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Thread: Wheelchair physics -- need an explanation

  1. #21
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    That is a perfect explanation, Chrissy. I can understand it, and Stephen is much smarter than me - his IQ, after all, is 212!
    Don - Grad Student Emeritus
    T3 ASIA A 26 years post injury

  2. #22
    I have fold-down aluminum side guards, 4-degrees camber, and <0.75" rear-wheel spacing at the backrest post. When my chair was brand new, the tires frequently rubbed the side guards. To remedy it, I shimmed the side-guard hinges with brass sheets so the guards tipped in just slightly. They have never rubbed since.

    Attachment 46254Attachment 46256

    When you turn, not only could your wheels be flexing, but so could your side guards (from your hip's pressure) causing them to rub.
    Last edited by chasmengr; 08-28-2012 at 01:56 AM.
    Chas
    TiLite TR3
    Dual-Axle TR3 with RioMobility DragonFly
    I am a person with mild/moderate hexaparesis (impaired movement in 4 limbs, head, & torso) caused by RRMS w/TM C7&T7 incomplete.

    "I know you think you understand what you thought I said, but what I don't think you realize is that what you heard is not what I meant."
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  3. #23
    Senior Member tooley's Avatar
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    Quote Originally Posted by stephen212 View Post
    I think I followed that. What kind of wheels are you running on your Oracing?
    I'm a SpinergyLX guy, 2 sets - the set with treaded tires do it more than the set with SpeedRuns. I love Dino's but just can't justify more wheels.

    Those Schmicking axles you posted are used on their rugby chairs and are indestructible. The SpinergySLX's with the 5/8" axles have experience catastrophic failures (very rare) but that Schmicking design is bullet-proof.

    As for Chrissy's comment about cambered wheels only doing it I would gamble otherwise. The user weight plays a big factor, as well as the torsional strength of the rim and spoke tension - my chrome hubbed/white spoked LXs (not a factory option) do it far more because whoever built them when they came on my Lasher barely tightened the spokes at all.

  4. #24
    Senior Member DaleB's Avatar
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    I think we have a winner!



    Sounds good to me!

    And accounts for my direct experience, as well.

    Thanks!


    Quote Originally Posted by ChrissyOT View Post
    The only way this can happen is if your chair has camber, so I'm guessing you probably have some.

    When you turn, the distance between the wheels at the bottom gets larger, because wheelchair tires are treaded to go straight. When you turn, the tire "wants" to go straight while the tires are actually turning, which causes the wheels to move apart, which effectively increases your camber by a few degrees - until you negate it by going straight again.

    It is for the same reason that wheelchair wheels tend to squeak on hard surfaces while not squeaking when going straight.

    Your tires will probably do this more on carpet (as the tires can't just slide about) and less on hard surfaces.

    I don't know if I explained that in a way that makes any sense, so... you'll let me know I am sure. All the wheelchairs I've ever had have done this.
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  5. #25
    Senior Member tooley's Avatar
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    Quote Originally Posted by ChrissyOT View Post
    When you turn, the distance between the wheels at the bottom gets larger, because wheelchair tires are treaded to go straight. When you turn, the tire "wants" to go straight while the tires are actually turning, which causes the wheels to move apart, which effectively increases your camber by a few degrees - until you negate it by going straight again.

    Isn't that what I tried to say?

    I knew I should have added an OT to my screen name when I joined.

  6. #26
    Senior Member DaleB's Avatar
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    Quote Originally Posted by tooley View Post
    Isn't that what I tried to say?

    I knew I should have added an OT to my screen name when I joined.

    Yeah, you said it, but I didn't read it.

    My bad.
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  7. #27
    Senior Member tooley's Avatar
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    heh, I'm just breaking balls...

    good question/discussion though. Made me think about why this happens (especially for those times when I get my thumb caught in between there.

    We really do need to start wiki'ing some of these things... chas?

  8. #28
    Quote Originally Posted by tooley View Post
    We really do need to start wiki'ing some of these things... chas?
    I am only partially tech literate (I'm retired you know). What is wiki'ing?
    Chas
    TiLite TR3
    Dual-Axle TR3 with RioMobility DragonFly
    I am a person with mild/moderate hexaparesis (impaired movement in 4 limbs, head, & torso) caused by RRMS w/TM C7&T7 incomplete.

    "I know you think you understand what you thought I said, but what I don't think you realize is that what you heard is not what I meant."
    <
    UNKNOWN AUTHOR>

  9. #29
    Senior Member tooley's Avatar
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    I thought wise had something setup so as to create CC's own version of Wikipedia. I haven't really looked into it, just noticed one day looking at other user profiles - "Wiki Contributions: x"

    Seems like a great way to spend time, creating your very own Encyclopedia Chastanica.

  10. #30
    Senior Member DaleB's Avatar
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    Quote Originally Posted by tooley View Post
    I thought wise had something setup so as to create CC's own version of Wikipedia. I haven't really looked into it, just noticed one day looking at other user profiles - "Wiki Contributions: x"

    Seems like a great way to spend time, creating your very own Encyclopedia Chastanica.
    On the bottom of the page:

    'CC Wiki' powered by VaultWiki 2.5.0
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