Obi rod or obi rope? - Printable Version

Obi rod or obi rope? - Printable Version

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Obi rod or obi rope? - AdrienMondot - 12-04-2021

Hello,

We are using Obi Rope & Rod objects to create worm-like creatures.
The Rods have been harder to setup, and we would be happy to have your feedback on the issues we encountered in order to choose whether we use them in our project, or just stick to Obi Ropes.

- When editing a path, the Rod seems to quickly add twists and distortions on the curves.
As you can see in the picture below, the wireframe of the rod shape suddenly rotates 180° in the middle, adding distortion to the mesh… this might be related to the varying thickness we applied to the different key points/particles ?
We do not seem to have this issue with Ropes, maybe as the particles are not oriented ?

- We cannot get the Rods to maintain their Rest shapes, in Play mode, they mostly seem to behave like Ropes (please see the attached video).
Is there any thing we could be missing in the way we build them ?
We followed the steps on your website, and made sure the “Keep Initial Shape” value is turned on in the BluePrint.

[Image: rod-edit.png]

sample video here :
http://docs.am-cb.net/faune/Rod_shape.mov

Thanks in advance,

Best,

Adrien Mondot

RE: Obi rod or obi rope? - josemendez - 12-04-2021

(12-04-2021, 11:59 AM)AdrienMondot Wrote: - When editing a path, the Rod seems to quickly add twists and distortions on the curves.
As you can see in the picture below, the wireframe of the rod shape suddenly rotates 180° in the middle, adding distortion to the mesh… this might be related to the varying thickness we applied to the different key points/particles ?
We do not seem to have this issue with Ropes, maybe as the particles are not oriented ?

The main difference between rods and ropes is that rods use oriented particles. You probably want to specify an orientation for each control point in the path, otherwise all control points will be oriented in the local "up" axis, twisting the path 180º when it crosses this axis. From the manual: http://obi.virtualmethodstudio.com/tutorials/ropesetup.html

Quote:Orientation tool (rods only)
This tool allows you to define the orientation of each control point. This lets you specify the rest twist of the rod.

(12-04-2021, 11:59 AM)AdrienMondot Wrote: - We cannot get the Rods to maintain their Rest shapes, in Play mode, they mostly seem to behave like Ropes (please see the attached video).
Is there any thing we could be missing in the way we build them ?
We followed the steps on your website, and made sure the “Keep Initial Shape” value is turned on in the BluePrint.

It just seems like your solver settings are too conservative. What evaluation order are you using for stretch/shear and bend/twist constraints? How many iterations for each? How many substeps for the updater?

All these greatly impact the quality of the results. Remember that low quality simulations = stretchy simulations (see http://obi.virtualmethodstudio.com/tutorials/convergence.html)

Also, the video tutorial on rods might be useful:
https://www.youtube.com/watch?v=2X2Ui8RGX1Y&list=PLnCR8_XCOgrYqv3fhBjG9K0Kns3UmsJ8B

kind regards

RE: Obi rod or obi rope? - AdrienMondot - 12-04-2021

Thanks a lot for the quick reply, we'll digg all this