Thinking this approach out, could someone correct me if I have this wrong.
So he gradually increases the energy transfer from the weight to the arm over the course of the drop. But that arm swinging around must have a lot of energy loss due to friction and air resistance.
This loss will rise exponentially with the speed increase right? So in a sense he is holding his energy budget in a very inefficient phase, with high losses.
Two things support this. A) he spent a lot of time trying to make the arm more arodynamic. B) The spool widening at the end, which is essentially changing back down gears, applying more torque, right at the end when you want speed.
An alternative would be to drop the weight, and let it fall unrestricted until it gets to it's highest speed (this would minimise friction and air resistance) and only at the end of its fall, transfer the energy into the arm.
In this case the arm would only need to rotate 180 degrees or whatever, and not waste energy rotating right?
And then, to take this a step further to make this work there would need to be some flexibility or elasticity in the system to take energy from the high speed falling weight to the arm.
And what you have ended up with is something that looks like.... A whip!
He could have also used some kind of chemical reaction contained within a rigid tube to transfer the energy to a projectile, but I think he just really likes trebuchets in particular.
Energy loss from air resistance typically is quadratic, not exponential, with regard to velocity. So it’s worth much less than you’re arguing. And the arm has to rotate from what I can understand, so the end rotational velocity - and hence, rotational energy - would be the same?
Isn't drag either linear (proportional to velocity) or quadratic (proportional to velocity squared) depending on the scenario? But yes quadratic for things at this scale?
Drag is linear with velocity under Stokes' Law which assumes laminar flow and a very very low Reynolds number, and does not apply to ballistic projectiles flying through air.
Aerodynamic drag on the kinds of things that are involved in trebuchets is always quadratic with velocity.
If I'm picturing what you're explaining correctly, I think this would be difficult. Suddenly accelerating the arm from zero to hundreds of mph would put immense stress on the arm, not to mention whatever you're planning on using to transfer that energy (you kinda hand waved that bit).
I think your assessment is correct about the energy losses. I'm just not sure about the fix.
I think the fix is essentially a whip, that's what I meant by elasticity and flexibility.
If you want to accelerate a weight quickly in a single swipe, (simplified) gradually reducing the mass along the length of the whip imparts more kenetic energy at the end (the whip crack).
So the arm would no longer be rigid, although you can see in the OPs video it isn't actually fully rigid.
I strongly suggest you get into trebuchet building! It is a fascinating mixture of art + science. You can start with legos or a few popsicle sticks, paint sticks + screws, etc.
To make things easier, start with an "integrated sling ballistic" (ie: a piece of thread between two lego pieces). Sling release is actually fairly complicated so chop it out!
The arm is generally a rigid lever, and the sling acts exactly as your "gradually reducing mass". In his design you can see the kindof bike gear shape at the axle and eventually coming like an "A" towards the tip (and reducing to "infinite thin-ness" via the string/sling).
After you've built one simple (small) trebuchet, test to failure! How much weight can you stack on it before a component breaks (bucket? arm? axle? sling? frame?). How heavy of an object can you throw before "everything starts messing up"?
My recommendation for ballistics is mini-marshmallow (desktop), regular marshmallow, mega-marshmallow, then switch to "hard" ballistics, eg: mini candy pumpkin (the connoisseurs choice), tennis ball, basket ball, etc.
Once you start throwing dense, solid objects (marbles, golf balls, baseballs) your risk of property damage and injury goes up fairly exponentially, so stick to marshmallows and tennis balls until you feel more comfortable.
Spend lots of time figuring out safe/reliable trigger mechanisms, WITH A SAFETY! For my tennis-ball treb, I did three eyebolts with a dumb screwdriver on a string, and a vise-grip (clamping) on the far side. Eventually, you're trying to safely "release" 100's of pounds that is being held in tension, and if you have a misfire (fail to release trigger) you're potentially approaching a "loaded" machine which is demonstrably "not working right". Lifting/loading 100's of pounds and then having an unlocked trigger (which _also_ may fail) is not safe for anyone.
The arm (or whip) would still have to accelerate from 0 to ~2000+ rpm on half a revolution even though its flexible. So there would still be enormous accelerations even though the whip eventually partly smoothens out the peak acceleration. it would be more like a collision which in turns introduces higher stresses (and probably vibrations too) to the system. Both requiring you to increase the strength + rigidity of the system and hence also increase weight on the arm. Which in turns increases inertia and the "collision" effect.
Not saying its impossible to create a successful system like that, in fact it sounds sort of a natural/organic design that potential could be closer to the optimal design, but it would be more difficult to accomplish and probably need more testing and design iterations. So I think OPs strategy is more simple and pragmatic in this case.
If you remove the arm, is it still a trebuchet? Even the current design is pushing definition of trebuchet. That said, a gravity powered supersonic whip-a-pult would be pretty awesome :)
You'd need to build a very large, very heavy whip, like a chain whip but those only work laying on the ground due to how heavy they are, because the mass at the very end of a whip gets going so fast /because/ it's extremely light compared to the rest of the whip. So scaling up the weight to even a few grams of projectile means the rest of the whip gets very heavy.
He talks about reducing the drag by improving the aerodynamics of various components and got a 17.8% increase in it's RPM with just a leading edge profile and wrapping it in mylar.
The big issue in your proposed version is building an arm that is light enough to not absorb a lot of energy (it still needs to be rotating at the same speed as the progressive version in the video) but rigid enough to survive that sudden acceleration. My bet is you'd lose way more to the arm flexing and the added weight than you would the benefit of not dealing with aerodynamic losses.
>And what you have ended up with is something that looks like.... A whip!
Had a similar feeling come to me as I watched this video a few weeks ago. It made me really want to see someone make a whip-based trebuchet that uses a big spring like https://www.youtube.com/watch?v=PkQZU-CBwhk
Whips work because they gradually get lighter and lighter along their length meaning the same energy as it propagates down the length results in higher and higher speeds. Strapping a projectile to the end throws all of that off unless you make the whip extremely heavy to compensate.
Not sure if you watched the video, but the chain they're using is extremely heavy. I would think the projectile would be on the order of one of the single chain links at the end of the small side.
A 3d printed ball like in the OPs video would only be less than 3grams I imagine.
