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
Hugues is onto something re: vibrations. As a keen cyclist (8000km a year), I have ridden 6061 frames and recently carbon monocoque designs. And the ride comfort of the carbon frames is leagues ahead of the Alu frames - this is all down to the vibration absorbtion properties of carbon.
Having said that, you do need good lengths and layups for it to be effective, but some of the inherent properties will be evident in even the simple and short deployments in multirotor frames. Apart from the critical or compression failure behaviours of carbon, carbon tubing is an extremely effective system for multirotor use. The 25 and 30mm tubing is notable for its large surface area for clamp mounting, and large motor fitment.
it is super strong and never bends at all :)
It does not look heavy lifting, but consider this a scale model because WHY would you start out with a full size to experiment?
It can be scaled UP or DOWN. The arms are still stable using the same base, with 24" arm length, which I find amazing.
Please do not edit posts if this gets out of hand we will ask you to close the thread. At DIY Drones we believe people own their own words and should be prepared to stand by them.
The proopgation of vibrations, is something I can relate to.
I have the understanding that a better wave propogation means that the material has a
great transfer of energy, which means in the physical world, that it is more rigid,
or stronger. The goal was to design a frame that is as strong as possible, while
staying light. I believe this is the strongest frame for its weight that is possibe.
The vibrations are around 3rd or 4th on the list of priorities, for me.
They are relatively low, Low enough to have stable video from the i4 which uses a
rolling shutter, causing waves in the video. There are minimal waves in the video and
it is very stable video. It could be better, so I am looking at gimbals now, probably
will put a little foam in between and that should do it. If there was a heavier camera there would be no problem. I am using a phone so it feels like it weighs less than the foam its attached to.
Thank you for noticing that this frame is super cheap. that was important to me
as well, because if it costs too much nobody will buy it.
I like the suggestion of an H design but it will be a little different forces
involved so a total redesign. I'm willing to work on it though.
I am glad that DIY stands for do it yourself
Some people think it means Don't Invite Yourself
I really hate to delete other people's posts, but Someone posted an attacking and non-related comment, but it did have one good observation so I will post that(mean parts taken out).
Mr.Schmit
Since the airflow below the propeller travels in a helical path (not straight down), the arms are keeping the direction of airflow perpendicular to the ground. The air flow is hitting the sides of the arm producing more lift. . Once you transition to forward flight, the flat arms become "wings" that will increase the flight efficiency much more than round tube type arms. These flat arms will also increase the effect that wind has on your machine.
Nice diy project.
I also tried, mostly unsatisfactorily, aluminum designs. My main personal take away from these Al designs is awful vibrations propagation.
This looks budget-driven and not good-engineering-practice-driven.
Better to say 'I used angle aluminum because it is cheap (or all I had)' rather than to try to rationalize add-ons and make pseudo-engineering arguments.
CF has a place just like my beloved plywood and square tube efforts.
On the other hand, building and testing is far better than sitting around watching someone else build and test.
Go for it! Just don't ignore several decades of engineering and technical work that has already been done before.
-=Doug
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....
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