Tom Stanton's supersonic trebuchet breaks sound barrier with gravity alone | Hacker News Reader

Tom Stanton's supersonic trebuchet breaks sound barrier with gravity alone

techeblog.com

293 pointsThorondor109 comments

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Here's a direct link to the video, to avoid the blogspam cruft...

https://www.youtube.com/watch?v=Co57SfcT-h0

To the blog's credit the video is right there at the top of the blog.

It was still completely encrusted in crap, however.

Still, why link some blog post about it instead of the actual source.

Because HN will downvote videos regardless its quality.

The amount of YouTube spam has really made submitting YouTube links just about anywhere a bad idea.

His trebuchet launched a 4 gram projectile at 776 miles per hour.

That's obviously extremely lightweight for trebuchet payload, but for comparison, his projectile is approximately 62 grains so approximately twice as heavy as 30 grain high speed 22LR rounds. And approximately 1.5 times as heavy as 40 grain subsonic rounds.

What does grains mean in this context?

It's a unit of mass used in the firearms world

It’s a super old unit of measurement for mass [0], idea being that a “grain” is a single seed of wheat etc.

1 gram is a little over 15 grains, and there are 7000 grains per (avoirdupois) pound.

0: https://en.wikipedia.org/wiki/Grain_(unit)

325 mg aspirin pills were originally 5 grains. A carat was 4 grains. The unit was used by apothecaries, jewelers, and bullet makers.

another way for america to avoid the metric system at all costs

No it's an old unit that's stuck around in the firearm world in basically every country. EU bullet makers specify their bullet weights in grains too.

The more important point, I think, is that it means that the trebuchet is lethal with similar range to a handgun.

This guy absolutely amazing to watch. He also has a 2nd channel that I only found out a few weeks ago: https://www.youtube.com/@TimStation

Not only is it a funny name it also appears in my subscriptions list alphabetically right below the main channel.

His dyneema driven drum is eerily similar to the dyneema driven drum (called "snek") https://rowingbike.com/nl/model/thys-222-revolver#content-7 on the Thys rowingbike https://rowingbike.com/nl/model/thys-222-revolver

Also (mentioned by Tom), this elastic-powered supersonic trebuchet is an excellent video: https://www.youtube.com/watch?v=gdXOS-B0Bus

the "shot you've been waiting for" was sort of anticlimactic, but the two plywood arm shots after show what it actually sounds like. I think the grass and tree dulled the sound a lot on the metal arm.

I actually have a camera that can shoot that at high speed (1200fps), but i'm sure other people have better cameras these days, mine has very low resolution.

Scientific research systems like the SCARF achieve 156.3 trillion fps but at greatly reduced spatial resolutions.

Is that the "nuclear potato cannon" one?

Slow Mo Guys have a Phantom that rocks up around 1.5 million FPS. They've used it to show how glass cracks etc. when you get to that speed though, you need a LOT of light, and a very low resolution.

i dont imagine the low resolution is per se essential the same way the light is. you could maybe figure out ways of syncing the data collection to match each other at that high of speed

It is because the main limitation for high speed digital video is the bandwidth of the pipeline from sensor to storage. Lowering the resolution increases the number of frames you can shove through the X Gbps pipe between the photons hitting the sensor and the highspeed memory the camera is buffering into.

That device is so much more scary! Both really demonstrate the ridiculous amount of energy stored in a pinch of gun powder. And I presume gun powder is quite inefficient at driving the projectile, too.

I’m not sure dropping 50 kg 4 feet… is my idea of demonstrating the ridiculous amount of energy stored in something…

Well, let that drop on your feet. Or have those fat rubber bands slap you in the face... The small pinch of powder in a cartridge got the same punch.

It's not a nuclear bomb obviously, but I feel you would be just as dismissive, anyway.

This would qualify more as a Ballista than a trebuchet

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

No it wouldn't... the projectile is still launched by the same angular motion of an arm and a sling basket the power for the rotation just comes from a different source.

How do you responsibly test something like this? The payload isn't going to follow a ballistic trajectory, it's going to follow an aerodynamic one. You'd probably have to design something special to load into it to aim the damned thing.

Which is a road trip to some place very empty in something like a 180º arc. Maybe 225º.

It's shooting 3d printed balls, I imagine they don't stay supersonic for very long. Significantly less dangerous to others than driving a car.

You'll shoot your eye out, kid.

It's absurdist to be concerned about this and be okay driving a car from a total harm to society perspective.

Merry Christmas

Heartily disagree. It's the Frankenstein problem.

