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Thread: Help me pick out my first manual chair

  1. #31
    Quote Originally Posted by Oddity View Post
    I think of it like 'armor' for my atrophied, osteopathic, little legs. It is handy for transfers, but like I said before, I use my outer wheel. (That's probably a function of my strength to weight ratio and narrowness of the chair. Most people can't imagine that working, but I get the biggest lift and easiest xfer that way.) Moral of the story: It Takes All Kinds For The World To Go 'Round!

    FWIW, my recent ZR spec CAD drawing came back with a 'stability warning' regarding my CoG and wheel hub to caster hub distance. Maybe they've since added 'reasons why' to the process?
    Your confounding the issues. User occupied frame length determines stability not seat tubing. I think you know this so why bring it up in this context? It is only going to confuse people who are new to this by suggesting seat tubing affects stability. It does not.

  2. #32
    Occupied Frame Length can be used to verify that a proposed frame length + angle will provide the same foot placement as an existing chair. Going with more frame tubing and a more-vertical frame angle will generally result in greater forward stability (and a more functional wheelie) because the caster arm will be shorter--increasing the wheelbase. For example, the caster arm for an 80 degree frame is longer than the caster arm on an 85 degree frame.

    I could have got the same wheelbase on my 17X17+1 85 degree Apex demo by going with a 17x17 80 degree frame, but the caster would be swept back farther.

    I'm not sure if the CC CAD Repository still has examples of this or not.


  3. #33
    Senior Member Oddity's Avatar
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    That's a misunderstanding of my post. OFL is critical to getting your feet where you want them, so you can then spec the tubes the best you can, while still getting the placement you want. Seems like you said your tube spec desires created foot placement issues. The suggestion is to do OFL/foot placement first, then spec tube design with available parameters of that. Unless tube design is more important, to you, than foot placement. Maybe it is?

    The second paragraph (aka subject) was in regards to Tilite not giving you feedback on the problems they saw with your request.

    Quote Originally Posted by August West View Post
    Your [sic] confounding the issues. User occupied frame length determines stability not seat tubing. I think you know this so why bring it up in this context? It is only going to confuse people who are new to this by suggesting seat tubing affects stability. It does not.
    "I have great faith in fools; self-confidence my friends call it." - Edgar Allen Poe

    "If you only know your side of an issue, you know nothing." -John Stuart Mill, On Liberty

    "Even what those with the greatest reputation for knowing it all claim to understand and defend are but opinions..." -Heraclitus, Fragments

  4. #34
    Quote Originally Posted by SCI_OTR View Post
    Occupied Frame Length can be used to verify that a proposed frame length + angle will provide the same foot placement as an existing chair. Going with more frame tubing and a more-vertical frame angle will generally result in greater forward stability (and a more functional wheelie) because the caster arm will be shorter--increasing the wheelbase. For example, the caster arm for an 80 degree frame is longer than the caster arm on an 85 degree frame.

    I could have got the same wheelbase on my 17X17+1 85 degree Apex demo by going with a 17x17 80 degree frame, but the caster would be swept back farther.

    I'm not sure if the CC CAD Repository still has examples of this or not.
    You're talking about a mono tube chair. A dual tube chair has that extra horizontal bar that serves to adjust the caster position forward even if the front angle bend is reduced. That's because the caster arm attaches in two places not just one. In other words, if attachment point 1 is recessed because of the reduced front angle bend, attachment point 2 can still be advanced because of the bottom horizontal tube. As a result, the caster doesn't have to be swept back farther like in a mono tube design.

  5. #35
    Quote Originally Posted by Oddity View Post
    The suggestion is to do OFL/foot placement first, then spec tube design with available parameters of that.
    That is exactly what I did. I recall our discussion about a year or so ago and I took your advice. I wrote that earlier today.