Either way, the weight of the whip is hardly important right, as you are just doing an energy transfer from the falling weight into the small ball, the lighter the whip the better, as long as it doesn't break. If the whip is heavier, it will soak up the energy budget in momentum
So what you're saying is he should extend the drop height a bit to run a vacuum pump before engaging? Sounds like he's on the path to launch some satellites!
He has some great videos. I watched this one and was impressed at the calculations, the transparency and the celebration at the end when he reached supersonic speeds.
Or, in other words: There was some text to read and some pictures to look at. For topics in the range of "supersonic trebuchets", I'm absolutely okay with quickly reading some lines of text; dynamically deciding how quickly/thoroughly I read, what paragraphs to skip, etc. What I'll definitely NOT do: Watch a video clip about it.
So you won't support the creator, but support a person who summarizes the creator. You could have just pasted the link into Claude and asked for a summary of the blog post.
Maybe that's even the same guy?! But I don't know...
A thing that I completely don't care about: Supporting some YouTube guys.
YouTube "creators", even if they are not basically "influencers" (a.k.a. advertizing), even in the best case, a YouTube guy is for me the same as someone at RTL, DMAX, Fox, or any other random TV station. It might even be that I watch their show every now and then... But I'm not constantly thinking about how I can support these guys. And IF they actually disappear tomorrow, there will be other ones coming up.
There is DEFINITELY no scarcity in YouTube guys...
PS: The narration inside the community is fundamentally more romantic. But guess what, I don't care. ;)
PPS: With all my browser addons (incl. "Sponsor Block" - every YouTube consumer should have it!!!), I'd not be so much of a support anyways.
PPPS: The first thing when someone would ask me to consume a YouTube clip would be to ask Claude or whatever service to generate a summary/transcript for me. I reject to constantly burn multiple minutes in order to consume random/funny/pointless content that could be a matter of 10 seconds if provided as text together with four of five images.
Tom is an amazing engineer. His journey in incrementally engineering a plane powered by compressed air has been awesome, both to see the iteration, but also to see his skills grow.
I suspect that with a little iterative modelling of the whole system with derivatives, efficiency could be bought from ~40% to ~80%, giving you an extra few hundred mph...
A LLM may produce OpenSCAD compliant syntax, I don't doubt that, but how do you make it produce designs that fit engineering constraints? How do you even express those to a LLM? How do you validate those? How do you iterate upon them?
The domain of ML-driven design optimization isn't exactly new, is quite specific, and I would need convincing that Claude has anything to contribute to it.
I’m pretty sure Claude has been trained on high school physics textbooks, yo. And if it hasn’t there are plenty of other models out there that have.
It’s not a problem of the ML model. It’s a problem of the human setting up the description of the problem in such a way that the model can operate. OpenSCAD gets a long way towards that target. Use it with a model thats been trained for the purpose - just the same way that ML has been used to produce optimal rocket engine nozzles and fuel transfer systems.
> Claude has been trained on high school physics textbooks, yo
The very fact that physics textbooks have little bearing in the real world is the whole damn reason why Mechanical Engineering exists as a separate discipline, yo
> It’s a problem of the human setting up the description of the problem in such a way that the model can operate.
It's a problem of defining the initial state (which is the trivial part that OpenSCAD may be a contributing element of), defining constraints and variables (what is allowed to be changed and not, for what can, in which ways, to what extent, i.e. what is the library of allowed material, fastening, machining, assembling techniques available to your very specific situation), defining evaluation and fitting criteria.
I see very little adequacy of general purpose LLMs in that
> the same way that ML has been used to produce optimal rocket engine nozzles and fuel transfer systems.
Which has nothing to do with "just use Claude, yo"
there might be several gaps before that, even. From the top of my head:
- text description to 3D geometry gap: you can't easily describe complex geometry in a language that's common and convenient to both humans and machines
- 3D geometry to physical model gap: material , geometrical constraints induced by manufacturing (machines, tools, costs, …)
- physical model to model fit for simulation gap: meshing, constraints, stress modelling, …
- simulation outcome to fitness assessment gap: now you have a high-dimensional and numerically heavy simulation to weigh against a non-rigorously defined acceptance criteria
- simulation outcome to geometry profiling gap: how do you even start to guide the LLM into the vast space of possible changes to apply to the 3D geometry and reboot that loop?
LLMs don't strike me as a particularly relevant technique to apply here, to be honest.
You can probably keep this kind of unconstructive comments to yourself. Even if this was a place to discuss one's beliefs, nobody was attacking yours to begin with.
I mean I can link a conversation with Claude that says it knows about materials and various details on their various strength but I don't think that'll convince you of anything.
Indeed, it won't: I can link a conversation with XYZ-bot that tells me that I'm handsome and my ideas are brilliant and I'm en route to tremendous success. The point is that LLMs are, by design and current models norms, sycophantic and incapable of describing their own knowledge and workings/processes. This is not a matter of "my opinion vs yours", that's what few minutes spent legitimately trying to understand how this works will tell you.
I'm pretty sure the only reason the video trebuchet wasn't a proper bullet is because it's made out of plastic instead of a ball bearing. Aren't most handguns subsonic?
This is nonsense. You're going to double the efficiency by using "derivatives". As if the expert in this video didn't do any modeling themselves (shown in the video) and wouldn't have considered acceleration at all.
I say, put your money where your mouth is and prove you can double the efficiency.
All the energy is lost to air resistance and left in the machine in the form of parts still moving when the projectile detaches.
Both of those can be modelled - rather precisely if you have the compute power. By modelling the derivative of all of those things with respect to every parameter of a parametric design, losses can be minimised with gradient descent and a huge Jacobian matrix.
A few parameters are obvious (string length, arm length, etc), but there is no need to keep the set small - you could model the exact shape of the projectile latch as a spline with 100 parameters for example, and let gradient descent find the best shape to minimize losses.
AI can set up and run all those simulations, and all you have to do is pay the AWS bill for all the open foam instances you'll be running.
Other trebuchet fans who dream of building one some day may be interested in googling "walking trebuchet" for a surprisingly high complexity/results ratio.
Every time I see a strandbeest[1] on the beach somewhere, I wonder to myself why it hasn't got an array of trebuchet included, also recharged by the wind, to pick up sand balls and throw at people.
I suggest having a BBQ with your neighbors. That should minimize the pre-launch problems. If you use a steel ball bearing like he originally thought, that bullet will be the start of your legal problems.
