minitaur with closed loop chains

Hello!
I have a urdf file for minitaur robot, I want to use it on Mujoco environment. I have already converted to xml that runs on Mujoco, however I still got open loop for legs, how can I get closed loop chains? I have tried something like：
<equality>
<connect body1='lower_leg_front_rightL_link' body2='lower_leg_front_rightR_link' anchor='0.2 0 0' solref='0.005 1'/>
<connect body1='lower_leg_front_leftL_link' body2='lower_leg_front_leftR_link' anchor='0.2 0 0' solref='0.005 1'/>
<connect body1='lower_leg_back_rightL_link' body2='lower_leg_back_rightR_link' anchor='0.2 0 0' solref='0.005 1'/>
<connect body1='lower_leg_back_leftL_link' body2='lower_leg_back_leftR_link' anchor='0.2 0 0' solref='0.005 1'/>
</equality>

But didn't work. I have attached my current xml file and the original urdf file below, can anyone point me a direction on how to start? I'm new to Mujoco and have never written model in xml before. Any response will be much appreciated!