Carbon Fiber and radio signal blocking.

[highnitro]

Hello All,

Recently I've had some issues with a quadcopter of mine just falling out of the air randomly as if the radio has lost signal. I 3d printed the entire frame with Carbon Fiber PLA and didn't think too much of it. When after replacing every part on the quad and it was still falling out of the air i did some googling about CF and RC. I read a couple stories of people using carbon fiber rods for support in their plane and having radio issues until changing to fiberglass or other material. I reprinted my frame in just standard PLA and sure enough it quit falling out of the sky. Does anyone here know anything about Carbon Fiber cause issues between the TX and the RX? It seems crazy to me that it was my problem, especially since they sell quad frames made of CF.

Matt

 

[PHugger]

Where were the antenna(s)?
Some pictures might help.

PS - your 3D printed CF frame sounds awesome.




Best regards,
PCH

 

[highnitro]

In my first build i ran the antenna parallel with the main frame (maybe this was a mistake) you can barely see it in this pic (red tubing on the rear left of the quad.



Then i moved it to the top plate attached to a zip tie so it would be vertically mounted.



And here is a pic of the whole 3d printed Carbon fiber frame just for reference.

 

[highnitro]

What is weird is that even in the vertically mounted pic I'm only using carbon for a couple of the frame pieces and it still had the effect of signal loss. Once i went to all non carbon frame my problem seemed to go away.

 

[PHugger]

I think you'll need to figure out how to test for best placement.
I use a Futaba (dual antenna) receiver and have a little rabbit ear antenna holder that keeps them in a V configuration.
I'm guessing with a single wire, straight up would be best.
I haven't seen this same problem on other CF frames like a Blackout.
Start testing and make sure there isn't something wrong with the antenna wire or receiver. Those wires and connections are pretty delicate. It does seem strange. Make sure the receiver (if it's naked) isn't shorting on the CF frame.


Best regards,
PCH

 

[ZoomNBoom]

CF is electrically conductive and does shield RF. You have to try to maintain line of sight between your tx and antenna, which is why most quad pilots use diversity (dual antenna) receivers and put them in V shape. I use tie wraps and some heatshrink for that.

I am curious however, how good that CF PLA filament is. Ive been looking in to it, but I honestly doubt its stronger than ABS. I would expect it to be stiffer though. Have you done any load testing comparing it to ABS or nylon ?

 

[highnitro]

CF is electrically conductive and does shield RF. You have to try to maintain line of sight between your tx and antenna, which is why most quad pilots use diversity (dual antenna) receivers and put them in V shape. I use tie wraps and some heatshrink for that.

I am curious however, how good that CF PLA filament is. Ive been looking in to it, but I honestly doubt its stronger than ABS. I would expect it to be stiffer though. Have you done any load testing comparing it to ABS or nylon ?

Thanks for the Diversity idea, Ill look into that.

I would not say its "stronger" than ABS, but its really stiff. I felt like my quad handles better with the stiff carbon frame over the more flexible PLA frame. The filament i used is Proto-Pasta CFPLA, i actually work for proto-pasta so I'm quite bias to it. I just love it, nothing prints like carbon. If you want I can send you a sample spool just PM me your address.

 

[PHugger]

The first hit is always free......



Best regards,
PCH

 

[highnitro]

Well I have some interesting developments for this antenna blocking carbon. I have a friend who works at an antenna production plant that says we can test the carbon to see how it affects reception at 2.4ghz. He said we can use a network analyzer to see the signal loss and where in the frequency band it has the most effect. I'm going to print a few different shapes and sizes of test pieces so that we can actually test to see a loss of gain due to the CF over the bare antenna. Anyone have any advice or things to consider during this testing?

 

[ZoomNBoom]

There is no question CF shields RF, both through abortion and reflection. Its used specifically for RF shields, like in cell phones.
And while googling for some evidence, I stumbled upon this:
http://www.researchgate.net/publica...e_shielding_effectiveness_of_carbon_materials

Which suggests that the short and thin carbon strands in thermoplastic composites (read: your PLA filament) are even far more effective shields than woven CF:

EMI shielding is one of the main applications of
conventional short carbon fibers [99]. Due to the small
diameter, carbon filaments (catalytically grown, of diam-
eter 0.1 mm) are more effective at the same volume
fraction in a composite than conventional short carbon
fibers for EMI shielding, as shown for both thermoplast
[54,100] and cement [80,101] matrices. For example, in a
thermoplast matrix, carbon filaments at 19 vol.% give an
EMI shielding effectiveness of 74 dB at 1 GHz [100],

whereas carbon fibers (isotropic pitch based, 3000mm
long) at 20 vol.% give a shielding effectiveness of 46 dB
at 1 GHz [54].

I know from my gliders that a woven CF fuselage blocks my 2.4 radio signal pretty much completely (we bring the antenna's out for good reason), your 3D printed stuff could be even worse.

 

[Quadville]

Ok..I chuckled at that..

The first hit is always free......



Best regards,
PCH

Quadville

 

[mpturp]

This is interesting. I knew CF was conductive, but hadn't thought it would block RF.

At the risk of sounding like a complete caveman, would it work for your purposes to add some sort of landing legs and just keep the antenna below all that carbon fiber? I feel like the signal would be strong enough to get it off the ground, and once it's above you there should be no carbon fiber in the way to begin with!

Then again, take that with a grain of salt, as I know zilch about quads, just lurking about the forums tonight. Hope this helps!

 

[Revere]

My last quad was carbon fibre, I used dual 6 inch aerials, one pointed directly upwards from the top of the body and one pointed horizontally directly out the rear of the body. That way it didn't matter how the quad was oriented, one or both aerials was always within line of sight of the Transmitter. Used a single cloverleaf for video though and depending upon the orientation video could become very weak.

 

[razor02097]

This is interesting. I knew CF was conductive, but hadn't thought it would block RF.

At the risk of sounding like a complete caveman, would it work for your purposes to add some sort of landing legs and just keep the antenna below all that carbon fiber? I feel like the signal would be strong enough to get it off the ground, and once it's above you there should be no carbon fiber in the way to begin with!

Then again, take that with a grain of salt, as I know zilch about quads, just lurking about the forums tonight. Hope this helps!

You might not know much about quads but you're correct. That is the exact reason my tricopter has one antenna on the top and another on the bottom. Between the carbon fiber and giant PDB the top antenna would be completely blocked when the copter is above and going away from me. Same if I'm up on a hill and the copter is below and going away from me...the top antenna takes over. That is where diversity antennas really help.

As David W pointed out in a video, you want to make sure your transmitter and receiver antenna can "see" each other. Literally you want the antennas to have an unobstructed view of each other. Although you could get away with putting the antenna inside an airframe that isn't conductive, it is still better to get that antenna out in the open away from motors, electronics, batteries, etc.

 

[Glen]

I realize this is an old thread, but it is worth reviving it to clarify the issues with 3d printed carbon composites.

The pla/carbon and nylon/carbon materials used in 3D printing contain about 20% carbon fiber in the form of tiny chopped-up particles of carbon fiber suspended in the plastic material.

Since the carbon fiber particles are mostly not touching each other, the printed material is not very conductive, but the individual carbon particles ARE conductive and WILL absorb high frequency RF.

At low frequencies (1-30 MHz) there is very little to no absorption, but at the SHF frequencies used by RC equipment, the rf absorption by the carbon fiber particles could be quite high. If you use carbon fiber, make sure it is NOT enclosing the antenna so that the receive antenna has an unobstructed "view" of the transmitter signal, and you should experience fewer problems.

Glen