Calculating the frame strength of a 40-kilogram copter

[DroneDen]

Hello everyone, we are designing a heavy-lift multirotor using RuiH-Tech PX-18 motors (datasheet attached). The copter will operate at low RPM for higher energy efficiency.

We have run into a problem choosing the frame and would like to do it properly rather than just picking something at random, so if anyone can help, our whole team would be very grateful.

What kind of strength/structural calculations should be performed, and do we need to take fatigue (multi-cycle) loads into account? We are thinking of using a 40×1.5 mm duralumin alloy tube, but due to its relatively low Young’s modulus we believe it may be prone to vibrations. In this case, would it be better to consider a carbon-fiber frame instead?

 

[Houndpup Rc]

In this case, would it be better to consider a carbon-fiber frame instead?

Yeah, CF it very strong and light, and it can flex a bit without breaking or saying permanently deformed, so it might be a better option.

A good idea may be to design your frame in a software like Onshape or Fusion 360, then if you set the material for each part you can find out the all up weight. Also, that way if you need some parts of it manufactured you can just give the file to PCBWay and they can cut it out for you from pretty much any material!

 

[cosmocop]

You'll need to do bending analysis for the arms and center frame/fuse. As for fatigue, I wouldn't think that'd be a big concern but if I were to look into it I would focus on the motor mounts.