I suggest start by making sure the mass and moment of inertias are close to realistic values. Then to get rid of the smooth-slow motion you are seeing, slowly increasing damping coefficients for the joints. Unfortunately, realistic damping coefficients are hard to come by, and for PR2 we got them by simply trying out different values and comparing joint responses when given a joint trajectory command. Note that when damping coefficient is too large, the joint may become unstable, at that point, you can optionally reduce time stepping size or increase quickStepW in your world file.<br>
John<br><br><div class="gmail_quote">On Thu, Aug 5, 2010 at 9:35 AM, Ugo Cupcic <span dir="ltr"><<a href="mailto:ugo@shadowrobot.com">ugo@shadowrobot.com</a>></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;">
<div text="#000000" bgcolor="#ffffff">
Hi John,<br>
<br>
Ok. I'm having trouble getting a realistic behaviour for my model in
gazebo... It acts really really smoothly, with really slow movements
when I'm not sending commands to it. For example when the hand
hasn't received any command yet, it will close its fingers in maybe
10 seconds as if it were in oil or something. <br>
<br>
Any idea on how to improve this? <br>
<br>
Cheers<div><div></div><div class="h5"><br>
<br>
On 05/08/10 17:30, John Hsu wrote:
<blockquote type="cite">Hi Ugo,<br>
Friction is not modeled in ode at this point, if it's something
you need, please file a feature request ticket <a href="https://code.ros.org/trac/ros-pkg/newticket" target="_blank">here</a>, and
set simulator_gazebo as the component. Modeling coulomb friction
at a joint is possible in ODE, but has not been tested.<br>
thanks,<br>
John<br>
<br>
<div class="gmail_quote">On Thu, Aug 5, 2010 at 5:13 AM, Ugo
Cupcic <span dir="ltr"><<a href="mailto:ugo@shadowrobot.com" target="_blank">ugo@shadowrobot.com</a>></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;">
<div text="#000000" bgcolor="#ffffff"> Thanks a lot. I missed
this!
<div>
<div><br>
<br>
On 05/08/10 13:11, Adolfo Rodríguez Tsouroukdissian
wrote:
<blockquote type="cite"><br>
<br>
<div class="gmail_quote">On Thu, Aug 5, 2010 at 1:17
PM, Ugo Cupcic <span dir="ltr"><<a href="mailto:ugo@shadowrobot.com" target="_blank">ugo@shadowrobot.com</a>></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;"> Hi all,<br>
<br>
I'm currently trying to get a better control on
our gazebo model of the<br>
Hand. I'm having trouble finding any kind of
documentation regarding the<br>
parameters you can apply to a joint (e.g.
friction). Is there a place I<br>
could start with?<br>
<br>
For the time being, my joints look like this:<br>
<joint name="trunk_rotation"
type="revolute"><br>
<parent link="${parent}"/><br>
<child link="shadowarm_trunk"/><br>
<origin xyz="0 0 0.01" rpy="0 0 0" /><br>
<axis xyz="0 0 1" /><br>
<limit lower="-${M_PI/2}"
upper="${M_PI/4}"<br>
effort="10" velocity="1.0"/><br>
<dynamics damping="1"/><br>
</joint><br>
<br>
</blockquote>
<div>You can add static friction to the dynamics
joint element. This link documents all the valid
elements for a URDF joint:<br>
<br>
<a href="http://www.ros.org/wiki/urdf/XML/Joint" target="_blank">http://www.ros.org/wiki/urdf/XML/Joint</a><br>
<br>
HTH<br>
<br>
Adolfo<br>
<br>
</div>
<blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"> <br>
Cheers,<br>
<br>
Ugo<br>
<br>
--<br>
Ugo Cupcic | Shadow Robot Company | <a href="mailto:ugo@shadowrobot.com" target="_blank">ugo@shadowrobot.com</a><br>
Software Engineer | 251 Liverpool Road |<br>
need a Hand? | London N1 1LX | +44
20 7700 2487<br>
<a href="http://www.shadowrobot.com/hand/" target="_blank">http://www.shadowrobot.com/hand/</a>
@shadowrobot<br>
<br>
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<br clear="all">
<br>
-- <br>
Adolfo Rodríguez Tsouroukdissian, Ph. D.<br>
<br>
Robotics engineer<br>
PAL ROBOTICS S.L<br>
<a href="http://www.pal-robotics.com" target="_blank">http://www.pal-robotics.com</a><br>
Tel. +34.93.414.53.47<br>
Fax.+34.93.209.11.09<br>
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Ugo Cupcic | Shadow Robot Company | <a href="mailto:ugo@shadowrobot.com" target="_blank">ugo@shadowrobot.com</a>
Software Engineer | 251 Liverpool Road |
need a Hand? | London N1 1LX | +44 20 7700 2487
<a href="http://www.shadowrobot.com/hand/" target="_blank">http://www.shadowrobot.com/hand/</a> @shadowrobot</pre>
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<pre cols="72">--
Ugo Cupcic | Shadow Robot Company | <a href="mailto:ugo@shadowrobot.com" target="_blank">ugo@shadowrobot.com</a>
Software Engineer | 251 Liverpool Road |
need a Hand? | London N1 1LX | +44 20 7700 2487
<a href="http://www.shadowrobot.com/hand/" target="_blank">http://www.shadowrobot.com/hand/</a> @shadowrobot</pre>
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