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Power consumption in a rotating system

  1. Jul 29, 2010 #1
    Hi there,

    i have a specific question concerning power consumption in a rotating system and hope that somebody out there can help me out.

    Lets say we have a wheel, powered by an e-motor, that is surrounded by magnets that are attached to the edge of the wheel ( like a cog wheel but magnets instead of the cogs ). Now i place an identical wheel aside so that it is brought to movement by the first one (by the magnets). My question is: How much more power do i have to put into the e-motor that is making the first wheel spin, to make a second, third and so on.. wheel spin at the same rotation speed, that are aside the first one? Is there any other power stopping the additional wheels instead of the friction of air and the attachment? Important: i mean the additional power that is consumed when the system is already running!

    Any help would be really nice ;)
    Last edited: Jul 29, 2010
  2. jcsd
  3. Jul 29, 2010 #2


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    Gold Member

    I gather you are describing a system with frictionless cogs. Will such a setup with magnets act as frictionless cogs?

    I suspect not. I suspect that eddy currents will be generated. The energy cost of the eddy currents acts in the same way as energy cost from friction. In fact, generating eddy currents is sometimes used as the basis of a braking system design.
  4. Jul 29, 2010 #3
    my idea is to build a system in which you align many of these wheels but only one is powered by the motor. in addition i want to attach to each wheel a parallel one on which there are magnets attached to the edge but with the poles directed to the spinning direction. these should move through many aligned coils so that a current is induced over each wheel. now, if the additional power that is used to make the additional (magnet instead cog) wheels spin, is very low, maybe i can induce more current over the coils on each parallel wheel than necessary for powering the e-motor?!? it is an open system so nothing would offense the laws of physics for creating a higher output.

    please bombard me with ideas ;)
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