Rigging a Bow

[ariel]

I am having some problems trying to create a rig for a Bow (as in bow and arrow). I've tryied using spline IKs and Bend NL Deformers, but so far haven't had any real luck in getting a realistic reaction on the string and the bow itself.
This is the problem: The string has to drive the bend of the bow, but only at the time of the pull. When the cord is released the bow "unbends" (if that's a word) until it is straight, but the string has to bounce and vibrate like a gitar string until it stops, but it has to do so without driving the bows bending anymore. And it all has to happen with both ends of the string attached to the bow and never slipping or moving off the ends of the bow.
Right now i modeled this as two objects, maybe combining them into one single poly object might, help.
Any ideas?

[goggle]

I would probably keep it as two separate objects. Put some bones in the bow and make a wire deformer curve for the string. When creating your wire, put two CVs very close together in the center and two close together at each end. Cluster the pairs of CVs. Constrain the outer clusters to the ends of the bow.

Group your bow and bowstring together.

Create a Set Driven Key relationship between the bones in the bow and the center cluster on the bowstring such that when the cluster moves back the bow bends.

Now duplicate the bowstring. Use the duplicate bowstring (without the Set Driven Keys) for the vibration section of your animation. With careful keying of the cluster positions and the visibilities of the bowstrings the changeover should be unnoticable.

Hope this helps.

-James

[goggle]

Actually you can parent the end clusters to the end bones in the bow too and it'll work fine. And I guess if you do the Set Driven Key properly you wouldn't need to duplicate the bowstring either.

-James

EDIT:

Like this?

Thanks for asking this question. It's been a while since something interested me this much.

[ariel]

Thanks arcsecond. This seems to be working properly. I tried it and actually, creating a second string might not be necessary because after the string goes past a certain point when coming back to the unstretched position, the bow should stop moving automatically and this leaves room for the vibration to occur without bending the bow. One thing, though. When using the wire deformer, after a certain point, the stretch in the string creates a pinching efect, similar to the one that occurs in elbows with the default skinining in Maya. Sort of the "water hose" elbows we all hate. Do you have any ideas on how to fix this?

Hmm, maybe deforming a lattice instead of the string directly might help. I'll try it.
huge thanks again

[ariel]

Exactly!
That's just wat i need to create. I loved the example. Nice motion on the vibration too. I know I already asked nut since i saw how your example looks, i'll ask again. How did you create the smooth deformation on the string without the pinching (it is rounded where your hand pulls, instead of sharp and pointy like what i had)? And, did you use the two strings like you suggested, or did you get the effect with just one?
Thanks

[kmp3d]

thats pretty cool arcsecond I was wondering about how you would go about that...... can you make it shoot an arrow?

[goggle]

Just one string in this case. I was able to set up the Set Driven Key so that the bow doesn't start bending until the center cluster is far enough out to accomadate the vibration.

The deformation of the bowstring was just a simple wire deformer. The pinching you talk about is probably caused by the distance between the two center points on the wire curve. Farther apart would equate to less pinching.

Now I'm going to have to model an archer character. :-7

-James

PS. checked out your website. pretty cool models. I named one of my computers Actaeon.

[goggle]

Thanks,

and,... by request:

A simple arrangement of constraints and locators. Although in my personal opinion I think the animation seriously sucks. The bowstring doesn't vibrate properly. Nor does the draw have any feeling of weight. You can tell I was messy when creating my wire deformer as the ends of the bowstring goes weird when rotated. But I guess you can't expect much from 5 minutes work.

-James

[kmp3d]

dude that was awesome ...... could you write a tutorial on that or something.... just for some more insight......please

[ariel]

Thanks for the comments. Actually the bow is for Actaeon himself. I'm starting to model his equipment and clothing (I'm battling with cloth at the same time as you can see from the examples .avi's on my website).
Your response has been a great help.
So were your cool movie files for demonstration. I greatly appreciate it.