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Thread: divided kinematic chains in Collada 1.5

  1. #1
    Junior Member
    Join Date
    Jun 2009
    Posts
    3

    divided kinematic chains in Collada 1.5

    Hello,
    I want to create a serial kinematics in Collada 1.5 that is divided like a tree (more specific - an anthropomorphic robot hand).
    If I understand the documentation correctly, it is only possible to divide the chain by insertion several
    attachment_full elements within the same link.
    Code :
    <link sid="A"> 
       <attachment_full joint="model/jointB"> 
          <link sid="B"/> 
       </attachment_full> 
     
       <attachment_full joint="model/jointC">  
     
          <link sid="C"/> 
       </attachment_full> 
     </link>

    However, this means the subchains start at the exactly the same point with exactly the same orientation.
    I think it would be much more useful if you could specify several links after an attachment_full.
    Is there any possibility to achieve this without the need to introduce additional (synchronized) joints?

    Thank you a lot in advance,
    Stefan

  2. #2
    Junior Member
    Join Date
    Apr 2009
    Posts
    16

    Re: divided kinematic chains in Collada 1.5

    Hello Stefan,

    the transformation of an attachment element is done within the element itself. So you can put to different joints under a link with different transformation.

    Code:
    <link sid="A">
    <attachment_full joint="model/jointB">
    <translate>10 0 0</translate>
    <link sid="B"/>
    </attachment_full>
    <attachment_full joint="model/jointC">
    <translate>20 0 0</translate>
    <link sid="C"/>
    </attachment_full>
    </link>

    The rule is the same as for nodes. The transformations within a node element defines the frame relative to its parent.
    So, the transformation within an attachment element defines the frame relative to its parent link element, and the transformation within a link element defines the frame relative to its parent attachment element.

    Looking to the spec, there seems to be a bug on page 10-6 in the example. But the example on page 10-8 looks correctly.

    Regards

    Steffen

  3. #3
    Junior Member
    Join Date
    Jun 2009
    Posts
    3

    Re: divided kinematic chains in Collada 1.5

    Thank you very much Steffen. I think this should be pointed out more clearly in the documentation - perhaps place there an example of a forked kinematics?

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