Hello there, I am currently rigging a robot and I am encountering this issue with the leg. The knee joint is positioned toward the back of the leg (not in the middle) so when i position the leg guide, the root leg, knee and ankle triangle is pointed in the wrong direction. I am wondering if there would be a way to keep this model and still get a proper IK controller or do I have to change the model? Any ideas how I could fix this issue would be very appreciated.
I don’t know. There might be some tricks/hacks/math you can do. For example, have an opposite angled IK, and read the rotations from it, to indirectly drive the backwards one. (I don’t know if it would work. I’m just guessing ideas.)
Or experiment with the “reverse” attribute on the IK solver. It’s a float from 0-1, so you might be able to smoothly transition. But that could be annoying during animation. Maybe you could figure out a way to do an automatic driver based on the length of the limb. (Same as how a stretch driver works.)
But no matter what you do, and even if you can get it working, I think you’ll experience some pretty difficult pops/counter-animation when the chain bends back to a forwards position when the knee bends. Soft IK would help too, but it changes the neutral position.
This is likely what I would suggest, if you want to try to keep the proportions of the model the same.
- Rig this as it is.
- Turn on “reverse”
- Lower the hips until the leg has a slight forward bend.
- Freeze out the model, and re-rig it in that pose. It should all be relatively the same.
- If/when you want to fully extend the leg back to this backwards pose, you can use the reverse attribute again to get there.
Or another idea: just ignore the cylinder in the knee. Put the bone closer to the front of the square part of the knee. That square could maybe rotate 50% between the upper and lower leg, which might help hide the pivot location. The cylinder could just follow that square. And it could rotate in place, as an effect.
Thank you Chris for the reply, I didn’t know about that reverse attribute. I applied the suggested method and it works really well ! The difference in the pose isn’t that big so the design of the character is still very similar. That robot will be able to walk soon!