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pic: Carbon fiber monocoque drivetrain Top view
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Guess I'll take the obvious first question: How much does it weigh? :rolleyes:
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Very neat. Any idea on how one would build this? Have you done any simulations to check the stress resistance compared to the "standard" aluminum chassis?
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currently, it is made of five peaces. One C channel on each side, and a dropped center piece that would be vacuum molded into a "top hat" shape. Quote:
Based on the sample peaces I have seen from our sponsor, I think that this would be very strong. |
Re: pic: Carbon fiber monocoque drivetrain Top view
No.
Based on the sample peaces I have seen from our sponsor, I think that this would be very strong.[/quote] It will also be a major pain to drill any holes in. |
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And, OBTW, what's plan B if it does actually break? I was nervous about our welded aluminum chassis in 2013 (though not as nervous as I should have been now that I know more about aluminum grades and welding and heat treating), but this is a whole 'nother level of "no way to repair". |
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But really, carbon fiber is quite the science. I'd recommend checking out acpsales online as they have decent guides on carbon fiber. Consider a filler material like foam or a hex shaped layering for some added strength along the rails. You want carbon fiber to have some flex, but not too much. Also be careful about hole placement. |
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Any clue on how expensive this would be compared to if it was made out of standard drivetrain steel or aluminum?
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There are a number of ways to fabricate carbon fiber structures. The first is to use dry cloth and saturate with epoxy. Generally speaking this is what home-builders use. It's going to be heavier than a well made vacuum bag or pre-empregnated setup, but doesn't require expensive materials or specialized building techniques. Your next choice is how to form the parts. Will you make a male mold? A female mold? Use a spacer material like polystyrene that can be chemically removed? Fastening things in carbon fiber can be tricky. The strength in a fiber structure comes from the fiber itself. The epoxy is merely there to hold the fiber in the shape you need. Fastening to the carbon fiber incorrectly will crack the epoxy and destroy the structure's strength. You also tend to need backing plates to spread the pressure out. Then there's cure times, cure temperatures, mixing ratios, substrate materials...... Starting around 2:10: https://www.youtube.com/watch?v=504I_hJDFck Wet Layup - what many FRC teams would do in their shops: https://www.youtube.com/watch?v=-sOU3zEigt0 Vacuum Infusion: https://www.youtube.com/watch?v=hEyF5KOkhUY The last two months of my life finally coming to a close (and why I know so much about fiber construction): ![]() |
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Personally if I were to build something like this, I'd use a high compression strength foam core material rather than building it monocoque (plus it's a bit easier to do the layup). Then simply use a lightweight wood for the center material in areas you need to drill holes (sitka spruce is a good option) and then use just 1-2 layers of carbon fiber cloth. You could also make the walls of this design much thinner using such a method. Quote:
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Examples: www.chiefdelphi.com/media/photos/27823 www.chiefdelphi.com/media/photos/31319 |
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The gearbox plates would be cut from stock plate on a CNC router. Quote:
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You can also use a space heater and half of a cardboard box to speed up the epoxy setting process if you want (don't leave it unattended though, for obvious reasons). In the case of your design, you could use this method to basically make the whole thing with 5 pieces (or as one big piece if you were feeling really ambitious) and you wouldn't have to make the frame walls so wide (leaving more space for electronics and such). And now for some related old pictures... 1, 2, 3, 4 Edit: After re-reading your previous comment a few times, I'm thinking you might have been referring to how the construction method would be used in this situation, and not so much how it works (correct me if I'm wrong)... >_> Answering that question might require some CAD work to explain unfortunately. |
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This is how I've personally done a few of our parts, it uses really only 4 +-2 layers of carbon fiber and is much easier to shape your parts. We just get the desired shape we want and make it out of foam core, plan around hole placement and how much carbon fiber needs to be in the pockets, and then lay the carbon fiber. I'm not sure how it would work on a frame of your size, but it can help with rigidity and cut costs.
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Like some of the other posters, I'm no expert; but I immediately wondered why the design includes so many 90 degree corners and edges.
Aren't sharp corners/edges the exact places where structures made from carbon fiber, or similar materials, are most likely to fail, when the entire structure flexes? Isn't the key to success allowing many fibers to share a load instead of letting the load get concentrated onto a few fibers (at corners/edges)? Color me curious. Blake |
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Imagine a flat piece of carbon fiber that is 4" wide. In some directions it is strong, but in others it is very flexible and not very strong. Now imagine that same amount of carbon fiber is instead a 2" by 1" C channel. In that configuration, it might break along its corners if enough force is applied, but it would be a lot stronger and more rigid for the same weight. |
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Carbon fiber bicycle frames are made of roundish tubes, not box shapes. Antenna towers, crane booms and frames, car roll cages, are generally made from (round) tubes, not boxes. Rounded shapes might be worth investigating. Definitely ket us all know how the eventual frame holds up, if one gets built. Blake |
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Cool concept. Unless your team doesn't have the in-house resources to make a drivertrain, this would likely take a lot of time and delay the rest of the robot. On top of that, unless you design in a standard mounting system, later in season it may be tricky to modify the robot to improve it. How would you repair it at a regional if it broke?
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Every year since 2006 I have found some component of the robot that could benefit from a composite material and lead the team on it's construction. Do we have to use composites - NO. We do it to expose the students to them. As far as doing a whole frame or chassis, this would require expertise and considerable experience. If a team does not have this, don't attempt it. Start off with some smaller lay ups. There is always fiber glass pulltrustions to work with. Done right composites can can be wonderful. Done wrong you have some expensive trash.
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I forget the VA/NC team who usually does carbon fiber. They've been next to us in the pits a few times, so I got to talk to them. IIRC, a lot of their super structure was rounded tubing. The edges of the drive train frame were filleted with a small (0.25"-0.5") radius but otherwise the faces were straight. On the plus side, this stuff is so lightweight you can disassemble the vast majority of the superstructure into COTS parts and the carbon fiber frame while still being under the withholding limit. The downside to that is that you're spending all day on Thursday re-assembling... |
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Ah - found them - 1829, the Carbonauts:
http://www.thebluealliance.com/team/1829/2015 Looks like for 2015 they went to Aluminum. I'll see them this weekend at Rumble in the Roads, anyone have any specific questions for them? |
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