Massive difference between Baxter Gazebo7 and real Robot

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Hi all. I am running a cerebellar controller on Baxter robot using Gazebo 7 simulator. The robot is supposed to draw different trajectories but after learning process (400 trials ) although the error decreases the results I get from the simulator is almost 10 times worse than the real robot and the robot cannot draw a nice shape. Does anyone know what could be the problem? I also tried to change some parameters including the gain of the controller but it did not help much. I the problem with Gazebo simulator?