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Re: [SeattleRobotics] hovering mini ornithopter

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  • Peter Balch
    John ... Those are nice papers but don t really answer what I was asking. For instance, what s the Reynolds number of your bot? More than 1e7 or have I worked
    Message 1 of 51 , Oct 4, 2009
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      >> > > Can an underwater bot be used as a relevant parallel?
      >> > Well, I can link you to papers if you want.
      >> Yes please. As long as it's for bird-sized ornithopters. I don't believe
      >> that fly-sized ones will be possible for decades.
      > http://www.lcp.nrl.navy.mil/~ravi/papers/Bristol_pap.pdf
      > http://jeb.biologists.org/cgi/reprint/205/10/1507.pdf

      Those are nice papers but don't really answer what I was asking. For
      instance, what's the Reynolds number of your bot? More than 1e7 or have I
      worked it out wrong? Which would put it into the category of a light
      aircraft rather than a bird-sized ornithopter. So can an underwater bot be
      used as a relevant parallel to an indoor ornithopter?

      For instance, you can adjust your fin's shape in a leisurely way. To do that
      with a mini-ornithopter isn't practical.

      >> Anyway, that applies to a robo-fish. I can imagine that subs _might_ work
      >> better with fins. But I was questioning the wisdom of ornithopters. In
      >> the
      >> video of the mini-ornithopter, it was flapping its wings so fast, I bet
      >> they're using mechanics to do all the complex motions.
      > I haven't seen the paper, but I'm pretty sure it relied heavily on
      > whats called 'passive curvature'. Its when you intelligently select a
      > wing shape and stiffness so that at a particular natural frequency it
      > natural bends in just the right way to optimize thrust. This requires
      > serious fluidic-structure interaction CFD calculations, so I think
      > they used experiments to guess a good design.

      Which implies that, if the wing is passive, they'll have huge difficuly
      adjusting the curvature within a single flap to change the direction of the
      thrust (as your fins do).

      I still don't see that a practical indoor ornithopter can do anything that a
      heli can't. And it's harder to make and much less efficient.

      >> For an ornithopter (or submersible), for a given
      >> manoeuverability or speed, which would move a vehicle around for longest
      >> with the same battery?
      > What if your mission is for low speed maneuverability about an
      > obstacle course? Say, for mine inspection about a pier system? In that
      > case, high speed efficiency is useless.

      Yes. So how does the low speed efficiency compare?

      > You can also argue that a fin
      > is quieter than a prop (for secret spy missions or something).

      I'll believe that. I don't have any trouble believing in robot fish. (But
      I'd still like to see your efficiency figures ;-).) It's ornithopters that I
      don't see a future for. I think an indoor ornithopter would be noisier than
      a prop-plane - its wings would have to flap too fast. It wouldn't be

      I really don't see why they're worth funding other than at a low level as
      blue-sky projects.

    • Xandon Frogget
      I think it is Yaw, Roll, Pitch (orientation of the aircraft) and x, y, z ( thrust vectors ). I could be wrong...
      Message 51 of 51 , Oct 8, 2009
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        I think it is Yaw, Roll,  Pitch (orientation of the aircraft) and  x, y, z ( thrust vectors ). I could be wrong...

        On Oct 8, 2009, at 8:42 PM, dpa_io wrote:

        > > You can say a vehicle as a whole has X DOF. The heli has 6 of these.
        > > Roll, yaw, lift, x, y, and z translation.

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