  6. #36
    Quote Originally Posted by August West View Post
    You're talking about a mono tube chair. A dual tube chair has that extra horizontal bar that serves to adjust the caster position forward even if the front angle bend is reduced. That's because the caster arm attaches in two places not just one. In other words, if attachment point 1 is recessed because of the reduced front angle bend, attachment point 2 can still be advanced because of the bottom horizontal tube. As a result, the caster doesn't have to be swept back farther like in a mono tube design.
    Provided the fork and caster diameter are identical, what I said still holds true with most dual tube frames. I superimposed the CADS for these chairs and the short segment of ovalized tubing between the front frame and "bullet" caster housing appears identical. That said, as that segment and front frame go their separate ways, the lesser the frame angle, the greater the divergence will be. The greater the footrest length the greater this distance becomes. It may be possible to offset the amount with a custom caster placement, but the engineers would probably need to validate that the placement wouldn't adversely affect forward or lateral stability
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  7. #37
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    Hey everyone,

    Rekindling this thread to get any feedback on the measurements that I had my DME write up for me. Just curious if anyone sees any red flags among these for my condition, or for a newbie in general. Or anything that I should think hard about before I make the final decision. For reference, I'm a reasonably fit 6 ft tall C5-C6 with good triceps but no hands and no core. Here's what he came up with (on a TiLite order form, if that's helpful):
    -16" rear seat width
    -1" taper front seat width (3" narrower than RSW)
    -17" seat depth
    -19" front seat height
    -17.5" rear seat height
    -80? front angle
    -17" seat to footrest
    -16" rear seat width (outer)
    -14 in footrest width (no taper)
    -15-19.5" integrated fold down seat back, set to 17"
    -86-89? folding back seat angle (93-94? non-folding)
    -1" COG
    -1" rear wheel spacing
    -5"x1.5" front wheels
    -24" rear wheels
    -9.5-12.5" swingaway armrests

    Thank you for any advice!
    Emmett

  8. #38
    Senior Member Oddity's Avatar
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    1.5" of dump seems a little shallow for a C5 quad with zero trunk control. I'm a T12 and I'm most comfortable with 2.5". Have you tried a chair setup like that already and figured out that's what's best for you? 17.5" rear with 24" wheels seems like you'll be awfully high from the top of the wheels/center of the hub for pushing dynamics too. We're all different, just thinking out loud.
    "I have great faith in fools; self-confidence my friends call it." - Edgar Allen Poe

    "If you only know your side of an issue, you know nothing." -John Stuart Mill, On Liberty

    "Even what those with the greatest reputation for knowing it all claim to understand and defend are but opinions..." -Heraclitus, Fragments

  9. #39
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    Quote Originally Posted by Oddity View Post
    1.5" of dump seems a little shallow for a C5 quad with zero trunk control. I'm a T12 and I'm most comfortable with 2.5". Have you tried a chair setup like that already and figured out that's what's best for you? 17.5" rear with 24" wheels seems like you'll be awfully high from the top of the wheels/center of the hub for pushing dynamics too. We're all different, just thinking out loud.
    Thank you! This is exactly the sort of thing I was hoping to uncover. I have not had the opportunity to trial any chairs set up like this. Frankly, I'm not sure how and where I'd be able to do that. Seems like the process as I understand it is for a rep from a DME to take these types of measurements and then get you a chair and hope for the best. Is it typically more interactive than iterative? How does a newbie like me really dial in a chair prior to purchasing it?

  10. #40
    Senior Member Oddity's Avatar
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    A wheelchair is a medical device, and your needs have to be evaluated by a medical professional, a PT or OT with a ATP RESNA certification. A DME (or random folks online) can't really do this properly. Getting it wrong can have serious (and even life threatening) consequences. See an ATP OT. There have to be some in your region. There is a look up function on the RESNA dot org website. edit: Spaulding Rehab Hospital has one on staff.
    Last edited by Oddity; 07-08-2019 at 07:18 PM.
    "I have great faith in fools; self-confidence my friends call it." - Edgar Allen Poe

    "If you only know your side of an issue, you know nothing." -John Stuart Mill, On Liberty

    "Even what those with the greatest reputation for knowing it all claim to understand and defend are but opinions..." -Heraclitus, Fragments

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