Take a look at how we rigged our Jelly Bow using Jelly Bones, Constraints, and IK. Our goal was to create a sophisticated rig with a single control point. You can see the final result here. Continue reading for a full breakdown.
The first thing we did was connect the bendable top and bottom sections of the bow to a set of Jelly Bones. We did this by creating three bones for the bow: one for the main body and two for the bendable top and bottom (these are children of the main body bone). Note that there’s also a bone on top of the drawstring above (also a child of the main body bone). This is our draw bone. We’ll get back to it later.
The top and bottom bones were then subdivided into Jelly Bones using the new Jelly Bones options in the Selection Panel.
We activated the Jelly Bones toggle and set the segments to 5. We also created a new Node as a child of the main body bone (make sure you don’t make it a child of your top or bottom bones), set it to display as a Target, and set it as the Out Target for the Jelly Bone. Note that moving this Node now allows you to manipulate and animate the curve of your Jelly Bones. We repeated this whole process for the bottom part of the bow.
Then we moved the newly created Nodes to the right of the bow (see image above) and set their Ease In value to 0, which created a good arc shape that resembled our bow.
We then connected the middle bone and the top and bottom Jelly Bones to the mesh of the bow (see the highlighted bones in the image below). Note that we did not connect the large top and bottom bones to the mesh, we only connected the Jelly Bones.
We then went into Edit Weights and tweaked the weights until we were happy with the deformation results. You should get something similar to our image below. If you’re not familiar with how Edit Mesh and Edit Weights work, take a look at our blog post on Meshes.
We then created IK target nodes at the tips of the bendy parts of the bow.
We wanted these to influence the big top and bottom bones that were segmented by Jelly Bones so that as the tip moved, the bone would follow it creating the curving deformation we set up in the previous step. We did this by adding an IK Constraint to both the top and bottom big bones and then choosing the tip target node as the target to follow.
Finally, we needed for the tip targets to move progressively as the drawstring was pulled back. We used Distance Constraints to make this feel natural. The further the draw point, the more the bone would curve. We first added the Distance Constraint to each of the big bow bones:
We then set the root draw bone (the bone we will animate) to be a distance target for the tip targets. Nima automatically chose the distance to constrain by for us.
Note that the Distance Constraint allows you to change the distance as necessary or calculate it automatically based on current settings. We set the mode to Exactly. We will be updating the manual with more information about the three different modes this constraint offers, but for this example we wanted it to constrain to exactly the distance we set.
Now animating the X translation of the root draw bone will bend the bow realistically. You’re ready to animate!
Originally published at 2Dimensions.com on January 17, 2018.