I think the idea is that at the end the sling starts to unwind too, increasing the effective arm-length (that non-linearity is one of the reasons trebuchets are so efficient to begin with). As a result it's possible that decreasing the spool to near zero is like putting the gears of your car too high. Reducing the spool size ensures there's enough torque left to put more power into the final swing.
As long as there have been forums there have been guys and gals making extremely deep and long deep posts and threads about their projects. Video and YT just make it 100x more accessible.
I would love for this to be optimized to the point that its portable and can be carried around, assembled on the side of the mountain, and used as a low-cost, efficient way to throw things from one mountain to another, maybe for avalanche control, or cloud seeding, or indeed for seed bombs intended for re-wilding hard to access places, or something.
It just seems like such an obvious tool, rather than a weapon.
Or if you have a limited supply of gunpowder but a way to make sufficient numbers of appropriately shaped projectiles, an air rifle would do the job and is much lighter and simpler than a trebuchet.
This is so obviously wrong. Show me a field-rechargeable gunpowder-based device for launching things, and I will show you someone who is about to run out of ammo on the side of a mountain they’ve just climbed after a single day of work.
Honestly, what the hell. Where do you think gunpowder comes from, thin air? Oh, is gravity a subscription service in your country?
Come on, try to at least be sensible about your response.
Guns are already ~20-50% efficient at turning chemical energy into kinetic energy. If you're not using a direct chemical reaction for energy, then you're using a human which is a lot less energy-dense than a backpack full of ammo.
And yes, people who do avalanche control typically fire explosives out of a cannon or drop them from a helicopter. Getting a machine supply all the energy is the whole idea instead of climbing mountains yourself.
Do you not understand your argument is exploring a made-up scenario where we're no longer an industrialized civilization where these things are manufactured cheaply by the billions?
And if you INSIST on making everything completely low-tech and renewable, build a potato gun and use high-proof alcohol as fuel. It'll weigh less and last longer than whatever rube-Goldberg trebuchet design you have.
A good one will weigh about 5 pounds and not have moving parts to break. Ferment your own alcohol from plants you grow yourself. You can at least do that much, right?
A good one will have as few parts as possible, and be optimized for both portability and distances.
>Ferment your own alcohol from plants you grow yourself
I suppose I could just harvest gunpowder from the bullet trees that grow all over candy-land, too.
Or, I could just have an ultra-optimized trebuchet in my backpack for throwing things with very little effort besides the energy (me) required to reload it, wind it up, and let ‘er rip ..
Nobody in this thread has demonstrated anything but a distinct lack of imagination and a willingness to be as boring as fuck about a really cool idea, though, so I’m not bothered by convincing anyone.
It’s like saying “why would you use a bow and arrow when you’ve got a 50 caliber machine gun industry right there, ready to help you blow things up”.
I’d use a bow and arrow in the same context - so that I don’t have to have an entire industry dependency just to survive and/or do stuff in the wild.
And before you change the context and say “yeah, why don’t use just use a bow and arrow to do your seed-bombing, huh hippy?”, that thought of course crossed my mind. Soon as I find a supersonic capable bow, that is.
I, for one, would absolutely love to see you carrying up a mountain the contraption in the video with its full 50kgs weight, then raising said weight by three meters with the power of your muscles to launch each single 4 grams pellet, and doing that for several hours every day. I am curious though if you have considered how much you would have to eat to power your muscles, how do you plan to procure the abundant food supply you'd certainly need (and which of course it should have been produced without chemicals and industrial processes of any kind), and how would you carry that up the mountain as well.
What part of "I can't wait to see this optimized into a portable version" did you not understand?
Yes, this prototype is big and unwieldy. So?
The development process is obviously on its way towards the construction of a smaller, lighter version.
BTW, there are rocks up the mountain. They can serve as the weight once you get there.
It's the math of the thing that is going to end up becoming optimal. Not just the material design - which is important once the loading and tolerances are understood. The gearing/screw mechanism is especially interesting from this perspective - it provides a clear path for optimization.
Once he has the equation dialed in, it will be interesting to see it scale down. The winding gear provides a path to optimization on the horizontal plane, and that is going to be very interesting to see go through a few more iterations. Pun, intended.
> What part of "I can't wait to see this optimized into a portable version" did you not understand?
The part where you don't need to load into the system at least as much energy (actually a multiple) as you get out of it.
But there are already a lot of simple, portable and lightweight mechanical systems to launch objects at high speeds, and optimised to be loaded by muscle energy: they're called sling, slingshot, bow, crossbow, etc. They have excellent performance. Since air drag is dominant on small projectiles, speed decays exponentially and the range only increases little with more energy. Claude calculates that a bow can double the video's trebuchet at throwing distance because of the arrow's shape and weight, despite shooting at much lower speed and needing about a quarter of the energy input.
>lift the weight for every shot, which requires energy.
All harvesting requires some secondary-energy source.
Gravity is a resource, it takes effort to convert it to a form that can be applied - just like wheat, photons, air guns, etc.
> It's not obvious whether a trebuchet is better than compressed air, like a BB gun.
True, it’s not obvious yet, but it sure is fun following along and imagining the final, highly optimal version making its way through the process. I’d use it for some seed bombing hijinks, anyway. Green up the place, I would.
Multiple locations, thus the need for it to be easily portable.
I guess a couple hundred launches a day would be useful for seed-bombing/re-wilding, especially on rugged terrain.
Seed-bomb weight: I’d say anywhere from 1-10 grams, maybe?
Accuracy - it’s a seed bomb, you want dispersal to happen, so maybe the more interesting question is, how would you design a seed bomb to survive the trebuchet speeds and g-forces while also allowing for directed dispersal in the intended area. Seed-bomb design for impact conditions is also something of interest - some seeds need to be embedded in a layer of soil, some don’t. There are many parameters to optimize in the seed-bomb side of things, too.
Transport method: backpack-friendly, I think. I’d hike to an area, set up the trebuchet, and spend the day dispersing in a wide circle around the base. If the terrain is rugged, portability is especially important.
Operational time - one thing I think is important is that the trebuchet be resilient for long term use. If Toms’ engineering efforts prove fruitful, I’m sure the material construction will get some optimization such that, perhaps, the only thing that would need to be maintained would be the line - however, this is a known science, see for example the sailing industry, rappel lines, etc.
Solar/electric? I think a wind attachment for rewinding might be a bit more productive.
