not realistic simulatoin

edit

Hi,

I am trying to simulate robots using neural networks and genetic algorithms. here is the link to the video.

I don't know why when the two legs being in the air the cube link don't fall down like it should be in real life. even if I put its mass to 100. The gravity is set as default.

I know that the real time factor can affect, but what are other properties that I have to adjust ?

thank you very much !

here is the SDF file :

<?xml version='1.0'?>
<sdf version='1.4'>
<model name="fourlegs">

  <static>false</static>

  <!--**********************body************************************-->
  <link name='corps'>
      <pose>0 0 .04 0 0 0</pose>

      <inertial>
        <mass>100</mass> 
      </inertial>

      <collision name='collision'>
       <geometry>
        <box>
         <size>.1 .1 .02</size>
        </box>
       </geometry>
     </collision>

     <visual name='visual'>
      <geometry>
       <box>
         <size>.1 .1 .02</size>
       </box>
      </geometry>             
     </visual>
</link>
<!--*********************left leg *******************************-->
<link name='jambeDG'>
<pose> .06 .04 .01 0 0 0</pose>

<inertial>
  <mass>10</mass> 
</inertial>
<collision name='collision'>
  <geometry>
    <box>
      <size>.02 .02 .06</size>
    </box>
  </geometry>
</collision>

<visual name='visual'>
  <geometry>
    <box>
     <size>.02 .02 .06</size>
    </box>
  </geometry>             
</visual>  
</link>
<!--*********************right leg*******************************-->
 <link name='jambeDD'>
  <pose> -.06 .04 .01 0 0 0</pose>

<inertial>
  <mass>10</mass>
</inertial>

<collision name='collision'>
  <geometry>
    <box>
      <size>.02 .02 .06</size>
    </box>
  </geometry>
</collision>

<visual name='visual'>
  <geometry>
    <box>
      <size>.02 .02 .06</size>
    </box>
  </geometry>             
</visual>
</link>

<!--*************************************************************-->
<!--**********************JOINTS*********************************-->
<!--*************************************************************-->

<!--**********************joint left leg************************-->
<joint type="revolute" name="jointJambDG">

<pose> -.01 .0 .03 0 0 0</pose> 

<child>jambeDG</child>
<parent>corps</parent>
<axis>
  <xyz>1 0 0</xyz>
  </axis>
</joint>
<!--**********************joint right leg************************-->
<joint type="revolute" name="jointJambDD">
 <pose> .01 .0 .03 0 0 0</pose>
 <child>jambeDD</child>
 <parent>corps</parent>
 <axis>
   <xyz>1 0 0</xyz>  
   </axis>
</joint>
</model>
</sdf>