8 ms·

Optimising a Trebuchet [video]

128 points by montrose 8y ago

jcims 8y ago
Most of the means of optimizing trebuchets make sense after the fact, but would not be intuitive to me at first glance. For example, making the frame more rigid improved the outcome here, but if you put the whole thing on wheels you would likely still get more increase because the weight could take a more direct path downward as the frame moves.
- gonzo 8y ago
  https://classes.engineering.wustl.edu/2009/fall/ese251/presentations/(AAM_13)Trebuchet.pdf https://classes.engineering.wustl.edu/2009/fall/ese251/prese...
- schiffern 8y ago
  >the weight could take a more direct path downward as the frame moves. That should change how long it takes the arm to drop, but it shouldn't change the amount of potential energy released (and thus, projectile speed).
  - foota 8y ago
    It does, another commenter posted the same person's explanation. But, the idea is that it doesn't matter how much GPE is released, it matters what the velocity of the projectile at release is. If the trebuchet can't move then the weight starts to slow down before all it's GPE is used up. When it can move, it coincides with the time that the projectile is at maximum velocity.
  - jcims 8y ago
    Projectile velocity is a function of power rather than energy alone because you only have so much time to accelerate it.
jimmy1 8y ago
If you enjoyed this one, the video where he adds the wheels is equally fascinating: https://www.youtube.com/watch?v=KpFTyE-wiNo https://www.youtube.com/watch?v=KpFTyE-wiNo
- remarkEon 8y ago
  Wow that was awesome.
- masklinn 8y ago
  To me it's way more interesting than TFA, as it's really not obvious why the wheels would work, and the wheels don't work "out of the box" either, you can't just slap wheels on a tuned "static" trebuchet and need to do some re-tuning to get the correct synchronisation between the arm and counterweight. Really neat.
ramgorur 8y ago
Very interesting. Is it possible to make a trebuchet that can throw stuffs beyond escape velocity?
- 0xBA5ED 8y ago
  Probably not exactly what you had in mind, but there's something called a skyhook which might act kind of like an orbital trebuchet. https://en.wikipedia.org/wiki/Skyhook_(structure) https://en.wikipedia.org/wiki/Skyhook_(structure)
  - herbstein 8y ago
    Video going into detail on Skyhooks: https://youtu.be/TlpFzn_Y-F0 https://youtu.be/TlpFzn_Y-F0
- NickNameNick 8y ago
  The closest thing I can think of is the 'slingatron'. https://en.m.wikipedia.org/wiki/Non-rocket_spacelaunch https://en.m.wikipedia.org/wiki/Non-rocket_spacelaunch
- rebuilder 8y ago
  Naively, I'd think a simple lever could do that, but it becomes a materials science problem: with no constraints on the length of the lever lenght, and no constraints in the density of the counterweight, you should be able to achieve any velocity, right? Well, up to where relativistic effects become an impediment, of course. The question is, is it possible to create such materials as this would require? As you can probably guess, I'm not a physicist. Maybe someone with expertise can chime in here.
  - masklinn 8y ago
    > Well, up to where relativistic effects become an impediment, of course. I don't think relativistic effect would enter the equation for escape velocity (there's a 5 orders of magnitude difference), your issue will be basic material science, namely: * That you'll need to add enough headroom that the payload is still at escape velocity after going through the atmosphere, which means the projectile needs to be launched way beyond escape velocity in a very dense atmosphere. Which means it will instantly burn up / blow up as it leaves the launch system, probably alongside the sling and part of the arm… * except for the counterweight and material rigidity you need for the arm to not be feasible either, you'd need a long arm multiple miles long and a counterweight in the megaton range… before even accounting for the length of the long arm itself, or how you'll actually bring the bloody arm down
simooooo 8y ago
Now THIS looks like an opportunity to use machine learning
bwbw223 8y ago
The superior siege weapon.

128 points by montrose 8y ago

Most of the means of optimizing trebuchets make sense after the fact, but would not be intuitive to me at first glance. For example, making the frame more rigid improved the outcome here, but if you put the whole thing on wheels you would likely still get more increase because the weight could take a more direct path downward as the frame moves.

gonzo 8y ago
https://classes.engineering.wustl.edu/2009/fall/ese251/presentations/(AAM_13)Trebuchet.pdf https://classes.engineering.wustl.edu/2009/fall/ese251/prese...
schiffern 8y ago
>the weight could take a more direct path downward as the frame moves. That should change how long it takes the arm to drop, but it shouldn't change the amount of potential energy released (and thus, projectile speed).
- foota 8y ago
  It does, another commenter posted the same person's explanation. But, the idea is that it doesn't matter how much GPE is released, it matters what the velocity of the projectile at release is. If the trebuchet can't move then the weight starts to slow down before all it's GPE is used up. When it can move, it coincides with the time that the projectile is at maximum velocity.
- jcims 8y ago
  Projectile velocity is a function of power rather than energy alone because you only have so much time to accelerate it.

jimmy1 8y ago

If you enjoyed this one, the video where he adds the wheels is equally fascinating: https://www.youtube.com/watch?v=KpFTyE-wiNo https://www.youtube.com/watch?v=KpFTyE-wiNo

remarkEon 8y ago
Wow that was awesome.
masklinn 8y ago
To me it's way more interesting than TFA, as it's really not obvious why the wheels would work, and the wheels don't work "out of the box" either, you can't just slap wheels on a tuned "static" trebuchet and need to do some re-tuning to get the correct synchronisation between the arm and counterweight. Really neat.

ramgorur 8y ago

Very interesting. Is it possible to make a trebuchet that can throw stuffs beyond escape velocity?

0xBA5ED 8y ago
Probably not exactly what you had in mind, but there's something called a skyhook which might act kind of like an orbital trebuchet. https://en.wikipedia.org/wiki/Skyhook_(structure) https://en.wikipedia.org/wiki/Skyhook_(structure)
- herbstein 8y ago
  Video going into detail on Skyhooks: https://youtu.be/TlpFzn_Y-F0 https://youtu.be/TlpFzn_Y-F0
NickNameNick 8y ago
The closest thing I can think of is the 'slingatron'. https://en.m.wikipedia.org/wiki/Non-rocket_spacelaunch https://en.m.wikipedia.org/wiki/Non-rocket_spacelaunch
rebuilder 8y ago
Naively, I'd think a simple lever could do that, but it becomes a materials science problem: with no constraints on the length of the lever lenght, and no constraints in the density of the counterweight, you should be able to achieve any velocity, right? Well, up to where relativistic effects become an impediment, of course. The question is, is it possible to create such materials as this would require? As you can probably guess, I'm not a physicist. Maybe someone with expertise can chime in here.
- masklinn 8y ago
  > Well, up to where relativistic effects become an impediment, of course. I don't think relativistic effect would enter the equation for escape velocity (there's a 5 orders of magnitude difference), your issue will be basic material science, namely: * That you'll need to add enough headroom that the payload is still at escape velocity after going through the atmosphere, which means the projectile needs to be launched way beyond escape velocity in a very dense atmosphere. Which means it will instantly burn up / blow up as it leaves the launch system, probably alongside the sling and part of the arm… * except for the counterweight and material rigidity you need for the arm to not be feasible either, you'd need a long arm multiple miles long and a counterweight in the megaton range… before even accounting for the length of the long arm itself, or how you'll actually bring the bloody arm down

simooooo 8y ago

Now THIS looks like an opportunity to use machine learning

bwbw223 8y ago

The superior siege weapon.