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Optimising a Trebuchet [video]

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Re: Optimising a Trebuchet [video]

#11

Post by jcims »

schiffern wrote: post #7
jcims wrote: post #2

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.

>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).

Projectile velocity is a function of power rather than energy alone because you only have so much time to accelerate it.

Re: Optimising a Trebuchet [video]

#12

Post by rebuilder »

ramgorur wrote: post #6

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

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.

Re: Optimising a Trebuchet [video]

#14

Post by masklinn »

jimmy1 wrote: post #3

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

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.

Re: Optimising a Trebuchet [video]

#15

Post by ColinWright »

ramgorur wrote: post #6

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

Orbital Velocity at grazing altitude is 8 km/s, and escape velocity is sqrt(2) times that, or about 11.3 km/s. Thing is, anything travelling that fast in the atmosphere tries to turn to plasma, so your launch arm would need to be a bit special.

Or at very high altitude.

Or have ablative heat shielding.

But atmospheric drag would probably prevent you from getting anything like those speeds with this kind of mechanism.

Re: Optimising a Trebuchet [video]

#16

Post by masklinn »

rebuilder wrote: post #12
ramgorur wrote: post #6

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

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 pr…

> 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

Re: Optimising a Trebuchet [video]

#17

Post by ygra »

ColinWright wrote: post #15
ramgorur wrote: post #6

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

Orbital Velocity at grazing altitude is 8 km/s, and escape velocity is sqrt(2) times that, or about 11.3 km/s. Thing is, anything travelling that fast in the atmosphere tries to turn to plasma, so your launch arm would need to be a bit special. Or at very high altitude. Or have ablative heat shielding. But atmospheric drag would probably prevent you from getting anything like those speeds with this kind of mechanism.

So on the moon it might work ;)

Re: Optimising a Trebuchet [video]

#18

Post by herbstein »

0xBA5ED wrote: post #8
ramgorur wrote: post #6

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

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)

Video going into detail on Skyhooks: https://youtu.be/TlpFzn_Y-F0

Re: Optimising a Trebuchet [video]

#19

Post by ColinWright »

ygra wrote: post #17
ColinWright wrote: post #15

Earlier quoted context omitted.

Orbital Velocity at grazing altitude is 8 km/s, and escape velocity is sqrt(2) times that, or about 11.3 km/s. Thing is, anything travelling that fast in the atmosphere tries to turn to plasma, so your launch arm would need to be a bit special. Or at very high altitude. Or have ablative heat shielding. But atmospheric drag would probably prevent you from getting anything like those speeds with this kind of mechanism.

So on the moon it might work ;)

Vacuum helps, certainly. Also the escape velocity on the Moon is about 2.4 km/s.

That's still rather fast ...

Re: Optimising a Trebuchet [video]

#20

Post by dividuum »

ColinWright wrote: post #15
ramgorur wrote: post #6

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

Orbital Velocity at grazing altitude is 8 km/s, and escape velocity is sqrt(2) times that, or about 11.3 km/s. Thing is, anything travelling that fast in the atmosphere tries to turn to plasma, so your launch arm would need to be a bit special. Or at very high altitude. Or have ablative heat shielding. But atmospheric drag would probably prevent you from getting anything like those speeds with this kind of mechanism.

This happened before: https://en.wikipedia.org/wiki/Operation_Plumbbob#Propulsion_...
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