9 ms·
Toroidal propeller allows a drone to operate more quietly [pdf]
- pacbard 4y agoI was wondering about performance, but I cannot find any data on how these toroidal propellers are preforming compared to traditional airblades. The two-pager just says: > Achieves thrust comparable to that of a multirotor drone propeller which isn't saying anything. My gut reaction is that these propellers require more material than traditional ones, which makes them weigh more, which should make them perform differently than traditional propellers. At a minimum, they should spin slower and/or strain the motor more for the same RPM. Maybe I'm completely off base. I found this other website [1] which reports thrust differences between traditional and toroidal propellers for boats. At least under the conditions reported in the graph, it seems that toroidal propellers might outperform traditional boat propellers. Again, I'm not sure how much air behaves like water. My layman understanding of fluid dynamics tells me that air is different from water just because air propellers don't look like water propellers (e.g., they require longer, thinner, blades; air engines need to spin way faster than water ones; water probably requires more torque) and you can't turn a boat into a helicopter if you turn it sideways. [1]: https://newatlas.com/aircraft/toroidal-quiet-propellers/ https://newatlas.com/aircraft/toroidal-quiet-propellers/
- p_l 4y agoThe main difference is compressibility, to the point that liquids are commonly used as air analogs in wind tunnels. Ship propellers end up working in different density material, with also different speed requirements and that's why they are differently shaped even if the equations are the same.
- chrisdalke 4y agoRelated thread from a few months ago discussed the Sharrow propeller mentioned in this article, which applies the same concept to boats: https://news.ycombinator.com/item?id=33949895 https://news.ycombinator.com/item?id=33949895 The difference in geometry for air vs. water propellers has a lot of complicated reasons but above all the fluid density of water is about 1000x air: ~1000kg/m3 for water vs ~1kg/m3 for air. Air propellers are optimized for very high-speed operation which is needed to produce any significant thrust in low-density fluid. Boat propellers are very "built up" and physically sturdy since they are used in low-speed operation with high torque. I have seen people use RC airplane propellers in water for small autonomous boats -- They do work but look very comical (think 10x the size of a boat propeller, running at 1/10 intended speed) Cavitation effects -- microscopic bursts of vacuum at low-pressure boundaries along the propeller -- come into play much sooner than with air propellers.
- someweirdperson 4y ago> Cavitation effects -- microscopic bursts of vacuum at low-pressure boundaries along the propeller -- come into play much sooner than with air propellers. In liquids vapor-bubbles of the liquid (not vacuum) are caused by low pressure (or high temperature, boiling), and cavitation is the collapse of the vapor back to liquid state when pressure rises (or temperature drops). Propellers in air do have issues with the speed of sound, but that's a different matter than cavitation in liquids.
- chrisdalke 4y agoThanks for the corrections: So the bubbles are not a vacuum but low-pressure vapor and cavitation is the name for the collapse, not the bubble itself. And this can only happen in liquids where there is a potential phase transition. I've got a little marine knowledge but my physics is lacking so I appreciate the clarification! I assumed cavitation had similar parallels in air propellers with high tip speeds (as you approach the speed of sound) but seems that is a different effect?
- aqfamnzc 4y agoI would say it's still a vacuum in the more common meaning of the word: A reduction in pressure, not necessarily a complete vacuum.
- peepeepoopoo3 4y agoThey should produce more thrust per a given unit of energy than a conventional propeller by eliminating induced drag. Winglets on jet airliners work by the same principle, converting the wingtip vorticity, due to the pressure difference above and below the wing, into an apparent forward thrust.
- Eddy_Viscosity2 4y agoPropeller efficiency (both and air and water) are factors of torque, RPM, and advance speed (effectively the speed of the vehicle). You can't be efficient for all conditions. For example, a tug boat needs really high thrust at low and even zero advance speeds as it pushes up against a giant ship like a tanker. That design would be very different from what you'd need for a high speed boat with high advance speed. Similarly, props for drones can be designed for efficiency at hover (zero advance speed), or for going fast. Designing for noise will also have trade-offs for different conditions. Like it might be really quiet AND efficient in hover, but then be crap at when moving forward at high speed. Efficiency is always about trade-offs.
