Stretchy bones technique is frequently used in Facial rigs to drive the complex expressions of the face and in muscle rig systems. While learning rigs in 3D, we work with stretchy bones so often. It’s pretty much a beginner level thing, and in this tutorial you will be learning how to create stretchy bones in 3DS Max using few animation constraints. So, here we go.
Let’s get started with creating a bone chain in front Viewport.
Now Create a point helper through Create » Helpers » Point, select the Point helper and align it to the root bone (Bone001) using Align tool.
Tip: You can access Align tool by clicking Align button over main toolbar or you can use the hotkey ALT+A.
Now do the same thing with other three bones.
Now we have each bone with a point helper aligned to it. Select all bones and helpers, press Alt+Right Click and Freeze Transform. Now what we gonna do next is to position constrain each bone to the point helper aligned to it. For example, Bone001 should be position constrained to Point001 as Point001 is aligned to Bone001.
So, go ahead and select bone Bone001 then go to Animation menu » Constraints » Position Constraint then click on the point helper Point001. Now Bone001 is position constrained to Point001. Repeat the same step with other three bones.
Now, select a point helper and just move it, you can see that bones start stretching. Well it works fine on z-axis but notice when we move the point helper in x or y-axis it starts breaking the bone chain.
To fix this, we have to add a LookAt Constraint to every bone and the look at target should be the helper present at the top of that bone. To add LookAt Constraint, first select a bone then go to Animation menu » Constraints » LookAt Constraint, now click on the point helper present at the top of that bone.
Now, if we move a point helper in any axis, it stretches correctly without breaking the bone chain.
That’s it. Hope you liked the tutorial. Feel free to comment and share your views.