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Re: Loki (David Buckley robot)

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  • dan michaels
    ... led R.J. Full to conclude that, across the animal kingdom, legs and ... Raibert found a similar result relating quadruped gaits to a virtual biped ... crab
    Message 1 of 212 , Jan 2, 2008
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      --- In SeattleRobotics@yahoogroups.com, Alan KM6VV <KM6VV@...> wrote:
      >
      >
      > >Yeah, I think Rbt Full was mainly comparing the more common gaits,
      > >biped walk/run with quadruped trot with hexapod tripod gait.
      > >
      > >Hence the quote:
      > >===============
      > >These measurements, plus the considerations mentioned above, have
      led R.J. Full to conclude that, across the animal kingdom, legs and
      > >locomotion work in an analogous fashion - namely, "... 1 human leg
      > >works like 2 dog legs, 3 cockroach legs and 4 crab legs ...".
      Raibert found a similar result relating quadruped gaits to a virtual
      biped
      > >gait [Raib84].
      > >===============
      > >
      > >
      > I like that observation! Although I see it the other way around, 4
      crab work like 3 cockroach, which work like 2 dog, or 1 human.
      >


      BTW, this was all discussed several months ago before you got into
      the conversations, but I have been working on a new quad, named Poco.
      I **finally** built and operated the first leg yesterday, while
      everyone else was celebrating college football bowl day. I've been
      gathering parts and making plans for months. Doing mechanical stuff
      is like getting root-canals for some of us.

      In any case, I was looking at the Toejammer design for sometime, and
      thought the hip rotator mechanism might be good on a quad. Peter has
      talked about adding the fore-aft axis to aid turning, while I'm
      trying the vertical rotation axis for this. It's similar to how
      humans do most turns. While standing straight, rotate the foot into
      the new direction, and step forward, etc.

      So, I scrapped Toejammer [R.I.P.] to build the front end of Poco. The
      idea is to attach regular 2-DOF legs to the frame with the hip
      rotators. We'll see how this goes. Basically, the idea is to get
      something similar to the dogs turning in these pictures.

      http://www.oricomtech.com/projects/leg-walk.htm#Turn2

      To a large extent, the dog turns by angulating its entire body,
      and "crossing-over" the front foot, while Poco will turn by rotating
      the foot like a human, to produce approximately the same effect. The
      trick will probably be to make sure the CoG stays inside the
      stability triangle.
    • PeterBalch
      Dr. Bruce. ... have ... OK, I looked it up. In Danaidae (monarchs), Satyridae (whites, graylings) and Nymphalidae (emperors) the two front legs are very short,
      Message 212 of 212 , Jan 14, 2008
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        Dr. Bruce.
        > Interesting question and explanation - except that butterflies actually
        have
        > 6 legs.... 4 long and 2 short.

        OK, I looked it up. In Danaidae (monarchs), Satyridae (whites, graylings)
        and Nymphalidae (emperors) the two front legs are very short, have no claws
        and are useless for walking. I thought Papillionidae (swallowtails) were
        the same but they're not, they have 6 good legs.

        It gets wierder. In Riodinidae, the males have 4 walking legs but the
        females have 6.

        Lycaenidae (blues) and Hesperidae (skippers) all have 6 legs.

        What on earth can one learn from that?

        Anyway, Alan asked what "bugs" are quadrupeds. I said mantises, monarchs
        and swallowtails. I was wrong about swallowtails. I was taught all this
        stuff decades ago so forgive me if I'm a bit rusty. I even spent one summer
        as a student doing fieldwork in the west of Virginia catching swallowtails
        and monarchs so I certainly _ought_ to have remembered the details.

        I still can't think of any other arthropods with just 4 walking legs. I
        think some crustacean larvae have only 4 legs but they don't use them for
        walking.

        Peter
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