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View Full Version : Why is leg flip flopping?



Boobyman
08-28-2013, 07:34 PM
It's a simple as can be rig and the darn leg flops on me. Never happened before.

Leg flop in motion...

https://www.youtube.com/watch?v=CMedHDj76mE



http://i61.photobucket.com/albums/h47/lan73nb/leg-crae-2_zps0da14909.jpg


http://i61.photobucket.com/albums/h47/lan73nb/leg-crae-1_zpscf922200.jpg

Ryan Roye
08-28-2013, 07:53 PM
This should help. Hit "m" for motion options and tweak the settings shown in the picture to values that prevent the extreme bending. This will give your character added flexibility without the... quite painful-looking leg snapping.

http://www.delura.tanadrine.com/image_manualupload/LW_setlimits.jpg

RebelHill
08-29-2013, 02:19 AM
Use an IK PLANE bone at the top of the chain...

Boobyman
08-29-2013, 08:10 AM
When moving the leg up, I don't have that flopping problem. When the leg is moving to the front it flops backwards.

http://i61.photobucket.com/albums/h47/lan73nb/AO-2_zps71520c7a.jpg

http://i61.photobucket.com/albums/h47/lan73nb/AO-1_zpsa2b8cc09.jpg

Ryan Roye
08-29-2013, 08:38 AM
When posting these problems I recommend also posting a snapshot of the rig's leg hierarchy (scene editor is fine). That way we can see better if its an issue related to hierarchy setup or otherwise.

Neither IK plane or limiters will help you if the bones are setup incorrectly. It looks like you're using a 3rd bone in the upper/lower leg from the screenshot provided.

RebelHill
08-29-2013, 09:28 AM
When moving the leg up, I don't have that flopping problem. When the leg is moving to the front it flops backwards.

Yes...

PUT AN IK PLANE IN THERE AND IT WONT HAPPEN!!!!

Boobyman
08-29-2013, 09:32 AM
What's an Ik Plane?

RebelHill
08-29-2013, 09:45 AM
Booby... no offence, but you keep coming back with Ik problems, and I keep giving you the same answer...

http://www.3dworldmag.com/2012/12/20/tutorial-get-to-grips-with-lightwave-ik/

This is how you setup IK... every time, no alterations, no exceptions.

Boobyman
08-29-2013, 12:08 PM
Mr Hill, you don't have to be such a rebel with this one. I loved you since the first day I saw your post. I sent you cakes and roses. You never responded. So, please calm down, damn you! You need the almighty saviour in your life. I will pray to Elvis to deliver your soul!

Dexter2999
08-29-2013, 12:32 PM
Did you pre-bend your leg when rigging?
If you did then the knee should have bent properly when in that position, shouldn't it?

RebelHill
08-29-2013, 02:23 PM
Pre-bend alone is insufficient to completely hold it together... It gives preference to the given prebend angle, but if an alternate solution is available the IK solver can also choose that (note that motion limits dont solve this either, since they only restrict motion of the item, the IK solver still doesnt "know" that its a disallowed solution, so will try it, and fail, causing straight snapping). The solution is the IKplane, which pre-rotates the system giving a reduced domain in which the IK solve needs to operate... thats why this method isnt ONE way of doing IK in LW... its THE way.