NewtonPlayGround

Share with us how are you using the powerrrr of the force

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Postby Sascha Willems » Tue May 10, 2005 11:15 am

I went back to medieval times with my current version of the playground ;) :

(Clicky for 800x600)
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And here is a 10sec video of it in action (WMV, 1,5 MBytes).

I'm really surprised how nice this thing acts. It totally feels like a real catapult (in fact it's a "Tribock", but I don't know the english translation for that word), and only the part that holds the bullet could be modelled better so the sphere would fly along a nicer curve than now. So once again Newton surprised me by not only its simplicity but also by it's realistic behaviour.
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Postby Assembler » Tue May 10, 2005 11:32 am

cool!
Programming is just for 15 year old boys! Not for grown ups! :)

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Postby Julio Jerez » Tue May 10, 2005 9:29 pm

Man if you keep making this kind of demos, soon we will have take out the word Game for NewtonGameDynamics and call it NewtonModelingSimulationDynamics.
This is very nice. I like the fact that when the weight is coming down the whole trebuchet moves forward, a behavior that is not obvious by just looking at the design, but it makes perfect sense after you see it working. Now I know why in the movies using these weapons they always place a big wedge on the front wheels. It will be interesting to see if the rock will travel farther by doing that, the reason is that the trebuchet converts a lot of its potential energy to kinetic energy when it slides forward, but if it is stopped by a wedge then almost all the energy will be transferred to the rock, allowing it to travel farther.
It is just a speculation but if this happens in the simulation isn't wonderful how that famus law nothing is lost nothing is destroy it only change form.

There are some hidden powers in the Newton engine some people in the physics arena may consider unnatural.
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Postby walaber » Tue May 10, 2005 11:48 pm

that is glorious. I beleive in English we just use the French word "trebuchet". reminds me of the "Age Of Empires" games... the trebuchets were my favorite weapon. :D
Independent game developer of (mostly) physics-based games. Creator of "JellyCar" and lead designer of "Where's My Water?"
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Postby Sascha Willems » Wed May 11, 2005 3:52 am

You're totally right Julio. I just tried and put a box with zero mass in front of the trebuchet (thanks for the name correction walaber ;) ) and it ends up throwing the ball much far than when it has no stopper in front of it.
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Postby Code-R » Wed May 11, 2005 7:18 am

walaber wrote:...I beleive in English we just use the French word "trebuchet"....

"Catapult" has more English Correctness, The first time I actually saw "Trebuchet" used in an English context was AoE2.
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Postby Julio Jerez » Wed May 11, 2005 7:27 am

And the crowd ask for a video of the two side by side, one owth the stopper and the other without.
Video, video, video, ehhhhh
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Postby JoeWright » Wed May 11, 2005 8:54 am

I remember seeing a reconstruction programme on BBC about Trebuchets. In it they found that letting the trebuchet move (i.e. wheels, no block) made the projectile go further than a model with no wheels.

Any thoughts on the discrepancy?

Joe

Nice demo btw
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Postby Sascha Willems » Wed May 11, 2005 9:05 am

Julio Jerez wrote:And the crowd ask for a video of the two side by side, one owth the stopper and the other without.
Video, video, video, ehhhhh


Oh well, to make the crowd happy it should look at this video (~3 MBytes).

You'll see 3 times the same catapult, the first without any stoppers, the second with one stopper in front and a third with stoppers front and back (which makes it static). As you can see from the video, the bullet will fly further when there is at least one stopper. In my opinion this seems (although Joe mentioned something opposite, dunno what they did in that documentary) logically, since a moving catapult will "burn" some energy for it's movement which is then lost for accelerating the bullet. But that's just some wild guess ;)
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Postby registration information » Wed May 11, 2005 9:37 am

Code-R wrote:
walaber wrote:...I beleive in English we just use the French word "trebuchet"....

"Catapult" has more English Correctness, The first time I actually saw "Trebuchet" used in an English context was AoE2.


Catapults and trebuchets are not the same thing :-P




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Postby Julio Jerez » Wed May 11, 2005 10:07 am

Oh not discrepancies. Here is what happens
The trebuchet made by Sascha only has one arm, for that particular case if it does not move then more momentum is transferred to the rock.

I you observe the real model they have a double arm so the ball gets more velocity because it has a longer arm. The wheels allow the double arm mechanism to fully extend by moving forward when the counter weight fall.

