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Thread: A fun little technology demonstration project

  1. #1

    A fun little technology demonstration project

    After many months of strength/durability testing on the carbon fiber tennis frames, it was time to build an everyday frame.

    Using many of the same materials and construction techniques that continue to prove themselves on the tennis chair, an everyday chair presented some interesting challenges. While not entirely completed, I thought I'd share a few photos of the project. This chair specs out nearly the same as the name brand titanium frame I've been using for several years. 16" width, 16" depth, 2" dump, 25" wheels. The bare frame weighs less than 3lb. while the titanium frame was over 8lb. I didn't bother to get a total final weight because I'm using many off the shelf accessory items (footrest assembly, backrest frame, caster forks, etc.) that weigh quite a bit more than the versions that I will eventually produce.

    The results so far are extremely positive. The chair rides as smooth as silk, no noticeable flex in the frame, effortless to lift in and out of the car (my main motivation for building this chair).

    I'll add some additional photos as things progress, but there are a few more in my gallery now.

    Let me know what you think.

    Ben
    Last edited by Black Alloy; 08-04-2012 at 09:23 AM. Reason: Right-size photo.

  2. #2
    Nice!!
    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. #3
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    Looking good!

    Curious, how did you do the bends in the front like that w/ the carbon fiber tubing?

  4. #4
    Senior Member sowseng's Avatar
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    Quote Originally Posted by Black Alloy View Post
    After many months of strength/durability testing on the carbon fiber tennis frames, it was time to build an everyday frame.

    Using many of the same materials and construction techniques that continue to prove themselves on the tennis chair, an everyday chair presented some interesting challenges. While not entirely completed, I thought I'd share a few photos of the project. This chair specs out nearly the same as the name brand titanium frame I've been using for several years. 16" width, 16" depth, 2" dump, 25" wheels. The bare frame weighs less than 3lb. while the titanium frame was over 8lb. I didn't bother to get a total final weight because I'm using many off the shelf accessory items (footrest assembly, backrest frame, caster forks, etc.) that weigh quite a bit more than the versions that I will eventually produce.

    The results so far are extremely positive. The chair rides as smooth as silk, no noticeable flex in the frame, effortless to lift in and out of the car (my main motivation for building this chair).

    I'll add some additional photos as things progress, but there are a few more in my gallery now.

    Let me know what you think.

    Ben
    carbon fiber tube for the whole frame?
    I do remember reading someone's carbon fiber camber tube broke, wonder how durable compare to aluminium and titanium.
    Life is meaningles, though you create the purpose.

  5. #5
    Quote Originally Posted by eliotk View Post
    Looking good!

    Curious, how did you do the bends in the front like that w/ the carbon fiber tubing?

    I believe the tubes woud have to be built bent. The mold you use to layup the carbon would already be bent to the proper specs.

  6. #6
    could you get some close pics, because i just see there a black chair, i don`t see any carbon fiber.

  7. #7
    Yeah, you can't bend carbon fiber components like metal. Parts are built in molds that produce the desired shapes.

    A fair number of ideas were tossed around before coming up with a rather simple (albeit time consuming) process to create the curved tubular sections. Several steps and several molds were required, but the results were very satisfactory. I'm sorry I can't provide more details on exactly how they're made.

    I've read any number of carbon fiber component failure stories over the years, spanning several industries and it almost always comes down to some combination of poor design and poor construction. Every material has strengths and weaknesses. Simply applying a "stronger" material to a given task is a recipe for disaster and there's no shortage of cases where a strong material like carbon fiber has been applied poorly and resulted in a weaker structure than its predecessor. Applied properly, carbon fiber composites can deliver a combination of properties that no metal can match. But it's not a matter of replacing metal with carbon fiber, it's a matter of designing a carbon fiber structure to replace a metal one.

    I've done some destructive testing on a few of my components and I would consider having my camber tubes fail as "highly unlikely", even under loads well outside what could be encountered from the intended use.

    totoL1, I'll post some closer photos, but the entire frame and backrest are CFRP.

  8. #8

  9. #9
    These are actually old photos of a tennis chair frame in process, but you get the idea.

  10. #10
    Just marked 5 years of continuous service on the prototype 1 carbon fiber wheelchair. Several sets of tires and casters; and other than swapping several accessory components for testing, zero maintenance or failures.

    This isn't a credit to just the use of carbon fiber composites in general, but a credit to a design that takes advantage of the material strengths and compensates for its weaknesses.

    It's a shame that composite wheelchairs are still so rare. Wish I could have done more to change that.

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