motors cancelling each other out + adding speakers underneath the drone, i'm wondering if anyone tried this
i don't think anyone
has tried that
>>2869161Not sure how the motors cancel each other out, but a mic with a speaker sending an inverse wave would be cool.I have seen an increase in rpm putting most of the sound outside of average hearing range. Drones only children can hear.
>>2869165>I have seenBullshit.
I saw an early 90's UFO doc from discovery channel2024 mind can clearly see drones. Damn.... we are so dumb
Don't know about fancy technology but you can get toroidal blades for drones>A toroidal propeller is a type of propeller that is ring-shaped with each blade forming a closed loop. The propellers are significantly quieter at audible frequency ranges, between 20 Hz and 20 kHz, while generating comparable thrust to traditional propellers. In practice, toroidal propellers reduce noise pollution in both aviation and maritime transport.
>>2869161>>2869165>motors cancelling each other outIt's an active area of research, not just on those little toy drones, but on full fledged multirotor UAM (urban air mobility) and military aircraft. The big issue is technically not the motors themselves, but the rotor blades. There's a number of different physical mechanisms that produce noise on a rotor, and they each have their own frequency signatures and directivity patterns. I.e. you hear different noise depending on the relative position of you and the aircraft, which way it's moving, how fast, etc.There has been a bunch of academic work on how to predict the complex noise signatures of rotorcraft, and at this point it's possible to come up with pretty good predictions in real-time on hardware equivalent to an average laptop, meaning active cancellation is in theory possible. If you want to use your rotors to cancel each other's sound, you need to have a bunch of them to be able to satisfy the necessary degrees of freedom and power for controlling your vehicle in flight, and have rotors left over to tweak for noise control purposes. You might see that on a hex- or octacopter, but not a quad like OP's pic.If you'd rather use speakers, then you'd need a bunch of them to be able to produce the complex directivity patterns. They call that a phased array.If you want to look more into the subject, there are plenty of scientific papers out there on the topic. There are a couple of journals published by the AIAA that generally cover topics in aerospace engineering, there's the vertical flight society which focuses on rotorcraft, and maybe the acousitcal society of america for noise specific stuff.I've got a masters degree in aerospace engineering, rotor aerodynamics was my bread and butter.
>>2869224There's been plenty of weird rotor geometry like this developed for the sake of noise reduction. The general consensus is you can optimize either for low noise emissions, or for high performance, but you can't do a really good job of both. If you want high performance, it's gonna be loud. If you want it to be quiet, it's gonna be inefficient. If you want both, it'll be a compromise that isn't really great either way.>In practice, toroidal propellers reduce noise pollutionIn practice, nobody uses them, outside of a few academic studies like the one referenced by the article you copied that from.The only way to improve a rotor's performance AND reduce noise is to make it bigger. A larger diameter results in better theoretical aerodynamic efficiency, and allows for slower rotational speed, and consequently a lower tip speed. The tip speed is the single biggest factor in the amount of noise produced by a rotor. Relative air speed on the advancing side blade tip can get up to the high subsonic range, reaching Mach numbers of around 0.8. That leads to a lot of compressibility effects in the aerodynamic interactions, which produce more noise.So aerodynamically speaking, you want your rotors to be as big as possible. Acoustically speaking, you want them to be as big as possible, so they can rotate slower. But if you have huge rotors, it's hard to fit a bunch of them on a single aircraft, and you kinda don't need so many since one bigger one produces more thrust anyways. Now you understand why helicopters were dominant in the rotorcraft industry for so long. These days engineers think they're smart enough to make a shitty solution work anyways for the sake of "innovation", meanwhile they're too fucking stupid to see the obvious answer right in front of their face.
>>2869160A gun fired into the offending drone will cut the noise
>>2869503>If you'd rather use speakerswhy not both?
>>2869512they can be hard to hit, you need to be a good shot for that
>>2869512Then shartmart sends the freemasons to your house to arrest you
>>2869618If you're gonna use speakers, there's no reason you couldn't use the rotors as well. You might not want to use speakers at all because it would add a bunch of size and weight to the system. More weight means you've gotta burn more power to get (and stay) off the ground, and rotors are already not very efficient compared to a fixed wing, or airplane-like configuration.
>>2869160Just put active noise canceling headphones on them. There is also a whole thread for drones /rug where all the expert opinion are >>2869503>>2869503Jesus except this dude. Kick ass reply and info. I just saw an ad for a company that is reducing noise by messing with harmonics and rotator speed. Don’t remember the name though.
>>2869161>>2869165Won't work. The sound is not a point source, you would need to create a 3D version of the inverse sound, using techniques like an array of speakers like the other anon mentioned. What you are tackling is the acoustic equivalent of active optical camouflage. Sound cancelling headphones work because they are really close to your ear and they benefit from at least a little passive isolation.
>>2871435>you would need to create a 3D version of the inverse soundcan that be done with a hexa copter?
>>2871448No! While there are ways to design a flying thing so it makes less noise, adding stuff on it for active cancellation will require stronger motors, larger batteries and will alter the parameters requiring even more active cancellation.