As an engineer, if you can't even start a process with sobriety, rigor, and safety in mind, that cavalier attitude only amplifies as you go down the road from experimentation to design to unleashing your ideas onto the public.

It's a harbinger of what is to come if you're being a suicidal idiot during the prototyping phase. If you don't even have respect for your own safety...

In terms of safety to me and others this endeavor is far below what is societally acceptable and if you think otherwise you are bad at evaluating danger.

Yes. That’s why he does it in a large open field where there are no eyes in vicinity. He has a trigger mechanism where he is standing several feet away from the side.

And he uses light weight biodegradable plastic instead of steel balls.

Most of his projectiles land in the ground not too far away.

Responsible engineering.

He has fairly specific mechanically timed release control over it — within 0.5 degrees.

But he also used an extremely lightweight ball projectile — a few grams of 3D printed plastic — because he was only interested in the launch speed. And he pointed it in a direction where there were no people for miles.

He explains that the field he is shooting towards is over 5km of empty field. He also started his tests with much lower weight and speed to ensure proper behavior before getting up to full speed.

Very early in the video, he explains that while previous builds used steel ball-bearings, that's not responsible at these energy levels, so he switches to lightweight balls made of biodegradable plastic. There's comparatively little energy in the projectile after release, and it's only supersonic for a few feet.

Further, you test in an enormous empty field, as he's doing.

One possibility is to mount the trebuchet on a tiltable platform and tilt it to a suitable elevation, say 45 degrees.

Why? The release angle is fully controlled by design of the mechanism if you wanted to fire it into the ground for safety you could just advance the release timing by a few degrees.

> How do you responsibly test something like this?

Into the ocean, I would hope

Sir, the orcas have declared war on California.

Seems like such an advance in this ancient technology. It would be really cool to see it applied in interesting ways.

I really wonder just how effective this could be as a defense system .. the mind wanders with every update Tom makes .. I imagine an aiming/targetting system would make this an effective, easily replenished, low-resource weapon system for some applications. Attacking feral animals, perhaps?

How could an auto-loader work for this .. I'm sure there's a means.

Another thing that I keep thinking about, is whether this would be an effective way to launch seed-bombs, or deal with avalanche conditions on a mountain without requiring fire-arms training.

A truly fascinating bit of engineering. I hope to see it evolve into an effective delivery mechanism.

I also loved the video. But I'd think if one wanted to deploy "simple" mechanical projectile weapons at scale, pneumatic launchers would be easier, more compact and more reliable (way less cool-looking and operating, though!).

like a potato cannon?

I helped design the "reloadable" part of a golf-ball shooter that used acetylene as the accelerant. I don't think it went supersonic, though. There's videos (embarassing ones) on youtube. He eventually designed one that can shoot full cans of monster energy hundreds of yards.

the reason i bring it up is we used to design and build pneumatic ones, that could send C and D batteries thousands of feet if you arced it right. that was with ~125psi, we always wanted to build out to 200+ psi, but instead went into accelerant-based cannons and he got a job doing machine drawing with autocad. the rest is history.

edit: https://nextcloud.projectftm.com/index.php/s/cobra5x we show off the part i designed, toward the end on the "reload" - he designed and built the entire thing.

Sorry to be a bore [that's a firearms joke], but -- while I encourage everyone and their family to experiment with building such devices, with safety in mind of course, it is a lot of fun -- please don't dispose of your old batteries in the natural environment!

Really not trying to call you out here, as a teenager I once had the idea to load up my marble cannon with dead AAs (they're free!) and got a "do you really think that's a good idea?" from an environmentally conscious adult when I went asking for dead batteries.

We moved on to oranges really fast after realizing that batteries coming out of the sky randomly was probably a bad idea, even if there were no apparent people around.

Don't get me wrong, oranges are dangerous too, coming out of the sky at terminal velocity, but at least when they hit the ground they disappeared into a fine, 3 meter wide mist.

oh my god, were it not for your redundant comment I might've gone to the forest to discard my collection of depleted batteries, thank goodness.

I dunno, takes a lot of energy to get a pneumatic system up to the same speeds that this trebuchet can accomplish. I see it really as a super-efficient machine requiring very little effort to load ..

But yeah, the fact that it's super cool looking - and sounding - is a key factor in my willingness to play with one too, one day. ;)

Basically anyone can go buy a pellet rifle that will easily and consistently clear 1500fps. They're still pretty cool, and will go through both doors of a car

I think the cycle time on this would be far superior to a pneumatic system: cycling this system effectively means lifting ~100 pounds ~8 feet, which a reasonably fit person (who could reach that high) could do several times a minute for extended periods.

