bullet tags in sdf file

asked 2015-05-12 00:34:40 -0500

PML gravatar image

I am using Gazebo 5.1.0 and it seems that in sdf the bullet tags to define parameters have some problems.

An example where apparently it will read values from ode instead of bullet:

      <friction>
        <ode>
          <mu>0.543426</mu>
          <mu2>0.543426</mu2>
          <fdir1>1 1 0</fdir1>
        </ode>
        <bullet>
          <friction>0.643426</friction>
          <friction2>0.643426</friction2>
          <fdir1>1 1 0</fdir1>
        </bullet>
      </friction>

when running the simulator with bullet (gazebo -e bullet) and then inspecting the frictions of the link the value shown is 0.543426, not 0.643426.

And an example where bullet parameters apparently are ignored:

      <contact>
        <ode>
            <soft_cfm>0.0</soft_cfm>
            <soft_erp>0.2</soft_erp>
            <kp>1000000</kp>
            <kd>100</kd>
            <max_vel>0.01</max_vel>
            <min_depth>0</min_depth>
        </ode>      
        <bullet>
            <soft_cfm>0.0</soft_cfm>
            <soft_erp>0.2</soft_erp>
            <kp>1000000</kp>
            <kd>100</kd>
            <split_impulse>0</split_impulse>
            <split_impulse_penetration_threshold>-0.01</split_impulse_penetration_threshold>
        </bullet>
      </contact>

In this case if the simulator runs with ODE, inspecting the link surface parameters shows that the defined values were loaded and the model behaves according to such values. However, if the simulator runs with Bullet (gazebo -e bullet), inspecting the link surface parameters shows that all values where set to 0 and the model misbehaves. Just in case someone wonders the model is a bipedal robot and in order to ensure proper foot contact without undesired sliding/rotation these parameters are essential.

In regard to this issue:

If bullet tags in sdf do not work appropiately, can I set those parameters programatically via a plugin with certainty that doing so works?

Are there undocumented sdf tags for bullet that solve this? (in my humble opinion sdf documentation lacks a lot of much needed information at the moment)

or

Should give up on trying to use Bullet and stick with ODE?

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Comments

Can you confirm that the physics engine is actually bullet? Try calling 'gazebo::physics::PhysicsEngine::GetType()' from a plugin.

AndreiHaidu gravatar imageAndreiHaidu ( 2015-05-12 02:59:27 -0500 )edit

I can confirm it is bullet, done so by checking the /gazebo/default/physics topic, first line of message is type: BULLET

PML gravatar imagePML ( 2015-05-13 12:02:15 -0500 )edit

From what I see there are other questions stating problems with the Bullet physics engine.

PML gravatar imagePML ( 2015-05-26 15:52:23 -0500 )edit