Stretchy FK?

#1

Anybody knows for a good, simple, way to make stretchy FK (arm or leg) tutorial in 3ds Max? It is supposed to follow stretchy IK in “lenght”…

#2

Hello there,

Did you already check this thread: FK/IK seamless switching in 3ds max 8 ?
Don’t remember if this one covered follow part, but that is basicly x position of blend chain bone adapting to length (x-position) of IK bone and FK bone, depending on blend value.

#3

Yes I have seen this thread… It shows classic IK/FK switch with the “fake swivel” for FK (better tutorials are at the PEN’s site), and it says that stretchy FK chain CAN be made, but not HOW… I know how to make stretchy/bendy IK chain (leg or arm), with a combination of IK solver, expose transform node, splines, and bunch of stretchy bones… but there is no real tutorial on the Internet how to make this in Max… there is a few for Maya but those methods are not applicable in Max (lot’s of usage of Maya’s groups etc.)…

#4

Benzin:

Paul’s tutorial, as far as I remember is a well explained video and there was extra stuff for visuals. But technically the same stuff, only different method used to deliver the message.

"it says that stretchy FK chain CAN be made, but not HOW… " - I think I already explained core idea.

I’m not sure what is your definition of stretchy FK?

My definition for stretchy FK would be: Have a IK limb that stretches when pulled further than total length of combined IK chain bone lengths is smaller than distance to IK goal. At the same time, FK arm either follows these IK bone lengths OR has it’s own controls for lengths. When blending between FK and IK chains, blend chain takes these lengths into account when user changes blending value (In Paul’s video it’s a spinner). Then there could be spinners or other controls for additional adjustment for length (x-position offsets) of IK joints too, which too should be taken into account when you do blending or matching of FK to IK.

“I know how to make stretchy/bendy IK chain (leg or arm), with a combination of IK solver” - Technically I’d call stretchy bones a secondary layer on top of FK-IK rig, so if you can do this, just add it on top of FK-IK rig, when it’s working.

That’s how I’ve done it. FK-IK blend rig, addition tuning of FK bone lengths and IK bone length, both upper and lower limb. Match and blend take these into account. Then additionally, softIK is there too, and must be taken care of like global scale of rig too. Bendy controls and bones are on top this setup.

#5 
    That's also my definition of a good rig...and stretchy FK...

    Known territory...

  Now we are talking... this is what I'm after ... also it would be nice that all of this is "gimbal proof"...

 It's not "a must"... 

  Done that already... 
 
 I don't want to be rude... but this is all nice theory and a description of a perfect IK/FK squash/stretch/bend cartoony rig...

I already know how and what it should look like and be able to do…in theory…
I need practical solutions and examples… so I’ve asked for a tutorial in the first place…
Again, I don’t want to be rude, but I’m sick and tired of a “theory of a cartoony rig” and “something CAN be done… but I won’t tell you how…” threads… nothing personal…

#6
  1. Create 2 helpers.
  2. Create a bone with end bone.
  3. Select the bone, apply position constraint, and select first helper as target.
  4. Select the bone, apply look at constraint, and select second helper as target.
  5. Select end bone, apply position constraint, and select the second helper as target.
  6. Select the bone, and in look at constraint parameters, uncheck Select Upnode -> World, click None button and select the first helper.
  7. Link second helper to first helper.
    And with this you have 1 fk bone. You need to repeat this action between more helper, and you got FK strechy bone chain. Or you can use this little old script I have made, you only need to add the helper or object list, and it creates all the bones for you:
    https://dl.dropbox.com/u/472186/Forums/CGTalk/createBones.zip
#7

Who’s the parent to this one? Shoulder helper? If this is let’s say the elbow?

Shouldn’t this be linked second helper to third helper?

I know how to make stretchy bones, the problem was how to incorporate them in a FK hierarchy without wild flipping (thanks to lookat constrain and the famous up node) in some poses.

#8

Well, i have find that you really no need, a third bone. To control the angle you can use the first bone to, here an example of a simple fk arm.
https://dl.dropbox.com/u/472186/Forums/CGTalk/fk-arm.zip

#9

Thanks A LOT ! But can you please explain the role of smaller helpers, I’m trying to understand their purpose? They have “empty” lookat constrain?

#10

Sorry I have not commented this, they are really end bones, only to have a more"clear" chain. I have updated the first post too, and removed the bone angle controller helper.

#11

Again, thanks a lot! I realized that a bit later… :lightbulb:) , why bother for a cleaner chain ;)?
How would you force FK elbow point, to follow IK elbow point in length… of the upper arm?
Position constraint in one axis (Z)?
Would position constraint + reaction manager + slider be a good solution for IK/FK switch for the bendy/stretchy skin bones (bunch of stretchy bones constrained to a couple of splines)?
Of-course each stretchy bone’s driver (point) would have its “mother” (again point) to run to on both IK and FK chain…
Only one thing remains (under condition that all of this above works properly)… that is the swivel problem. i.e constantly updating /matching position of the swivel target to the orientation of the upper arm (or thigh) or vice/verse…
Does this makes any sense?

Or to make THE SWITCH to Softimage :twisted: ;)…

#12

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