A long time ago I built a fixture and used carbon fiber roving like I would have done fiberglass. (Mold, release agent, epoxy, fiber, epoxy, bag it, dry, release, sand/drill wearing a mask)
I’m clearly missing the time/effort/cost in building a carbon fiber chassis.
So tell me, in beginner robot terms, what is involved with building a carbon fiber chassis.
I imagine one hiccup in a carbon fiber robot concept would be the expense of building prototypes. Teams could in theory build low cost fiberglass prototypes then do final designs out of carbon fiber.
When I was on 423 we used carbon fiber hockey sticks for a number of mechanisms. Never had a single one break. We used it for the arms of our catapult in 2014 and the carbon fiber tubes actually bent the steel rod hard stop. I wouldn’t think they’d be good for precision work (I’d stick with aluminum if you need to keep a tight tolerance), but they’re plenty strong for most non-precision mechanisms. IIRC we often got them donated for free from a local hockey team when the blades broke off but the handles were still intact.
I built a carbon chassis in 2015, and it saved us about 5 pounds! Here is a picture of the process as it was being done, and here is a picture of the finished product.
The way that I’ve always done carbon in the context of FRC is by wrapping thin wall aluminium with carbon to reinforce the strength of thicker aluminium, while cutting down on the overall weight. Granted, I’ve also built carbon mechanisms in FRC by molding and whatnot, but that’s a different conversation. PM me if you want more in depth information! I’ve done a lot of custom carbon on robots
To really do it properly and obtain all the benefits of using carbon fiber, step one imho would be to design a drivetrain that uses the strengths of CF in it’s structure. Instead of just taking something like a WCD (which is proven that alumium works fine) and recreating it out of CF.
I’ve though about doing something with foam core, like on a longboard/surfboard. Using some high density foam machined/shaped to your design and then doing a few layers over it with expoy. Afterwards sanding it smooth and clear coating.
I’ve seen battlebot teams do solid CF chassis made from prepreg, example hypershock: Redirecting... Worked out pretty well, obviously for FRC it’s a bit overkill on the thickness they used but it was solid.
Overall it’s very labor intensive in doing the layups correctly and then even more intensive if you want it to look nice. I don’t think the effort is worth the returns on trying to do an entire drivetrain out of CF when alumium is cheap, easy to work with, can be welded and so many COTS products designed around it. After design, it took us less then a weekend to produce our two drivebases. But using CF on mechanisms can be beneficial, we bought CF thin wall tubs and made rollers out of them. Definitly lighter and stiffer then it would have been compared to aluminum. Also CF plate is stiffer then anything plastic or aluminum for the weight but however it will crack vs flex.
Edit: </insert obligatory safety warnings with working with fiberglass and carbon. It’s nasty stuff>
I will strongly caution teams considering carbon fiber on their robots: you will not be allowed to machine (drill, sand, grind, cut) carbon fiber parts at competition. With so many un-masked people at the competition, there’s no way it can be done safely. It’s likely that any machine shop resources at competition won’t have the proper equipment or ventilation in place to work on it for you either.
So, don’t plan to make changes, and bring plenty of spares for anything that may break!
I’m not sure this is actually true based on any rules. Please cite one if you do spot one.
CF splinters and that’s an issue, but otherwise I think your concerns are more valid with fiberglass.
If you also spray water in the area you are working in, it should damp down most of the dust, if any, when you are cutting. Additionally, all teams should use a mini shop vac when cutting anyway, so this should capture a lot of the dust.
Keep in mind the venue can make any safety rule it wants to. A process that creates dangerous dust could be easily prohibited. For example machining lead. I don’t know enough about processing carbon fiber to have an opinion on the actual danger. Ssafety rules are tuned towards the novice operator, not the expert.
The filter on a shopvac is unable to capture carbon fiber dust. The risk of carbon fiber dust is similar to Asbestos. The fibers are so tiny that they pierce through things on a cellular scale and mess with cell activity like mitosis. Cutting underwater is a good solution.
From my limited composite experience I’d probably CNC route a 3D plug out of foam with ridges and grooves where I wanted to add structural rigidity. Aluminium bearing blocks and threaded mounting plates would be added where needed. I’d then layup the carbon and vacuum bag it. It’s kind of similar to the way surf boards are made.
Keep in mind some CF can be scored and cut as well, so I wouldn’t necessarily assume any cuts and repairs are being done with a dremel or something like that.
I still think that wetting the area (if being cut) helps a ton. I would not recommend sanding anywhere at an event though.
But yes, as Jon said, probably avoid alterations to CF parts at events if possible.
