bone locking and bone dynamics

basshole · Post by **basshole** » Wed Jan 21, 2009 1:00 pm

Ok, two questions in one here:

With bone locking, it seems like a relatively simple concept, but gives me issues. For instance, If a character's arm has two bones, upper arm and lower arm, and I'm trying to see how the movement of the lower arm as it rotates will look, I'll lock the upper arm to try to keep it from moving. Sometimes, this works like it should, but sometimes, the lower arm (still unlocked) won't move anymore after I lock the upper arm. Why would this be? Is it a glitch or something I did?

Regarding bone dynamics, I found a few threads on here, but nothing about the real basics of how they work. Am I given to understand that you can't see the dynamics in action until export out a movie? that seems very cumbersome. But if I just set up an animation in the timeline and watch it, I don't see the dynamics working. Is this how it is? Also, I read on here that you can't just give the dynamic bones certain settings (for torque force, etc.) and expect them to work correctly in all situations, that depending on the speed of the animation, they may need tweaking. Does that mean they're keyframe-able? Can someone give me some settings to start with for something like hair? say, a ponytail?

thanks.

slowtiger · Post by **slowtiger** » Wed Jan 21, 2009 1:11 pm

1. In your example I just would use the Rotate Bone tool to grab and rotate the lower arm, it will leave all other bones untouched.

The Lock Bone feature only makes sense if you want to reverse the Kinematic Chain, say locking a foot or two on the ground to be able to just grab the body and let it dance, so the knee will bend automativally.

2. Bone dynamics works in playback in the normal workplace view.

funksmaname · Post by **funksmaname** » Wed Jan 21, 2009 1:12 pm

Hey Basshole

Q1: if you use the bone rotate tool (R) rather than the bone manipulate tool (Z) then it will only rotate the bone you move rather than the entire chain - no locking necessary.

Q2: I never use dynamics - personally i find that animating secondary motion by hand gives better/quicker results than messing with dynamics options... but as far as i know, they will show when you 'play back' your animation, no need to RENDER...

----

edit: damn you tiger :d ... i'll get you next time

synthsin75 · Post by **synthsin75** » Wed Jan 21, 2009 1:15 pm

Bone locking only works for the last bone in the chain. Either that upper arm is the last in the parent chain, or you are mistaken that it actually worked.

Bone dynamics show up differently in the workspace depending on how you have it zoomed in. Zooming it to default should show them correctly without rendering. Any other zoom will show them as more or less dynamic than they really are.

Dynamics must be tweaked for each motion.

Basically:
Torque - how much the parent bone's motion starts the dynamic moving
Spring - how much the parent's motion keeps the dynamic moving
Dampening - how quickly the dynamic is stopped

basshole · Post by **basshole** » Wed Jan 21, 2009 2:00 pm

Thakns for that rotate bone tip. . .I've never messed with that in a frame other than 0. . .who knew?

Maybe you're right about not using dynamics at all.

Post by **Víctor Paredes** » Wed Jan 21, 2009 2:03 pm

synthsin75 wrote:Bone dynamics show up differently in the workspace depending on how you have it zoomed in. Zooming it to default should show them correctly without rendering. Any other zoom will show them as more or less dynamic than they really are.

For me, it depends of the complexity of the animation too. Bone dynamics will work fine in preview if you haven't a very complex scene, but if you have it, F5 is your key. The same thing happens with bone locking, sometimes in editing view you see errors that really doesn't exist when rendering.

heyvern · Post by **heyvern** » Wed Jan 21, 2009 9:12 pm

I've explained this in other topics but bone locking depends very much on the bone chain itself. It uses an algorithm to determine how each bone reaches a specified target.

If the bones in your chain don't allow some of the bones to "reach" their "targets" correctly you get odd results, spinning, popping, and the locked bones "floating" and not staying locked in position. The trick is to allow enough "play" or slack in the chain and making sure you don't move the bones not locked to extreme positions to break the IK solver algorithm. Sometimes "forcing" rotation keys on bones in the chain will fix pops and spins.

The bone lock feature doesn't care about direction of rotation to reach a target. It doesn't know you don't want a leg to bend backwards. It uses the shortest rotation distance to reach the target specified by the IK solver.

-vern

chucky · Post by **chucky** » Thu Jan 22, 2009 1:08 am

with dynamics , under the Animation drop down un-check Allow Frame Skipping. Also after tweaking restart from the beginning rather than playing from elsewhere in the time line.
Dynamics are cool , but a bit tricky for short loops.