I have a model of a die-line that I would like to fold together with a rigid bind. The rigid bind has a joint cluster flexor and I have several. I am fairly new at rigging and wanted to take a shot at making a folding carton, seemed easy enough. I ran into many issues and still to find the best way to tackle this.

1. Should this skeleton be connected?

2. Is my model incorrect for this process?

3. Should the joint XYZ all facing in some direction?

As you can see with the images I attached rotating the joint incorrectly works with the flap/panels. The .zip contains the .mb and screen shot. Please help with find a correct skeleton technique to fold a die-line.

Thank You
Zack

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folding_dieline.zip

You could make that work, but a smooth bind would be better… here’s why:

A rigid bind will move each vertex all or nothing, because that is how it is weighted. However, near each joint you have several rows of polygons that I am thinking you want to move in a manner that resembles folding cardboard. So I am thinking you want to distribute the bend across these rows of polygons, otherwise there would be no reason to have so many.

So lets reference the right side large flap, with 4 rows of polygons and then a large polygon that would form a side. You would want to have the flap it is attached to weighted 100% to the ground joint that stays still, then each of the 4 rows weighted incrementally ranging from the ground joint 80/20 flap joint to ground 20/80 flap joint, with the flap itself 100% flap joint. That will make the 4 rows curve as you bend, and the ground part and the flap move absolutely with the joint rotation. Put the joint itself in the middle of these 4 rows.

You can do a better job of forcing the weighting for this by selecting vertices and using the component editor that by trying to weight paint it. Get an initial smooth bind with max 2 influences by using smooth bind, and then edit the weights afterward.

The last suggestion is that you have extra joints you don’t need, and are missing a root joint. Place a joint in the very center of the box and make your existing joints a child of that (parent each joint chain to it). And the end joint of each chain is unnecessary… think of the joint as being a hinge, instead of a bone, and you will see the final one you have on each chain is unnecessary to obtain the needed animation. You move your whole box by translating and rotating the root joint, and you would only rotate the other joints to fold and unfold the box.

For characters many riggers usually place the X axis pointing at the next joint, the Z for the main bend direction and the Y ‘up’, which may not be perfectly up. But for animating inanimate stuff I usually orient them with the world, that makes it easier to remember which axis to rotate.

You can also place constraints on each joint, so that it only will rotate on a single axis, and you can also set limits on how far it can rotate on that axis (say 0 minimum and 90 maximum). That will make your animating easier. Look for those in the attribute editor for each joint.

Good luck.

<* Wes *>

Flap and side panel. If I understand what you mean, the flap is on one end of the side panel, the other end of the side panel is attached to the main box.

Make the flap a child of the side panel, and the side panel a child of the root. Weight at 100% each. Here is what happens… side panels bends, and flap does not bend, but existing flap bend moves with side panel. Place a bend on the flap, only the flap moves. If you want a smooth bend between the flap and side panel, the geometry needs to be made so that there are multiple vertices to spread the influence over.

<* Wes *>

Some pictures of issues with joint chain and influences.

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Now it looks OK to me, meaning I think I could make that work the way I think you want it to work. So I don’t quite understand what the problem you are asking about is.

I went back and looked at your question, and in the design you showed the only polygon I would have weighted fully to the root joint is the one that is right above it. I can’t quite tell if there are some slender polys at the seams between that and the next two joints, but it looks to me that you understand the smooth skinning process.

So back to the 100% question. All your influences for any vertex should always add up to be 1.0 (100%). If you have a joint that is a child of another, it will ‘inherit’ all the influence from the parent. So on each of the flaps attached to the root, anywhere you move the root all of the other joints will follow, as will all vertices weighted to those other joints. If you have the different flaps all weighted to the appropriate joint, when you rotate the root joint, the entire box will rotate, because the children of the root will follow the root, their children will follow them, and so on, and the vertices will follow the joint(s) they are weighted to.

Just like your arm and hand. When you move your shoulder joint, your hand also moves, even though the skin and muscle is attached to the hand and not to the shoulder.

<* Wes *>