Silent Drones

[Possums]

Active Noise Cancellation System for UAVs?
Looks like a team overseas started trying to figure this out.
The aim of this Project is to complete a first study of Active Noise Cancellation systems applicability to Unmanned Aerial Vehicles. The main motivation to this research is the EASA request to minimize noise from UAVs in populated areas
---CONCLUSION---To sum up and collect the main ideas of the project, the team has come up with the following conclusions: • As the result of the analytical model detailed previously, it has been proved that the ANC system performs very well on UAVs when it is cancelling low frequency noises • Also as the result of the analytical model, it has been proved that the ANC system can be used on several vehicles flying close without causing interferences • The ANC system has an affordable price and light weight.

https://pdfs.semanticscholar.org/d737/03bc3b24f7155b1f279b37dff406cb9561cb.pdf

Sounds like a good idea.

 

[MAvic_South_Oz]

Interesting read, you wonder just how hard it might be to minimise noise by such tech as the forces to lift and keep a drone aloft by x number of motors doesn't generally lend itself to being silent.
It may be not much more difficult to do this than it is with very good noise cancelling headphones now available.

The main motivation to this research is the EASA request to minimize noise from UAVs in populated areas

The military applications as listed in their introduction would be far more sought I'd imagine.
Noise for hobbyists and commercial flyers is hardly an issue now once you are 20m to 30m or more away from the ground, well, unless you're having some fun and games with it in sports mode
I am still amazed how quite my MP is with the 8331 props, comparing to my Spark, brother-in-laws Air, or sons P4.

 

[passedpawn]

Not physically possible. While local noise cancellation is possible, it's not so with global cancellation.

 

[gnirtS]

Not physically possible. While local noise cancellation is possible, it's not so with global cancellation.

Correct. Active noise cancellation is going to involve phase cancellation which due to physics is only going to be effective at the correct physical location where the waves meet. Outside that, its either going to do nothing OR make it worse if it creates constructive interference.

The article also states low frequency noise - that isnt the issue. Humans find higher frequencies more noticeable and more annoying. Thats why the MPP worked - despite a modest actual noise reduction the greatest benefit is the frequency of the noise is reduced so its not as annoying or noticably annoying.

Physics works against you on small drones. The smaller the drone, the smaller the props, the higher the RPM and the more high frequency sound produced in general. Thats why a spark and mavic air sound FAR more annoying than a bigger Mavic 2 at the same distance etc.

 

[Racin8de]

Active Noise Cancellation System for UAVs?
Looks like a team overseas started trying to figure this out.
The aim of this Project is to complete a first study of Active Noise Cancellation systems applicability to Unmanned Aerial Vehicles. The main motivation to this research is the EASA request to minimize noise from UAVs in populated areas
---CONCLUSION---To sum up and collect the main ideas of the project, the team has come up with the following conclusions: • As the result of the analytical model detailed previously, it has been proved that the ANC system performs very well on UAVs when it is cancelling low frequency noises • Also as the result of the analytical model, it has been proved that the ANC system can be used on several vehicles flying close without causing interferences • The ANC system has an affordable price and light weight.

https://pdfs.semanticscholar.org/d737/03bc3b24f7155b1f279b37dff406cb9561cb.pdf

Sounds like a good idea.

I don't buy that for one second... Sorry, unless you have a magic wand or something

 

[mfc]

Noise for hobbyists and commercial flyers is hardly an issue now once you are 20m to 30m or more away from the ground.

You may have some hearing problem, especially of high frequencies? I can easily hear my Mavic Pro when it is 80m above me, and I have noticed people turn to look for it when it a similar distance away from them. [I'm using the 'quiet' DJI Platinum props.]

 

[Classic flyer]

I personally like being able to hear my Mavic...it helps me keep track of it and it's not as though it's loud enough to be obnoxious, I really don't understand the folks that say it's soo offensive, but that's just my take onit...be smart fly safe!

 

[mfc]

I personally like being able to hear my Mavic...it helps me keep track of it and it's not as though it's loud enough to be obnoxious, I really don't understand the folks that say it's soo offensive, but that's just my take onit...be smart fly safe!

It's unlikely to be offensive to the owner/pilot .. it "comes with the territory". But, like sports cars and motorcycles, the noise is offensive when you are not expecting it or don't want it. Or you are just in a quiet place with your own thoughts and no background noise except perhaps a few birds singing ... that's when artificial sounds (e.g., of engines) can really upset one.

 

[Classic flyer]

It's unlikely to be offensive to the owner/pilot .. it "comes with the territory". But, like sports cars and motorcycles, the noise is offensive when you are not expecting it or don't want it. Or you are just in a quiet place with your own thoughts and no background noise except perhaps a few birds singing ... that's when artificial sounds (e.g., of engines) can really upset one.

Thanx for your input, point well taken...another thought on silent drones is that the drone haters might be more inclined to think you're spying on them because they can't hear it...just a thought...be smart, fly safe!

 

[Kilrah]

Not physically possible. While local noise cancellation is possible, it's not so with global cancellation.

