Ik Blend vs three chain rig?

[litote]

Regarding IK/FK blending: I have seen a common method that creates three joint chains for the arm — one for the controlling FK rig, one for the IK rig and one for the joints to be controlled —  to allow simple switching between IK and FK modes. This system uses orient constraints.

What is the benefit of this complex rig compared to just keying the ikHandle’s IkBlend between 0 and 1 to switch between IK/FK? Is it just to make it simple for the animator to switch using an attribute? It seems like a lot of work to set up if you are not going to switch often.

Also, using this tip of rig, to make the arm stay in position when you switch between IK/FK, is there another step? If so what is used — some kind of expression?

Finally, I can not find a good tutorial on using the ikBlend parameter correctly so that the poses match when you switch. Any links to tutorials would be appreciated.

[litote]

P.S. I did find someone mention that the three chain rig allows for the use of curve controllers, while the ik Blend method may not as they may not be able to be parented while using Ik Blend. Is this correct?

[Anonymous]

In my experiences (none professional, just in student projects), I have found that using the ikBlend attribute is far less reliable than than having separate joint chains for IK/FK. Having separate chains also makes rig debugging much easier as it is more modular by nature.

Having a reliable ease-in, ease-out of your IK/FK switches is important so that you don't have to be so precise with matching the pose when you switch. When you use the ikBlend, as you said, it doesn't really work with constraints, so you have to do it over 2 frames, which can cause jumping during the transition if you don't match the poses well enough. If you have two separate chains with parentConstraints to the bind skeleton then you can smoothly transition between the two over however many frames you want making the switch unnoticeable and the pose matching far less important.

As far as pose matching between IK and FK, you either have to eye-ball it and get as close as possible, or use a script. I can try to whip one up here in the next couple days for you if you want.

[litote]

@Anonymous

Thanks for your reply. I assumed using Maya's inbuilt IK blend would not require pose matching since it would match perfectly when switched as this seemed to be the case in my first experiment. Perhaps it is more noticeable if you animate movement, causing a brief stall over the switching frame?

I would appreciate your script if it is not too much bother.

Thanks!

[litote]

@Anonymous

Hello, could you answer my further question about your point that the IK/FK blending causes jumping? Thanks.

[Anonymous]

What other questions do you have? Or are you still waiting on the script?

[litote]

Hello. You said that using Maya's inbuilt Ik Blend parameter causes "jumping". I'm not sure what you mean. When I tested the Ik Blend, changing its parameter from 0 to 1 over one frame, the pose seemed to match perfectly.

If you have a script for the three chain method I'd certainly appreciate it.

[litote]

P.S. On further experimentation, the only major disadvantage I find in using the Ik Blend parameter seems to be that there is a pause over one frame when you switch between IK/FK. But I don't notice any "jumping".

[Anonymous]

Sorry if I wasn't clear in my first response.

The jumping should only happen when switching from the IK to another driver (such as FK) while the controls are moving. You were correct in one of your earlier responses that the jumping only happens if there is movement happening. In your testing, if it's just causing a pause, then you have probably done a pretty good job of matching your IK/FK poses, but a pause is still a problem if you are trying to get a fluid movement.

[litote]

@Anonymous

Again, it is not clear what you are referring to. What do you mean by "while the controls are moving"? What controls?

Are you sure you know what I am referring to? If you use the Ik Blend parameter (Maya’s inbuilt parameter, not a 3-chain rig IK blend system) then you do not need to “match poses”. They will always match perfectly and automatically. There is no manual matching.

[litote]

P.S. You said you should keyframe the ik Blend over 2 frames, but this is not the case as far as I can see. This does not eliminate the pause; in fact it prolongs it.