The scenario: a team of 5 is off for a month in rugged terrain, with the intent of dispersing targeted seed packages over a wide region. The seed bombs are designed to protect the seeds, the trebuchet is designed to deposit them sufficiently well that they remain viable in their final destination. We hike out there for a couple weeks, do a mass trebuchet dispersal, we come back a year later and observe the results.
The railgun guy might have been having a giggle with you, but you gave him some actual numbers so I'll give you some actual math to go with them.
Your biggest problem here isn't the launcher, it's the projectile. It's going to be damn near impossible to get a 1 gram projectile more than a couple hundred yards unless it's a dense metal. Doesn't matter how fast it's going, drag always wins here.
10 grams is more plausible, but then you're looking at ~1000ft-lbs cranking energy to get 10g supersonic (@ 40% efficiency) It's doable and you'll only be burning an extra ~100 calories per day for 200 shots. You might get bored though. An airgun will have far worse efficiency most of the time, though it can launch dart-shape things which can go much further for the material density.
You mentioned a bow, which is probably the tradeoff point of everything discussed so far. Flight bows are designed for distance shooting, are lightweight and can go 500 yards easily. The downside is you'll need to make the arrows yourself, cause there ain't no supply chain to sell hundreds at a time cheaply.
For the "jUsT uSe a hElIcOpTer lol" comment;
No, that's not practical, but you CAN get an RC plane that will carry a couple pounds for a tiny fraction of the cost. In terms of how much area it can cover vs supplies needed, that plane is going to be the least thirsty thing on the mountain, assuming you even need to climb it then.
Would it not be much faster and more efficient to just a use a helicopter to disperse it instead of hiking and setting up a trebuchet? If you are just launching the seed bombs anyways, i feel like a helicopter can cary way more then one person every code, and could just drop a seed bomb every X seconds? Why the need to have people hike out just to launch the seed bombs
Seriously, rich people, get out of your own bubble heads now and then.
A low-tech, low-resource-intensive, no-dependency application of this technology has huge applications around the world.
Do you know how much it costs to operate a helicopter per hour? Now scale it to month-long efforts to turn desert into forests. Scale it to a thousand villagers. Scale it to ten thousand villages.
>Why the need to have people hike out just to launch the seed bombs.
Because re-wilding requires a hands-on approach to be very effective. Just look at what China has done with the Great Green Wall - this was a labor intensive mega-project. Low-tech, highly effective solutions for seed distribution could be of great benefit in that context - without a bit of fancy speculation on our part, we'd still just have deserts and nothing to eat.
YES, you could 'just use a helicopter'. You could just sit back on your deck chair and be served mocktails, too.
Sometimes, kids, you need to do a bit of hard work.
Carrying an extra 50kg weights up a mountain seems inefficient to me, unless you mean a much lighter one or one that you can use stones you find around where you are?
Seed bombs aren't consumables, they're reproducibles. I could harvest a thousand of them in the time it took you to make a kilo of gunpowder, from local (mountainside) resources ..
>Also pretty sure several parts of the mechanism would need to be considered consumable if operating over a long period.
Well, that remains to be seen after the optimization steps complete. Fine with me if it takes a year before I have to replace a string.
Meanwhile, I'm guessing you are suggesting the "ma' gunpowder" deliveries happen via drone, or helicopter, or methane-powered rocket ship or some such nonsense, lol ..
Seed bombing is pretty fun. Re-wilding is a huge industry. Field-reloadable ultra-trebuchets that can be carried and deployed across the landscape, instead of stored in a weapons depot, also a big win for energy harvesters, everywhere.
Thinking this approach out, could someone correct me if I have this wrong.
So he gradually increases the energy transfer from the weight to the arm over the course of the drop. But that arm swinging around must have a lot of energy loss due to friction and air resistance.
This loss will rise exponentially with the speed increase right? So in a sense he is holding his energy budget in a very inefficient phase, with high losses.
Two things support this. A) he spent a lot of time trying to make the arm more arodynamic. B) The spool widening at the end, which is essentially changing back down gears, applying more torque, right at the end when you want speed.
An alternative would be to drop the weight, and let it fall unrestricted until it gets to it's highest speed (this would minimise friction and air resistance) and only at the end of its fall, transfer the energy into the arm.
In this case the arm would only need to rotate 180 degrees or whatever, and not waste energy rotating right?
And then, to take this a step further to make this work there would need to be some flexibility or elasticity in the system to take energy from the high speed falling weight to the arm.
And what you have ended up with is something that looks like.... A whip!
He could have also used some kind of chemical reaction contained within a rigid tube to transfer the energy to a projectile, but I think he just really likes trebuchets in particular.
Macgyver Gets Lazy https://xkcd.com/444/
Energy loss from air resistance typically is quadratic, not exponential, with regard to velocity. So it’s worth much less than you’re arguing. And the arm has to rotate from what I can understand, so the end rotational velocity - and hence, rotational energy - would be the same?
Isn't drag either linear (proportional to velocity) or quadratic (proportional to velocity squared) depending on the scenario? But yes quadratic for things at this scale?
Drag is linear with velocity under Stokes' Law which assumes laminar flow and a very very low Reynolds number, and does not apply to ballistic projectiles flying through air.
Aerodynamic drag on the kinds of things that are involved in trebuchets is always quadratic with velocity.
Any idea how adding a flywheel to the system would change it? Could we store more energy in the arm?
If I'm picturing what you're explaining correctly, I think this would be difficult. Suddenly accelerating the arm from zero to hundreds of mph would put immense stress on the arm, not to mention whatever you're planning on using to transfer that energy (you kinda hand waved that bit).
I think your assessment is correct about the energy losses. I'm just not sure about the fix.
I think the fix is essentially a whip, that's what I meant by elasticity and flexibility.
If you want to accelerate a weight quickly in a single swipe, (simplified) gradually reducing the mass along the length of the whip imparts more kenetic energy at the end (the whip crack).
So the arm would no longer be rigid, although you can see in the OPs video it isn't actually fully rigid.
I strongly suggest you get into trebuchet building! It is a fascinating mixture of art + science. You can start with legos or a few popsicle sticks, paint sticks + screws, etc.
To make things easier, start with an "integrated sling ballistic" (ie: a piece of thread between two lego pieces). Sling release is actually fairly complicated so chop it out!