- Tostino 4y agoAnd one of those tradeoffs can be complexity. For example, you could integrate a variable pitch propeller with a control computer and your throttle to ensure you are always at the highest efficiency possible within the geometry constraints of the propeller.
- mschuster91 4y agoIn some applications warfare and anything in residential areas (e.g. thermal or roof damage inspection), I'd expect that pilots will gladly go for the lower noise even if it means a bit less flight time.
- ilyt 4y agoI'd expect commercial drone pilots to not give shit unless law tells them to give shit.
- mschuster91 4y agoLess noise makes for less complaints by neighbors during longer flights in my experience.
- ilyt 4y agoRight, why would a contractor care? You flying your own drone in backyard, sure.
- SkyPuncher 4y ago> At a minimum, they should spin slower and/or strain the motor more for the same RPM. Maybe I'm completely off base. Only when adjusting RPM. At constant RPM, a heavier properly will actually reduce impulses to the motor.
- someweirdperson 4y agoSomeone simply needs to invent a motor that provides constant torque through a full revolution. To control the amount of thrust changeable rpm is needed, or a changeable geometry, like pitch. I imagine the latter wouldn't be easy with the toroidal propellers.
- eurasiantiger 4y agoYou could mount each toroidal blade on an angled pivot and use rpm control to change the pitch. This enables thrust vectoring.
- taneq 4y agoThis might be what you're referring to, but Tom Stanton built a swashplateless 4 axis R/C helicopter (albeit not with toroidal blades) based on this principle: https://youtu.be/d80oXSCcHTk https://youtu.be/d80oXSCcHTk
- morcheeba 4y agoI too was also expecting a same-thrust controlled study. From the fundamental frequencies in the two graphs, we can see the toroidal propeller (72 Hz) is spinning slower than the traditional (88 Hz). Assuming, of course the same fundamental vs. rpm relationship -- the toroidal has twice the number of "blades" as standard, but I'm not sure how that manifests sonically. I wonder how a 3-blade or 4-blade propeller would compare to the standard 2-blade. Also, a big difference between quadcopter and other propellers (boat, plane, heli) is that they use change speed to carefully control thrust - most quadcopters use fixed pitches. Adding mass to the propeller can reduce responsiveness, which means less stability ... but I don't know enough about the magnitude of this effect to know if that's a problem.
- thatcat 4y agoair is compressible, water is not. This effects not only the mechanics, but also the acoustics. Air is actually a much worse conductor of sound so making a quieter propeller should be easier. The principle of using a toroidal shape to reduce creation of vortices and thus sound should hold for either medium and may even be more efficient since a vortex causes drag and they are known to improve efficiency in boats.
- falcolas 4y agoAt least this PDF shows dB graphs, but the graphs are so noisy that you can't make much out of them. They have fewer harmonic peaks, and the peaks do seem to be up to 10 dB smaller. But the average appears to be pretty similar. Again, hard to be concrete on the differences given the noisy data. 10 dB is a lot (2x the sound pressure) since dB is an exponential scale, but at the peak of 55dB, you're still below the range of a "normal conversation".
- ec109685 4y agoThey claim where the peaks are is less annoying to humans.
- irjustin 4y agoYeah this is when I don't like it. I can't tell if this is truly an improvement. The graph definitely looks tighter, but the overall level appears the same? I can agree it is "less annoying" but if the loudness is effectively the same then I don't think it's truly an innovation.
- bbhi 4y agoI wonder how the acoustic measurements were taken. From my own experience propeller noise is highly direction-dependant. For a fair comparison a lot of angle-dependant measurements would have to be considered.
- keizo 4y agoWow like Sharrow boat props.
