target bone issue

[Mick]

I'd love to be able to use target bones... but I've got one problem with them I just can't get past. When I create a leg and use a target bone at the feet, the knee will only bend one direction. I'm not limiting the bones rotation with "angle constraints", but the bone will only allow the knee to bend one way. Either clockwise or counter clockwise... it seems to be random. What am I doing wrong?

[Greenlaw]

...When I create a leg and use a target bone at the feet, the knee will only bend one direction...Either clockwise or counter clockwise... it seems to be random. What am I doing wrong?

IK needs a little pre-bend to tell it which way to bend. When there is no pre-bend, Moho has to guess which way you want the joint to bend, thus the randomness. So on frame 0, give the knee joint a slight angle. You don't need to bend the art, just the bones. This will make the IK with target bend the knee in the preferred direction.

During animation, you can change the direction of the bend. To do this, keyframe the leg bone just before the direction change, then using Manipulate Bone, scrub the lower leg bone toward the opposite direction. If the knee still has a slight bend when you keyframed it, you will see it pop and change direction, and a keyframe will be created there.

If you do get that pop, you can smooth it out by raising the character's root (hip) bone slightly or by keyframing the length of the leg bone. Using a Squash And Stretch Constraint on the leg bones is another way to smooth it out.

Hope this helps.

[Mick]

Nice... that worked. That's going to be a big help. Really appreciate it.

[Greenlaw]

Cool, glad to help.

BTW, I left out something: when rotating the bone with the Manipulate Bones tool, you need to also hold down Alt. This temporarily changes the MB tool to FK mode so it rotates only the one bone. (Alternatively, you can switch the the Transform Bone tool to rotate the bone, but I think holding down Alt with MB is easier because then I don't need to switch tools.)