The arm is generally a rigid lever, and the sling acts exactly as your "gradually reducing mass". In his design you can see the kindof bike gear shape at the axle and eventually coming like an "A" towards the tip (and reducing to "infinite thin-ness" via the string/sling).
After you've built one simple (small) trebuchet, test to failure! How much weight can you stack on it before a component breaks (bucket? arm? axle? sling? frame?). How heavy of an object can you throw before "everything starts messing up"?
My recommendation for ballistics is mini-marshmallow (desktop), regular marshmallow, mega-marshmallow, then switch to "hard" ballistics, eg: mini candy pumpkin (the connoisseurs choice), tennis ball, basket ball, etc.
Once you start throwing dense, solid objects (marbles, golf balls, baseballs) your risk of property damage and injury goes up fairly exponentially, so stick to marshmallows and tennis balls until you feel more comfortable.
Spend lots of time figuring out safe/reliable trigger mechanisms, WITH A SAFETY! For my tennis-ball treb, I did three eyebolts with a dumb screwdriver on a string, and a vise-grip (clamping) on the far side. Eventually, you're trying to safely "release" 100's of pounds that is being held in tension, and if you have a misfire (fail to release trigger) you're potentially approaching a "loaded" machine which is demonstrably "not working right". Lifting/loading 100's of pounds and then having an unlocked trigger (which _also_ may fail) is not safe for anyone.
Nothing above absolute zero is fully rigid.
You're going to transfer the energy quickly, you'll just break any "arm" that's light enough to accelerate with the energy available.
You could maybe use an 'already broken' arm (rope, like a whip) but then it's not a trebuchet.
The arm (or whip) would still have to accelerate from 0 to ~2000+ rpm on half a revolution even though its flexible. So there would still be enormous accelerations even though the whip eventually partly smoothens out the peak acceleration. it would be more like a collision which in turns introduces higher stresses (and probably vibrations too) to the system. Both requiring you to increase the strength + rigidity of the system and hence also increase weight on the arm. Which in turns increases inertia and the "collision" effect.
Not saying its impossible to create a successful system like that, in fact it sounds sort of a natural/organic design that potential could be closer to the optimal design, but it would be more difficult to accomplish and probably need more testing and design iterations. So I think OPs strategy is more simple and pragmatic in this case.
If you remove the arm, is it still a trebuchet? Even the current design is pushing definition of trebuchet. That said, a gravity powered supersonic whip-a-pult would be pretty awesome :)
One could test this manually with a whip, right? Attach the ball at the end and try to crack it.
You'd need to build a very large, very heavy whip, like a chain whip but those only work laying on the ground due to how heavy they are, because the mass at the very end of a whip gets going so fast /because/ it's extremely light compared to the rest of the whip. So scaling up the weight to even a few grams of projectile means the rest of the whip gets very heavy.
He talks about reducing the drag by improving the aerodynamics of various components and got a 17.8% increase in it's RPM with just a leading edge profile and wrapping it in mylar.
The big issue in your proposed version is building an arm that is light enough to not absorb a lot of energy (it still needs to be rotating at the same speed as the progressive version in the video) but rigid enough to survive that sudden acceleration. My bet is you'd lose way more to the arm flexing and the added weight than you would the benefit of not dealing with aerodynamic losses.
>And what you have ended up with is something that looks like.... A whip!
Had a similar feeling come to me as I watched this video a few weeks ago. It made me really want to see someone make a whip-based trebuchet that uses a big spring like https://www.youtube.com/watch?v=PkQZU-CBwhk
Whips work because they gradually get lighter and lighter along their length meaning the same energy as it propagates down the length results in higher and higher speeds. Strapping a projectile to the end throws all of that off unless you make the whip extremely heavy to compensate.
Not sure if you watched the video, but the chain they're using is extremely heavy. I would think the projectile would be on the order of one of the single chain links at the end of the small side.
A 3d printed ball like in the OPs video would only be less than 3grams I imagine.
Either way, the weight of the whip is hardly important right, as you are just doing an energy transfer from the falling weight into the small ball, the lighter the whip the better, as long as it doesn't break. If the whip is heavier, it will soak up the energy budget in momentum
So what you're saying is he should extend the drop height a bit to run a vacuum pump before engaging? Sounds like he's on the path to launch some satellites!
I thi k the G forces involved to accelerate the arm to supersonic speeds in one rotation would tear it apart.
Tom Stanton has a raft of cool videos, I like the engineering iterations he often goes through to find a working prototype.
Agree!
He has some great videos. I watched this one and was impressed at the calculations, the transparency and the celebration at the end when he reached supersonic speeds.
https://news.ycombinator.com/item?id=49232110
At least this is a direct link to the video and not blog spam
Or, in other words: There was some text to read and some pictures to look at. For topics in the range of "supersonic trebuchets", I'm absolutely okay with quickly reading some lines of text; dynamically deciding how quickly/thoroughly I read, what paragraphs to skip, etc. What I'll definitely NOT do: Watch a video clip about it.
So you won't support the creator, but support a person who summarizes the creator. You could have just pasted the link into Claude and asked for a summary of the blog post.
Maybe that's even the same guy?! But I don't know...
A thing that I completely don't care about: Supporting some YouTube guys.
YouTube "creators", even if they are not basically "influencers" (a.k.a. advertizing), even in the best case, a YouTube guy is for me the same as someone at RTL, DMAX, Fox, or any other random TV station. It might even be that I watch their show every now and then... But I'm not constantly thinking about how I can support these guys. And IF they actually disappear tomorrow, there will be other ones coming up.
There is DEFINITELY no scarcity in YouTube guys...
PS: The narration inside the community is fundamentally more romantic. But guess what, I don't care. ;)
PPS: With all my browser addons (incl. "Sponsor Block" - every YouTube consumer should have it!!!), I'd not be so much of a support anyways.
PPPS: The first thing when someone would ask me to consume a YouTube clip would be to ask Claude or whatever service to generate a summary/transcript for me. I reject to constantly burn multiple minutes in order to consume random/funny/pointless content that could be a matter of 10 seconds if provided as text together with four of five images.
I'd much rather read a blog post about it than watch a video. Maybe that's just my preference, but it's a better format for me.
SpinLaunch: https://www.thebrighterside.news/post/spinlaunch-looks-to-sl...
Tom is an amazing engineer. His journey in incrementally engineering a plane powered by compressed air has been awesome, both to see the iteration, but also to see his skills grow.
agreed I love following this guys stuff!
