FT Sensor shows zero values

Hello, I am working on an implementation of a FT sensor using Gazebo 2.2, ROS Indigo and Ubuntu 14.04. I have written my SDF model like follows: false0 -0.4 1.14 0 0 0 0.042 0.042 0.74 0 0 .8 10 -0.4 1.14 0 0 0 0.042 0.042 0.74 0 -0.358 1.3 0 0 0 0.042 0.042 0.042 0 0 .8 10 -0.358 1.3 0 0 0 0.042 0.042 0.042 0 -0.332 1.3 1.5708 0 0 0.01 0.01 0 0 .8 10 -0.332 1.3 1.5708 0 0 0.01 0.01 true true ftBase obstacle 0 0 1 0 0 ftBase ftButton 0 0 1 0 0 true 10.0ft_sensorobstacle_ftBase_joint This spawns a pillar with a button . I want to measure the force applied to the pillar when the robot collides with it. I use `rostopic echo /ft_sensor` to view the forces. While I can see the topic and the corresponding WrenchStamped message, I hit the pillar with the robot and the forces are always zero. I have tried 1. using different plugins (gazebo_ros_f3d)item 2. using the force_torque SDF sensor 3. using different joints and links as measurement sources 4. implementation of the whole environment in URDF instead of SDF. I have seen similar questions related to FT implementation asked online, but the closest I get is to view the topic with zero forces. I would be thankful for any suggestions. Thanks!