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Carbon Fiber custom work

  1. Feb 25, 2005 #1
    Im looking to have several gas powered scooter parts made in carbon fiber from a cad file. Such things as steering pole, rims, deck, air scoop, and a distant goal of a frame. scooters in question www.goped.com.

    I understand some basics of carbon fiber, but pretty much just what you can learn from watching too much TLC. Im working on the steering poles right now, and where the pole will mount to the frame it will be through two sandwhiched pieces of aluminum bolted up securely. The upper part however, is where i am hesitant.

    Im going to make a billet Aluminum part that will have a cylinder that will slide into the cf shaft, then the outer aluminum shell (still the same billet part) will slide over the cf shaft but this time from the outside-so the cf is sandwhiched. I will have threaded holes tapped into the machined aluminum part, then drill some holes in the cf and bolt the aluminum part to the cf shaft, which will (i believe) be secure because of the compression of the two aluminum layers pressed against the cf.

    My questions are, is there a more effective method of bonding cf to Al? Will this kind of bond i have described result in a point of weekness below the Al part? The shaft will be about 3.75 feet tall and as i said used on a gas powered scooter ranging anywhere from 19mph to 60+mph, what kind of cf should i specify to ensure that it is safe for riding street and also for riding off of ramps and other instances where the steering pole would be stressed.

    This kind of thing has been attempted before with cf, but it failed because the cf would break and nearly impale the riders. Where they have failed, i will succeed. Any suggestions on this amazing material would be appreciated.
  2. jcsd
  3. Feb 25, 2005 #2
    I would think that if the cf , in the walls of the tube ,were thick enough , that it should be as strong as any Aluminum part..let us know how it works out..BTW you can find sources for CF on Ebay..
  4. Feb 26, 2005 #3
    is a carbon fiber flywheel something possible? For those who know, the engine can rev much faster if the inertia of the flywheel is reduced. with these scooters, people trim off fins to save weight and improve acceleration. could a cf flywheel be made? these engines rev to about 10k rpm or more. the flywheel would be about 5 inches wide 2inches deep
  5. Feb 26, 2005 #4
    The function of a flywheel is to add rotational inertia. If you want less inertia, then you can take mass off of an exiting flywheel. Why would you switch to a different material?
  6. Feb 27, 2005 #5
    well im talking about small two stroke engines 62 cc. People lighten flywheels to decrease initial rotational inertia which would add to acceleration, but i suppose a slower top end? I guess i was thinking that if the flywheel weighed nearly nothing then the engine would take off like no other, but obviously top speed would drop. If only there were a medium.
  7. Feb 28, 2005 #6


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    oldunion - CF is a composite and while the tensile strength is largely due to the carbon strands in parallel with the tension, the compressive and shear strength is more a function of the resin used to construct the material. Lets say you use a standard 2x2 twill weave so each layer is thin and light (and somewhat inexpensive).

    The orientation of the strands/weave of the carbon and distribution of the forces from your aluminum piece to the carbon cannot be dismissed. The holes in the carbon tube and 'squeeze' points could easily caused high stress areas that are likely to fail. Bonding the aluminum to the CF is likely to distribute the loads more evenly.

    Below is a link to a website where a guy made his own CF bicycle frame. He made a foam core to lay the CF against and built test models that he purposesly tested uner loads to determine how many layers he needed. This type of stress testing would be a wise way to go to avoid being impaled...

    Note how he used low-tech, low-buck methods of pencils and paper to determine his first attempt (tested to 400lbs) flexed to much. Also, testing it to failure it snapped at 432lbs, meaning there was little saftey margin so a big bump could have been very bad. Also note how he used a 0,30 degree pos, 30 degree neg offset for layers of the carbon weave, meaning that the criss-cross pattern changes 30 degrees between layers so the tensile strength is more uniformly distributed in every direction. If you look at pictures of aircraft or race cars the orientation of the fibers is much more purposeful to allow high-strength in one dimension but maybe lower strength in another (to save weight or costs or for energy absorbtion in crashes).

    On the other topic, reducing the flywheel mass will assist in reaching higher RPMs in addition to faster acceleration at the expense of low-speed performance. TINSTAAFL though, the flywheel's function is to smooth the pulses between power strokes so the short-duration high-intensity pulse is easier to harness and not wasted in the drive belt/chain slipping/stretching. In addition there is only so much power that can be extracted before some other element (bearings, connecting rods, pistons) will be pushed beyond their mechanical limits. Going fast isn't cheap!

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