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
Thanks for all the comments I will update, maybe help others or post a round a little bit, or just shup for a while.
The Eflite motors are really good I have not had a problem yet. Even after that crazy crash.
Because the arms are so thin, the cost per inch is very low and can be made longer with little weight added.
I will update later
http://www.instructables.com/file/F28SQLKI07YNNQE
a the good thing is its all the same part, you can add more for more strength or take off for less weight.
2.yea that explains a lot
3.time to show you this
4.was directly attached to the motors so added mass to motor = decrease vibration.
behind the dampening it was lucky. But on the crash it send all the shock to the motor.
5.ya, was loose which could have caused the crash but never has before, so it probably was a combination
That's a contradiction. You're flying it here, with the "no spar" at the top of the frame.
And it's not just arm length that will show up this fundamental frame weakness - weight will too. Like the contraption you have hanging below it.
You have the following fundamental problems here.
1. No cross spar, causing a massive weakness point in the frame. As a result, the arms will move up and down, and worse - possibly weakening the hot glue joins you used to secure the electronics tub to the frame. Ironically, your pictures from inventables show both spars in place.
2. You replaced the tensioning wire with string. String stretches...congrats, your motor oscillations are back.
3. The mounts on the front arms are probably now fundamentally weakened from your first crash (it's 6061 afterall), and vibrating badly. I've seen your first video, and frankly with the amount of bend you put into them, I've have chucked them. Yes, Alu can be bent back...but it doesn't come for free.
4. You added extra weight (the legs) to the greatest point of leverage (the end of the arms). This leverage feeds into point 1.
5. Where is the battery? In the tub? What's it secured with?
And that's before we even get to the APM logs.
and im still using the same frame just keep hammering it back.
Well the reason for "No Spar" is to allow attachments. It is fine for this arm length.
When I increased the arm length to 24" it needed the bottom spar. but 12 inches is easy.
And please don't tell you were flying the frame like this...with no bottom spar...
This is from your first crash...when you flew without a battery warning beeper.
That's unfortunate.
No logs? APM always logs...
GOOD NEWS for all the haters!!!!!
Here is a crash video!
LOL!
https://www.youtube.com/watch?v=d2-1RjnhqqA
Broke 4 motors, 4 props, frame bent(repairable), and phone(camera) scratched and saying SD card errors and battery empty shutdowns even when it's charging.
At least it worked long enough to get the video off!
there was some dust and rocks being blown around and I am mostly sure that when It lifted off, posibly some got inside the motor, causing it to work but fail when power was applied. I did my usual check for loose motors, and it seemed to hover fine, and I didn't notice anything strange. It looked like both front motors were bad, not sure how the algorithm handles (keeps Yaw, then level, then height?) It was not leveling out even as I decreased the throttle and pulled all the way back. Then I tried to increase and it just accelerated the back two motors and caused it to smash into the ground even harder.
All 4 motors should be replaced and if anyone wants the broken parts I will trade them probably for anything.
I still have to test the ESCs to check they are ok.
No logs only the video. happy flying sad crash
I will answer your questions after a little work on getting lower cost parts so that the cost does not look so ridiculous. I just liked eflite for the quality but today blew up my budget and plans. Low cost parts that are easily repairable or at minimum replaceable because of the maintenance importance of the bearings and general corrosion that takes place which is unavoidable unless you have self-healing materials embedded. being able to repair bearings add oil or at least replace them is important to keep replacement costs down. If you bend a bearing I amnot sure it would be fixable. Anyway just trying to get weight down and strength up thanks.
Having better battery technology is elons job now so we should at least follow or experiment around that, I think batteries will be printed soon which makes them lighter and have more power, but they will still have resistance and temperature considerations. The batteries now are good enough for 30 minutes flights. The ADrone frame has an open space in the middle which allows the 3s 5AH zippy or 2 3AH's or you can have your own configuration of batteries and gimbal that just inserts into the 5x5 opening.
If someone wants a frame kit for testing or building I will be happy to see someone else make measurements.
You might have seen my Instructable... HERE is the DIYD blog link about some of it (last year).
-=Doug
Good to see MHefny still around! He did *much* work with software and his controller. I enjoyed his discussions and explanations.
Any project, unless for fun, should have specifications.
You will never be able to determine if you project meets goals or specifications with them.
Do I always have a set of goals and specs? No. I do a lot of projects for fun (nobody else thinks they are fun - another subject in itself) and for the learning experience they provide.
The multirotor world is exploding with new people that have a wide variety of experiences and backgrounds. Some people have given up on trying to market a product. Some people are looking for a niche portion of the market. I simply enjoy it and the challenge it provides...as well as the ability to blow leaves around my yard without a rake.
-=Doug
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