Hexapod simulation not working

edit

Hello,

I want to create a simulation for a simple hexapod. When I spawn the model in Gazebo, I get a behavior like the following:

The behavior I was expecting was the hexapod at its zero position; standing.

I, also, implemented a simple plugin for setting the joints to their zero position at every update, but if I use SetPosition physics explode and if I use PID controllers and SetForce I need to specify the PID gains (which I want to avoid - setting dummy pid gains like 1,0,0.1 does not work). Here's what I get when I use SetPosition: C:\fakepath\hexa.gif

Any ideas?

For reference I am attaching the sdf file: C:\fakepath\pexod.sdf

Thanks in advance!