I've answered inline

On Thu, Jan 27, 2011 at 10:37 AM, Jim Rothrock <jim.rothrock@wunderkammerlab.com> wrote:

I am applying a torque to an axle like this:

apply_effort = rospy.ServiceProxy("gazebo/apply_joint_effort",
ApplyJointEffort)
apply_effort("axle", 0.01, rospy.Time(), rospy.Duration(-1))
rospy.sleep(0.05)
apply_effort("axle", 0, rospy.Time(), rospy.Duration(-1))

I expected the axle's angular velocity to accelerate for 0.05 seconds,
then remain constant. In reality, the axle continues to accelerate. It
appears that apply_joint_effort is cumulative, and my code actually
needs to be like this:

apply_effort("axle", 0.01, rospy.Time(), rospy.Duration(-1))
rospy.sleep(0.05)
apply_effort("axle", -0.01, rospy.Time(), rospy.Duration(-1)) # Cancel
previous torque.

Is my understanding correct?

yes, the forces applied are cumulative. I've updated the wiki to reflect so.

I tried to use gazebo/clear_joint_forces instead of applying a -0.01
effort, but it appears that clear_joint_forces is no longer in ROS, even
though it is in the Gazebo package documentation in the ROS wiki.

which release are you running? I see the clear_joint_forces service calls in both cturtle and unstable(diamondback alpha) files.

Thanks,

John

--
Jim Rothrock | Wunderkammer Laboratory
jim.rothrock@wunderkammerlab.com

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