Mechancial Rig Question

[RobertoMolvado]

Hello,

I've created a mech robot and now I want to create a rig for it. But the problem is, that none of the joints are 'ball and socket joints'. So the joints can only rotate in one dimension, like a typical mechanical joint. My first solution was simply locking two out of three rotation axis for the bones and this works fine for FK animation. For IK animation however, it doesn't work. The locks are simply ignored.

Is there any way to lock a rotation axis for an IK bone system?

This is very hard to explain, I hope it suffices. 

Picture attached below. The blue and green cilinders refer to axis where the two joints should rotate around.

[samab]

Select an object in your IK chain. In the motion panel, select IK. There you can set up your joints on each axis.

[RobertoMolvado]

Thank you very much for your reply.

I couldn't find anything IK related under the motion panel, however, there was  an IK tab under 'hierarchy'.

I unchecked all the axis I want locked. This seemed like exactly what I wanted, but now for some the reason the IK barely works at all. I attached the file for clarification.

[jknutson2]

I'm guessing you are having the same problem that I am.  The HI IK Solver appears to work in a single plane.  In other words all joints must be coplanar.  If they are not, then you will get twisting occuring even if you set the preferred rotation axis.  To see an example video clip of the problem, see: http://www.youtube.com/watch?v=WSLNUnPFGAI.

I've tried figuring out how to replace the HI IK Solver with the HD IK Solver, but I think it has the same constraints, but allows for sliding in addition to rotation.  It's hard to tell since I can't seem to find much docs on how to use the HD IK Solver.

Anyway, if someone has an idea of how to rig joints that are not coplanar, I'd like to know about it.

[jknutson2]

After a bunch of experimentation, it appears that having the goal out of plane with the root bone rotation is possible.

You create the bone chain, add the HD IK Solver, select the root bone, use the heirarchy IK panel to constrain the rotation axis, select the terminator bone, delete the position end effector, create your position dummy and align it to the terminator bone, bind the end effector to the dummy, then create the position end effort.

Don't ask me why the last two seem reversed. If I do it the other way around the end effector jumps way off and I can't get the dummy and end effector to align.

[jknutson2]

By the way, I created a couple of short videos illustrating the HI and HD IK usage pattern:

3ds Max Mechanical Rigging - Part 1: HI IK Solver

3ds Max Mechanical Rigging - Part 2: HD IK Solver