Joint Friction

Joint friction reduces a force based on how heavy an object is.

The force balance equation:

\[ F=m\ddot{x}+b\dot{x}+kx \]

where \(F\) is an applied force, x is position, \(\dot{x}\) is velocity, and \(\ddot{x}\) is acceleration. \(m\) is mass, \(k\) is a spring constant, and \(b\) is a viscous damping term.

When you plot applied torque versus speed for the unloaded system, the friction losses will be the y-intercept.

Example code snippet

    <!-- Damping -->
      <joint name="wheel_joint" type="revolute">
        <parent>wheel_support</parent>
        <child>wheel</child>
        <pose relative_to="wheel_support">0 0 0 0 0 0</pose>
        <axis>
          <xyz>0 0 1</xyz>
          <dynamics>
            <damping>0</damping>
            <friction>1</friction>
          </dynamics>
          <limit>
            <lower>-1e+16</lower>
            <upper>1e+16</upper>
          </limit>
        </axis>
      </joint>

Comparison

color	friction
green	0
teal	1
blue	10
pink	100
red	1000