Hello,

You can reduce the torque parameter, and play with the masses.

You can also modify the friction of the wheels. To do this add a the
following parameters to a geom:

<geom ...>
  <kp>100000000</kp>
  <kd>1.0</kd> <!-- Damping constraint -->
  <bounce>0.0</bounce> <!-- How bouncy the surface is -->
  <bounceVel>10</bounceVel> <!-- MAx velocity before bounce is applied -->
  <mu1> BIG NUMBER </mu1>
  <mu2> BIG NUMBER </mu2>
  <slip1> small number (0.01) </slip1>
  <slip2> small number (0.01)</slip2>
</geom>

The ODE manual has descriptions of all these parameters.

-nate

On Sun, Mar 28, 2010 at 9:41 PM, David Michal <[email protected]> wrote:
> I have modeled a differential drive robot in Gazebo.  The problem is
> that when I driver the robot from Player it seems to have quite a bit of
> inertia. When turning to the left or the right it overshoots the target
> quite a bit.  The real robot uses stepper motors so that once you tell
> it to stop turning it does.  Is there a way to get Gazebo to better
> model a stepper motor?  I am using Player 3.0.1, Gazebo 0.9.0, and ODE
> 0.11.1.
>
> Here is what I have in the model file.
>
> <body:cylinder name="left_wheel_body">
>  <xyz>0.0 0.1325 -0.2032</xyz>
>  <rpy>0 90 90</rpy>
>  <geom:cylinder name="left_wheel_geom">
>    <size>.0635 .032</size>
>    <mass>0.5</mass>
>    <visual>
>      <rpy>0 0 90</rpy>
>      <size>0.127 0.127 0.032</size>
>      <mesh>drivewheel.mesh</mesh>
>      <material>Gazebo/Black</material>
>    </visual>
>  </geom:cylinder>
> </body:cylinder>
>
> <body:cylinder name="right_wheel_body">
>  <xyz>0.0 -0.1325 -0.2032</xyz>
>  <rpy>0 90 90</rpy>
>  <geom:cylinder name="right_wheel_geom">
>    <size>.0635 .032</size>
>    <mass>0.5</mass>
>   <visual>
>      <rpy>0 0 90</rpy>
>      <size>0.127 0.127 0.032</size>
>      <mesh>drivewheel.mesh</mesh>
>      <material>Gazebo/Black</material>
>    </visual>
>  </geom:cylinder>
> </body:cylinder>
>
> <joint:hinge name="left_wheel_joint">
>  <body1>left_wheel_body</body1>
>  <body2>chassis_body</body2>
>  <anchor>left_wheel_body</anchor>
>  <anchorOffset>0 0 0</anchorOffset>
>  <axis>0 1 0</axis>
>  <erp>0.8</erp>
>  <cfm>10e-5</cfm>
> </joint:hinge>
>
> <joint:hinge name="right_wheel_joint">
>  <body1>right_wheel_body</body1>
>  <body2>chassis_body</body2>
>  <anchor>right_wheel_body</anchor>
>  <anchorOffset>0 0 0</anchorOffset>
>  <axis>0 1 0</axis>
>  <erp>0.8</erp>
>  <cfm>10e-5</cfm>
> </joint:hinge>
>
> <controller:differential_position2d name="controller1">
>  <leftJoint>right_wheel_joint</leftJoint>
>  <rightJoint>left_wheel_joint</rightJoint>
>  <wheelSeparation>0.265</wheelSeparation>
>  <wheelDiameter>0.127</wheelDiameter>
>  <torque>1</torque>
>  <interface:position name="position_iface_0"/>
> </controller:differential_position2d>
>
>
>
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