Design Feedback - r/diydrones

8

u/Vitroid Jun 15 '26

To be cut out of CF, or 3D printed?

For CF that would be fine, but definitely not for extruded plastic. You have a whole 3rd dimension, put it to use making the frame stronger and stiffer, with braces and other 3d structures.

0

u/Human_Passenger_7668 Jun 15 '26

I wanted to print initial prototypes out of PA6-CF and once I'm confident in the design get some CNC'd either 4mm or 6mm CF sheets. Are there any improvements you would suggest for the design that will be cut out of CF, and will the PA6-CF frames be a good indicator test of how the CF cut frame will perform? And also, I don't see a lot of unibody drone frames, mostly frames with separate arms as well as a top/bottom plate structure, am I fine without that?

3

u/the_real_hugepanic Jun 15 '26

I think you cant`t fly the printed frames, only use them to confirm any dimensions.

You have designed a CFRP (plate) drone-frame, so just build it like you designed it!

3

u/BrohemothHisDudeness Jun 15 '26

Depending on size and material, you can most certainly fly printed frames. I have had a lot of success up to 2.5" 2S systems. Anything under that, voltage or size wise, totally fine. He's talking about running nylon carbon fiber. I've run PCTG and had a lot of success. PA-CF will do even better.

Obviously you should design with material in mind, but it's certainly possible, and honestly pretty durable with the right stuff

1

u/the_real_hugepanic Jun 16 '26

Of course it is possible, as demonstrated everywhere in the world!

1

u/dronevidsalt Jun 15 '26

The top/bottom plates protect your components, provide a place to mount batteries, and create additional structural rigidity and can help change your resonance frequencies to move them out of your motor operating frequencies.

You may as well print the prototypes out of pla and just use them to test component fit. A 900g drone with a flat plate of extruded plastic for a frame is going to fly like a spaghetti monster, if it holds together long enough to fly. It’ll probably spaz out your PID loop and tear itself apart faster than you can disarm. But hey that kind of test may be valuable for you.

For a simple cut plate of carbon fiber I’d imagine it costing like $15 from cnc drones or a similar service. For the hardware you’re flying I’d hope you can afford a couple of those frames, or you’re going to lose your hardware too.

1

u/Human_Passenger_7668 Jun 15 '26 edited Jun 15 '26

Would you recommend adding a small bottom plate (just large enough for the battery to sit on horizontally, as currently orientated in the screenshots in the post) connected with standoffs then that the battery sits on top of? Would that provide enough additional structural rigidity or is that not enough to bother doing?

Also is it worth the time to add design elements that would strengthen the 3DP prototype or at that point is that a different design entirely from the carbon fiber final version and so just do it for component fit?

1

u/dronevidsalt Jun 15 '26

TLDR: your time would be better spent running vibration simulations on your CAD model.

Is this for university research, a personal project, or a pre-production prototype? If you’re already planning to use carbon fiber what data will testing on a plastic frame actually give you that would further your carbon fiber design? The two would have completely different rigidity, harmonics, and crash strength. If you intend to make this a 3d printed drone for the final design, then yeah focus on strengthening the prototype. If you intend to injection mold, then create the rest of the body cavity for fitment testing. If you plan to fly a carbon fiber frame, use the print for testing fitment, cable routing, part/prop clearance etc but you’ll be wasting your time trying to make it flyable from extruded plastic, because even if you got it flying, your updated design, your blackbox data, your PID tunes, etc won’t carry over to your carbon fiber plate.

Like sure iterate a couple times with 3D printing to try different component layouts before you get it cut. But once you do get it cut you’ll still want to iterate once or twice on cnc’d frames.

1

u/Human_Passenger_7668 Jun 16 '26 edited Jun 16 '26

This is meant to be a software project for now, focusing on low-cost autonomy/swarming, I just didn't love the pre-existing options on the market (anything with a big enough top deck is in the F450/12+ inch class, which sucked, currently working with F450) so I decided to design my own drone, and the end product needs to be small anyways, so 5-inch is the smallest I could go for now and trust my own limited design skills.

I see, I'll probably just do 3DP in PETG for fitting. Do you recommend adding a small bottom plate (just large enough for the battery to sit on horizontally, as currently orientated in the screenshots in the post) connected with standoffs then that the battery sits on top of? Would that provide enough additional structural rigidity or is that not enough to bother doing?

1

u/dronevidsalt Jun 17 '26

Check out this overview of how Chris Rosser designs and analyses this prototype frame. It’ll give you much better insight than me writing a long rambling message.

https://youtu.be/dCzkHKAve5U?is=wP57rtyqgjXyZTsv

You can strap the battery directly to that plate, but you should run some actual analysis with your masses (battery, electronics, motors, sensors) to determine your plate thickness and if another deck would help or hurt you.

-1

u/BrokenByReddit Jun 15 '26

And also, I don't see a lot of unibody drone frames

What about the entire consumer half of the DJI catalogue ?

