Question about carbon fiber use.

Discussion in 'Materials' started by Schoonner, Feb 2, 2012.

  1. Schoonner
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    Schoonner Senior Member

    I have decided I can make just about anything for my model. This might even include carbon fiber or fiberglass gears. =0) I am curious whether or not this is a good idea.

    I think that carbon fiber gears would be lighter by far than brass or aluminum and maybe even be self self lubricating.

    I can buy little plates of carbon fiber, but I want to use rods. My question is whether or not to try using rods that are cut into dime or quarter, or even half dollar size pieces then adding a layer of carbon fiber to the sides of the gears so that the teeth have more grip.

    SAY! Maybe I can use something like a cookie cutter and cut a bunch of layers of mat at once?

    I wish I had a 3D printer that could print carbon fiber!! Would I just have to make the gear in CAD or something then if I had one and it would print it out for me?
     
  2. Schoonner
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    Schoonner Senior Member

    Maybe there is a tiny hole saw that will chuck up into a drill motor and have a tiny drill bit in the center?
     
  3. Petros
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    Petros Senior Member

    the only way a composite is useful is when the fibers are oriented in the direction of the primary loads on the part. There is no way that will happen if you cut gears out of rod stock, all of the fibers will be going the wrong way. The stress loading on the gear teeth is complex, but unless you are making very large ones where you can actually lay the fibers in the correct direction, the gears will not hold up well at all.

    There are reason gears are not made from composites, particularly small ones.
     
  4. Stumble
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    Stumble Senior Member

    Petros,

    The real question is what the loads on the gears will be. There are plenty of plastic gears that carbon could emulate if the loads are light enough. But generally I would agree with you that composite gears are unsuitable for most applications.
     
  5. messabout
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    messabout Senior Member

    Making gears that work well is not a home workshop job. You need hobbing machinery in order to form the teeth satisfactorily. For very small gears, the weight difference will be very small, fractions of grams actually. Get your gearing from the hobby supplier. There is a huge array of them available for RC cars. Some are actually plastic but they will not stand much loading.
     
  6. Schoonner
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    Schoonner Senior Member

    I want to make gears that are shaped differently than 'normal' gears. If I made a long block of composite just larger than the diameter of the gear, could I theoretically make them like a thick cylinder with a diameter the same as the thickness along it's axis instead of like normal gears? I basically want to make a planetary gear because it will take up less space if I make it like a ball bearing set that has teeth angled teeth in it. maybe angling the tooth and grove to something like 45 degrees off axis will make the teeth stronger, but still transfer torque through the teeth to the other two edges? I have made gears before for other projects out of soft stainless steel discs cut with a file. I also make springs from 1/2 hardness spring steel wire or sometimes just wire. I'm thinking about maybe using a short rod and pulleys because maybe they will be lighter. I have not found good pulley blocks that I want to pay very much for though. =0) also, the spindle will have to turn many times before the booms will move very far because I want to use tiny servos that don't have a tonne of torque. I want it so that I can change the angle of the sail infinitely variable like rather than just allow the wind to blow the sail past center to the other side so I can make the jib move differently from the main and heave to if I want to. =0)
     
  7. upchurchmr
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    upchurchmr Senior Member

    Dont make the gears out of carbon fiber plate. The guys above are completely right that the fibers are in the wrong direction.

    Gears have been refined for 100 years as the result of lots of failures. Don't change the teeth shape, cause they are going to fail no matter what you make them out of.

    You will waste a lots of money and time by making them "better" without lots of science and machining behind them. A planetary gear set is particularly difficult to make even with standard, well know shapes, due to the precision required to assemble them. A lack of precision will introduce lots of friction and blow your idea of very tiny servos.

    If you want some real feedback, draw up a plan and let everyone look at it.
     
  8. Schoonner
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    Schoonner Senior Member

    Oh okay. well I don't have time to draw one right now. =0) I think I can get away with making blocks better than I can get away with making gears.
     
  9. rwatson
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    rwatson Senior Member

    The nylon gears they use for slot cars (1/24th electric) and/or RC electric cars, are the lightest and toughest you will ever get.
     

  10. Schoonner
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    Schoonner Senior Member

    Okay, I just found one of the correct dimension for $3.00. seems expensive, but it comes with a tube of water proof lithuim grease. =0) I'll have spent thousands of dollars on this project in no time. =0)

    LOL!
     
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