ah.  got it.
On May 11, 2014, at 10:01 AM, Benoit Landry <notifications@github.com> wrote:

> In examples/MassSpringDamper/MassSpringDamper.urdf:
> 
> > @@ -1,8 +1,5 @@
> >  <?xml version="1.0"?>
> Actually the MassSpringDamperThrust.urdf is used to test the thrust input, while the MassSpringDamper.urdf is used to test a prismatic joint transmission (one of the them is a force_element and the other is a transmission element).
> 
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