- deleted 4y ago[deleted]
- moffkalast 4y agoWas about to say this too, didn't they already have a patent for this already or does it only cover boats?
- finnh 4y agoAlso today: https://news.ycombinator.com/item?id=34571282 https://news.ycombinator.com/item?id=34571282 and a couple months ago: https://news.ycombinator.com/item?id=33949895 https://news.ycombinator.com/item?id=33949895
- moistly 4y agoThese previous discussions have links to papers and videos that are convincing. The sound reduction is astounding. The power graphs are impressive. The price of the boat propellers is gobsmacking… but if the efficiency claim holds true, will easily pay the upgrade, and the dolphins & whales will be ever thankful.
- zawy 4y agoBe careful of the boat propellor claims. For example, they filmed the regular prop in slow motion to hide that it was going at a much faster speed that caused more cavitation to make it look worse. Also when they claimed it needed a LOT less steering, I'm extremely skeptical because that should be mostly caused by the boat riding higher in the water at a faster speed. Also they disabled comments on videos. https://youtu.be/_KkIqC7arnU?t=74 https://youtu.be/_KkIqC7arnU?t=74
- anigbrowl 4y agoINTERESTED IN ACCESSING THIS TECHNOLOGY? Contact the Technology Ventures Office tvo@ll.mit.edu LOL good luck trying to corral that. These will be an $11.99 upgrade on Banggood within 3 months.
- DennisP 4y agoEspecially since they've barely started optimizing it. Should be pretty easy for other people to achieve similar or better performance. > the team's best-performing B160 design was not only quieter at a given thrust level than the best standard propeller they tested, it also produced more thrust at a given power level – pretty remarkable given that standard props have more than a century of development behind them and these toroids are at a very early stage, with plenty of optimization yet to come. https://newatlas.com/aircraft/toroidal-quiet-propellers/ https://newatlas.com/aircraft/toroidal-quiet-propellers/ This article also suggests that 3D printing would be the best way to manufacture these. Just need a file on thingiverse.
- steve_adams_86 4y agoI thought it would take a really, really long time for additive manufacturing to become commercially relevant, but I guess people are building rockets with it now. It isn’t about to replace injection moulding and casting completely, but it’s wild that a file on thingiverse can actually be meaningful now. A toroidal prop could absolutely be shared and optimized there, and metal printers will rapidly improve and yield better products. I won’t have one in my garage any time soon (I can still hope), but I can already hire someone else’s printer online. I wouldn’t be surprised if toroidal plastic props for drones end up on there in a usable state fairly soon. What a cool thing — I wouldn’t have thought this would be possible in my life time when I was a kid.
- nabla9 4y agoIt seems to have smaller diameter and more surface area than same sized normal propeller. This means it could have lower RPM for same power and generate less noise. Are they better than long-screw propeller with the same diameter, area and RPM?
- Havoc 4y agoI can totally see this taking off (pun intended) - has sufficient weirdness factor that marketing teams can leverage it as a "stealth" design while actually being somewhat credible Wouldn't be surprised if we see this on a major commercial drone soon
- hdevalence 4y agoUnfortunately for those who care about noise reduction, LL patented the design, preventing its widespread use.
- digdugdirk 4y agoThis seems to be the patent in question: "Claims: 1. Toroidal propeller comprising: a hub supporting a plurality of elongate propeller elements in which a tip of a leading propeller element curves into contact with a trailing propeller element to form a closed structure with increased stiffness and reduced acoustic signature. 2. The toroidal propeller of claim 1 having two or more propeller elements." That's it. Honestly, that's pretty easy to get around, even without arguing against its validity from prior art in the submarine world.
- IshKebab 4y agoHow would you get around it? Sounds fairly solidly written to me.
- superjan 4y agoPerhaps if your design does not improve stiffness? The way it’s phrased suggest that that is a necessary part of the design.
- IshKebab 4y agoI don't see how you could use this design without it improving stiffness. And that isn't really a workaround - you're giving up half the benefits of doing it in the first place!
