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Support for multiple degrees of freedom joints #195

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ShravanTata opened this issue Aug 28, 2019 · 2 comments
Open

Support for multiple degrees of freedom joints #195

ShravanTata opened this issue Aug 28, 2019 · 2 comments
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feature New feature proposal/idea for Phobos. merge requested Feature waiting for merge by developers.
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@ShravanTata
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Currently Phobos only supports single degrees of freedom joints. In my models it is essential to have multiple degrees of freedom. From a robotics points of view it is understandable to have single DOF since they represent motors. But I am working on more abstract simulation models which would require multi DOF joints.

Describe the solution you'd like
To support all the joints described in SDF format.
[http://sdformat.org/spec?ver=1.6&elem=joint]

@cjaverliat
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cjaverliat commented Nov 5, 2020

I encountered the same issue regarding ball joints.
As of now, there are three joints missing for the SDF format (Cf. joints section):

  • ball: 3 rotational degrees of freedom
  • screw: 1 coupled rotational/translational degree of freedom
  • universal: 2 rotational degrees of freedom

As Phobos is mainly based on URDF it explains the lack of such joints.

What would be the ideal solution in that case ?

  • On the one hand, adding all the SDF joints types would resolve the issue, but on the other hand they would be useless and not exported for the URDF format.
  • It looks that you can build up a ball joint/spherical joint by composing fixed and continuous joints (Cf. this discussion). Maybe it would be possible to convert automatically the ball joint into the four equivalent joints in case of a URDF export.
  • Do not change anything and let the user create its own ball joint the way I mentionned before, but adding it somewhere in the documentation for the kinematic skeleton.

@hwiedPro hwiedPro added feature New feature proposal/idea for Phobos. pre_v2.0.0 To be tackled in v2.0.0 labels Jun 16, 2022
@hwiedPro hwiedPro removed the pre_v2.0.0 To be tackled in v2.0.0 label Nov 29, 2022
@hwiedPro
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Adding a ball joint is no problem, exporting it to URDF will lead to an error message, so that the user has to take care of it. I'll update this when I found time to tackle this.

The other two need some more changes, especially the coupling of the screw joint. This will rather happen in a later iteration.

@hwiedPro hwiedPro added this to the Phobos 2.1.0 milestone Mar 13, 2023
@AlpenAalAlex AlpenAalAlex self-assigned this Mar 25, 2024
@AlpenAalAlex AlpenAalAlex added the merge requested Feature waiting for merge by developers. label Oct 9, 2024
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