best Muni under $500?

Discussion in 'rec.sport.unicycling archive' started by Duncan, Jul 5, 2004.

  1. Eenwieler

    Eenwieler Guest

    i should go for the KH24 in your case. But in my case I
    will safe a lot of money and buy a stronger one because I
    have already bent my KH crank ( after 3 months:( ) So if
    you do a few drops. Not very big ones, you bent you crank.
    I have jumped 4 thimes of a 5 foot skate ramp. So it isn't
    strong enough.

    Ferko

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  2. John_childs

    John_childs Guest

    eenwieler wrote:
    > *i should go for the KH24 in your case. But in my case I
    > will safe a lot of money and buy a stronger one because I
    > have already bent my KH crank ( after 3 months:( ) So if
    > you do a few drops. Not very big ones, you bent you crank.
    > I have jumped 4 thimes of a 5 foot skate ramp. So it isn't
    > strong enough.
    >
    > Ferko *

    A five foot drop to flat is pretty big. If you don't roll
    out properly on a drop that big you're going to be bending
    or breaking cranks. I'd bet you could even break a Profile
    crank if you do repeated 5 foot drops to flat with poor
    technique.

    How smoothly can you land a 3 foot drop to flat? Can you
    roll it out every time? Do you land with a thud and a double
    bounce? Are you able to land lightly and collapse your body
    to absorb the impact?

    Technique has a lot to do with how well your unicycle will
    survive big drops, especially to flat. If you're a big guy
    and you land big drops like a ton of bricks, you're going to
    be breaking or bending almost any crank.

    I can do 3 foot drops to flat fairly smoothly. I still
    sometimes mess up and land poorly, but most of the time I
    land them smoothly. I don't land 4 foot drops as well. I'll
    land and sometimes get a double bounce because I don't roll
    out and/or collapse my body properly to absorb the impact.
    Until I can get 4 foot drops as smooth as my 3 foot drops
    I'm not going to do anything higher.

    KH cranks can handle 5 foot drops. Kris uses KH cranks now
    and he does big drops. He just lands all of his drops very
    smoothly. If you're 180+ pounds and you land a 5 foot drop
    poorly, yeah, you probably can bend the crank.

    Adding just a foot to the drop height adds a lot of
    additional energy that needs to be absorbed. It's an
    exponential increase in energy. Doubling the height does a
    lot more than double the amount of energy. I'm too lazy
    right now to go get my physics book to find the exact
    equation, but I know it's exponential.

    Anyways, if you're bending cranks like the KH cranks it
    would be a good idea to get real smooth at smaller drops
    before going for the bigger drops. The alternative is to get
    a Profile hub and Profile Dirtjumper cranks and hope for the
    best. But even Dirtjumper cranks can break.

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  3. Ooh, threads on physics. Time for one of my essays then...

    Kinetic energy is proportioanl to the ssquare of the
    speed (KE =
    (1/2)mv^2 ) But speed doesn't increase linearly with drop
    height. Notice from tennisgh32's numbers that speed
    from 100' is only 10 times higher than 1', where it
    would be 100 times if it was linear. Potential energy
    is PE = mgh ( or mass x gravity x height as words) so
    it's linear with height increase. When you drop, all
    that potential enegry is converted into kinetic energy,
    so your kinetic energy when you hit the floor will
    increase linearly with drop height. Because you
    accelerate as you fall, for the last foot you're
    travelling faster, so while you're still accelerating
    (at 9.8m per second per second) the actual time for
    which you are accelerating is shorter, so you don't
    speed up as much. If you start from 0 vertical speed,
    v^2 = 2as, so velocity is the square root of
    accelearation x height (ie distance travelled) x 2.
    Which makes sense, 'cause the kinetic energy is the
    square of a square root, so it'll be linear.

    Just as a vague nod to the topic, that means that weight is
    as important as height, so you should get the onza. Or have
    a smaller lunch before a ride.

    John

    P.S. If anyone's doing GCSE or A-level physics this year, I
    hope you paid attention to that. You never know when
    questions on unicycling will turn up. That, and ping
    pong balls.

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  4. John_childs

    John_childs Guest

    johnhimsworth wrote:
    > *Ooh, threads on physics. Time for one of my essays
    > then... *

    Looks like I should dust off my physics book. I used to know
    all that stuff pretty well. It's just been a long time since
    I've used any of
    it. At least my vague recollection of kinetic energy was
    right. Unfortunately my vague recollection of velocity
    due to drop height was not right.

    Knowing how drop height and mass affects the jolt (impulse)
    when you land is a good thing to know. It's linear.

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  5. Tennisgh22

    Tennisgh22 Guest

    I just calculated this out, i dunno whether i helps your
    arguement or what. its pretty interesting tho

    DROP HEIGHT: SPEED WHEN YOU HIT THE GROUND:

    1 foot 3.9 mph

    2 feet 5.4 mph

    3 feet 6.7 mph

    4 feet 7.8 mph

    5 feet 8.7 mph

    6 feet 9.5 mph

    and if you're kris holm,

    100 feet 39 mph

    does all that sound right? check my math if you think im
    crazy.

    -grant

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    labels off of everything and let the problem solve itself?
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  6. John_childs

    John_childs Guest

    Ken Cline wrote:
    > * Still, the amount of energy goes up linearly with
    > height. The equation is E = mgh, where m is mass, g is
    > gravitational acceleration, and h is the height dropped.
    >
    > Ken
    >
    > *

    That's for potential energy. For a drop we're interested in
    the kinetic energy and the impulse and the momentum. Kinetic
    energy increases with the square of the velocity. That's
    where the exponential component would come in.

    Ugh, It's been a long time since I've done any physics. I
    hope I've got that right. I might have to dust off my
    physics book.

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  7. Ken Cline

    Ken Cline Guest

    "john_childs" <[email protected]> writes:

    > Adding just a foot to the drop height adds a lot of
    > additional energy that needs to be absorbed. It's an
    > exponential increase in energy. Doubling the height does a
    > lot more than double the amount of energy. I'm too lazy
    > right now to go get my physics book to find the exact
    > equation, but I know it's exponential.

    I'm not surprised that adding height feels dramatically
    harder. There's only so much energy your body can absorb,
    only so far you can roll out without losing balance, plus
    everything happens faster as you hit harder.

    Still, the amount of energy goes up linearly with height.
    The equation is E = mgh, where m is mass, g is gravitational
    acceleration, and h is the height dropped.

    Ken
     
  8. Ken Cline

    Ken Cline Guest

    "tennisgh22" <[email protected]> writes:

    > kinetic energy = 1/2 (mass)(velocity)^2

    Quite. However, the kinetic energy is converted from
    potential energy, and is therefore bounded by PE (by the
    First Law of Thermodynamics).

    > thus, velocity is being squared, so it is in fact
    > exponential.

    No. Velocity is proportional to the square root of distance,
    so it (energy) is in fact linear (with distance).

    But this is a roundabout way to analyze kinetic energy of a
    falling object. Step back and ask yourself what kinetic
    energy is. A very relevant answer is the capacity to do
    work, e.g. exert a force over distance. But exerting a
    force, m*g, over a distance, h, is exactly how that kinetic
    energy was acquired.

    > looks like you dont have to worry about getting out your
    > physics book after all, john :)

    You might want to have another look at yours :)
     
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