107 more comments here: https://news.ycombinator.com/item?id=49232110
I suspect that with a little iterative modelling of the whole system with derivatives, efficiency could be bought from ~40% to ~80%, giving you an extra few hundred mph...
https://www.thebrighterside.news/post/spinlaunch-looks-to-sl...
I wonder if Claude has guardrails against hyper optimizing a trebuchet projectile into a proper bullet
How would you even get Claude involved in that? This isn't your git repo that a language model can scrape for textual content.
Convert the model to OpenSCAD, put it in a repo, and off you go. OpenSCAD is very LLM-friendly.
A LLM may produce OpenSCAD compliant syntax, I don't doubt that, but how do you make it produce designs that fit engineering constraints? How do you even express those to a LLM? How do you validate those? How do you iterate upon them?
The domain of ML-driven design optimization isn't exactly new, is quite specific, and I would need convincing that Claude has anything to contribute to it.
I’m pretty sure Claude has been trained on high school physics textbooks, yo. And if it hasn’t there are plenty of other models out there that have.
It’s not a problem of the ML model. It’s a problem of the human setting up the description of the problem in such a way that the model can operate. OpenSCAD gets a long way towards that target. Use it with a model thats been trained for the purpose - just the same way that ML has been used to produce optimal rocket engine nozzles and fuel transfer systems.
Not that difficult, really.
Are you familiar with the problem space at all?
> Claude has been trained on high school physics textbooks, yo
The very fact that physics textbooks have little bearing in the real world is the whole damn reason why Mechanical Engineering exists as a separate discipline, yo
> It’s a problem of the human setting up the description of the problem in such a way that the model can operate.
It's a problem of defining the initial state (which is the trivial part that OpenSCAD may be a contributing element of), defining constraints and variables (what is allowed to be changed and not, for what can, in which ways, to what extent, i.e. what is the library of allowed material, fastening, machining, assembling techniques available to your very specific situation), defining evaluation and fitting criteria.
I see very little adequacy of general purpose LLMs in that
> the same way that ML has been used to produce optimal rocket engine nozzles and fuel transfer systems.
Which has nothing to do with "just use Claude, yo"
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It could make simulations and read the CNC templates and the files for the 3D printed parts.
And then do what? Do you have any evidence that Claud would do anything relevant with those?
I have had Claude run fluid simulations for me to check machines work. Seems to manage fine.
Many people are stuck in 2023.
It could come up with design adjustments and measure their impact in the simulation. But the sim2real gap may be too large.
there might be several gaps before that, even. From the top of my head:
- text description to 3D geometry gap: you can't easily describe complex geometry in a language that's common and convenient to both humans and machines
- 3D geometry to physical model gap: material , geometrical constraints induced by manufacturing (machines, tools, costs, …)
- physical model to model fit for simulation gap: meshing, constraints, stress modelling, …
- simulation outcome to fitness assessment gap: now you have a high-dimensional and numerically heavy simulation to weigh against a non-rigorously defined acceptance criteria
- simulation outcome to geometry profiling gap: how do you even start to guide the LLM into the vast space of possible changes to apply to the 3D geometry and reboot that loop?
LLMs don't strike me as a particularly relevant technique to apply here, to be honest.
Next year some LLM will do something like that, and y'all gonna claim it's still unimpressive because reasons.
You can probably keep this kind of unconstructive comments to yourself. Even if this was a place to discuss one's beliefs, nobody was attacking yours to begin with.
I mean I can link a conversation with Claude that says it knows about materials and various details on their various strength but I don't think that'll convince you of anything.
Indeed, it won't: I can link a conversation with XYZ-bot that tells me that I'm handsome and my ideas are brilliant and I'm en route to tremendous success. The point is that LLMs are, by design and current models norms, sycophantic and incapable of describing their own knowledge and workings/processes. This is not a matter of "my opinion vs yours", that's what few minutes spent legitimately trying to understand how this works will tell you.
I'm pretty sure the only reason the video trebuchet wasn't a proper bullet is because it's made out of plastic instead of a ball bearing. Aren't most handguns subsonic?
This is nonsense. You're going to double the efficiency by using "derivatives". As if the expert in this video didn't do any modeling themselves (shown in the video) and wouldn't have considered acceleration at all.
I say, put your money where your mouth is and prove you can double the efficiency.
All the energy is lost to air resistance and left in the machine in the form of parts still moving when the projectile detaches.
Both of those can be modelled - rather precisely if you have the compute power. By modelling the derivative of all of those things with respect to every parameter of a parametric design, losses can be minimised with gradient descent and a huge Jacobian matrix.
A few parameters are obvious (string length, arm length, etc), but there is no need to keep the set small - you could model the exact shape of the projectile latch as a spline with 100 parameters for example, and let gradient descent find the best shape to minimize losses.
AI can set up and run all those simulations, and all you have to do is pay the AWS bill for all the open foam instances you'll be running.
Great video.
Other trebuchet fans who dream of building one some day may be interested in googling "walking trebuchet" for a surprisingly high complexity/results ratio.
Every time I see a strandbeest[1] on the beach somewhere, I wonder to myself why it hasn't got an array of trebuchet included, also recharged by the wind, to pick up sand balls and throw at people.
Just for the fun of it. Pure whimsy.
[1] - https://www.strandbeest.com/
Love it! But shouldn't that be "high results/complexity ratio"?
Depends on if the journey and not the destination is what's important to you. ;)
https://youtu.be/gdXOS-B0Bus
Really wondering up to what point I can build a trebuchet in my backyard before the authorities start to complain
There are three issues that arise
- structural: There are height and size limits on things you can build without a permit
- trespassing: flinging objects onto others people property is illegal
- endangerment: any activity that can endanger other people is illegal
All of these three depend on how rural you live I guess. So in a suburban neighborhood I would assume they get involved very quickly.
I suggest having a BBQ with your neighbors. That should minimize the pre-launch problems. If you use a steel ball bearing like he originally thought, that bullet will be the start of your legal problems.
The key is to live in a place where the authorities are willing to look the other way for some other rewards.
Surely that depends on the side of your back yard?
Maybe it depends more on the vicinity to others' back yards... ?
Interesting that his spool goes bigger at the end...?
I would think you want it decreasing to near zero to extract all the kinetic energy from the mass, leaving the mass stationary as it hits the ground.
