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Blender: managing bone roll angles
tetsujin0
Posts: 0Member
I'm hoping someone can help me with this problem.
I recently added a "double piston" to my Zaku Kai mesh, in the upper leg. The piston is supposed to extend as the knee bends.
I'm having a few problems with this. First off, I can't get the bone roll angle quite precise - which means that if I use a locked track to make the two halves of each piston track each other, and lock the direction of the bone's X axis, the piston tilts off-target slightly as it extends. It'd never be noticeable in practice but as a modeler I hate that kind of sloppiness. I've mitigated the problem by getting the orientation of the bones' X axes as close as possible to the intended direction, and then using an IK solver (with Y rotation locked, Z limited to a few degrees, and X limited to reasonable limits) instead of a locked track. It works, but what it really means in practice is that the pistons are rolling relative to the leg (slightly) as the knee bends. I could solve the problem if I could just make the Z axis of the bone point straight forward (as much as is possible without changing the positions of the bone's endpoints, anyway) but I don't know how to do that in edit mode - apart from doing it manually.
The other problem is that when I grab the IK target for the leg, move it, and then abort, the piston will sometimes wind up pointing out the side of the leg. I'm guessing it's just a bug in Blender - I can fix it by grabbing the armature again.
I suppose it might be possible to fix this by having the model's "neutral pose" be such that the leg bones would all be parallel to the YZ plane, rather than at a 10 degree angle from it: it seems that roll angles on bones that are parallel to one of the main axis planes are more stable - one of the bone's axes will be perpendicular to the plane. I think it'd be preferable not to do that, though, as with those big legs and big feet it's really not a design that's supposed to have its legs be straight up. (<shrug> - I guess I can still do anything I want in pose mode, so maybe I should rethink that - but it makes me wonder how I'm supposed to handle situations where that kind of thing simply isn't an option.. What if the robot were bow-legged? Some designs, like the Sazabi, are visibly bow-legged, so it's not entirely an academic question.) It seems I can't even solve the problem by creating the bones parallel to the YZ plane and then rotating them around the Y axis - the act of rotating them fouls up their roll angles again.
I recently added a "double piston" to my Zaku Kai mesh, in the upper leg. The piston is supposed to extend as the knee bends.
I'm having a few problems with this. First off, I can't get the bone roll angle quite precise - which means that if I use a locked track to make the two halves of each piston track each other, and lock the direction of the bone's X axis, the piston tilts off-target slightly as it extends. It'd never be noticeable in practice but as a modeler I hate that kind of sloppiness. I've mitigated the problem by getting the orientation of the bones' X axes as close as possible to the intended direction, and then using an IK solver (with Y rotation locked, Z limited to a few degrees, and X limited to reasonable limits) instead of a locked track. It works, but what it really means in practice is that the pistons are rolling relative to the leg (slightly) as the knee bends. I could solve the problem if I could just make the Z axis of the bone point straight forward (as much as is possible without changing the positions of the bone's endpoints, anyway) but I don't know how to do that in edit mode - apart from doing it manually.
The other problem is that when I grab the IK target for the leg, move it, and then abort, the piston will sometimes wind up pointing out the side of the leg. I'm guessing it's just a bug in Blender - I can fix it by grabbing the armature again.
I suppose it might be possible to fix this by having the model's "neutral pose" be such that the leg bones would all be parallel to the YZ plane, rather than at a 10 degree angle from it: it seems that roll angles on bones that are parallel to one of the main axis planes are more stable - one of the bone's axes will be perpendicular to the plane. I think it'd be preferable not to do that, though, as with those big legs and big feet it's really not a design that's supposed to have its legs be straight up. (<shrug> - I guess I can still do anything I want in pose mode, so maybe I should rethink that - but it makes me wonder how I'm supposed to handle situations where that kind of thing simply isn't an option.. What if the robot were bow-legged? Some designs, like the Sazabi, are visibly bow-legged, so it's not entirely an academic question.) It seems I can't even solve the problem by creating the bones parallel to the YZ plane and then rotating them around the Y axis - the act of rotating them fouls up their roll angles again.
Post edited by tetsujin on
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Posts
also sometimes, you might want to loc just the position of the bone in certain areas and not its rotation...but i never really had your problem before when i had animated a alien...
it also might be the view your in, sometimes if your not in the front top or side view and move things around you can move the bones rotation to and mess it up just slightly, but since i have seen your model i highly doubt this could be the problem
to clear the rotation i believe is ctrl-r when the bone is selected