Exotic materials, properties
 

Most of us aren’t familliar with modern, “space-age” materials in all the ways that we should be. Most of us know the highlights, but we may not know what sizes it comes in, where we can get some reasonably, or what its weaknesses are. This thread is about getting to know the properties of exotic materials, so that we can use them better.

A word of caution to jumpy readers; we’re just working out details here. Don’t panic if you already have a CF chassis (for example); it won’t fall apart on you overnight. We’ll work out the kinks soon enough, and then you’ll be wondering why you worried so much.

P.S.: Please move this thread to the XMODS Science thread. I would have posted it there, but it is restricted. Feel free to remove this post-script after you have done so.

Carbon Fiber, aluminum, and corrosion
 

Some time ago, as I was looking into carbon fiber for a completely unrelated project, I read about how using aluminum in direct contact with Carbon Fiber causes it to corrode. I have the source here, and will quote the relevant section...

http://www.machinedesign.com/BDE/FAS.../bdefj1_6.html

“Additionally, carbon-fiber composites may corrode galvanically if aluminum fasteners are used, due to the chemical reaction of the aluminum with the carbon fibers. Coating the fasteners guards against corrosion but adds cost and time to assembly. Aluminum fasteners are often replaced by more expensive titanium and stainless steel when carbon-fiber composites are used.”

How poorly does this bode for people who use Carbon Fiber chassis with aluminum GPM parts? To what lengths does this problem need correcting with current chassis, what solutions are there for current owners, and are there any CF chassis on the market that will not suffer from this problem?

well i guess if i were to use aluminum components on a CF chasis ill put a peice of paper between the 2 materials, also i was thinking, you could spray clear coat on the cf chassis to prevent corrosion, nice job tho i never thought bout this till now

The corrosion only occurs if the aluminum contacts the carbon fibers inside the sheet itself. Only screws actually contact the fibers themselves, so GPM aluminum parts are not going to have an effect on it.

One other point, Carbon Fiber (as used in RC chassis's) is a composite of laminated layers of cross-woven carbon fibers and EPOXY. I don't know if ever seen a raw layer of CF without an epoxy coating, unless it was the raw fabric stock used to make the laminated sheets or for reinforcement in RC airplanes and then it is always covered by epoxy to bond it to the airframe.

RP, good info though.............:D

Fibers only you say? That’s just the problem.
 

This is just the problem, though. When you drill holes into carbon fiber, you expose the ends of fibers that run throughout the plate. And where is the most likely place to put bolts and screws? You guessed it, through a hole drilled in a plate. Not to mention the holes the steering knuckles go through (my favorite aluminum part, by the way).

Now, granted, this may not be a big problem at all; maybe the weakening caused by the corrosion is trivial for our needs. Maybe the cosmetics of our CF aren’t even an issue. I certainly bow to more experienced users of the material, but let’s face it; there practically ain’t any. And that’s why I formed this thread, to discuss this stuff.

Caught red handed
 

Looks like ya caught me, Zero. I thought I’d let you know first, since you actually sell a sweet CF chassis. I don’t know how the aluminum thing affects driveshafts yet, but I’ll be looking into it.

You could avoid the corrosion in the by applying a small amount of epoxy. Not a whole lot, just enough to cover the exposed fibers.

I honestly don't have any major experience with the stuff, but all I have said is what I can understand of what you posted. Big RCs use CF and aluminum all the time, and they don't have any issues.

Experienced CF users will apply CA to all exposed machine cut edges. This is to keep the cut edges from fraying and chipping during use.........may act as the insulator???

Your points are well taken and have enlightened me with another "Take Care" area:D

That might be enough to do it, Zero-Man. I only wish I had more information on the subject. I’ll make a point of doing some websurfing on it.

Also, thank you for the compliment. I do what I can. :)

Now, if only we can get someone in here to talk about Titanium & other stuff.

Silver Texalium?
 

I was just poking through Zero’s “Chassis” thread, and read about the Silver Texalium chassis. Wondering what it was, I looked it up. It’s carbon fiber that has somehow been covered in Aluminum.

Now, it isn’t possible that someone took some perfectly good carbon fiber, and just slapped aluminum on it, which would let it corrode... (is it?) So; assuming that they took care to put SOMETHING between the carbon fiber and the aluminum, that something should be sufficient to protect any aluminum fittings, assuming of course that those fittings do not grind through the protection itself.

I also read in that same thread that carbon fiber is CONDUCTIVE. Zero, you’ve been holding out on this thread. :) The conductivity of carbon fiber is probably going to contribute very much to its corrosion process. Consider for the moment that we deliberately suspend these cars in an electromagnetic field (the transmitter’s radio waves), which gets amplified slightly by the receiver antenna (all antennas re-broadcast the original signal slightly), not to mention the high currents being fed to the motor (introducing more EMF); this is going to polarize the chassis, causing corrosion to occurr more frequently in one location than the others. Which means that the chassis goes bad even more quickly, because when one location goes, you may not be able to make repairs to it.

The same “Don’t panic!” policy applies, guys; we’re just trying to work this out so that our neat CF frames stay sturdy & purdy. :)

CF corrosion solutions
 

I just did a successful search on the whole “CF corrosion” issue. I found this website:

http://www.eng-tips.com/viewthread.cfm?qid=99143&page=1

Basicly it says that you will get almost no galvanic corrosion between aluminum and carbon fiber unless water is present. I don’t think the majority of us would let our cars anywhere NEAR water without a watertight mod of some kind.

However, it also says that any conductive material acting as an intermediary between WILL ALSO allow corrosion to take place. For example, if you have a corrosion-eliminating washer between a CF chassis and an aluminum post, and then you go and stick a conductive metal screw through the carbon fiber and into the aluminum post, you have just introduced a brand-new conductive path for corrosion to take place (even though the aluminum and carbon fiber are physically separated). So you pretty much have to seal up the carbon fiber at any point fasteners would touch to get the proper protection. This also means that, without protection, the Silver Texalium chassis are also at risk from conductive fasteners, even though the aluminum layer and the carbon fiber layer are separated (we hope).

This post also suggests ways to isolate carbon fiber from aluminum safely (although it needs some interpretation). Maybe someone who actually works with CF should contact the guy?

Re: Silver Texalium?
 

I don't think it matters that much. As I said before, people have been using CF chassis in the bigger RCs for YEARS now, and I haven't heard any issues with the carbon corroding, or delaminating. I still stand by my original suggestion that you just put a small amount of epoxy or CA glue on any place where there might be exposed fibers (i.e. the edges and any holes) to protect it, and you will be fine.

As for the conductivity issue: I'd be more worried about the CF chassis causing interference between the Tx and Rx than the emissions causing the CF to fall apart. You're much more likely to break your chassis crashing because of a glitch than if it delaminated.

The silver tex chassis's have nylon stand-offs to isolate their conductive properties. Steel screws are still used but they don't intersect.

All CF is conductive up to a point and the usual results of the conductivity are radio interference. This is usally remedied by simple isolation of the receiver with double sided tape. In our applications, these usual methods of attaching electronic components works fine. The antenna and it's lead has to be isolated.

A silly idea, just for kicks...
 

I’m just curious, has anyone tried using a carbon fiber chassis itself for an antenna? You’d probably have to connect it to the terminal wire with a gold connector to prevent corrosion, but if it worked it would eliminate both the interference, and the annoying whip antennas. :)