He got an efficiency over 40% (if memory serves, I watched this video yesterday) -- I wonder between pumping and discharge how efficient a pneumatic system would be, but I can't imagine that it's higher.

If the pump were operated by a bicyclist and the projectile feed automated I imagine the pneumatic system would win out by a very wide margin regardless of any reduction in overall efficiency.

Once this thing is dialed in, a wind- or stream- rechargeable version is the obvious next step.

I've seen potato guns (obviously much larger bore than this) and inflated bicycle tires to 100psi+

How do you imagine making the cycle time better "by a very wide margin" compared to lifting 100 pounds less than 10 feet?

Isn't it a simple matter of sustained energy output scaled by the overall efficiency? I'm saying that a human cycling can sustain much much higher energy output for much longer than most other forms of exercise. Running probably comes close and swimming likely exceeds both of those but in the latter two cases I'm not clear how you could productively harness energy from the activity with any sort of efficiency so it doesn't apply here.

Drone defense? :-)

Or we can just accept it as a cool gimmick, we don't have to kill animals with supersonic trebuchets really

Well, depends if killing the animal means having an actual ecosystem functioning again, afterwards. Some animals are living in the wrong place in the world; culling them requires special skills.

I get it - animal murdering is cruelty, mmkay .. but so is a wild boar, ripping up wombats and quokkas and witchetty grub-bearing paperbark trees ..

Anyway, I do see far more peaceful applications of this, if it becomes efficient and deployable. Could be a good way to launch things at sea, for example.

Or even certain forms of glider.

I don’t think this has much practical application as an entire system. Nor is it supposed to. It was built just to achieve and artificial goal with arbitrary constraints. That doesn’t make it any less cool or interesting, but that doesn’t make it useful.

Some of the features he used are pretty cool though, like varying the winding drum diameter to vary the delivered torque over the course of the weight drop.

I could for sure see it being used to launch seeds-bombs, or emergency rations, or make a pressure wave on a snow overhang - if the evolution of this interesting experimentation results in a portable version, it would be immensely useful. As a crop protection device, given some kind of energy-harvesting recharging method, a la wind.

A bit of imagination makes it very useful.

> without requiring fire-arms training.

You'd need trebuchet training instead, which is probably not better in the long run. I bet there's still lots of ways to kill/mangle yourself with one of these, especially once you've been around them long enough to get casual and sloppy.

All such weaponized technology carries the weight of danger, but de-weaponized technologies - which is what this represents to me - could mean some break-throughs, too. There are a lot of peaceful applications for a trebuchet.

And yes, it'd need training, but its not the training part of explosives training that I think needs to be rendered obsolete, but rather the explosives manufacture and distribution network, or in other words: peaceful applications for a trebuchet.

Peaceful use of weapons is cool. But that's exactly what avalanche-triggering guns already are, in full. They and trebuchets are both military artillery at heart. As far as I know they still need explosives at the terminal end, too, even when dropped by helicopter, so that part is also not going away (ignoring explosives needed for mining, etc).

I think the only real advantage of this, compared to gas driven projectiles, is the lack of need for gas sealing and explosion resistance of the projectile. The projectile is accelerated much more gently. You can launch combustible, rather fragile and irregularly shaped projectiles. That said, I don't think there is much need for supersonic exit velocities for most scenarios. Maybe you could use it for impact testing without introducing a gas blast or the need of a gas sealing delivery vehicle. But I don't think you would opt for a gravity powered, purely mechanical device then.

Could it be built using medieval (or earlier) technology? One wouldn’t be worth anything on a battlefield but a few hundred of them would be interesting. I don’t know if steel that a blacksmith makes would be uniform or strong enough for that spinning arm though.

I suppose the string is even worse, though.

I think, if you scale it up a bit and adjust the weight for increased friction losses, you may be able to do it considering available materials, but the required knowledge would be anachronistic. I mean, they could also have built compound bows and repeating, lever operated crossbows, but weren't smart enough.

For the string you could use a chain, or just a thicker rope. A presume a bow string has similar requirements and was available tech. For the frame, spindel/shaft and string, I don't see a problem as they appear to be scalable, not restricted by dimensions/weight much. Wood, natural fibers and steel would do. In theory, medieval people in "The East" had readily access (as in no advanced processing required etc.) to everything needed to make highly elastic rubber (for the original supersonic trebuchet), but it would be an anachronistic material AFAIK. You may conceive a variant using maybe an array of bows for quick release energy storage.

