Researchers build a solar-powered hovering drone that weighs only 9 mg | Hacker News Reader

Researchers build a solar-powered hovering drone that weighs only 9 mg

arstechnica.com

95 pointsthunderbong45 comments

Every time I see one of these drone tech demonstrations, I can't help but wonder how they will be adapted for warfare.

This one... I'm seeing flying solar powered landmines (skymines?) that can flutter around an active combat zone aimlessly for hours until it detects a personnel target and bops them near the temple with a small round. I wonder if there are any actual benefits over just putting a solar panel on a regular quadcopter and having them charge a battery, maybe staying stationary in field or ditch near the road, relocating once in a while and waiting for a target.

Slaughterbots, assemble! https://www.youtube.com/watch?v=9CO6M2HsoIA

https://en.m.wikipedia.org/wiki/Loitering_munition

> and bops them near the temple with a small round.

The smallest commercially available centerfire cartridge was the 2.7mm Kolibri round, which was too underpowered to inflict significant damage to a person other than maybe if you hit them right in the eyeball. That round weighed 5.3 grams while the OP article talks about a drone weighing 9 milligrams.

https://en.wikipedia.org/wiki/2mm_Kolibri

This drone just doesn't have enough payload for explosives/bullets to be useful against a person. More plausible is some sort of biological attack, like a nerve gas, although you'd be pushing the limits even there. The LD50 for sarin gas is 1 milligram, and you would need a delivery mechanism.

If you look carefully you see that they actually started with a much bigger drone and then shrunk it down. The minimum is 9 mg (that they could build) but it sounds like the design can be expanded to almost any size. A more obvious question would be is there any functional difference between this and a balloon.

Thanks for the insights on that half of the hypothetical! 9mg is indeed wild, and made me go check the article... The article is a bit confusing, or I'm missing some nuances. It seems to talk about 2-3 drones, I think, mentioning weights of: 9 mg, 1.13 g, and 4 g. I think the one in the video is not the 9 mg version.

From TFA:

> The total system required just over half a watt of power to stay aloft. Given a total mass of 4 grams, that works out to a lift-to-power efficiency of 7.6 grams per watt. But a lot of that power is lost during the voltage conversion. If you focus on the motor alone, it only requires 0.14 watts, giving it a lift-to-power efficiency of over 30 grams per watt....

> But one thing they don't have to optimize is the vehicle's size since they already built a miniaturized version that's only 8 millimeters high and weighs just 9 milligrams but is able to generate a milliwatt of power that turns its propeller at over 15,000 rpm.

9mg is just the smallest version they managed to make. Based on the size of the solar panel in the video, there's plenty of room to scale to tens of grams per drone. And this is a laboratory proof of concept, not a well funded weapons prototype.

I suspect a 5.3 gram shaped charge detonated right near the head will do much more damage.

Why do you think a shaped charge is the correct ordinance type in this hypothetical?

I think it could better penetrate the skull.

What’s the advantage to a 5.3g shaped charge here?

There’s already drones loaded with Hexanitrohexaazaisowurtzitane, such as the AeroVironment Switchblade.

But I suppose something that can fly all day… loitering … is even more terrifying if applied

Not the slaughterbots bullshit again. If someone wanted to replicate the slaughterbots video, they would use the small drones only for face recognition to find the target and then eliminate the target with a small mortar from a bigger drone above. You know, the boring stuff that terrorists have already done in the past.

The rudimentary stuff terrorists are stuck with doing. Slaughterbots are more terrifying because they can track you in all the enviroments a mortar can't reach.

Attacking with bacteria/viruses has the advantage that the payload can grow bigger by itself when infecting.

The gas ganisters would be too heavy. A better payload is razor blades / needles coated in some potent venom poison, like tetrodotoxin ricin or cone snail toxins. Launch 1000 of these drones and you can kill an army in no time.

Black Mirror S03E06

As others have said, it isn't a delivery platform. It'd do much better as a geostatic surveillance web, radio jammer, fire support, etc. Things that drones already do but set-and-forget.

Except that this one only hovers, so is wind-borne in terms of trajectory. It's a while away from being as useful as a real drone.

