I just tried to edit my post and I hope that all the comments didn't get deleted.
If so, I will have to go back through what I had, and try to add them in. oops sorry won't do that again.
There are fundamental principles such as:
Maximizing airflow, Minimizing weight, Frame Rigidity, Vibrations(mode, frequency, amplitude, localization), Torque.
In the arms specifically: There are torsional from the blades spinning, and lever forces, from the lift generated.
Compression is generally to be avoided, it can fail in a big way, so be careful with it. Oversize is better.
There are probably others so feel free to add. Those are common to all frames.
Most copters use a round boom or arm. This is bad in a wind tunnel. And if they get damaged, you have to replace the whole thing. My suggestion is to use vertical arms, allowing the downward force of the propeller to have the least resistance. Having vertical arms and using thin extruded aluminum not only make it easier to fabricate, it also makes it eco-friendly because you are not wasting fiberglass or carbon parts. You can bend the aluminum back into the proper shape effortlessly.
The torsion forces can be converted into bending/lever forces by appropriate locations of mounting points. This will increase stability because torsion is a pain to deal with. Tension is the best for most thin metals so trying to keep that in mind, putting some parts in tension will reduce needed material. Using a steel or similar wire around the arms will provide tension force against any torsion or bending because any individual arm's movement will be transferred to the other 3, causing them to act as a rigid body, it avoids sending vibrations down the arm.
By having the arms come to a central point, there is symmetry in the forces involved, makes them easier to design around.
If this is helpful at all, a thank you will do, and if you have anything to add, I will keep a record here AND in my heavy lifting design files, which will be used to make the next version of the ADrone. And I won't leave you out where credit is due. Collaboration is the future and we can do it together!
here is the work I am talking about, this is the first version, I know I am late to the drone field but that's no reason to quit.
http://www.instructables.com/id/Aluminum-sport-X-copter-frame-design-for-strength-/
Comments
Sorry guys but to be blunt "this design looks really stupid". What is so inherently wrong with existing CF tubes that requires such a bizarre design? I also have a hard time understanding how this can be called a heavy-lift design? I am not certain what you are trying to accomplish with such a design.
If you really want to affect radical change in multi-rotor design figure out a way to get enough battery power to last several hours worth of flight time from two double-AA sized batteries lifting full DSLR camera. Now that would be truly an improvement over existing designs?
Personally I do not see any major improvements in multi-rotor technology from additional weight savings over existing CF designs. Whatever you gain in additional weight savings using such unconventional designs will be minimal at best. The true fundamental change will only happen with the development of long lasting battery power systems with minimum power to weight ratios. Have you seen how heavy current 20000mAh 6S LIPO's are lately? I do not think your design would carry such loads especially when you factor in additional payload with gimble and camera. Although your efforts are commendable I think the focus is in the wrong area.
Chrisa- I see some genius in your design. The trick when choosing materials is making the best use of the unique properties inherent to the material.
Carbon fiber is best used in strips on the top of a wing because it has incredible tensile strength.
I totally get your idea re: the wire to stabilize the arms. I like using flat stock to eliminate some of the drag caused by pushing lift air past a thick boom.
So here's a couple of ideas in the spirit of not being an uAv-hole.
An "H" configuration using flat stock with carbon fiber rods to stabilize instead of wire.
Wire needs tension to get the job done, CF doesn't need to be preloaded....
Also, think about mounting the motors UNDER the booms and mount the props BELOW the arms.
No prop wash drag.
Also, you could use the CF for skids mounted on the outside booms, like heli skids. Keeping them out of the line of site of your cam.
And if your looking for a place to sling a payload, a light platform could be mounted between the skids.
Since no one here seems to be interested PM me and we can work on a napkin together as it may be a little difficult to visualize all this and I have no interested in being torn apart by the design nazis.
By the way, I've been flying my Nano QX "upside down" since the day I got it. Having the props below the booms works great. And it looks pretty awesome too. Kind of like a spider...
And the best part is, the booms don't split on hard landings.
Like the guys did who told me it was a stupid idea because it wasn't designed to fly like that....
The reason flat bar is not good is because the moment of inertia is very low compared to tube. The stiffness to weight is not as good as tube.
The Anti-vibration mounts are made so that you can modify them by changing the type of plastic, to get the perfect rigidity and absorption required. You have to lose a little energy to dampening or else its just a spring, the plastic is in compression most of the time so It is just a hard dampener. It does not lose any energy when fully tightened.
Hey I am not a certified mechanical engineer! I am an electrical so I value your feedback! LOL
You need to explain to me why you think its horrible, so I can fix those things.
I would use tube if it was a larger craft, for the bigger one I plan to make I may use 3x1 or something. Oh baby.
Anyway I did not see much talk about larger things so if there is a good resource I would like to see it.
Nobody should post something like this, and not expect feedback. Like I said I'm a big fan of aluminum. But this is just not right. Flat bar is only appropriate to use if it's purely in tension. This is not. It's a horrible combination of torsion, bending, cantilever, etc...
You must use tube. And if aerodynamics is a concern, use streamline tube.
I Hope it doesn't feel like everyone is "piling on".
Lol, Rob.
Wait until we're making them out of nano-tubes. How sexy will that be? :)
Gary! You got that right! Most frames feature lots of carbon fiber, not because it is appropriate in the application, but because of sex appeal.
Chrisa - Great step by step article. Is this your first build?
Judging by your prolific posting on the subject, it appears that you feel frustrated that your design is under appreciated. The idea of placing the structure of a multirotor frame under tension and/or compression in order to maximize it's strength while eliminating much of it's weight makes a great deal of sense, and it is certainly a concept worth exploring further. One need only look at the evolution of bridge architecture to see that tension/compression is a powerful tool, but also that it needs to be done properly. The more efficient the design the more exacting the science (or you end up with a Galloping Gertie or worse, as Sgt Ric and Euan have alluded too).
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