Where to buy Carbon Fiber Plates with full twill waves?

[jz11]

regarding cutting kevlar, the fabric I mean, everyone kept telling me that you need special scissors with unobtainium coating to shear it, but turns out basically any scissors will cut it, but need a 90 degree grind on them (when you look at the cross section of the cutting edge), preferably with coarse stone that leaves little serrations on the cutting edge, so the strands don't slip away, better scissors (better steel) ground this way will last longer, but even couple euro scissors sharpened to 90 degrees will cut it quite well for a while, I've successfully cut 400gr pure kevlar fabric this way, and the 150-200gr mixed fabric cuts way easier than that thick stuff

as for machining, I've never cut it with a router or milling machine type operation, only hand held with dremel like tool and diamond blade, and use a quick brush with a gas flame torch to smooth out frayed kevlar strands, I'd guess water jet would cut it easily, maybe a cnc router that has flood cooling, but I doubt there are many of those around... most larger milling machines will probably have too little rpm to this cost effectively with the tiny carbide bits

[Cold Fussion]

Excellent post. I think the key question is how weight critical is it? If you're willing to almost double the thickness purely for durability reasons then it suggests to me the weight isn't so critical and if that's the case, maybe considering making the arms out of E-Glass. E-Glass composites can potentially take 4-5x the strain of a CFRP part and the raw material costs will be on the order of 4-5x cheaper as well. You could design the arms as a sacrificial part in the event of an accident and just keep replacing them cheaply.

The arms actually are a sacrificial part in my design, they can be replaced easily

But glass fiber taking 4-5x the strain of carbon fiber? Really?

From memory E-Glass will fail around 5% strain while carbon fibre will fail around 1%. Obviously CF will take more force before failure though.

I don't know how the place you send it to cuts, but you can cut kevlar-epoxy composites with an ordinary dremel so long as you are careful.

[Andres125sx]

Excellent post. I think the key question is how weight critical is it? If you're willing to almost double the thickness purely for durability reasons then it suggests to me the weight isn't so critical and if that's the case, maybe considering making the arms out of E-Glass. E-Glass composites can potentially take 4-5x the strain of a CFRP part and the raw material costs will be on the order of 4-5x cheaper as well. You could design the arms as a sacrificial part in the event of an accident and just keep replacing them cheaply.

The arms actually are a sacrificial part in my design, they can be replaced easily

But glass fiber taking 4-5x the strain of carbon fiber? Really?

From memory E-Glass will fail around 5% strain while carbon fibre will fail around 1%. Obviously CF will take more force before failure though.

I don't know how the place you send it to cuts, but you can cut kevlar-epoxy composites with an ordinary dremel so long as you are careful.

Maybe I´m translating strain as a different word, but from your description I guess you must mean flexion, or how much it can bend before failing, because strain is the force the material must cope with, or at least that´s how I tranlate it


I was afraid about carbon/kevlar because of the warning about cutting the panel in this site
http://www.hillsidecomposites.com/carbo ... brid-panel


But anycase that does not matter now, as I think I found a bargain

https://www.ebay.es/itm/Hexcel-Carbon-f ... SwNRdX~ftR

It´s listed as quasi isotropic carbon, and aerospace grade! But even if it´s not, the 400x400x6mm I ordered for 110 euros shipped is a great price

I´ve trust the vendor, we´ll see if I did the right thing.


Now I only need the 2mm panel, wich I guess will be easier to find, but any recomendation will be welcome

[rscsr]

The arms actually are a sacrificial part in my design, they can be replaced easily

But glass fiber taking 4-5x the strain of carbon fiber? Really?

From memory E-Glass will fail around 5% strain while carbon fibre will fail around 1%. Obviously CF will take more force before failure though.

I don't know how the place you send it to cuts, but you can cut kevlar-epoxy composites with an ordinary dremel so long as you are careful.

Maybe I´m translating strain as a different word, but from your description I guess you must mean flexion, or how much it can bend before failing, because strain is the force the material must cope with, or at least that´s how I tranlate it
...

what you mean is stress. Basically the force per area.

[Andres125sx]

Yes that is. I guess translators don´t make a good job with technical terms

Thanks for the clarification

[Cold Fussion]

Maybe I´m translating strain as a different word, but from your description I guess you must mean flexion, or how much it can bend before failing, because strain is the force the material must cope with, or at least that´s how I tranlate it


I was afraid about carbon/kevlar because of the warning about cutting the panel in this site
http://www.hillsidecomposites.com/carbo ... brid-panel


But anycase that does not matter now, as I think I found a bargain

https://www.ebay.es/itm/Hexcel-Carbon-f ... SwNRdX~ftR

It´s listed as quasi isotropic carbon, and aerospace grade! But even if it´s not, the 400x400x6mm I ordered for 110 euros shipped is a great price

I´ve trust the vendor, we´ll see if I did the right thing.


