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Comment by mattivc | Hacker News Reader

I work with nano-UAVs. I am very skeptical that the 40 minute flight time is even close to being real.

Especially with a quadcopter design. They are way to inefficient.

I haven't looked into this drone in depth, but I think it may be feasible. The DJI Mini2, which any civilian can buy for $449, has a similar size, weighs 249g, and advertises a flight time of 30 minutes. (In my experience with the Mini 1, it's plausible).

Side note: the DJI Mini 1 is an excellent drone -- stable flight, great camera, and great range. I wouldn't be surprised if it outperforms this 'Bug' drone by most metrics, except for the critical (at least for military purposes) "not being made by a Chinese company" metric.

It's hard to express how awesome the Mini is. IMO it's an underappreciated technological achievement at the once-in-a-hundred-years level. Only a few years ago, it was hard to get a decent digital camera for $400 and change. The Mini is a decent camera that also happens to fly.

When that realization hit me, it reminded me of the first time I saw a $29 DVD player for sale at WalMart. Some incredible things had to happen to make that possible, almost all of of them going completely unnoticed by almost everyone.

The BAE drone probably costs $50,000 apiece, and doesn't appear to be substantially different from the current-generation (or even the original) Mini.

And the $29 DVD player often had more features than the $200 ones, especially the ability to play other regions discs.

I have to concur. I built many drones with 400$+ flight controllers that look like trash next to my mini 2.

Which drone flight controllers cost $400+??

Apologies as I was ambiguous here. I find myself including both the GPS and flight controller computer/ carrier board in that 400$ price tag. I’m using Hex Cube Orange with Here gps units. This says nothing of cameras, radios, batteries, flight time, and live camera feed/control.

"The BAE drone probably costs $50,000 apiece"

That may be a little high. UAVTek's site says they beat the FLIR Black Hornet 3 bid[1]. Estimates based on US Army budget requests say the Black Hornet 3 is coming in between $15k and $16k per unit[2]. Probably still 5 figures though.

[1] https://uavtek.co.uk/news/uk-mod-acquire-latest-nano-drone-t...

[2] https://www.thedrive.com/the-war-zone/26359/the-pocket-sized...

In addition you have to think of the trade-offs. If the army multiplied the price by 10 to get 10% better performance, that might save a soldier’s life.

Hmm, shades of Kipling‘s Frontier Arithmetic: “four thousand pounds of education/Drops to a ten-rupee jezail”....

That’s based on the value of the whole contract, which will include the costs of participating in trials, demonstrations, training, lifetime service and spare parts. There are likely to be a whole team of personnel dedicated full time to the contract for years, all included.

I have both the Mini and the Mini2. The mini2 is even more impressive. Better camera, better batteries, longer range.

I flew mine today in -15ºC for 35 minutes, and managed a range of 3km.

It's crazy.

That's because of the energy density (per mass) of Li-Ion batteries. You basically hit a wall at 20 minutes that's very hard to push past (it almost feels like a law of physics).

But maybe they're using non-rechargeable batteries: zinc-air or lithium-iron-disulfide (ie. a 'lithium' AA battery) or something else? Trade offs are different for military.

The amount of batteries soldiers need to carry is ridiculous; a 72 hour patrol load out includes up to 25 lbs of batteries already!

Yes but there are no convenient charging points, if the battery runs out then you need to replace it, not charge it. All the more reason to throw used batteries away (they’re cheap and it’s less to carry).

Military radio batteries are typically rechargable and they are heavy.

Based on the info sheet "A quick change battery" would suggest they went for the non-rechargeable route.

I don't think it necessarily means non-rechargeable. Since charging usually takes a long time, generally in the field you carry a bunch of batteries charged ahead of time and swap them as needed.

The classic example of a good military-only battery would be those using molten salts as an electrolyte (typically at 150-500 ºC) [1]. Very high energy density (around 74 Ahr/kg [2] compared to LiPo's ~50 Ahr/kg [3]) and very high power density. Not finger friendly.

[1] http://en.wikipedia.org/wiki/Molten_salt_battery [2] https://global-sei.com/technology/tr/bn76/pdf/76-06.pdf [3] https://blog.ampow.com/lipo-battery-size-chart/

If one could make such a battery small enough for this drone, I expect you would need all its power to keep the salt molten.

Don't a lot of the DJI models have a ~30 minute flight time? Point taken though, that there's a wall we hit with current battery tech.

The DJI drones that can do that are significantly larger. A 250 gram DJI mavic mini can do 30 minutes and with significantly larger propellers.

The efficiency goes down with smaller blade sizes (more losses to vortexes) so from the photo 20 min is the max to expect with regular lipo batteries.

The Mini 2 manages 31 minutes at 249g and it features a 3 axis gimbal for the camera. This military drone doesn't appear to have any gimbal.

Nitpick: plural of vortex should be vortices.

It actually appears both spellings are currently accepted in dictionaries, but in the fluid dynamics literature you will essentially only find "vortices", so that's a much better (more searchable) word to use.

41 minutes of spirited flying with hobby components weighing under 250g:

https://youtu.be/u2v1QLmhNxM

There's no reason to use rechargeables so if non chargeables give them a extra 30% then that would be how they are doing it.

But it will just be off the shelf batteries, so they would exist already on ebay if that's what they are doing.