- brookst 4y agoSomething other than a toroid? Maybe an 8 shape?
- digdugdirk 4y agoThe fun thing is just going word by word and thinking up alternatives. So... Toroidal: - What adjacent shapes will provide similar efficiency without technically being a toroid? Hub: - Can we connect it to a "shaft" instead? - What about adding a gearbox in between? Tip connection: - This specifically calls out connecting the tip of a leading propeller to a trailing body. This is where I'd probably focus first. Can you reverse it to connect a trailing propeller element to a leading element? Do you connect them back to the hub instead? What about a secondary/tertiary element? Patents are more of a threat than a firm legal protection. A large company can tie up a small business in court until they're bankrupt, so it's really a matter of cost/benefit and how close you want to get to the fire you're playing with.
- b3morales 4y agoInteresting development, but I'm not certain that I want drones to be quieter. They're not that noisy now, and making them silent would be sort of like taking the bell off the cat.
- macintux 4y agoI was at a ceremony a few years ago for victims of a workplace shooting. There was a drone overhead, I assume one of the local news organizations taking photos, and the noise was quite distracting for such a somber occasion. Whether or not there should have been a drone overhead, if there's going to be one at a memorial service I'd want it to be quiet.
- rgmerk 4y agoI’m pretty sure Wing, Walmart and the other very well-capitalised companies developing drone delivery services want quieter drones.
- monocasa 4y agoSort of reminds me of the design of Navy submarine propellers (there known as 'screws'), optimizing for similar noise dampening properties. For a very long time the design of modern submarine screws was one of the closest guarded secrets of submarine design, with submarines docked having cloth shrouds over the screw even in classified facilities. AFAIK, those weren't torodial, but they had similar long arcs of the blades. For more information: https://americanhistory.si.edu/subs/anglesdangles/taming.html https://americanhistory.si.edu/subs/anglesdangles/taming.htm...
- WirelessGigabit 4y agoThat's funny, because I remember watching a documentary about some form of caterpillar drive.
- ChrisMarshallNY 4y agoThat was the one that was "narrated" by Sean Connery?
- froh 4y agothe hishtorically accurate shientific account of a rushian boat being reshcued?
- BuckyBeaver 4y agoAnd all the while, the captain had a mouthful of shtew.
- jonstewart 4y agoThe order ish, engage the shilent drive.
- dylan604 4y agoOne ping only though
- stareatgoats 4y agoThe flying cars that are in development currently are largely mega-sized drones. Noise is one of the major obstacles to acceptance. Rather than reshaping the propellers I'm thinking active noise reduction might be the solution. Flying cars that whisk back and forth with a whisper? Could be!
- cush 4y agoExactly. Drones are so useful, but they screech like banshees, making them effectively useless for consumer applications within 200ft of any humans. Basically only aerial photography.
- klipt 4y agoI assume jetpacks have similar issues
- BuckyBeaver 4y ago"The flying cars that are in development currently are largely mega-sized drones." Mmmm, I'm not aware of any that are. The Terrafugia wasn't, but it has been abandoned apparently. The Samson Switchblade is a three-wheeled car with a pusher-prop design: https://www.samsonsky.com/models/ https://www.samsonsky.com/models/ The three-wheel strategy is pretty smart, because the vehicle can be licensed as a motorcycle and doesn't have to have all the heavy safety equipment of a car.
- cush 4y ago> I'm not aware of any that are 1. BCL 2. Boeing AFS 3. Kittyhawk 4. Ehang 5. Workhorse The list goes on... You might not have heard of them as they're absolutely unmarketable because of the unbearable noise they make
- BuckyBeaver 4y agoNone of those is a flying car. Flying cars are wheeled vehicles that can drive on the ground like a normal car, but also fly.
