rivet – changing leg from ik to fk and back to ik

[tanya]

I am playing with the rivet rig and what to change the leg from ik to fk and back to ik it sort of works.  This is what I did,

ik to fk 

– the leg is moving during he switch so I did what I think is called a blending of the two over several frames.

– keyed ik foot bone, fk-ik switch at 1

– set fk bones (thigh, foot, calf) using a visual loc- rot.

– went forward several frames and set the fk-ik switch to 0 and inserted key- frame

-this works pretty well, but he calf or knee is a little off

for the fk to ik 

–  I snapped it over one frame

-keyed the fk bones and keyed the switch on 0

– then what I googled said you should, I know the knee has a pole target, but am confused with this part.

1. Select the pole snap target (the pole target parented to thigh/upperarm), do Cursor to Selected. Deselect bones.
2. Select the real pole target and do Selected to Cursor. Insert a LocRot keyframe. Deselect bones.

– then you were supposed to do the same with the foot, which worked fine, with some tweaking. 

–  then went forward one frame and keyed he fk/ik switch to 1

 Since I don’t get the knee part the knee is off some.

Any help would be appreciated.

[Wayne Dixon]

Hi T,

Yeah you should snap over 1 frame.  It shouldn’t really be used as a slider but it’s way nicer for the animator to see it moving when they change this, it helps you recognise that there are 2 ‘positions/orientations’ the bone is in at all times (if that makes sense).

I usually don’t bother with IK/FK snapping, which is partly why the rig doesn’t have that feature but I think you might need to reset the rotations to zero on the FK bones while it is in IK.  (That is because I was trying to be efficient with my rigging and used the same chain for FK and IK).  This uses less bones and drivers (faster).  But the downside is that the FK can still shift the IK when it’s in IK mode.  Which is only a problem if the FK bones are animated while it is in IK (if they are held – it should be fine).

Hopefully you can make sense of drawing of what the GE might look like.

Let me know if any of that made sense haha

[tanya]

@waylow. –  thanks for the response,  I am still confused (surprise, surprise).  

1. What is the slider supposed to be used for?

2. how do you  flip between ik and fk, if you don’t bother with ik/fk snapping, I am guessing you just position the bones correctly?

3.  you where right, there were values in the fk bones.

4.  my understanding is the with fk, the leg follows the hip rotation unless I isolate it.  If the hip rotation is off, then the leg position will also be wrong, which would be really obvious when the switch from ik to fk happens, (pretty sure the answer to this is yes) right?  Hope this question makes sense, but I am still confused.

again thanks for the help, need to take a break, reaching my frustration level.

Thanks – T

[Wayne Dixon]

1. The slider switches from IK to FK.  But you wouldn’t use it as a slider, you would snap over 1 frame.  

2. Yep, just match it with my eye. But I try to avoid switching as much as possible.  EG – If the arms don’t need IK in a shot, I try to keep it in FK for the entire shot.  If it does need IK, then I do the entire shot in IK.  (whenever possible)

Usually the legs can stay IK unless you try to do some type of Ballet dance or something 😉

3. Lazy rigging – sorry.

4. That is correct.  But the confusing thing is that there is kind of 3 spaces on those FK bones.  They have IK, where they follow along with the IK (but you will still be able to rotate the knee),  They have FK to the hips, if the hips move the thigh moves.  And then they have FK to the Root (they are isolated).

The isolated version can be tricky because you need to find the correct starting direction.  Say if the character is facing forward and you switch to isolated FK – this will probably look pretty fine.  However, if the character turns 90 degrees and you switch, the isolated FK will twist back to their starting point, which will be facing forward and the body will be rotated 90 degrees.

I hope that makes sense.

5.  Don’t forget, you are awesome.

[tanya]

@waylow. thanks, that all made sense and naturally trying to make it do a ballet move. – T

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