Multirotor Project: Where to start from?

General Composites Discussions Composites Talk
#1

Hi Guys

I have been building some drones by myself, mostly 3d printing and aluminium and CF sheets.

I want to take a step further and try a molded carbon fiber multirotor.
There are 3 main criteria:

  1. It should look good
    2)It should be light in weight
  2. It should be strong and reliable

I am trying to figure out what GSM and 3k,6k,12k mean in terms of engineering.
I know GSM means grams per sq meter and 3k means each tow would have about 3000 fibers

In terms of strength and weight how different are they?

For example:
10 layers of 6k plain weave 400 gms vs 5 layers of 6k plain weave 800gm (Made up numbers)

If both are oriented similarly, will they have the same strength
Most importantly will they have same packing efficiency, ie will they require same resin under similar manufacturing method (example vacuum bagging of the same shape)

Similarly:

3k 200gsm be the same as 6k 200 gsm in terms of strength and weight (resin requirement)

Any idea what type of fabric should I start with?

I plan to vacuum bag. I have also found someone with years of experience in Glass fiber moulding. I guess my moulds will be sorted (and split mould friendly design).

Thanks

#2

Hi.
6K or 12K would be heavy for a drone. (I assume it is smaller than 1 meter)
Use 3-4 layers of 3K- 200 gr/m². (Would result with: 0.70mm-1mm thickness) You would be fine. Using one layer of heavy fabric would not be as efficient as using several layers of 200 gr/m² fabric in your application.

Good luck.

#3

I made a quad from 300gsm carbon fiber. Granted that one is a 14" prop size, so it’s not a smaller drone. I’m in the process of making a 250 quad (6" props) from 3d printed and carbon fiber parts. I"m toying with the idea of also making a ducted version.

I think for the carbon I"m going to use some unidirectional and some twill. My main concerns are high rigidity and low weight. Looks are low on my list! :smiley:

The first one I made from carbon was very rigid though, I did use uni in the arms. That one was pretty simply made with a layup over some rohacell foam and laid up on a glass table. No molds. Still it worked. Not quite as strong as i’d like but, then again some folks make them out of 1x2"s.

I just got the 3d printer figured out now, so I can start to really make it work. I’m going for a moldless design where I use 3d printed parts with carbon. Molds are a pain, would be nice to avoid them all together.

#4

@ Botus:

Thanks for your reply.
The size would be slightly less than 1m (motor to motor distance).
Using 3k 200gsm makes sense now.

Just for my knowledge, for larger (thicker?) applications, what would be more weight optimized/lighter? 3k 6k 12k? higher GSM?
I understand from manufacturing point of view, for large thickness, thicker 6k or 12k will mean lesser individual laminates, or faster lay up

Please correct me if I am wrong

#5

@ Sammymatik

My current (Aluminium) quad has 16" props.
Does Uni on their own work well for arms? I was told that Uni would be very poor unless their orientations are optimized. (say inner +45, -45 and outer at 0)

I also had the idea of using 3d prints, but since I don’t have one, it is turning out to be too expensive compared to molds (Found someone who’ll do very cheap molds for me).
Besides I doubt 3d print will be OK for such a large design (15"- 16" props)

Can I get a look at your previous quad?

#6

The one I built was ok… didn’t fly it much, as it was actually my first build and I was a bit put off by the large props so I decided to go to a 250 quad because it would be easier in some ways.

The arms were twill outer plys with some uni on the inner plys for some rigidity. I probably made it heavier and stronger than need be but, i was really just bored and wanted to make something. So not optimized what so ever. I didn’t use any 45 plys with the uni but did use fabric for the 45 plys. All in all it was just ok, but again I just wanted to build something.

I have some pictures on my old phone which I need to transfer over, I can post a few when I get back home next week.

As for the 3d printing… yah the larger size makes it a bit more challenging since I"ll have to print in multiple sections and then assemble them. Still very doable. but I’ll make the 250 next since it’s not so large and hopefully will be able to be scaled up to the larger size.