Hi Yoonsoo,<br>Seems like a custom transmission should work here.  You wouldn&#39;t have to specify anything additional in URDF, except adding a transmission block for corresponding joints.  Modeling your custom transmission after <a href="http://www.ros.org/doc/api/pr2_mechanism_model/html/classpr2__mechanism__model_1_1SimpleTransmission.html">SimpleTransmission</a> or <a href="http://www.ros.org/doc/api/pr2_mechanism_model/html/classpr2__mechanism__model_1_1WristTransmission.html">WristTransmission</a> should be a good starting point.<br>

Are you planning to run on hardware or in simulation?<br>John<br>

<br><div class="gmail_quote">On Wed, Oct 13, 2010 at 9:44 PM, Kim, Yoonsoo <span dir="ltr">&lt;<a href="mailto:yesarang.kim@gmail.com" target="_blank">yesarang.kim@gmail.com</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">



Thanks for your kind reply, John.<div><br></div><div>Let me try to explain simply how joint/actuators are coupled in my robot.</div><div><br></div><div>There 6 groups of coupled joints per a hand and all groups of 2 joints are driven by 2 motors and transform matrix(2x2 or 3x2) from joint angle/velocity/torque to motor angle/velocity/torque can be expressed in terms of some ratios and vice versa.</div>





<div><br></div><div>How can I express this relationship in URDF? Should I implement some supporting classes specific to my robot similar to PR2&#39;s SimpleTransmission, WriteTransmission, and PR2GripperTransmission? It may be helpful to understand how  the PR2-specific transmission element is designed?</div>




<div><br></div><div>- Yoonsoo</div>
<div><br><div class="gmail_quote">2010/10/14 John Hsu <span dir="ltr">&lt;<a href="mailto:johnhsu@willowgarage.com" target="_blank">johnhsu@willowgarage.com</a>&gt;</span><div><div></div><div><br><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;">






Hi Yoonsoo,<br>URDF does not support coupled joints.  Custom transmissions should most likely be able to do what you have described.   <a href="http://www.ros.org/wiki/pr2_mechanism_model" target="_blank">pr2_mechanism_model</a> has some examples and documentation on how transmissions are used in PR2.<br>








How are the joint/actuators coupled in your robot?<br>Thanks,<br>John<br><br><div class="gmail_quote"><div><div></div><div>On Tue, Oct 12, 2010 at 11:02 PM, Kim, Yoonsoo <span dir="ltr">&lt;<a href="mailto:yesarang.kim@gmail.com" target="_blank">yesarang.kim@gmail.com</a>&gt;</span> wrote:<br>









</div></div><blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div><div></div><div>Hi,<div><br></div><div>My robot is composed of various coupled joints for dexterous hands, in which M joints are driven by N motors.</div>









<div><br></div><div>I tried to find out how to express coupled joints in URDF but couldn&#39;t according to URDF XML reference.</div>
<div>What I only found was PR2-specific &lt;transmission&gt; element. Can this &lt;transmission&gt; element express coupled joints and relationship between joints and actuators?</div><div><br></div><div>If the element can&#39;t express coupled joints, any suggestion to do that will be appreciated.</div>










<div><br></div><div>TIA</div><div><br></div><font color="#888888"><div>- Yoonsoo</div><div><br></div>
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