# Animate a hollow cylinder rolling up on itself

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I’m still a beginner at Blender and leaned a bit about bone rigging, however I cannot find information on one particular animation that I want to do.

Essentially I have a hollow cylinder with several loop cuts. I have created it using the following technique:

1. Create a circle in the X-Y plane.
2. Extrude it several times in the Z direction.
3. Use the solidify modifier.

Essentially what I want to achieve is an animation where a the bottom two parts of the cylinder open up radially with respect to the axis of the cylinder. For example I want the portion labelled in red below to open up 90 degrees outwards and the bottom portion labelled in blue to turn 180 degrees, so that it point up. Essentially getting the effect of the end of the cylinder folding up/rolling up on itself.

I have figured out how to do this folding linearly with a simple slab. However I cannot figure out how to do it with a cylinder with a rotational symmetry around the central axis. Can someone explain or point me to some resources I can read?

Just to add, I have simplified the problem to the simplest possible case. I am actually trying to achieve this effect with a much more complex object that I have already imported from a CAD model, so starting from a slab, doing the modification on the slab and creating a circular array wouldn’t really work. I would like to know how to achieve that with a ready-made mesh. I was envisioning to create some kind of a 3 bone armature and have that armature control the entire mesh, but not sure how to do that or even whether it is even possible.

Any help is appreciated.

Hello and welcome aboard!

Well, how did you do it with a simple slab? Did you use an armature to do it?

If you can get a simple flat plane to fold how you want with an armature, then you can do it with a cylinder because a cylinder is nothing more than a bunch of flat planes joined together.

Sounds about right and yes it’s possible.

Let’s say you have an 8 sided cylinder. Each side of that cylinder is a flat plane, and each one would need a bone for the red areas, and a bone for the blue areas. That’s 16 bones, and you’d need an extra parent bone too, so 17 bones total. Then with the help of constraints, you’d control the 16 bones with only 2 bones.

If you need me to show you a simple example, just ask…

Randy

Dear Randy,

Thank you very much for your detailed response!

Regarding the way to bend a simple slab, I followed the procedure described here:
modeling - Bend straight object on corners 90 degrees - Blender Stack Exchange

The issue is that the object that I am trying to deform now has been imported from a CAD file and quite a few faces around - maybe even 128. So I was trying to avoid created bones for all these faces and thought that there might be an option to create only a single set of bones and somehow tell blender to have those bones control the entire circumference in spherical coordinates, not just a single face in Cartesian coordinates.

Your explanation of what I need to do is quite clear so I’ll just play around with some toy examples before I move on to my actual object and will ask again in case I get stuck.

Thank you once again for your reply and your willingness to help further.

Best wishes,
Georgi

I threw together an example, just to make sure I wasn’t sending you off in the wrong direction.

and the file -
cylinder_rig.blend (890.5 KB)

I created the top bone first - Master - in the center of the cylinder. Then I created the 2 non-green bones next - Mid_CTRL & Bottom_CTRL. To create the rest of the bones (green ones), I put the cursor in the center (bottom of Master bone) and set the cursor to be the pivot point. I duplicated the CTRL bones and rotated them 60 degrees and adjusted their roll angles by 60 degrees. And repeated this process till I had all the bones I needed.

Next I weighted the mesh to the bones by manually creating vertex groups.

Then I added copy rotation constraints to the bones (which is why they are green) so they would copy the rotation of the 2 control bones.

Not going to lie and say it was quick and easy, took me about an hour to throw this together, and it could be polished a bit more, but it works.

blender 3.6.5 file but it should work in newer versions just fine. 3.6.5 uses bone layers, versions 4 & up use bone collections instead.

In my experience, CAD files usually are a mess when brought into blender. They are not the nice quad faces like something I would model, but instead they are a mixture of quads and tris.

Randy

Hi Randy,

Wow, I’m super impressed and grateful for how much time you invested in this! Thank you so much! I really appreciate it. If it took you an hour with your experience, it would have taken me several days.

I will study your example and I’ll work on my own project based on that. It is super helpful!

You are right, the CAD-imported file does have triangles in addition to quads. I’m even thinking about re-doing so that it would be easier to manipulate.

Thank you so much once again!

Best wishes,
Georgi