Gazebo: Model is oscillating and breaking after spawning

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Hi, I am trying to spawn a model which i created in Solidworks and exported as urdf but when i try to use roslaunch to spawn it, I see the my model is breaking and oscillating.

I tried to experiment and try various stuff but its still not working and then I have to design a controller which can grab the object using links L1 and L2. I tried to use effort and position controller but i am just a novice and i am sure, I am making some mistakes. Here is the link to the repo: https://github.com/shane9669/gripper

Any leads on how to first resolve how to fix the model in gazebo or any edits in my urdf file would be appreciated and any suggestions on which controller to use is also welcomed.

Thanks for the help