This is a project that I started in order to learn Blender and also to improve plans that I’m creating for the construction of a physical model of the subject. Because I had created orthographic drawings of the design before I even started up Blender, a lot of the modeling process was just a matter of plugging in coordinates - though along the way I had to learn how to do things like extruding along a path (for the cables) and subsurf modeling (for the legs, among other things).
Right now my goal is to get the whole thing rigged so I can animate it: I’ve been experimenting with different foot rigging methods trying to get an idea of what will work best for this project: I’ve not animated before but ideally I’d like to find something that’s both easy to work with but also will help me maintain certain constraints in terms of the foot’s orientation with respect to the lower leg. (If you can visualize the parts in question, perhaps you can see that there’s not a lot of clearance for certain motions of the foot unless the leg rotates as well) I may just have to suck it up, however, and tweak those sorts of things manually in order to establish my walking animation.
One minor problem I’m trying to solve with the rig right now is shown in the second image: the mesh was designed and modeled with the knee in an upright, locked position. This means the knee joint is actually behind the hip pivot point, which means that the rig during IK doesn’t especially like to bend the knee. I think I can solve the problem by detaching the leg from the skeleton, manually posing the knee in a slightly bent position, adjusting the skeleton to match changes in the mesh’s neutral pose, reattaching the leg to the skeleton, and adjusting the skeleton’s IK rotation limits so it is still capable of going back to the “locked knee” pose.
The thing with the knee is this: like a human knee, it’s only able to bend one way, “backwards”. (“backwards” meaning the lower leg goes backwards as the knee bends) But when the pose is cleared, because of the way the knee was set up, the knee is bent slightly “forward” by default. This means that when I try to use IK to achieve a bent knee pose, it doesn’t always work. This is because the IK solver uses an iterative method to try and figure out how to bend the joints to get to the goal - if it’s trying to find a solution where the distance from the hip to the ankle is shorter (like a crouching position), it’ll try to bend the knee farther forward - and then hit the constraint that limits how far the knee can bend forward, and get stuck. In order to bend the knee backwards, it would make the hip-to-ankle distance longer before it made it shorter - so the IK solver doesn’t easily find that solution. (For an analogous situation - imagine you’re in a six-foot-deep trench next to the Grand Canyon, and you want to go “down”. If you understand the local terrain, you’ll know you need to go up first. But the IK solver doesn’t recognize that it could go up six feet and then down a few thousand - it just gets stuck) For this reason I’m going to need to alter the model a bit - make the knee start out in a “bent backwards” position and then get the “locked knee” pose manually when desired.
newkrg: Your English is probably better than my Japanese, and definitely better than my Portuguese (of which I know nothing).
