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Curious about MA noise

Jack Daw

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Having just seen a virtually silent drone on a TED talk, I'm wondering: where exactly does the noise from a Mavic Air (which I wish was a little quieter) come from? Is it the motors? The sound of the props cutting through the air? Some combination of the two? What would be entailed -- and what might be compromised -- by making the thing a lot quieter? Would adding some kind of soundproofing around the motors do it? Changing the shape of the props?
 

CanadaDrone

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Props cutting the air mostly. That is the reason, for example, the Mavic Pro Platinum and Phantom 4 Pro are quieter when all you do is change the props to the low noise variants which you can see are shaped differently for reduced drag (lower noise, more efficiency). The other thing that affects it is the speed of the props. With smaller rotors, you need to spin them faster to generate the same lift as a larger rotor, all else equal. Smaller, faster, props = noisier or at the very least, higher pitched, which humans tend to perceive as louder.

The "low noise" props spin slower and have more surface area, so they get the same lift with slower RPM and less noise.

Changing the shape of the prop could theoretically reduce noise on the Air - the MP Platinum and Phantom 4 Pro 2.0 props you will notice have special tips on them to reduce noise as they cut through the air. I'm not sure why the Mavic Air does not have these, but the advanced engineering that must go into drag, lift, RPM, motor load, etc. is above my head.
 
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Just_nick

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It's the design of the propellers. They are made to support the weight of the drone and to be able to reach the 40mph that they're capable of. You could change the design with the intent of making it as silent as possible, but you would lose the capabilities in exchange.
 

psloan

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My thinking is that the Air has shorter arms. Meaning the props overlap the body a fair amount. This could cause the louder prop noise when compared to the Pro.
 

William Ball

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The "noise" you hear is related to the KV of the motors, size and pitch of prop.. How these little motors work is: they are brushless motors that use magnets to spin the motor. One set of magnets is fixed to the bell housing of the motor, the other set affixed to the shaft part. What happens next is the ESC (electronic speed controller) sends voltage, to the windings in the motor, allowing the magnets to repel and attract hence spinning the motor. This is a very simplistic explanation. The noise comes from the voltage applied to the motor and the very fast rotation of the motor. The phantom series quads have a 960kv motor set in them so every volt that is applied to the motor will spin the motor at 960 rpm. so a 3 cell 11.1 volt battery pack will spin the phantom motors at 10,656 rpm at full throttle. The phantom is swinging something close to a 9" prop and quite slowly at that. The Mavic air is much higher in kv not exactaly sure but somewhere in the 2100kv range. So every volt applied is spinning it 2100rpm, putting it at 23,000rpm plus. This coupled with a smaller prop at 4.5 pitch or so, is giving you that "beehive" sound. You should hear my Strix 180 race quad running 2700 kv motors on a 4 cell pack. It is hitting nearly 40,000 rpm. running a 3 blade 4.5 pitch 5" prop. WOW is it a screamer! The mavic pro motors are bigger and at a smaller kv than the MA, swinging a larger prop so it is quite a bit quieter.
 

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