Quadcopter Material Selection: Aluminum OK?

Hi All,

This is one small step for me, one even smaller step for Quadcopter kind: my first foray into DIY Drones.

I have access to a machine shop.  As such, I was thinking of building my quadcopter frame in aircraft aluminum.  Is this a suitable material?

Am I accurate in assuming that my ability to do anything I want with aluminum is an advantage over an out of the box fiberglass frame?

Design consideration questions:

1) Is there a formula I can use to figure out the maximum weight of my frame?  I am assuming that I can treat the combined lift of all four rotors as one up force and therefore use the combined weight of all components as one down force and do a simple free body diagram: Is this a suitable approach?

2) What factor of Lift>Weight should I aim for?

3) I was thinking about using tubular aluminum arms with a 3y by 1x ratio and then gussetting to stiften the x-axis with tapered thin plate.  Is this a good setup?

4) Why does nobody brace in between the arms?

5) Any other material selection criteria you can think of to suggest along these lines?

That should help me get started.  

Thanks to all!

Wile E.

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  • Moderator
    #2: 1.15 to hover (try to get your max efficienty for motors at this thrust level)
    ~1.5 for agressive flying
    ~2.2 for hot rod.

    Really, if efficiency is a goal, then focus on the hover speed for the best grams thrust per watt ratio from your motor/prop combo. Most of the time, you'll be between 1.15-1.5

    #4: some do, mostly on smaller quads. The answer is: weight. It really adds up, gram by gram, and weight is king. Every single gram counts.

    Best wishes. Wish I had your aluminum fabrication options.
  • Aluminum is a fine material for multis and is widely used. Aluminum is easy to fabricate and can often be bent back into shape after crashes. If you have machine shop access, it would be an obvious choice for you. A big drawback is that it blocks RF (as does carbon fiber). That means you have to exercise a bit of care in how you place antennas on your craft. Another potential drawback, depending upon the actual design, is that aluminum can transmit vibration quite well.

    Your questions 1 and 2 are sort of combined. You should shoot for a max lift to weight ratio of 2:1 so that you can hover at around 50% throttle. My usual design path is to come up with a rough weight estimate of how much junk I want to have in the sky, then use eCalc to come up with a motor/prop combination that will lift twice that weight at max power.

    For 3, I'm not sure what sort of layout you are describing. Generally the arms should be as thin as possible in the vertical direction so the blocking of the prop downblast is minimized. This will also reduce frame vibration.

    4. Usually the forces of concern in the arms are either vertical flexing or torsional rotation of the motors. You can develop arm resonances which will create headaches for your flight controller. Also bracing with create more aircraft structure in the propwash stream.

    I'd say go with aluminum, at least for the arm. Another material you could consider is thin G-10 fiberglass sheet which is easily machinable (I got mine from Amazon). This is nice for the body area as it's RF transparent. It also makes nice motor mounts (as does Delrin). Finally, ordinary thin hobby plywood, while not nearly as sexy as carbon fiber or fiberglass, is a very good material for this sort of thing. It's cheap, RF transparent, takes brief structural overloads well, uses simple adhesives and dampens vibrations wonderfully.

    • whats a good type of aluminum to use 6160 7075 2024 6063 ?

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