Rigging a rope roller in blender. [Solved]

GlowingPotato

Hi,
I made this catapult and now I need to make a rig and animate it.


The problem is, I have no idea how to rig the rope.
I found this on youtube, its exactly what I want, but there is no info on how he/she did it.

I need to figure out how to roll the rope on the log.

RN

Hi. That looks beautiful, nice work.

What is the rig for? (game, cinematic, etc)

What degree of realism do you need from the rope? It'd be extremely challenging to make it realistically curl around that axle as it rotates. 

From that video you posted, it looks like they're using a trick: the rope is not textured, which simplifies things, and seems to always go inside the axle geometry. What's left is to make the curls progressivelly appear (or disappear) as the catapult does its rotation. So there's two separate pieces of rope: the curls around the axle, and the straight piece going from the beam to the axle.

GlowingPotato

RN said:

Hi. That looks beautiful, nice work.

What is the rig for? (game, cinematic, etc)

What degree of realism do you need from the rope? It'd be extremely challenging to make it realistically curl around that axle as it rotates. 

From that video you posted, it looks like they're using a trick: the rope is not textured, which simplifies things, and seems to always go inside the axle geometry. What's left is to make the curls progressivelly appear (or disappear) as the catapult does its rotation. So there's two separate pieces of rope: the curls around the axle, and the straight piece going from the beam to the axle.

Hi! Thanks!

This is an asset for a UE4 game. I already have a ballista working with sounds, FX and animations. So I would like to maintain the same level of detail, although the ballista animations are way easier/simple than a catapult. 
Since is for ue4, it must have an armateur deformer.

I still didn't solve the challenge (I'm modelling another asset while ideas growth...), but something I have in mind is to animate a belzier curve (lets call curve 1), following a path (curve 2),  and then constrain bones to the controls points of curve 1, and use this bones to deform a rope... what you think ?

Also, thanks for replying back!

gnoop

I  have no idea really  but think it may have one invisible curve  to guide / rail the rope mesh.

something like this :   https://www.dropbox.com/s/oddvpo3jchogmrt/ROPE.blend?dl=0

RN

If you want the rope to roll around the axle like in that cool demo that @gnoop shared, you'll need a bone chain to deform the rope properly. Depending on the context that this model is going to be used this could blow the bone budget.

If it's supposed to be used in something like an RTS game, with potentially tons of catapult units, imagine how many bones will be in view at a given moment. If this asset is for games like these then you could use tricks / approximations to give the illusion of a rope rolling around, so it's faster for the engine to process.

This is done with vertex alpha and a threshold shader, it discards the pixel if the vertex alpha at that pixel is less than some value that you can animate to make the rope look like it's unraveling.

GlowingPotato

gnoop said:

I  have no idea really  but think it may have one invisible curve  to guide / rail the rope mesh.

something like this :   https://www.dropbox.com/s/oddvpo3jchogmrt/ROPE.blend?dl=0

Thanks for that, very cool! I'll see if I can do it with armature now.

@RN This is a ingame screenshot, It will be only one catapult, so the bone budget is not really a problem. But, is very fair to discuss if I actually need this level of detail. Is a multiplayer third person game. Camera wont change its orientation, just position.


What you think? Its overkill what I'am trying to do ? The idea to do it in shaders sounds good too.

RN

You could say it's overkill, you could also say that it's attention to detail. It depends on your point of view.

I think using a bone chain is a brute force approach for something that will not have priority on screen. If there are cheaper techniques that can be combined to give the effect that you're after, I would use those.

GlowingPotato

Hi,
Iam back to this challenge! 
I've made progress but still... one issue persist. almost there!!!

here is the issue, I can't figure out how to maintain the bone orientation. There are very specific locations at the curve where the bones flip in the Y axis. I can't  constrain it! WHY ?!!??!



The Z axis should always point towards the center of the spiral. But it flips !!!
The file is here if anyone wants to take a shot at it. (please do!)

To manually animate the curve, just move the empty named Pull on the Z axis (or hit play in the timeline.)

GlowingPotato

I've made it !!!!
https://youtu.be/ahlDuofzwhA

https://youtu.be/G8BH1eLz4IQ

All I need to do was to make another constrains, but this time, a locked track constrain.  Then i locked the Y axis, pointing X to an empty far away on the X axis.

Victory!
Soo happy! =]

These are the links that helped me solve this rig. 
https://blender.stackexchange.com/questions/133012/line-of-bones-to-travel-and-conform-to-curve-like-train-on-a-track-snake
https://blender.stackexchange.com/questions/105799/rollercoaster-problem-bones-following-curve