Help: I'm desesperate with a Guitar Case Strap. (Rigging)

Nesskap

Hello, I’m new here and never asked for help on online forums but i don’t find any answers anywhere.

I’m currently making a guitar case with shape of a guitar pick for an animation (above image). The base rig it’s easy but im finding a nightmare and headache the strap that mantains the case opened at the maximum angle.

I have no idea how to make it work. I tried Fk but the two ends of the strap rotates. I tried a ribbon rig but its not working perfectly. I tried a little ncloth simulation with pined borders but i don’t seem to get the desired effect. I tried blendhsapes but not working as I want.

I want the strap to stretch when the case reaches the maximun aperture and to bend inside the case when it’s closed. I don’t want a realistic bend, a bend with no gravity would be perfect.

Do you have any ideas to help me out with this? I would aprecciate all. I run out of ideas. Please help me.

Mark Dygert

A simple IK rig or spline IK could probably work to get the basic deformation and then maybe some corrective blendshapes, probably driven by the joint angles to fix any minor issues that might look off.

GlowingPotato

"I want the strap to stretch when the case reaches the maximun aperture and to bend inside the case when it’s closed."

Looks like a spline IK with the ability to stretch would do exactly what you want to.

Nesskap

Mark Dygert said:

A simple IK rig or spline IK could probably work to get the basic deformation and then maybe some corrective blendshapes, probably driven by the joint angles to fix any minor issues that might look off.

GlowingPotato said:

"I want the strap to stretch when the case reaches the maximun aperture and to bend inside the case when it’s closed."

Looks like a spline IK with the ability to stretch would do exactly what you want to.

Thanks guys, i'll try again with an IK Spline.

How can do you use the corrective blendshapes?

Nesskap

Hey guys! I Finally made something of this! Thank you! I used the IK Spline and two soft clusters to deform the curve but now I have a little problem, the base of the strap rotates and I want it to stay on place. How can I block the rotation there?

.Wiki

Weightpaint these vertices to a object that does not rotate.

You already have a null object at the base of your strap, so you could use this one.

Mark Dygert

I definitely think skinning it to a null object is a good idea. Usually everything would be contained in a hierarchy, even for simple rigs like this. So there would be a root bone or main body bone for the lower part of the case, something that you could skin too that will move with the lower case and not the lid.

If that doesn't get  you what you need, then call in the blendshapes

Nesskap said:

How can do you use the corrective blendshapes?

You do that through two tools:
1) The Shape Editor  (Windows > Animation Editors > Shape Editor) 
This allows you to create blendshapes of the mesh, think of them as a deformed snapshot of your mesh. Usually they correct things like undesierable deformation around shoulders or hips, but they also get used to make speech much more expressive and easier to manage. Rather than dealing with a-ba-jillion joints around the lips and dozens of controllers to manage and weight, you have a list of phoname blendshapes and dial in those sounds. ANYWAY... you can use it to correct the strap, if it doesn't do exactly what you want. 

2) The Pose Editor (Windows > Animation Editors > Pose Editor)
This takes poses from your skinned joints, which is helpful when animating but most people prefer to use other more robust pose library tools like studioLibrary or Red9. The Pose Editor is still useful because it lets you marry those joint poses to blend shapes and as the points reach a certain position the blendshapes activate.

Workflow:

1. You create joint poses, like neutral, open and closed
2. Then make blendshapes of the objects in those poses that correct what you don't like. Maybe you even create some additional shapes like a squash shape for when it gets slammed really hard, or an overstuffed shape that gets used when the character hurriedly packs all of his cloths into his guitar case instead of his suit case, or whatever else you need...
3. Then in Pose Editor you tie the blendshapes to the poses
   

This seems to cover it pretty well, in the spot checking I did while scrubbing it quickly.
https://www.youtube.com/watch?v=QEmsEId_nYk



Good Luck!

Nesskap

I really appreciate all your answers! I got a  decent result with painting weights. I used the bottom joint to paint the weights because my IK spline is not moving there. But one last question. I didn't understood what you said with skining to a null object. It's like a standalone joint?

I'm asking because I think thats what I need to do at the top of the strap because when I move my clusters the straps leaves the case. Like here:

You do that through two tools

Thanks for this information btw. I think I'll try to use the Pose Editor for the bottom of the strap because there is no more rotation but a little weird deformation.

Mark Dygert

Yep, you want to do the same thing you did for the bottom case. You need to skin the top of the strap to whatever is driving the lid. You probably don't need a blendshape, you might be able to blend the weights and get decent falloff?

Does the case have a joint system at all? Or are you just animating the pieces? If you're animating the pieces, you probably want to come up with a simple joint system that everything gets skinned to. That way you're pivots won't get screwed  up and the history of the mesh isn't causing any conflicts with the rigging or animation.

Something simple like a joint for the bottom of the case, a joint for the lid placed where it rotates, that way you have something for each end of the strap to weight to and follow.

Nesskap

Oh ok, I'll try to blend the weights before trying the blendshapes, thanks.

And no, I don't have a joint system. I just used joints for the strap and the other pieces ar conected to controller curves.

If you're animating the pieces, you probably want to come up with a simple joint system that everything gets skinned to.

I'll try this too but I just have a question, the joint that will controll the weights of the lid(red one on image) would be controlled by the previous joint that is controlling the top of the strap (blue one), so when the top of the strap moves, its gonna move all the lid (left side image), and I want that lid joint(red) to stay in place and move with my lid controller curve (right side image)

(I didn't solve it in the image, I just manually moved the top joint for visualization)

Nesskap

I think, I made it work. I just added an extra joint outside the hierarchy and skined it to the strap, so now that joint controlls that weight at the top. I'll work on the weights and see if Ican get the result. Thanks!

Nesskap

Nesskap said:

I think, I made it work. I just added an extra joint outside the hierarchy and skined it to the strap, so now that joint controlls that weight at the top. I'll work on the weights and see if Ican get the result. Thanks!

I finally made it! @Mark Dygert thank's for all your support! I got a decent result on the rig.

Thanks to you too,  @.Wiki  and @GlowingPotato.



Maybe it's not the best but it was a great challenge and you helped me a lot, hope I can give you back something.

Take care all of you and good luck out there!

Happy Nesskap