Wood is plenty strong (in relation to weight), but the arm may critically depend on modern materials, as both supersonic trebuchets use specifically advanced materials there (structured titanium and carbon fiber composites IIRC). For a heavier arm, you would probably need a prolonged acceleration phase, which would be doable (for Stanton's trebuchet), but I am not sure the forces wouldn't tear lower strength:weight materials apart, or if a more voluminous arm may be able to overcome the drag. I could see the fat compressed part of the arm being aerodynamically shaped wood (like a wooden propeller; although "aerodynamic" anything may be considered anachronistic), and the thin tensioned part made from a thin band of steel/bow string.

I think, another potential show stopper may be bearings. Not sure you could have the rotational speeds of the arm without precision (ball) bearings and modern lubricants. 2342 RPM would probably the fastest spinning thing at the time. (I wanna see a washing machine gone trebuchet-y, now.)

But really, it would be just a curiosity in medieval times too. What's the point of supersonic speeds in a device you can hardly aim precisely? You could deliver the same or more energy by throwing a heavier projectile at slower speeds, without excessive aerodynamic losses.

> deal with avalanche conditions

Swiss solution: chuck some explosives out of a helicopter https://www.youtube.com/watch?v=H519qhLnRtM (start at 1:20)

(In the image at https://swisshelicopter.ch/de/aktuelles/721-lawinensprengen-... the explosive pack says "do not eat". I'm not reassured that we need this warning for people allowed to handle that.

> I'm not reassured that we need this warning for people allowed to handle that.

Not sure what type of explosive that is but the rumour is that C4 when ingested gives a high similar to alcohol. Or at least that is what some troops believe.

“Amongst field troops in Vietnam it became common knowledge that ingestion of a small amount of C-4 would produce a ‘high’ similar to that of ethanol, and it is possible that this was the reason for this episode.” From the clinical description of a c4 poisoning case.

https://pmc.ncbi.nlm.nih.gov/articles/PMC1279680/

If the trebuchet is breaking the sound barrier, a small fleet of trebuchets set in place on the snowfield and set off in an appropriate wave beam, could provide less explosive-manufacture-distribution-usage solutions to the problem.

I could imagine this thing gets even more efficient and resilient, attains some kind of wind or sun-based auto-recharging mechanism, and then deployed on mounted areas to shock-wave snow layers. Yes, its possible, no its not real until someone does it. I could imagine it being done.

Note: I also like the idea of not having to use explosives, is the starting base. If you would prefer to blow stuff up, that's not what I'm talking about.

The evolution of this technology towards an automated, resilient, field-portable version would be interesting. Imagine having a 6-pack of them.

Some parks in Utah use a howitzer.

I thought it was neat that the dyneema string he used is the same stuff they use on new (expensive) bike spokes

It would be interesting to scale this design up. Not necessarily in terms of velocity--supersonic velocity for a large trebuchet munition isn't necessarily desirable. What I mean specifically is scaling up the multi-revolution arm and sling release technology to be capable of launching a ~1 ton projectile.

Could it be done reliably with traditional construction techniques (wood, treenails, lashings, minimal metal hardware)?

AFAIK these are innovations that were not explored historically. It would be interesting to see if they would have been viable. It seems like you could probably achieve a lot more downrange energy using the same amount of materials this way.

The spiral drivetrain seems like the most innovative, and elegant, technology that could be built with old tech. It requires some very strong rope though, so if you went back in time you'd need to really focus on that.

Hemp ropes are quite strong, they've proven themselves for thousands of years in marine applications. You definitely need more thickness to achieve the same breaking strength as dyneema or steel cable but at slower speeds and higher projectile masses the aerodynamic consequences of a thicker sling rope might not matter so much. As for the "drive rope" for lack of a better term (the one that transfers power from the falling weight to the rotating drum) that one can be basically as thick as you like.

>> at slower speeds and higher projectile masses the aerodynamic consequences of a thicker sling rope might not matter so much.

You make an excellent point.

I think this ends somewhat at Spinlaunch: https://arstechnica.com/space/2025/04/spinlaunch-yes-the-cen...

What about the guy that jumped from space and broke the sound barrier?

https://www.guinnessworldrecords.com/records/hall-of-fame/fe...

Not a trebuchet is it

No, a baumgartner.

There were designs to hurl masses from the Moon also with a sling. Massively less infrastructure than a linear mass driver.