- compumike 4y agoVideo demo (with audio) comparing side-by-side with a conventional propeller at timestamp 1:12 - 1:22: https://twitter.com/MITLL/status/1611438712683958306 https://twitter.com/MITLL/status/1611438712683958306
- O__________O 4y agoAppears primary source of sound in helicopter blades is from blade-vortex interaction: https://wikipedia.org/wiki/Blade-vortex_interaction https://wikipedia.org/wiki/Blade-vortex_interaction Likely that even a non-toroidal half-crescent shaped tips would significantly reduce sound levels. Here’s comparable design: https://youtube.com/watch?v=dBS1NRsYuF8 https://youtube.com/watch?v=dBS1NRsYuF8 Possible even a vortex diffuser similar to those found on submarines might help too.
- jbay808 4y agoThis also makes me wonder whether, instead of an entirely toroidal propeller, you could just put a small, appropriately-shaped toroidal loop at the tip of the prop.
- beambot 4y agoVery curious, since there were commercialized versions reported back in 2019. https://www.boatindustry.com/news/32122/sharrow-amazing-propeller-geometry-to-optimize-performance https://www.boatindustry.com/news/32122/sharrow-amazing-prop... https://boattest.com/Sharrow-Propeller https://boattest.com/Sharrow-Propeller And there are examples from online forums dating back to 2012: https://www.boatdesign.net/threads/strange-propeller.44740/ https://www.boatdesign.net/threads/strange-propeller.44740/
- BuckyBeaver 4y agoAll of those differ from the one in this ad.
- beambot 4y agoThey are very similar, just with more toroids attached to the central shaft. They also render the patent completely invalid by way of prior art.
- maxerickson 4y agoFiling date was November 2017.
- beambot 4y agoIf you look at computer case fans, you can find commercial examples dating back to at least 2012 that are specifically meant to curb noise: https://www.overclock.net/threads/noiseblocker-nb-eloop-120mm-bionic-loop-propeller-fans.1289723/ https://www.overclock.net/threads/noiseblocker-nb-eloop-120m...
- maxerickson 4y agoYeah, I missed the 2012 in the other comment.
- bdowling 4y ago
- zawy 4y agoQuieter means more energy is possibly available for more thrust. I noticed SpaceX rockets sound a LOT more quiet and smooth compared to older rocket videos. Notice upward tilting winglets on the tip of large airplane wings these days are to reduce the same vortices that are seen on propellers (wings work on same principle as propellers) in order to be more efficient and more quiet is just a side effect.
- ilyt 4y agoMight be but they're not mentioning efficiency at all, which you'd think they would if that was the case (more efficient AND quieter would be even bigger selling point)
- voxelghost 4y agoIn many ways the toroidal prop is a more of a four-blade than a two blade, so it seems a bit disingenuous to compare it to two-blade DJI variants. (And as some other poster mentioned as well, I would like to see a comparison to prime prime number bladed props.) Finally I would like to see it compared to shrouded props.
- Maursault 4y agoNow fix single engine planes, helicopters and lawnmowers.
- LarryMullins 4y agoCould these be safer than conventional propellers? From the side, they seem less "sharp" than a conventional propeller, but they're still spinning pretty fast.
- CamperBob2 4y agoSo, this seems like the performance would be similar to that of a ducted fan, both acoustically and aerodynamically. Would it be better in in either respect? Worse? By how much?
- phs318u 4y agoThere was an article here a couple of months ago [0] on Sharrow Engineering's propeller, which looks very similar. Sharrow were granted their patent [1] earlier the same year as MIT's [2]. I wonder if this is yet another case of people independently reaching similar conclusions based on other work (tip vortex and cavitation research)? [0] https://news.ycombinator.com/item?id=33949895 https://news.ycombinator.com/item?id=33949895 [1] https://patents.google.com/patent/US9926058B2 https://patents.google.com/patent/US9926058B2 [2] https://patents.google.com/patent/US10836466B2 https://patents.google.com/patent/US10836466B2
- aleksandarbos 4y agoi'm happy for the science, and super sad at the same time for the people especially UA situation...