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View Full Version : FXWars! Catapult! (Trebuchet) : gaggle


gaggle
07-15-2004, 04:31 PM
Quite the interesting challenge.. I knew from the get-go I didn't have much time to spend on this, so I set my goals low: just a proof-of-concept would be good. Even that took longer to complete than I had anticipated, but oh well, I learned from it so it's all good.

But anyway, due to limited time this is pretty much as finished as my entry will ever be. Others will have to make the really cool stuff :).


http://gaggle.dhs.org/hosted/trebuchet/trebuchet.jpghttp://gaggle.dhs.org/hosted/trebuchet/lockingPinCloseup.jpg

So this is my barebones trebuchet system. The pouch is faked, there was no way I could complete this within my schedule if I added softbody interaction to the mix. So the projectile is attached by a keyframed constraint that turns off at the appropriate time. I know it's a big fat cheat, but.. oh well.

The rest is more or less dynamic though. Here's a rundown of the setup:
green: hinge constraint
yellow: pin constraint
red: pin constraints for firing-arm rope
blue: pin constraints for projectile rope


The firing-arm is kept in place by having the lockingpin collide with a pair of eyescrews (marked pink in 2nd image). The lockingpin and firing-arm is connected by a rigidbody rope (marked red). The rigidbody rope consists of simple geometry connected via pin constraints (see picture 3 for details, pin constraints marked with white).
At one time I had a solution where the machine fired as I pulled the lockingpin out, but I opted for just keyframe disabling the constraint in the end. For me it's enough to know that it works "physically correct" if I needed it, I just wasn't going to sit through simulation after simulation looking at that key being pulled out. Takes long enough to compute as is :).

http://gaggle.dhs.org/hosted/trebuchet/screencapture01.jpg


This whole project is about a days worth of effort. I don't know that much about (Maya) dynamics, that's why I was so interested in trying this out.

I learnt that I cannot get softbody ropes to interact with rigidbody objects. It is seemingly impossible to cock the firingarm by pulling an attached softbody rope. If anyone has a way to make this happen I'd be very interested, it seems like a simple action but I found little that worked.
So I ended up switching to rigidbody ropes instead, which works pretty well. The ropes are clearly extremly simplified, for "pretty" results they shouldn't be rendered but act as influence objects on a smoothskinned tube. Also obviously more segments are needed. But the simplified ropes made for quicker calculations, so horray.

Oh, also not all objects collides with eachother. Each rope (projectile- and firingarm-rope) only collides with itself and the ground, I know that's a cheat but I wasn't going to sit through all that collision.


Below is the link to the movie, and the project files. I hope by freely giving away the scene files someone outhere can learn something or other. Or learn what not to do perhaps.


Here's the movie (2,09 mb):

http://gaggle.dhs.org/hosted/trebuchet/stillFrames.jpg (http://gaggle.dhs.org/hosted/trebuchet/gaggle_trebuchetFiring.mov)
And the project can be aquired here (http://gaggle.dhs.org/hosted/trebuchet/gaggle_trebuchetProject.zip) (604 kb). It's Maya 5.0.1, and all rigidbodies are pre-cached.



Finally I'll just link a couple of playblasts I outputted. It turned out hitting that damned wall was damn difficult. Tiny changes in weight and tension generated (at times) wildely different results. I haven't optimized the playblasts so filesizes are on the large size.
blast2_cocking (http://gaggle.dhs.org/hosted/trebuchet/blast2_cocking.avi) (1.18 mb) - blast3_firstShot (http://gaggle.dhs.org/hosted/trebuchet/blast3_firstShot.avi) (634 kb) - blast5_completeDisaster (http://gaggle.dhs.org/hosted/trebuchet/blast5_completeDisaster.avi) (4.02 mb)

veanova
07-15-2004, 04:53 PM
Looks good, even with the lil' cheat :) But your playblasts crashes my winamp for some reason.. anyone else having that problem?

gaggle
07-16-2004, 12:12 AM
Ouch, must be the Cinepak codec. I know it's an awful old codec..

If you can't run them with the various Windows Media Players either I don't know what can be done. Thanks for wanting to check them out though :o), sorry for the lame encoding.

veanova
07-17-2004, 10:40 PM
Hey thanks for making your project available for download, I'm checking it out now! Looks good, but the outliner is really messy since you haven't named anything! :) Apart from that, it's great, learning lots here now!

Projectkmo
07-17-2004, 11:54 PM
I too want to thank you for being so kind as to share your scene file like that. The dynamics are giving me trouble, and this is helping a lot. Sadly though I dont get much when I play through your animation.....the rope sags but thats it. I'm going to continue fiddling around and see if I can figure it out. Thanks again!

**NM, I got it to work, errr your scene that is = )..still working on mine**

John

gaggle
07-18-2004, 10:31 AM
*blushes* yeah that outliner isn't pretty. Usually I keep better order, I swear! :)

Terrific to hear the files are useful! Thanks for taking time to say that. If there are questions 'n whatnot just fire away.

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