Like [1]. But for an "oh, that's cute", here's [2] Launching mass from the Moon helped by lunar gravity anomalies (2024). The Moon's gravity field has lumps (mascons), so low lunar orbits are unstable (increasingly elliptical until ground impact; timescale months; thus satellites requiring powered stationkeeping even with no atmosphere). Paper observes you can run the path in reverse: elliptical ground launch gets somewhat circularized. So for some locations and trajectories, a passive object (no circularization burn) can stay up for days, instead of the hours of a once around and splat. Making for an easier hypothetical catch. Tnx for the muroid runway!

[1] https://scholar.google.com/scholar?hl=en&as_sdt=0%2C33&q=+An... [2] https://arxiv.org/abs/2410.09616

That's absolutely incredible. I would never have thought of that. Thanks!

Projects like this are inspiring. Love it.

I should build something this weekend…

I mowed the lawn.

I've been enjoying his videos for years atp, does really cool stuff, and has the same fascination with flight as I do.

Ummmm. In 2007, near a certain defense contractor, we demonstrated a 319'-wire trebuchet mounted horizontally but slight vertical a-skewed for distance/aiming.

Used a gnarly large helical gear but with integral diminishing ratio.

Gravity-powered in same way but with a 20-meter-ish tower. (Cheaper than a standard 800'-tall trebuchet.)

At release time, achieved 10 G-force (payload goal), it's velocity speed was audibly a speed of sound (arguably higher, math says Mach 2.7).

That was our lunchtime project, all started from several stage bets, a napkin diagram, and different loser(s) pay for weekly food deliveries.

Even demonstrated to some brass from an unrelated project.

Fun-time.

Oh, yes, lest I forget, bunker-required for safety (where exactly would you stand?).

Would love to see some photos in action, but 2007..defense contractor...makes me think photos may have been frowned upon.

Done on company property. Design Owned by company. We did not object for maximum marketing.

Good old days. I'd love to see the design for that one. Any chance?

Napkin, someone literally used it at lunch time.

Some of us ribbed him: "Destruction of classified material!", "call Security!", "PM's (program manager) behind you".

No. Wasnt classified, but company-owned.

There are clues above.

> standard 800'-tall trebuchet.

As tall as the Golden Gate Bridge?

This is awesome! I wonder how far can you get with a wood and iron build

Not to be that guy, but this recent XKCD is suspiciously relevant: https://xkcd.com/3276/

A whip's end also breaks the sound barrier. It's not at all hard to do.

What a fascinatingly misguided dismissal of someone actually doing something to back up their words.

Just like a F-35 Lightning II does. Easy peasy.

What's extraordinary about this? You can get any amount of energy from gravity and transferring it to a small object doesn't sound like an especially complex feat. It's one of those influencer videos in which someone devotes a disproportionate amount of effort to accomplish something pointless- Mr. Beast does the exact same without any pretense of showing something useful.

You sound fun...

This is HN. The trip is the destination, bla bla.

No, I understand, it's the claim from the very first sentence that "gravity itself seemed to forbid" (reiterated later in the text) that annoyed me. It's just making up a non-existent obstacle to hype up the result.

It's a bit clumsily written, but I'm pretty sure that's a reference to what Tom mentions in his video, that since g = 9.81m/s^2 you're not getting close to the speed of sound just from falling from a reasonable height, even ignoring air resistance.

Thus a traditional trebuchet design cannot reach that speed.

But since potential energy from gravity is mgh and kinetic energy of a projectile is 1/2 mv^2, calculating height and mass of a weight to power the projectile is absolutely straightforward. The terminal velocity of a falling weight has nothing to do with it (even historical trebuchets used a leveraged system in any case).

The point was the leverage can't be simple, like in a traditional trebuchet. Tom ended up with a rope pulling on a cone, with the arm being accelerated over many revolutions before the projectile is let go.

Tom explained it much more straight forward in his video, the blog author tried to be fancy and made it worse.

What a sad and pathetic opinion, especially when targeted towards such an incredible contributor as Tom Stanton, a true educator and an energetic and excited engineering mind.

Mate, you are on HACKERnews. We are all about this.

Of course, but there is a continuum between "I spent years tackling this complicated problem and the solution will benefit us all" and "I've entered the same McDonald's drive-through 1000 times in one day to order always the same thing". Some achievements are closer to the first end, others lie more somewhere in between.

You will hate his stirling bike.

I love his entusiasmen for engineering and having the drive for a multi year project, even when the result is just another trebuchet. All while teaching physic in an entertaining way.

I don't get how this is close to driving through a drive through.

Yes right ?

How dare someone build something entertaining and tell about it.

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