Diameter recommendations for aluminum tubes for a 14 inch prop build

That is really great. I think 600g additional payload will changes the figures, but of course they are still great. What about windy conditions, there seams to be a lot of reserves for that?

And ecacl does give similar numbers for a 3s setup.

I have quite a bit of experience working with an aluminum frame, and I can’t recommend it. I also don’t like working with carbon fiber, but it is much better suited to frame building than aluminum. I personally would go straight to CF tubes and save a lot of headaches.

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yes, I agree with all the comments. What I conclude up to now is that my frame is to heavy. It would be fantastic to have a frame which is only 200 g. I would be very happy to buy one.

What I find hard to understand is why a 6s 380 kV solution should be significantly better than a 3s 700 kV solution. These pan cake motors are a little bit more efficient but the speed and the watts are the same.
For me it seems far more relevant which environmental conditions the craft has to deal with. And I could imagine that in situations with a lot of heavy gusts smaller motors and even smaller props perform better.

What do you think, what do I miss?

380/700kv example

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Thanks! I specifically made those videos so you and others can build lightweight frames yourselves. Birch plywood is much easier to cut and glue than carbon fiber and my design results in a VERY stiff frame. I’m still in the process of refining the design as far as the cutouts in the top and bottom plates. My current frame weighs 187g (without any cutouts!)

At this link, you’ll find a downloadable plan and the link to my assembly instruction videos:

Here’s a photo of my current prototype. It has everything necessary for flight, less props and battery:

  • 3508-380kv motors, ESCs, and all wiring
  • Pixhawk2.1 Cube
  • Here GPS
  • Telemetry radio
  • RX8R receiver
  • Power module and PDB hidden inside frame
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I’ve experimented with a number of different prop sizes in gusts, and as long as the motor has enough torque to react quickly, the prop size doesn’t make much difference in gusty conditions.

Tobias:

If you’re just experimenting, and assuming you’re in the U.S. somewhere, go down to your local Home Depot and it the “Bath” dept. you will find 15mm square aluminum towel bar. 30in will cost $5.

I’ve been fabricating arms for hexas and quads for the last 3 years. The aluminum is soft, easy to cut and drill, and yes, if you crash they will bend easily. But in a lot of cases, that’s a plus since the arm absorbs some of the crash energy.

There’s no motor mount involved as with a round tube, so the CF vs aluminum weight argument is kind of moot. The tube weighs 1gr/cm. I don’t even use a mount, screwing the motors, which are 113gms each, directly to the tube, using 2 screws. Never had a problem. The motors are Sunnysky X4108s KV480.

Only recommendation is to add a spacer in the tube where the screw goes through so the screw torque doesn’t crush the tube. You will also need to drill a 3/8" clearance hole in the center between the motor screw holes for the end of the motor shaft and circlip.

Drop me a PM if you want a picture of the arms.

Ron

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If one is going to use aluminum arms this is very clever Ron. I had a 550 size quad with the aluminum rail arms available on eBay and after one crash they were pretzels. I may revive that frame and try your idea for the heck of it.

I went for round arms which is definitely a bad idea. Next time I will use the 15x15 square tubes. I’m from Germany, it is very easy here to get any kind of materials… .

I am new to quads and drones and this is purely a suggestion but look into 4130 steel tubes if your heart is set on metals. Aluminum is a great material but better suited for flat/sheet metal applications where bent flanges and lightening holes can add rigidity. For tubes, carbon fiber is definitely the strongest per lb. However, 4130 “Chromoly” is what has been used in small aircraft construction for almost 100 years now and is not only very strong and rigid for its weight but its workability is where it gains on carbon fiber. You can bring tubes together and weld up a cluster where carbon fiber needs some kind of bracket and bolt assembly.

You can see some of my work at Edwardsaircraft.com

good luck on your build!

Dave:

Yeah, my first shot was a F550 hexa. I ran a single tube side to side through the frame plates. The whole thing was like a bridge girder.

My 2 MRs are a 650mm quad and 870mm hexa, both using the tubes. The latest addition is a quadplane. Crashed it, the front left portion of the motor rail hanging under the wing took the brunt of the impact. Bent the tube up and back. Pulled it off the frame, down to the Depot, since the rail is full tube 30in, no cutting required. I have a jig setup just for drilling the motor mounting holes. Replaced the whole thing in a couple of hours including the Depot trip. $5.00.

Ron

Ok, my build has mapped its first 180 ha. I’m quite satisfied, although it was windy (20-30km/h) it flew 27,5 minutes (with13" CamCarbon props) and had still 22% battery left. I guess with the 14" CF Props it I will be able to fly >30 min.

I think that is quite ok for a 3 kg aluminium tube build with a 550g payload.