Carbon Fiber Frame for Micro Drone 3

[DevilWAH]

Hi all,

so my first fory in to quad building is to make a carbon fibre mico drone frame out of 1mm CF sheet, but I would be grateful for some advice in two areas.

First of all here is a link to some 3D modeling I have done on the frame.



https://gallery.autodesk.com/fusion360/projects/micro-drone-carbon-fiber-fpv-upgrade

So far one major thing i found out was direction of weave is crucial!! 3-5mm arms are fine as long as the weave is along the arm and not across it!

and there have been a few revisions all to do with learning 3D package, Carbon fibre and various other bits. But I would apriciate some help one a few points.

1. Cutting thin CF sheet, I have been using a dremel on a small drill stand. Locking down a 0.6 mm grinding/routing bit and pushing the sheet aginst it. IT does work but if there is any one in the UK that has a CNC mill and like to cut small bits of thin carbon fiber sheet I might be interested in some help for future projects

2. What is the best way to glue thing carbon fiber sheet together. I have tried Cyanoacrylate, epoxy glues and finishing resin, with the last by far the best. But its still not a brilliant bond when its one sheet edge on. I do need a fairly strong join on this project so if any one has some suggestions on some methods to try I would be most grateful.

Cheers

### EDIT ###

Tips I have picked up.

1. with thin CF sheet (1mm) the arms need to be cut inline with the weave. For a drone that only weights 50-70g 1mm sheet is plenty strong enough. However CF bends very easly across the weave, but is very stiff in line with it. for an arm 3-5mm in width and with only a single layer you need to know what direction you need the stiffness in!

2. To glue thin CF sheeting togather like this (edge to face) use a finishing resin ( I used Zap z-proxy finishing resin). Mix as directed but I also mixed in a good amount of carbon fiber dust from when I was cutting the sheet. Also make sure to rough up the surfaces. My methods was to mix the resin with out the Carbon fiber dust in it, then apply a thin coat of this to the both surfaces. then mix in the dust to the rest. then I would leave for about 20-30 minutes until it started to thicken and apply it at this stage to help hold the parts in place. This way the first coat will still runny would bind well to the surfaces, and the thicker resi later on would mean more stayed on the joints and over all there was a much stronger bond.

3. To cut thin Carbon fiber by hand is a pain, so I came across this on youtube, the bit he suggests is perfect to make nice easy clean cuts. If you have a dremel though dont but there stand as from all reports it is poorly made and not stable. there are many others around that will hold a dermal. just get one that is rock steady, moves up and down cleanly, and that you can lock in the down position.

If I think of any thing else I will put it here also.

 

[DevilWAH]

So Been working away and thought I would share some of the progress so far.

So it all began with one of these, a microdrone 3.0 from extreem fliers. If truth be told not the best drone on the market but some thing to build on



And the idea was to replace the frame with Carbon fiber and add the FPV cam while keeping the whole thing light enough to carry the camara module (extreeem fliers are developing a mico gimbel version that is a direct replacement for the current static one that I want to be able to use on my new version)

First thing first was to make a card model to make sure the flight board and battery will fit.



the lenth of the model is about 120mm

 

[DevilWAH]

I then made the same thing in card, with the addition of some 65mm props to give and idea of size.

 

[DevilWAH]

Next came a few days learning Fusion360 and a number of iterations of design, finally ending up with



If you have Fusion360 you can see more of the designs here

https://gallery.autodesk.com/fusion360/projects/micro-drone-carbon-fiber-fpv-upgrade

 

[DevilWAH]

there was a bit of back and forth, designing in Fusion360, cutting and building in card to see how it would fit together.

this is an example of the close to final design.

 

[DevilWAH]

Before I got to my current stage of the first flying prototype



Red and black leads need to be wired in to LED's and the wiring its self needs a lot of clean up. Also the ends of the arms where the motors mount I had to change and so in the next version I wont need the extra bit of Carbon i had to add. I also want to cut out the sided of the body both for looks and weight reduction. But it does fly, the camara is out of a eachine QX70 so getting a nice clear picture. and it comes in at an almost identical weight to the original (which like I say I think i can better in version 2

One thing I do like about the micro drone is the battery slides in and out, which means swapping a battery is 5 seconds work and not fiddling with cables. That battery also has magnets on the bottom which double as the camera connections, so to fit the camera module is even less than 5 seconds.

For that I am intending to send away the CAD files and have the parts cut on a CNC machine.

 

[Hai-Lee]

Firstly I will say I admire the work you have done, (perhaps more being envious), but the little information you have provided does limit my understanding of your current issue with the GLUE.

From what I can see I would suggest that perhaps the problem with adhesion is more to do with tortional flexing of the CF arms and not a real fault of the adhesives you have been using.

I understand that a "T" cross section has a torsional centre, (rotation), which is precisely where you are gluing the pieces together. Because of this the pieces are transferring the forces upon the centre piece directly through the glued joint.

A simple fix is normally to use hollow tube though this would not suit your design and therefore you could consider either a triangular cross section arm or fit triangular webs to redistribute some of the forces applied directly to the line of glue.

The triangular cross section could be made up of an extra piece of thin CF bracing and the three glued together in a triangular beam. When twisting, (due to motor/propeller vibrations), the centre of torsion is in free air in the centre of the triangular shaped CF beam.

Just a thought! If my remote analysis of your issue is incorrect then ignore all recommendations.

Keep up the good works!

 

[DevilWAH]

Hi,

Sorry I had two issues with the Carbon fiber

1. I first cut the bottom of the frame with the pattern aligned with the sheet edges. this meant the arms were diagonally across the weave, this video might help explain

second was gluing the fiber together. Super glue, epoxy and other glues where suggested, but none of these gave a very good bond. it was not uptill the finishing resin was suggested that I manged to get a good join. Picture below, what i found was letting the resin start to harden I get a larger beed along the edges of the join and this gave it more strength.

 

[DevilWAH]

Oh and as for the ends of the arms. As you can see i mounted the motors using a rubber gromit (8mm inside diameter for 8.5mm motors). But this method was only decided on at the last minute I had a different way in mind.

to use the gromet's i needed a 10mm hole to put them in, but my origianl plan only required an 8.5mm hole so i designed the ends of the arm to be 12mm across. Drilling a 8.5mm hole would have left 1.75mm at the sides. but a 10mm hold reduced that to 1mm (assuming my hole was perfectly centered) with such little material for support pushing a groment in and then forcing the motor though was never going to work.

Next time I will make the ends 15mm so that will leave 2.5 mm at the edge which is more than enough to play with (i hope)

 

[DevilWAH]

Oh and thank you for the kind words its fun building drones, although this is my first attempt at a complete frame i dont intend it to be my last. I have a QX70 flight board for the next project.

At the moment trying to talk wife in to letting me buy a CNC mill and 3D printer. (i haven't posted it here but we have a 3D printer at work and i did try to print a frame on it. Trouble is for these small frames 3D printing does not really work. I have a plan for the QX70 to make a flat base out of Carbon fiber and then make the ducts on a 3D printer.

 

[Hai-Lee]

OK a different issue, though the use of grommets for the motors will reduce shock forces but not eliminate the average forces from their rotation and lift.

I will need to think further upon your issues but in the mean time have you considered reverting to the flat plate design for the arms and fitting 2 small CF bracing rods from the centre box to the arm outer end. This would not only supply greater rigidity but also a resistance to any twisting of the arm as well.

Keep up the good work!