It says autonomy, not flight time. They may intend this thing to land and remain active as a remote camera for much ot its mission.

In the article there is an image that says "flight times in excess of 40 minutes".

They're claiming flight time - in the battery section of the infographic it claims "flight times of more than 40 minutes".

Tri-blade props are not the most efficient - we use them in racing applications because we want to generate maximum thrust and we don't need more than around 2-3 minutes per battery but we wouldn't use them in an aerial photo rig where we want long flight times - 2 blade props would be the go to. Also the pitch of those blades in the photo are quite aggressive.

I wonder if they have different configurations - as photographed I can easily believe the 50mph top speed with small but high kv (fast but inefficient) motors but I'd expect a different configuration for longer flight times.

From the photo it looks like the battery compartment is shaped for 2 cylinders, its about the right dimensions for 2x 18650 cells but it's impossible to say for sure. That would give up to 8000mah of 3.7v (1S2P configuration) or 4000mah at 7.4v (2s1p). They could be using different chemistry though, e.g. I usually fly LiHV cells which have a higher nominal voltage in the same pack size & weight - you do get very slightly more watt hours out of those packs (not as much as the numbers would suggest).

The given all up weight looks plausible based on the size of what's shown and the weight of 2 cells.

In a military context, "flight" can mean "mission". I only suggest that something may have been lost in the language. I find that easier to believe than this thing hovering over a battlefield for 40 minutes.

On the other hand if it includes significant landed time as a fixed cam, 40 minutes seems miserably short.

Drone racer here, too! 18650s are amazing as far as power density is concerned.

Here's a guy who takes a 3" 1S quad, adapts an 18650 and gets 29 minutes of flight time: https://www.youtube.com/watch?v=BOZStU-QCSc

There's a few others, and in fact I considered doing this myself! But, I'd get bored of slowbelly 'flying' after about 15 minutes. I like to go fast.

I completely believe 40mins of flight time if you had actual resources to assign to this. Imagine using the 18650 as the frame and strapping motors to sticks, or other crazy ideas to bring weight down and time up.

Since you seem to have some expertise in this area, I am going to use the opportunity to ask a bit of a diagonal question I've wondered for a while:

I've seen claims about increase in airflow from bladeless fan designs (I know it's a bit of misnomer, as the blades are just hidden) for home applications. Is there a reason bladeless designs haven't been used in the UAV realm? I assumed the claims were just marketing, or the weight increase offsets the effeciency, or something like that, but thought I would ask.

Well out of my wheel house unfortunately but i do know that “air multiplier” marketing speak is called something like the coanda effect.

A Tom Stanton video with his coanda effect quadcopter https://m.youtube.com/watch?v=Irp_vnmUWZ4

are you talking about ducted fans? if so I've wondered the same thing. here's a plausible answer: https://aviation.stackexchange.com/questions/36726/why-dont-....

The ducting 'shadows' the blade during forward flight, massively reducing efficiency. During hover they can help though.

I dont find it that unbelievable, there are a number of youtube videos of hobbyist grade quadcopters with what I believe are larger motors running 20-30 minutes on a pair of 18650 cells albeit without any autonomous capability.

https://youtu.be/BOZStU-QCSc

Hahah that's fantastic, how that thing even takes off with a 1S2P 18650 I'll never know. That's 100 grams just for the batteries.

It's all about the cube-square law, the same reason a butterfly can remain airborne for hours or days on a few milligrams of chemical energy.

Getting RC aircraft to fly in the more laborious, sedate manner of a full-size aircraft instead of like an insect fluttering through the wind is something of a challenge for scale model builders. When you build an airframe around tiny batteries as a design constraint, expectations from larger aircraft don't carry over well.

Sure, but I'm an RC aircraft builder so my expectations are calibrated for that. Motors that small have a hard time lifting 180g at 1S.

I agree the photos are probably just mockups. No way they would be using that sort of prop. That said, Li-FES2 primary cells (at 400Wh/kg) have well over twice the energy density to LiPo/LCO rechargables (at 190 Wh/kg). If I can make a custom 7" bi-blade quadcopter fly for 30 minute, 40 minutes is doable with better battery density.

In my own builds it is much easier to get long flight times with larger props but that is probably on account of the lesser need for exotic material science at larger scales.

> I agree the photos are probably just mockups

The article makes it sound like they've got a whole bunch of these in active use by the Army (albeit for testing), so it'd seem a little odd to have a picture of a mockup. Maybe, I guess, but I'd have the assumption be that this is the real thing.

One thing people are not discarding is cost.

Given cost is not a problem, is it possible to get 40m flying time using exotic battery and ultra high strength/weight ratio materials?

I feel like the cost is deeply embedded in our psyche and people are comparing a military nano drone with DJI mini2 with entirely different engineering envelopes to work in.

DJI mini2 is made in thousands if not millions of quantities. There is so much cost optimizing. Even turning a part around is optimized because that’s more time to assemble.

Here's a hobby drone getting 41 minutes of spirited flying, with live HD feed, and it only weighs 50g more: https://youtu.be/u2v1QLmhNxM

It says "a quick change battery provides flight times of 40 minutes or more".

In other words, not on a single battery/charge.

Unlikely. It also directly says 40 minute battery life. If changes extended it, it would be unlimited.

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