I think the idea is that at the end the sling starts to unwind too, increasing the effective arm-length (that non-linearity is one of the reasons trebuchets are so efficient to begin with). As a result it's possible that decreasing the spool to near zero is like putting the gears of your car too high. Reducing the spool size ensures there's enough torque left to put more power into the final swing.
(too late to edit my comment, but I obviously meant increasing the spool size near the end, not reducing)
Interesting
Fuckin love this guy
If you like Tom you will probably also enjoy https://youtube.com/@stuffmadehere
You’ll also enjoy superfastmatt - he mostly does car projects.
I am familiar, and I love that guy too!
Another guy to love:
https://youtube.com/@SteveMould
I, too, enjoy competence porn YouTube.
But seriously, it's one of those things we had preciously little of before online video became a thing.
As long as there have been forums there have been guys and gals making extremely deep and long deep posts and threads about their projects. Video and YT just make it 100x more accessible.
Still have too little of it :(
I would love for this to be optimized to the point that its portable and can be carried around, assembled on the side of the mountain, and used as a low-cost, efficient way to throw things from one mountain to another, maybe for avalanche control, or cloud seeding, or indeed for seed bombs intended for re-wilding hard to access places, or something.
It just seems like such an obvious tool, rather than a weapon.
if you want low cost and portable, chemistry (i.e. gunpowder) always wins over gravity powered.
Or if you have a limited supply of gunpowder but a way to make sufficient numbers of appropriately shaped projectiles, an air rifle would do the job and is much lighter and simpler than a trebuchet.
Isn't it true that you can never generate a supersonic projectile with just air pressure?
I don't believe that is true - rockets produce a very supersonic airflow from gas pressure.
This is so obviously wrong. Show me a field-rechargeable gunpowder-based device for launching things, and I will show you someone who is about to run out of ammo on the side of a mountain they’ve just climbed after a single day of work.
Honestly, what the hell. Where do you think gunpowder comes from, thin air? Oh, is gravity a subscription service in your country?
Come on, try to at least be sensible about your response.
Guns are already ~20-50% efficient at turning chemical energy into kinetic energy. If you're not using a direct chemical reaction for energy, then you're using a human which is a lot less energy-dense than a backpack full of ammo.
And yes, people who do avalanche control typically fire explosives out of a cannon or drop them from a helicopter. Getting a machine supply all the energy is the whole idea instead of climbing mountains yourself.
Do you not understand the immense amount of energy and resources required to manufacture a single consumable cartridge?
The point is to avoid that entirely and harvest gravity.
Re-wilding teams already climb far and wide, and this would extend their reach without increasing their dependencies.
Ammo is a dependency.
Do you not understand your argument is exploring a made-up scenario where we're no longer an industrialized civilization where these things are manufactured cheaply by the billions?
And if you INSIST on making everything completely low-tech and renewable, build a potato gun and use high-proof alcohol as fuel. It'll weigh less and last longer than whatever rube-Goldberg trebuchet design you have.
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>This is false and unimaginative.
A good one will weigh about 5 pounds and not have moving parts to break. Ferment your own alcohol from plants you grow yourself. You can at least do that much, right?
A good one will have as few parts as possible, and be optimized for both portability and distances.
>Ferment your own alcohol from plants you grow yourself
I suppose I could just harvest gunpowder from the bullet trees that grow all over candy-land, too.
Or, I could just have an ultra-optimized trebuchet in my backpack for throwing things with very little effort besides the energy (me) required to reload it, wind it up, and let ‘er rip ..
Well I'd recommend you get out there on a mountain with a trebuchet and try it, because you're certainly not convincing anyone in this thread so far.
Nobody in this thread has demonstrated anything but a distinct lack of imagination and a willingness to be as boring as fuck about a really cool idea, though, so I’m not bothered by convincing anyone.
It’s like saying “why would you use a bow and arrow when you’ve got a 50 caliber machine gun industry right there, ready to help you blow things up”.
I’d use a bow and arrow in the same context - so that I don’t have to have an entire industry dependency just to survive and/or do stuff in the wild.
And before you change the context and say “yeah, why don’t use just use a bow and arrow to do your seed-bombing, huh hippy?”, that thought of course crossed my mind. Soon as I find a supersonic capable bow, that is.
I, for one, would absolutely love to see you carrying up a mountain the contraption in the video with its full 50kgs weight, then raising said weight by three meters with the power of your muscles to launch each single 4 grams pellet, and doing that for several hours every day. I am curious though if you have considered how much you would have to eat to power your muscles, how do you plan to procure the abundant food supply you'd certainly need (and which of course it should have been produced without chemicals and industrial processes of any kind), and how would you carry that up the mountain as well.
What part of "I can't wait to see this optimized into a portable version" did you not understand?
Yes, this prototype is big and unwieldy. So?
The development process is obviously on its way towards the construction of a smaller, lighter version.
BTW, there are rocks up the mountain. They can serve as the weight once you get there.
It's the math of the thing that is going to end up becoming optimal. Not just the material design - which is important once the loading and tolerances are understood. The gearing/screw mechanism is especially interesting from this perspective - it provides a clear path for optimization.
Once he has the equation dialed in, it will be interesting to see it scale down. The winding gear provides a path to optimization on the horizontal plane, and that is going to be very interesting to see go through a few more iterations. Pun, intended.
> What part of "I can't wait to see this optimized into a portable version" did you not understand?
The part where you don't need to load into the system at least as much energy (actually a multiple) as you get out of it.
But there are already a lot of simple, portable and lightweight mechanical systems to launch objects at high speeds, and optimised to be loaded by muscle energy: they're called sling, slingshot, bow, crossbow, etc. They have excellent performance. Since air drag is dominant on small projectiles, speed decays exponentially and the range only increases little with more energy. Claude calculates that a bow can double the video's trebuchet at throwing distance because of the arrow's shape and weight, despite shooting at much lower speed and needing about a quarter of the energy input.
Gravity is not "harvested", it just stores the energy briefly. Someone or something has to lift the weight for every shot, which requires energy.
It's not obvious whether a trebuchet is better than compressed air, like a BB gun.
>lift the weight for every shot, which requires energy.
All harvesting requires some secondary-energy source.
Gravity is a resource, it takes effort to convert it to a form that can be applied - just like wheat, photons, air guns, etc.
