Hello forum! I'm fairly new to Houdini, very experienced in Maya. It's my first post here, so please be gentle.

I'm having some trouble getting IK to work properly with Apex. When I blend between FK and IK, the left hip flips 360-degrees (not the right hip, nor the arms). When I activate smooth-IK, there is severe popping when manipulating the end-effector.

Been trying for over a week to debug these issues, and I'm getting nowhere... can anybody point me in the right direction? Attached is a crude repro file.

Hi, looks like you are getting popping because the mainaxis parm for the strech is set to X, it should be set to the axis that faces down the bone. In most cases this would be Z.

That should fix it.

william_harley
Hi, looks like you are getting popping because the mainaxis parm for the strech is set to X, it should be set to the axis that faces down the bone. In most cases this would be Z.

That should fix it.

Hi William. My joints do point down the x-axis. I tried your suggestion (as well as setting it to Y) just in case, but that did not resolve the issue. Instead it caused the joints to stretch sideways when the leg was over-extended.

UPDATE: Support got back to me about the flipping. The solution was to slerp the local transforms of the joints, rather than the global xforms. I don't fully understand why that would have caused an issue, but this resolved the flipping problem.

Still working on the smooth-IK popping.

I just checked on the smoothik. try setting the value for the smoothik falloff to about 0.5. it seems that the current default is off.

esttri
I just checked on the smoothik. try setting the value for the smoothik falloff to about 0.5. it seems that the current default is off.

Where can I read more about main axis, smoothik and smoothstretchfalloff, thanks

esttri
I just checked on the smoothik. try setting the value for the smoothik falloff to about 0.5. it seems that the current default is off.

Esther, thanks for that suggestion. Support had a similar recommendation at about the same time and I've been testing it out. It sort of works, but not perfectly. Setting the smoothstretchfalloff value between 0.6 and 0.8 does mitigate the popping, but pre-stretches the limb quite a lot. Values under 0.6 have less pre-stretch (which is desirable) but still exhibit popping. Values over 0.8 also pop.

I've been told that a new node is coming soon which may work better. Until then I think I'll just keep smoothIK off.