Contact sensor not sensing collisions in Bullet Physics engine

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Hello,

So I am having problems running tests using the Bullet physics engine through Gazebo. Initially I set up a world with the ODE physics engine, a block model with a contact sensor and another block model both floating in space. I created a model plugin that pushed the block with the contact sensor towards the other block, once the blocks collied I got data from the contact sensor. Now I have set up a world file with these physics properties

<physics type="bullet">
            <gravity> 0.0 0.0 0.0</gravity>
            <max_step_size>0.001</max_step_size>
            <real_time_factor>1</real_time_factor>
            <real_time_update_rate>1000</real_time_update_rate>
            <max_contacts>10000</max_contacts>
            <bullet>
                <solver>
                    <type>sequential_impulse</type>
                    <iters>50</iters>
                    <sor>1.4</sor>
                    <min_step_size>0.0000001</min_step_size>
                </solver>
                <constraints>
                    <cfm>0</cfm>
                    <erp>1</erp>
                    <split_impulse>1</split_impulse>
                    <split_impulse_penetration_threshold>0</split_impulse_penetration_threshold>
                    <contact_surface_layer>0</contact_surface_layer>
                </constraints>
            </bullet>
        </physics>

Keeping everything else the same, and for some reason when the blocks collide I do not get any information from my contact sensor with regards to a collision occurring. Its as if nothing happened, however visually the models bounce of each other since they are floating in space.

I was hoping maybe some one could explain to me why I am getting no data. Could it be because of my physics properties? Or could it be because my control plugin doesnt have something set with respect to Bullet? I would assume the the control plugin used to detect collision when running the program in ODE should also work in Bullet.

Any help would be greatly appreciated :)

Thanks Francis123