I wonder how feasible would be adding an actuator that slightly tilts the propeller axis, driven according to the direction from which the drone is receiving sunlight, so that the drone would turn always to the sun, remaining airborne as long as it can follow its light.

I think you might be describing a (photosynthetic) moth!

> remaining airborne as long as it can follow its light.

Given how fast the biggest free source of light moves relative to the ground, I don't think it would help outdoor operational times that much unless it can travel at speeds closer to Mach 1.

... Well, closer to the equator anyway, but I suppose it could stay aloft longer near the poles.

Every time war gets automated more or mil-tech improves, the value of information and information processing goes up, and so does the ability to mess with the enemy's information.

No point in having an ICBM unless you know where to point it and how to guide it there. No point in having a loitering kill-drone swarm if you can't keep it from getting hacked.

Paper link, includes videos of the prototypes:

https://www.nature.com/articles/s41586-024-07609-4

https://archive.is/Yi8Fn

...but that's still paywalled.

Still paywalled.

Here's the unlisted demo video: https://www.youtube.com/watch?v=LBoee1l4OXo

This is probably not the same paper, but it's by the same author on this topic:

https://assets-eu.researchsquare.com/files/rs-3909633/v1_cov...

"Sunlight-powered hovering of an ultra-light micro aerial vehicle" (PDF)

This looks like the free preprint of that paper:

https://www.researchgate.net/publication/378206931_Sunlight-...

Localizers (from A Deepness in the Sky)!

> is able to generate a milliwatt of power that turns its propeller at over 15,000 rpm.

How do you every do 15k rpm on 1 milliwatt? This sounds very odd to me, because unless You're in vacuum this is going to be a lot of air resistance..

By being very small. 15k rpm is 250 hertz. This is slightly lower than the lower bound wing frequency of a female mosquito, which can hover using approximately 100 μW - a tenth the power of this drone.

Citations: https://humbug.ox.ac.uk/sound https://pubs.aip.org/aip/pof/article-abstract/36/2/021907/32... https://www.dupagehealth.org/DocumentCenter/View/147/10-Thin...

I'm aware of several past solar-powered airplanes. Is this the first solar powered rotary-wing aircraft? (Looking for 'solar drone' mostly turns up drones used to clean solar panels)

I would guess the key here is the "researchers reported that they had developed a drone they're calling the CoulombFly, which is capable of self-powered hovering for as long as the Sun is shining."

It only seems to operate off the solar power, no additional power. So the light keeps shining, the drone keeps flying.

Right, I'm can see that. I'm asking, is this the first example in the solar rotary-wing (miniature) aircraft category, or are there any other prior examples?

Also.. ground effect?

For those curious about solar powered fixed wing airplanes:

https://en.wikipedia.org/wiki/Airbus_Zephyr

> One Zephyr can replace 250 cell phone towers. It can be used to perform intelligence, surveillance and reconnaissance (ISR) with a wide visual payload coverage of 20×30 km (12.4×18.6 mi) and can be equipped with radar, LIDAR and infrared technologies.

Article says 4g title says 9mg

> However, the design can be miniaturized, and the researchers built a version that weighs only 9 milligrams.

Ars A/B tests their titles so I don't know if the submitter editorialized or if they saw a different title than the rest of us, but the text of the article does include building a 9 mg version.

Interesting. Thanks for clarification

A/B test or not, 9mg is impossible. That would be half the mass on a grain of salt.

At those length scales the interesting forces at play are not fluid mechanics, but capillary forces and surface tension. It also trivially easy to make - just rip a piece of gold foil weighing 9mg

A mosquito weighs 2.5 milligrams. It also has almost exactly the same hovering power to weight ratio. At 8mm high it is indeed a very tiny "drone", and exceedingly fragile, but it is certainly not impossible.

The second and penultimate paragraphs both explain that.

Only? Can it carry any extra onboard chips and sensors?

Ever heard of wind?

Not remotely controlled or autonomous. It's cool but it isn't a drone.

>9mg

Yeah, just make stuff up...

Agreed. In one sense it's trivial - just publish a spec of dust.

On the other, any non trivial mechanical system at those lengths scales is dominated by surface forces and they hardly care to discuss "easy" problems like voltage converters.

Video: https://www.youtube.com/watch?v=LBoee1l4OXo

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