Answered

I can't rotate knee to swing legs when using IK

Elsiehar 2 weeks ago updated by Peter - Soxware Developer 1 week ago 3

I want to get my character to swing their lower legs below the knee.  I have set up the IK wizard, but after I select all and set the FK/IK Blend to 1, rotation doesn't seem to work.  Nothing happens when I try to rotate the leg (the position works okay).  I thought it might be the way the character is rigged but I am having the same issue with Robot Kyle.  The only rotation that seems to work is the shoulder & hand?  

If I change the FK/IK blend back to 0, I can get it to work using the FK, but is this how it is supposed to work?.

I have looked at the manual under FK to IK conversion but I really don't understand it and am not sure if it applies to my situation.

I am sorry if this is a silly question, but I am not sure what I am missing or how this should be done.

It also won't let me select the IK bones in the scene just the poles, is this correct?

UMotion Version:
1.25p02
Unity Version:
2020.3.9f1

Answer

Answer
Answered

Hi Elsiehar,

thank you very much for your support request.

Yes this is expected, that's how IK works. The IK rig (the blue bones) are controlled solely by the IK algorithm. This algorithm automatically adjusts the rotations of the individual leg bones in such a way, that they reach the IK handle of the corresponding foot. So if you select the IK handle (this is the wired cube at the ankle) and move it with the move tool, your legs are going to bend/rotate so that they end up at the IK handles position (FK/IK Blend needs to be at 1). By moving the pole target, you can define where the knee is pointing to.


The FK rig on the other hand gives you full control by allowing you to rotate every bone manually with the rotation tool. As you might already think, both methods have their advantages that's why the FK/IK Blend control exists which allows you to switch between them (even during an animation) so that you can use the best fitting solution for your animation scenario.


I recommend that you play around by moving the IK hande/pole handle so that you get the hang of how things behave. Btw. rotating the IK handle is going to rotate the foot bone.

For more information, please check-out the IK video tutorial:


Please let me know in case you have any follow-up questions.


Best regards,

Peter

Answer
Answered

Hi Elsiehar,

thank you very much for your support request.

Yes this is expected, that's how IK works. The IK rig (the blue bones) are controlled solely by the IK algorithm. This algorithm automatically adjusts the rotations of the individual leg bones in such a way, that they reach the IK handle of the corresponding foot. So if you select the IK handle (this is the wired cube at the ankle) and move it with the move tool, your legs are going to bend/rotate so that they end up at the IK handles position (FK/IK Blend needs to be at 1). By moving the pole target, you can define where the knee is pointing to.


The FK rig on the other hand gives you full control by allowing you to rotate every bone manually with the rotation tool. As you might already think, both methods have their advantages that's why the FK/IK Blend control exists which allows you to switch between them (even during an animation) so that you can use the best fitting solution for your animation scenario.


I recommend that you play around by moving the IK hande/pole handle so that you get the hang of how things behave. Btw. rotating the IK handle is going to rotate the foot bone.

For more information, please check-out the IK video tutorial:


Please let me know in case you have any follow-up questions.


Best regards,

Peter

Great, thank you, I thought as much.  I have however tried to change from FK to IK & or reverse with no luck at all.


In the following screenshot I have made the FK/IK Blend to 1 and adjusted the feet.  You will see that the FK bones stay where they are.

As soon as I change the blend back, at a different frame,  you can see that the feet move back to the original position because that is where the FK bones are?

Is there a step that I am missing?

Thanks

That is expected. The IK skeleton and the FK skeleton are two separate skeletons. You can move them independently, and the FK/IK Blend slider is going to make the mesh either follow one or the other.


The "Set FK to IK" button (under Tools in the Pose Editor) is going to adjust selected FK bones to the respective IK bones pose. The "Set IK to FK" is doing the reverse (moving a selected IK handle to the FK position). So in your case, you would use the "Set FK to IK" button on the last IK frame to set the FK skeleton to the same pose as the IK skeleton so that there is no visible difference when transitioning to FK.

I hope that explains it for you. If not, let me know.

Best regards,
Peter