> It's not obvious whether a trebuchet is better than compressed air, like a BB gun.
True, it’s not obvious yet, but it sure is fun following along and imagining the final, highly optimal version making its way through the process. I’d use it for some seed bombing hijinks, anyway. Green up the place, I would.
You'd probably be better off using a rail gun if you want a carriable launcher
I thought human-carried railguns were relegated to sci-fi? The power requirements are so high, the only practical mobile railgun is on a ship.
You can buy some on the market now, technically they are coil guns I think.
Problem is the muzzle velocity is pretty paltry right now. I think we are stuck behind the energy density of the power source
Really? With the required infrastructure to charge it, also in the backpack, for a few weeks of work too?
Is gravity a subscription service in your world?
Depends entirely on the specifics of your usecase what concessions you want to make.
One launch location or multiple?
What frequency of launch?
How heavy are the payloads?
How good accuracy?
What transport methods are available?
How long should it operate without maintenance?
Is solar an option if we go electric?
Etc.
Multiple locations, thus the need for it to be easily portable.
I guess a couple hundred launches a day would be useful for seed-bombing/re-wilding, especially on rugged terrain.
Seed-bomb weight: I’d say anywhere from 1-10 grams, maybe?
Accuracy - it’s a seed bomb, you want dispersal to happen, so maybe the more interesting question is, how would you design a seed bomb to survive the trebuchet speeds and g-forces while also allowing for directed dispersal in the intended area. Seed-bomb design for impact conditions is also something of interest - some seeds need to be embedded in a layer of soil, some don’t. There are many parameters to optimize in the seed-bomb side of things, too.
Transport method: backpack-friendly, I think. I’d hike to an area, set up the trebuchet, and spend the day dispersing in a wide circle around the base. If the terrain is rugged, portability is especially important.
Operational time - one thing I think is important is that the trebuchet be resilient for long term use. If Toms’ engineering efforts prove fruitful, I’m sure the material construction will get some optimization such that, perhaps, the only thing that would need to be maintained would be the line - however, this is a known science, see for example the sailing industry, rappel lines, etc.
Solar/electric? I think a wind attachment for rewinding might be a bit more productive.
The scenario: a team of 5 is off for a month in rugged terrain, with the intent of dispersing targeted seed packages over a wide region. The seed bombs are designed to protect the seeds, the trebuchet is designed to deposit them sufficiently well that they remain viable in their final destination. We hike out there for a couple weeks, do a mass trebuchet dispersal, we come back a year later and observe the results.
The railgun guy might have been having a giggle with you, but you gave him some actual numbers so I'll give you some actual math to go with them.
Your biggest problem here isn't the launcher, it's the projectile. It's going to be damn near impossible to get a 1 gram projectile more than a couple hundred yards unless it's a dense metal. Doesn't matter how fast it's going, drag always wins here.
10 grams is more plausible, but then you're looking at ~1000ft-lbs cranking energy to get 10g supersonic (@ 40% efficiency) It's doable and you'll only be burning an extra ~100 calories per day for 200 shots. You might get bored though. An airgun will have far worse efficiency most of the time, though it can launch dart-shape things which can go much further for the material density.
You mentioned a bow, which is probably the tradeoff point of everything discussed so far. Flight bows are designed for distance shooting, are lightweight and can go 500 yards easily. The downside is you'll need to make the arrows yourself, cause there ain't no supply chain to sell hundreds at a time cheaply.
For the "jUsT uSe a hElIcOpTer lol" comment;
No, that's not practical, but you CAN get an RC plane that will carry a couple pounds for a tiny fraction of the cost. In terms of how much area it can cover vs supplies needed, that plane is going to be the least thirsty thing on the mountain, assuming you even need to climb it then.
Would it not be much faster and more efficient to just a use a helicopter to disperse it instead of hiking and setting up a trebuchet? If you are just launching the seed bombs anyways, i feel like a helicopter can cary way more then one person every code, and could just drop a seed bomb every X seconds? Why the need to have people hike out just to launch the seed bombs
You lost me at "just use a helicopter".
Seriously, rich people, get out of your own bubble heads now and then.
A low-tech, low-resource-intensive, no-dependency application of this technology has huge applications around the world.
Do you know how much it costs to operate a helicopter per hour? Now scale it to month-long efforts to turn desert into forests. Scale it to a thousand villagers. Scale it to ten thousand villages.
>Why the need to have people hike out just to launch the seed bombs.
Because re-wilding requires a hands-on approach to be very effective. Just look at what China has done with the Great Green Wall - this was a labor intensive mega-project. Low-tech, highly effective solutions for seed distribution could be of great benefit in that context - without a bit of fancy speculation on our part, we'd still just have deserts and nothing to eat.
YES, you could 'just use a helicopter'. You could just sit back on your deck chair and be served mocktails, too.
Sometimes, kids, you need to do a bit of hard work.
> Do you know how much it costs to operate a helicopter
Do you know how easy and cheap it is to make gunpowder?
I was making black powder rockets from grocery store ingredients when I was 12.
Carrying an extra 50kg weights up a mountain seems inefficient to me, unless you mean a much lighter one or one that you can use stones you find around where you are?
So, a firearm?
Why move gun, when gun can move bullet?
You do know that this thing doesn’t require consumables to operate, right?
What are you throwing that isn’t a consumable, boomerangs?
Also pretty sure several parts of the mechanism would need to be considered consumable if operating over a long period.
Seed bombs aren't consumables, they're reproducibles. I could harvest a thousand of them in the time it took you to make a kilo of gunpowder, from local (mountainside) resources ..
>Also pretty sure several parts of the mechanism would need to be considered consumable if operating over a long period.
Well, that remains to be seen after the optimization steps complete. Fine with me if it takes a year before I have to replace a string.
Meanwhile, I'm guessing you are suggesting the "ma' gunpowder" deliveries happen via drone, or helicopter, or methane-powered rocket ship or some such nonsense, lol ..
Something reproducible is still consumables? Bread is reproducible and consumable, they dont mean opposite things
Bullets don't reproduce.
Seeds do.
Bread is consumed - it does not self-multiply.
You’ve got the solution. Now you just need the problem.
Seed bombing is pretty fun. Re-wilding is a huge industry. Field-reloadable ultra-trebuchets that can be carried and deployed across the landscape, instead of stored in a weapons depot, also a big win for energy harvesters, everywhere.