View Poll Results: Have you been thrown out of your cantilevered rigid frame wheelchair

Voters
28. You may not vote on this poll
  • No. 75 or 80 deg frame angle. Seat depth 16" or less.

    2 7.14%
  • No. 75 or 80 deg frame angle. Seat depth 17"+.

    4 14.29%
  • No. 85 or 90 deg frame angle. Seat depth 16" or less.

    2 7.14%
  • No. 85 or 90 deg frame angle. Seat depth 17"+.

    3 10.71%
  • Yes. 75 or 80 deg frame angle. Seat depth 16" or less.

    3 10.71%
  • Yes. 75 or 80 deg frame angle. Seat depth 17"+.

    2 7.14%
  • Yes. 85 or 90 deg frame angle. Seat depth 16" or less.

    7 25.00%
  • Yes. 85 or 90 deg frame angle. Seat depth 17"+.

    5 17.86%
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Results 31 to 38 of 38

Thread: Who has been pitched out their cantilevered frame wheelchair because of an endo?

  1. #31
    Gordy, It's very important that the front casters are at 90o or the chair becomes very in eficient when pushing and harder to control. For me, a lot depends on if the person is a higher break and doesn't have enough dump in the chair to keep them in the chair.

    Higher break more dump; lower break, less dump.

  2. #32
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    Quote Originally Posted by Patrick Madsen View Post
    Gordy, It's very important that the front casters are at 90o or the chair becomes very in eficient when pushing and harder to control. For me, a lot depends on if the person is a higher break and doesn't have enough dump in the chair to keep them in the chair.

    Higher break more dump; lower break, less dump.
    I should clarify that I did keep the casters at 90deg...I swapped the casters round on the quickie, as it made the casters move further out horizontally, whilst still keeping them vertical (sorry, my post would have been clearer using pictures!).

    Regarding dump, we've gone for zero, on the basis that my son needs specialized cushioning to keep his (developing) hips straight. That seems to go against most people's recommendations on here, but it was what we were advised to do. He always wears a seatbelt, which I guess has a similar affect in terms of stopping him from falling forwards/out.
    Gordon, father of son who became t6 paraplegic at the age of 4 in 2007 as a result of surgery to remove a spinal tumour.

  3. #33
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    Quote Originally Posted by SCI_OTR View Post
    . Truth is, however, that a cantilevered frame will be more likely than a box frame to endo at speed over surface discrepancies if improperly configured.
    SCI_OTR, that's the bit that I don't really understand - presumably any chair, if improperly configured, can be made more likely to endo at speed? Or are you implying that a cantilevered frame is more likely to be improperly configured than a box frame?

    I think I need to learn how to edit and post pictures like you do!

    Cheers,
    Gordon
    Gordon, father of son who became t6 paraplegic at the age of 4 in 2007 as a result of surgery to remove a spinal tumour.

  4. #34
    Compared to a box frame, a cantilevered frame has a slightly higher center of mass due to the lack of a lower frame rail. In addition, the lack of that rail means that the bend for the front frame compresses when resistance is encountered at the caster during an impact. Of course, the bend doesn't stay compressed, it springs back. To prevent a cantilevered frame from becoming a catapulting frame, one must try to keep the center of mass as low as possible, ensure there is enough wheelbase for stability, that there is miimal weight over the front casters, and that the casters themselves hve some impact absorbing properties.
    Last edited by SCI_OTR; 03-08-2011 at 12:09 AM.


  5. #35
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    Quote Originally Posted by SCI_OTR View Post
    Compared to a box frame, a cantilevered frame has a slightly higher center of mass due to the lack of a lower frame rail. In addition, the lack of that rail means that the bend for the front frame compresses when resistance is encountered at the caster during an impact. Of course, the bend doesn't stay compressed, it springs back. To prevent a cantilevered frame from becoming a catapulting frame, one must try to keep the center of mass as low as possible, ensure there is enough wheelbase for stability, that there is miimal weight over the front casters, and that the casters themselves hve some impact absorbing properties.
    SCI_OTR, many thanks for taking the time to explain. I knew that a couple of your pictures would make it all clear! I must admit that I hadn't considered the catapult effect, but that's probably because my son's chair is not particularly high, so the vertical height of the front frame probably isn't enough to make that a huge issue (but as the height increases, the effect would be more noticeable, I agree).

    Sounds like your recommendation would be to use frogs legs if you have a cantilevered frame?

    Cheers,
    Gordon
    Gordon, father of son who became t6 paraplegic at the age of 4 in 2007 as a result of surgery to remove a spinal tumour.

  6. #36
    Quote Originally Posted by Gordy1 View Post
    SCI_OTR, many thanks for taking the time to explain. I knew that a couple of your pictures would make it all clear! I must admit that I hadn't considered the catapult effect, but that's probably because my son's chair is not particularly high, so the vertical height of the front frame probably isn't enough to make that a huge issue (but as the height increases, the effect would be more noticeable, I agree).

    Sounds like your recommendation would be to use frogs legs if you have a cantilevered frame?

    Cheers,
    Gordon
    Not at all. The endo factor when traveling at speed has to do with dynamic forward stability with the chair in motion. There is also static vertical stability. I define the concept as the ability of the stationary chair to maintain it's stability when it is subjected to a load down the front frame. When under load, the chair is basically a lever where the casters are the fulcrum. Sharper front frame angles typically bring the footrest in closer to the casters--increasing static vertical stability (provided there is minimal compression of the forks, casters, or frame. In some configurations FrogLegs forks can have an adverse impact on vertical stability due to compression. Of course, reversing the casters can mitigate this effect.

    The key to achieving good dynamic forward stability is to to ensure the front of the chair is light, the proper size & type of caster is used, that the center of mass is as low as possible, and the wheelbase is long enough to provide adequate stability.


  7. #37
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    Quote Originally Posted by SCI_OTR View Post
    The key to achieving good dynamic forward stability is to to ensure the front of the chair is light, the proper size & type of caster is used, that the center of mass is as low as possible, and the wheelbase is long enough to provide adequate stability.
    Agreed - in which case the cantilevered frame is not necessarily worse for endos than a box frame, PROVIDED the centre of gravity/mass is kept low enough...(as that would be the main contributor to the endo, as all other things can be designed the same, apart from maybe the catapult effect, which I would think would be relatively minor in comparison to the cog issue).

    I think this needs to be my last post on this subject - I have work to do! (But do you have a response to my thread about thoracic supports, as that's a more pressing issue for us at the moment?!?)

    Cheers,
    Gordon
    Gordon, father of son who became t6 paraplegic at the age of 4 in 2007 as a result of surgery to remove a spinal tumour.

  8. #38
    Quote Originally Posted by SCI_OTR View Post
    There is also static vertical stability. I define the concept as the ability of the stationary chair to maintain it's stability when it is subjected to a load down the front frame. When under load, the chair is basically a lever where the casters are the fulcrum. Sharper front frame angles typically bring the footrest in closer to the casters--increasing static vertical stability (provided there is minimal compression of the forks, casters, or frame.
    One reason why I'm intrigued by Lasher's Bt-Trail & Bt-X Multi-terrain mode.


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