model mass compensation spring for torso lift (ros ticket #5022)

[ahendrix]

This might reduce some of the stiffness experienced at the torso_lift joint.

To cancel mass of upper body, one can do this for now: {{{ rosservice call gazebo/apply_joint_effort '{ joint_name: "torso_lift_joint" , effort: 462.56 , start_time: 0, duration: -1 }' }}}

trac data:

• Owner: hsu
• Reporter: hsu
• Reported at: Tue Feb 15 15:29:58 2011
• URL: https://code.ros.org/trac/wg-ros-pkg/ticket/5022

[ahendrix]

[hsu] turns out this is not necessary with the new screw constraint being tested.