Now I only need the 2mm panel, wich I guess will be easier to find, but any recomendation will be welcome

Strain is the percentage of elongation the material is under. Materials that are resistant to more strain are able to absorb more deformation energy before failure. I haven't run the numbers but I imagine a fibreglass part of the same thickness would be able to absorb more energy before failure because of it's much higher strain resilience. Such a part would be much heavier than it's carbon counterpart of course but that goes back to our question earlier.

In regards to cutting kevlar parts, you have to be very careful when your cutting. When you cut carbon you can really feed the dremel into the part and it cuts very easily but if you do that to a kevlar part you can very easily shatter the blade.

[Tommy Cookers]

if we have a part made eg from CFC and an identically sized part made eg from GRP and they are equally loaded ....

the strains of each will depend on the elastic modulus of their material ie .....
'carbon fibre' has a large E and so the deflection will be small (CFC is very stiff)
'glass fibre' has a small E and so the strain will be large (GRP is not very stiff)

the strain energy eg to failure will depend on the load and the deflection ie .....
the greater strain of the GRP part does not necessarily make it need more strain energy to fail
neither material is particularly good for this

[J.A.W.]

Exactly T-C, you wouldn't consider a motorcycle rear spocket built from C-F, but good old nylon can handle the task..

So given the impact/flex/resilience requirements, why not a current 'organic' design, but in the older plastic material?

[jz11]

I doubt unreinforced plastic would work for this quad frame application, not if you consider the extra weight it would have to have, and then heavy gauge plastic sheets aren't all that cheap either, and you will spend more time machining them, deburring can be a pain, so it is all trade offs

If it was up to me, I would probably make the frame out of aluminum sheet metal, profile it where needed after the flat patterns are cut, anodize and rivet together, such a frame would probably be on par with the CF weight wise, and might survive crashes better, would be quite cheap to make too (material wise - probably under 5EUR/frame), after the initial tooling investment of course

[Andres125sx]

Even when I´m drooling thinking about that posibiliy, I disagree abour aluminium as a better option. Een if CF is not the best material to resist impacts, resistance, rigidity and weight are still crucial parameters wich means CF despite its handicaps is still the best option

Any lack of rididity has a direct impact on the stabilization, motor smoothness and flying behaviour, any gram difference makes a difference, and these must take dozens of crashes, some of them are a direct impact on the CF, some impact on a prop, motor or any other piece and CF must not take the impact, but on every crash the frame must resist the strain caused at the crash, so any other material means more weight or replacing the frame almost daily

That´s the reason I´ve designed TPU dampers, to reduce as much as possible the first impact so the CF must only cope with a progressive strain. I hope it makes sense, I´m strugling to find the correct words in english

[Andres125sx]

Exactly T-C, you wouldn't consider a motorcycle rear spocket built from C-F, but good old nylon can handle the task..

So given the impact/flex/resilience requirements, why not a current 'organic' design, but in the older plastic material?

No way any plastic offer the necessary resilience or rididity. I didn´t mention it before, but the flexion wich would aid the frame to resist, would be a disaster on normal flying. Racing drones are stabilized hundreds times per second wich means motors are constantly modifying the power applied. Any flexion on the arm supporting the motor means the thrust will be modified on this and next corrections, as the flexion and then the return to its position will cause motor oscilations

Imagine a rubber arm. When throttle is applied the arm bend upwards, then it stops pushing and the arm return back to level position, but meanwhile the next correction is being applied, and if the motor is moving backwards the power applied to the motor for that correction will be unpredictably modified because of the arm movement, causing oscilations or vibrations on the whole quad

Again, I hope my explanation makes sense in english

[Tommy Cookers]

interesting
presumably the frequency limit of the 'rotor' lift variability is known or can be calculated
in principle the structure could be 'rubber' if the rotor lift variation frequency was kept above the structural frequency
and software cleverness could escape even this limitation

btw
the behaviour seems to be the same reason that some jets eg Eurofighter Typhoon need a CFC primary structure
structures needs a natural frequency maybe 3x the frequency of the stabilising and/or control signal
and signal frequency will need to be high in planes that have aerodynamic stability so relaxed they are actually unstable
(most eg from the F-4 Phantom c.1958 are neutrally stable or weakly unstable and so manage with a lower frequency signal)
such relaxed aerodynamic stabilities importantly reduce trim drag but don't exempt planes from Newton's laws of motion
ie violent manoeuvres still require correspondingly large forces from the wings etc
and stability relaxation is severely limited in civil aircraft by regulation

[J.A.W.]

Indeed T-C, going way back, resilent rubber was successfully implemented for use as 'springs' in Mosquito aircraft,
& in racing BMC 'Mini' cars, & as rubber rings within the road wheels of Tiger tanks, plus Norton Commando chassis mounts..

Nylon has been in use for model aircraft props - successfully, & for a long time too.