why my biped robot breakdown when the foot landing the ground? [closed]

edit

I create a biped robot in gazebo and try the walking task. When the right leg swing up then landing the ground, the whole robot breakdown? (the ode engine fly because of sudden contact force? ).
Any one knows the reason?

I guess the PID(high gains) of the each joint is the main course, the Kp i choose is very large( i use the PD control), but if i choose a small Kp, the joint angle may not track the desired angle well.

So how should i solve this problem???

addition: i use the atlas.world in the drcsim:

<?xml version="1.0" ?>
<sdf version="1.4">
<world name="default">
<gui fullscreen='0'>
  <camera name='user_camera'>
    <pose>1 -5 1 0 0 1.571</pose>
  </camera>
</gui>
<physics type="ode">
  <gravity>0 0 -9.81</gravity>
  <simbody>
    <accuracy>0.005</accuracy>
    <max_transient_velocity>0.005</max_transient_velocity>
    <contact>
      <stiffness>1e8</stiffness>
      <dissipation>20.0</dissipation>
    </contact>
  </simbody>
  <ode>
    <solver>
      <use_dynamic_moi_rescaling>true</use_dynamic_moi_rescaling>
      <type>quick</type>
      <iters>500</iters>
      <sor>1.0</sor>
    </solver>
    <constraints>
      <cfm>0.0</cfm>
      <erp>0.2</erp>
      <contact_max_correcting_vel>100.0</contact_max_correcting_vel>
      <contact_surface_layer>0.0</contact_surface_layer>
    </constraints>
  </ode>
  <real_time_update_rate>1000</real_time_update_rate>
  <max_step_size>0.001</max_step_size>
</physics>
<!-- A global light source -->
<include>
  <uri>model://sun</uri>
</include>
<!-- A ground plane -->
<include>
  <uri>model://ground_plane</uri>
</include>

</world> </sdf>