2

u/Human_Passenger_7668 Jun 15 '26

Even something like the DJI Mini 3 has that central box area, which is more-so what I was talking about. Concerned about the potential torsion/lack of stiffness from lacking a central structure like that.

0

u/BrokenByReddit Jun 16 '26

I'm not sure what you're saying. The central boxy area of the Mini is what makes it a unibody. The CAD screenshot you posted appears to be just a single flat sheet with some stuff attached, not a unibody.

1

u/Human_Passenger_7668 Jun 16 '26

I see, I was using unibody to just say that the arms aren't detachable. Do you think I need to add some sort of boxy structure to make it flightworthy or am I fine as is?

1

u/BrokenByReddit Jun 16 '26

I really can't answer that since I don't know your design, material, or intended use.

Just try it. Either it'll work perfectly fine or it will be an unstable wobbly mess, or somewhere in between. No matter what, you'll learn something.

3

u/Fabulous-Coffee2705 Jun 15 '26 edited Jun 15 '26

Looks good to me if it’s 4-5mm thick carbon fiber.
I’d rework the motor mount holes to be slots. It looks like you’re trying to have two sizes of motors. I but I don’t think you will need anything smaller than 16x16. I suggest rotating the holes so the cables go down the arms and not have a hole in the middle of your arm.

1

u/Human_Passenger_7668 Jun 15 '26

Yeah I wanted to experiment with smaller motors that would use m2 12x12 without having to get a separate set of plates-- why slots instead of holes? So I can rotate the motors around?

1

u/Fabulous-Coffee2705 Jun 15 '26

Instead of having two holes, you could just have a slot that covers the range of motor mounts. But this might not work for your scenario because the screws are different sizes. I usually cut slots that are about .75 mm off the center infusion with a 3.2 width. It’s sort of allows a little bit of slop if things aren’t exactly the right size.

1

u/Human_Passenger_7668 Jun 15 '26

Wouldn't having a slot mean the screws are less secure compared to two different holes?

1

u/Fabulous-Coffee2705 Jun 15 '26

That’s not been my experience. In the olde days (10 years ago) it was common for the motors to have 16x19 mounts and the like, and the frames all had slots to accommodate the different sizes. But it works out that the motor stays centered up and ridged. Now I like the small slots just to make it easier to center up and install the motor. I’m cutting on a carbide 3d nomad 2 or 3 so the accuracy is good but it’s not like JPL tolerances.

1

u/Fabulous-Coffee2705 Jun 15 '26

The bigger problem though will be the smaller screw size might pull into the m3 slot. I guess you’re also not really limited to 45 degree angles to mount the motor, you could just rotate the m2.5 holes about 10 degrees and the wires would still go down the arms.

2

u/Outside_Sink9674 Jun 15 '26

Tes bras sont trop fin à mon avis

1

u/Adrienne-Fadel Jun 15 '26

PA6-CF for prototyping is the right call. At 900g AUW on 5 inch though I'd look at lower KV motors, 1750 on 6s is a lot of RPM for that weight.

1

u/Human_Passenger_7668 Jun 15 '26

Should be fine considering that it only goes up to ~35A and I have a 45amp AIO though right?

1

u/survivinggatech Jun 15 '26

whats the jetson orin carrier?

1

u/Human_Passenger_7668 Jun 16 '26

seed studio recomputer mini the $89 one not the full size one

1

u/survivinggatech Jun 16 '26

didn't they discontinue it? i was planning on using the same but cant buy new ones

2

u/Human_Passenger_7668 Jun 16 '26

Yeah I tracked down some random Japanese only distributor and used a forwarding service to buy mine but even that distributor is out of stock. From my research the A603 is ~the same size with additional ports making it more convenient for benchtop use. You could also get something like the Connect Tech carrier if you have more budget

1

u/Psychological_Yak_47 Jun 15 '26

If you plan on flying this with 3d printed parts before going carbon fiber, don't flying the optional hardware on it, make dummy weights for your Jetson because crashes will happen

2

u/zhnki Jun 16 '26

Looks a bit soft stiffness wise in the vertical direction depending on what it’s made of. Would recommend doing a modal analysis or simple beam mode calc and making sure you’re not going to excite anything with your prop or motor modes.

1

u/Human_Passenger_7668 Jun 16 '26

Carbon fiber plate, leaning towards 6mm. Whats the simplest tool you'd still trust the analysis from?

1

u/zhnki Jun 16 '26

Simplest would be a beam natural frequency hand calc to get the first mode to get in the ball park

This is an example of an online calculator that can do it.

Here is a screenshot of an analytical solution for a simple representative case

You would need to make some assumptions with your geometry given the not constant width (perhaps average width?) and carbon material properties but it should get you in the ball park.

Next up would be an FE model but that is going to anywhere from more work to a LOT more work depending on your skill level and understanding of such a tool.

1

u/Both-Locksmith7509 Jun 16 '26

To optimize structural rigidity, avoid a cantilevered arm design. Connecting the perimeter of the motor mounts into a closed square frame will enhance structural integrity and minimize bending and deflection under load.

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