Heavy lifting VTOL technology, frames.

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-desig...

Views: 5467

Comment by chrisa on October 8, 2014 at 11:38am


Moderator
Comment by Sgt Ric on October 8, 2014 at 11:48am
You have used flat arms specifically for minimum drag, but the addition of the anti-torque cables have introduced drag back into the design.
Much like a WW1 biplane, the rigging wires were a large drag factor.
Comment by Euan Ramsay on October 8, 2014 at 11:52am

The "rigging" has the potential to introduce vibration and harmonics back into the airframe as well the drag Sgt Ric has observed. Rigging is a bit of a black art.

Comment by Euan Ramsay on October 8, 2014 at 11:56am

Nor does it eliminate torque effect - it just transfers the energy elsewhere. Into the rigging. Thermodynamics and newtonian physics an' all that.

Comment by chrisa on October 8, 2014 at 12:14pm

Thanks. Good point. Was the rigging the cause of the drag in WWI or was it the extra wings?

I wish I had the tools to measure the actual difference in drag. That would be great.

The counter rotating blades will cancel each other out. It adds more power by forcing the motors rigid against their own torque.

The 2m  quad does fly, and it uses the same rigging. It weighs the same. It did vibrate without the wire, but with it becomes very strong. 

Comment by Euan Ramsay on October 8, 2014 at 12:22pm

The counter rotation only cancels out torque against the airframe, not against the immediate mounting point.

It does not add more power - I'm not even sure what you're saying there. Besides, your anti-vibe mounts will be sucking away power and stability/control more than anything, as they allow rotation against the Z axis (if I understand the pictures correctly).
Your 2m frame does not weigh the same as the one picture above. C'mon...
Re: drag - it will depend on what harmonics are present. Theoretically, the drag loss should be low.

Comment by Acorn on October 8, 2014 at 12:40pm

How about angle iron (er. aluminum) for your arms instead. More rigidity. You might not need the cables.


Moderator
Comment by Gary Mortimer on October 8, 2014 at 1:00pm

99% of the sale is in the look

Comment by Quadzimodo on October 8, 2014 at 1:13pm

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).

Comment by Rob_Lefebvre on October 8, 2014 at 1:18pm

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.

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