one of the questions I'm probing is this: in the act of balancing a mass on two wheels (as in a dolley cart) is more power required to balance 2000 lbs than 200 lbs (for example) if the diameter of the wheels are proportionally larger as well (say 20cm to 200cm diameter)?

    It seems to me (this is probably where I get in trouble) that if forward motion is applied to this balanced mass, in order to keep the mass from falling backward, the angle of balance needs to be adjusted forward. Yes? No? Have I lost you?

    I guess my concept is not to create a perpetual motion machine, which according to physics as we understand it is impossible. Rather, I'm thinking of utilizing known physics to decrease the amount of energy input required to produce the same motion of mass.

    A picture speaks a 1000 words. Here is the new link. To enlarge photo, save .jpg and open in viewer. Thanks.

    http://www.geocities.com/rghusted/mypage.html
     
    Last edited: Feb 2, 2006
  6. Feb 2, 2006 #5

    russ_watters

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    And even if you aren't talking about converting "the falling" into forward motion (just using it for the controls), the fact that "the falling" is a force/acceleration means that a constant force/acceleration needs to be applied to counteract it. So your device wouldn't be able to maintain constant speed. The difference between that and using your leaning to create a turn is that a turn is a constant acceleration, so a constant lean-angle translates into a constant turn rate via the controls.

    Now, all that said, I'm not really sure how a Sedgeway works - it may be that to move forward, you decouple yourself from the device, (you lean back while pushing the handlebars forward), keeping the system stable, but causing the Sedgeway itself to lean forward and thus (via controls detecting the lean) move forward.
     
    Last edited: Feb 2, 2006
  7. Feb 2, 2006 #6

    Cliff_J

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    Robert - the flaw comes from thinking that the balance of mass could be used to improve efficiency, because your equation is factored without proper regard to time.

    Yes, you could set up a scenario where moving the center of mass forward of the balance point could cause additional acceleration. But this (or really any) use of potential energy converted into kinetic energy requires you to examine the system with respect to time as longer than the event that occurs. Something had to put the potential energy there in the first place.

    Even a hydro-electric dam that 'makes' all of its power from converting the potential energy of water stored at a high elevation into kinetic energy driving generators is actually using the sun as its energy source. Something had to evaporate that water and allow it to fall and collect in those high elevations so that in turn gravity could do its thing. Since the sun added the additional energy to the water molecules to allow them to have that additional potential energy, its exclusion would allow for an efficiency approaching infinity.

    Just the mere act of balancing like a Segway uses a lot of energy compared to a 3 wheeled vehicle that would not need to balance. Since it needs to perform accelerations (as tiny as they may be) each applicaton of force is going to use energy. Its to the credit of the designers that it works as well as it does and is very efficient at using minimal energy to do its job. But adding mass and increasing the force necessary sound like ways to end up on the wrong side of an equation about economies of size.
     
  8. Feb 2, 2006 #7
    Ok. Silly question: What type of energy is gravity? Potential? Kinetic? Other?
     
    Last edited: Feb 2, 2006
  9. Feb 2, 2006 #8

    Cliff_J

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    Its effectively only potential energy, but gravity is really just a force and not a form of energy at all. The force of gravity accelerates a body in freefall at 9.8 m/s^2 on earth. The amount of energy is determined by 'height' of the fall.

    Kinetic energy is related to motion, its what a layperson would call momentum (even though they are different).

    If you drop a baseball one inch, as it falls the acceleration from gravity means the potential energy is converted into kinetic energy based on its velocity. A large drop would convert more of that potential energy into kinetic energy - in other words, it will continue to increase speed over the entire fall and the kinetic energy is related to the square of the velocity.

    But regardless, since energy can neither be created or destroyed, the potential energy needed to be input there in the firstplace before gravity would even have a chance to convert it.
     
    Last edited: Feb 2, 2006
  10. Feb 2, 2006 #9
    rghusted,
    Gravity is not energy. A weight suspended in a gravitational field has some potential energy which you can harness if you turn it into kinetic energy by letting go of it. The problem with your scenario is that the mass is not moving, it's balanced. If it does move so that you can harness some of it's kinetic energy, it can only move so far before it either hits the ground or hangs directly beneath the wheels and can no longer provide any kinetic energy to provide propulsion. Don't let it deter you, your next idea may be better !
     
  11. Apr 7, 2009 #10
    Last edited: Apr 7, 2009
  12. Apr 7, 2009 #11

    russ_watters

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    No one objected to the vehicle configuration, just your proposal to bypass the laws of physics to propel it, so "the concept" that we were discussing is not addressed in that article - and is still flawed.
     
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