It IS local in this context. You're locally cancelling the emitted sound that has known characteristics to prevent it from spreading, the emitter and the ANC system don't move respective to each other.
What you say is applicable to the room-scale noise cancelling scams.

 

[MAvic_South_Oz]

You may have some hearing problem, especially of high frequencies? I can easily hear my Mavic Pro when it is 80m above me, and I have noticed people turn to look for it when it a similar distance away from them. [I'm using the 'quiet' DJI Platinum props.]

You might be right mfc.
I do have bad NIHL from working with high pitch hand tools all my life.
Almost all high level hearing lost

I will have to take someone out into the field with me some day and give me some feedback on what they hear / think is annoying.

 

[mfc]

You might be right mfc.
I do have bad NIHL for working with high pitch hand tools all my life.
Almost all high level hearing lost

I will have to take someone out into the field with me some day and give me some feedback on what they hear / think is annoying.

That's interesting! Thanks for the feedback .. and do report back here when you've done that!

 

[MAvic_South_Oz]

That's interesting! Thanks for the feedback .. and do report back here when you've done that!

Yeah I will do that, in the interest of all.
I do notice a lot of older members on board here too.
Fact. I’m very susceptible to NIHL.
Total bilateral loss is 72% overall with 100% loss in high htz ranges, perfect hearing at lower frequencies.

 

[mfc]

Yeah I will do that, in the interest of all.
I do notice a lot of older members on board here too.
Fact. I’m very susceptible to NIHL.
Total bilateral loss is 72% overall with 100% loss in high htz ranges, perfect hearing at lower frequencies.

Understand the issue. I have a 'notch' at around 4000Hz where I can hear little (probably due to that frequency being the base flyback frequency of displays I helped develop in the 1970s and 1980s). But happily normal/above average at higher frequencies. But this does have the disadvantage that a dentist's drill is way too loud ...

 

[Floater]

It IS local in this context. You're locally cancelling the emitted sound that has known characteristics to prevent it from spreading, the emitter and the ANC system don't move respective to each other.
What you say is applicable to the room-scale noise cancelling scams.

True, the propeller is local; at 200Hz (6,000 rpm w/two blades) the wave length is about five feet. The diameter of the propeller disk is then about 1/8 of the generated wave length. All good.

But what about the phase angle of the noise? If one is in line with the rotation (hovering directly overhead), all is good, but if one is in the rotation plane (hovering in front of you) the phase angle at a given instant will change with the angle of the system. How would one superimpose the "anti-noise" wave to account for this? If ANC transmitter cancelled the waves in one direction, it will double the wave 90° away. So one could compensate at specific aspects, at the cost of being noisier in other, say quiet in front, but loud from the sides.

Be very interesting to see the test setup, assumptions and the test data.

Updating this after sitting down and reading the report (the link at the beginning). I certainly recommend those here give it a quick scan, it is short and has some nice graphics. They do make a critical assumption; "For this study, each engine and its propeller are modelled as a punctual sound source emitting an omnidirectional harmonic pressure wave. ..." Propellers do not generate noise in an "omnidirectional harmonic pressure wave." This would imply that the pressure waves are spherical, that the peak of the wave will be found at a constant distance from the sound source (at least for an instant). Propellers generate a rotating wave that is a spiral, and a steep one in this case at that considering the tip speed is just a couple of hundred feet/second, or ~0.2 Mach so the wave is propagating through the diameter of the propeller tips at about 80º (20º off the radial line through the rotation).

No actual testing or actual test hardware was discussed. This was all theoretical, using a basic assumption that I consider erroneous. Be very interesting to see the test setup, assumptions and the test data.

 

[MPPilot]

if ever perfected this would be a boon to not only the military but peeping toms and perverts everywhere (yes CIA and NSA, that includes you).

 

[mfc]

if ever perfected this would be a boon to not only the military but peeping toms and perverts everywhere (yes CIA and NSA, that includes you).

To be fair, the camera-on-a-long-selfie-stick is almost as bad ... and silent.

 

[DanMan32]

Understand the issue. I have a 'notch' at around 4000Hz where I can hear little (probably due to that frequency being the base flyback frequency of displays I helped develop in the 1970s and 1980s). But happily normal/above average at higher frequencies. But this does have the disadvantage that a dentist's drill is way too loud ...

Maybe the dentist can adjust the drill RPM to your sweet spot.

 

[Drgnfli]

I personally like being able to hear my Mavic...it helps me keep track of it and it's not as though it's loud enough to be obnoxious, I really don't understand the folks that say it's soo offensive, but that's just my take onit...be smart fly safe!

Folks that don't like UAVs to start with will say... "they are too noisy" just so they can complain about them...

 

[DroneToJoy]

Seems that a solution for silent drones or drones that will be much quieter is on its way. See the links below. Anyone aware of this product (shrouds) for props?

Our Technology - Ground breaking audio technology for UAVs

Dotterel has developed a unique audio system. It uses an array of small microphones and a new processing algorithm for end-fire beams. Dynamic adjustable beamwidths can be focused on the target, while rejecting off-axis noise including noise from the drone itself.

www.dotterel.com

How to Make a Drone Quieter [Stealth Mode Engaged!] – Transcend FPV

transcendfpv.com