The trebuchet with the double arm is just using more of the potential energy left, by allowing the arm to fully expand, but the wheels are stealing momentum from the system by allowing the base to slide, that energy can not come from the vacuum.
If not wheels are added then arm does not expand and the energy is eaten by the friction with the ground, and the ball does not travel too far.

The double arm trebuchet is like a sling shot that by tuning the resonance you can make so it uses the most possible energy of the system.

If they made the trebuchet with a very long single arm of a length equivalent to the length of the double arm extended, then ball would travel even farther than the double arm on wheel but this was physically implausible because the was not way to get a light material that long and that strong. If you notice the second arm is a wire with very little weight.

Here is what I predict:

Double arm not wheels – very short range
Double arm on wheel – medium range for the rock
Single arm equivalent to double arm fully extend not stopper– medium range for the rock
Single arm equivalent to double arm fully extend – the longest range

Here is a site that show and explains why the double arm wheels had longer range,
http://www.pbs.org/wgbh/nova/lostempire ... heels.html

but remember the comparison is to other double arm without wheels, there was not way to make a trebuchet with a really long arm.

Sascha: beautiful isn't the Law of conservation of momentum beautiful.
You can almost feel it when you can see it so close in action.
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Postby Sascha Willems » Wed May 11, 2005 10:41 am

Thanks for those deep insights into how those things work. I've put that one together quickly and in the dark middle ages I'd propably gotten hung for building such an ineffective Trebuchet ;)

But as soon as the new version of my Playground is released (I think I'll wait for the next minor NGD-release) people will be able to build catapults/trebuchets/whatever like they want tho have them.
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Postby Sascha Willems » Wed May 18, 2005 12:28 pm

Since I won't release the new version of NewtonPlayGround before the next NGD-Release (1.35, not 1.5) I decided to upload some recent (taken today) screenshots (as usual click for a bigger version) :

Image
The before posted constellation with three catapults. All catapults are the same, with the same bullet. The only difference are the stoppers.

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This shows how one can use compound collisions to make (almost) tri-colliders. You can see a chain where each chain-part is made up of a ring constructed with several compounds.

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A very basic Newton's cradle rebuilt (see my Newton's cradle demo for a nicer implementation) in NewtonPlayGround.

Image
And this is one of the most recently integrated features. You can now freely place (there is a special dialog for it) and configure buoyancy volumes as much and as many you like.

Compared to the changes between the other versions (e.g. 1.1 to 1.2) this will be the biggest updates, and the list of changes is already rather large and with the release of 1.35 will even get longer :
Code: Select all
 - New ego mode (press "t" to toggle)
 - Added compound collision (can only be loaded from 3DS files)
 - Support for Buoyancy features of NGD. User can spawn buoyancy volumes with own parameters
 - New dialog for all global scene settings concerning newton (material, solver, fps, gravity)
 - New dialog to change rigid body's properties after it's creation (position, rotation, mass)
 - Global newton settings for scene are now also exported and imported to and from XML
 - Joints can now be offset relative to their parent
 - Joints visualized during their finalization
 - Added axis-helper in lower left screen corner
 - New prebuilt scenes
 - Starting the demo with the parameter "-window" will start it windowed
 - Possibility to take screenshots (press "s" and see the "screenshots"-folder for the JPG then)
 - Changed rendering code for convex hulls. They now can also have textures on them.
 - Changed rendering code for collision tree environment. They now can also have textures on them.
 - Changed rendering code for vehicles. They now can also have textures on them.
 - Fixed wrong decimal separator when loading/saving vehicles into XML files
 - Spiced up graphics a bit
 - Some changes to the user interface
 - Now comes in form of a handy installer

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Postby Sury » Wed May 18, 2005 12:50 pm

This is starting to look as a very powerfull physics editor for Newton, especially with it's import/export functionality.
Can't wait to try it out in action.
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Postby Sascha Willems » Fri May 20, 2005 5:06 am

And that's what it's intended for ;) I hope people start using it for prototyping or even maybe constructing physics scene, since XML can be easily parsed.
The only thing missing in the current version is a material system that exposes Newton's power material interface. But I already started working on it and already have some ideas on how to implement it in my NewtonPlayGround. But since it's a quite complex matter (and I want it to be done proper, no quick and ugly hack with a bad UI) materials won't be in the next version, but a version later.
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