code: def head_speed(
              self, combined_speed=None,
              x=None, y=None, z=None, a=None, b=None, c=None):
          
          user_set_speeds = {'x': x, 'y': y, 'z': z, 'a': a, 'b': b, 'c': c}
          axis_max_speeds = {
              axis: value
              for axis, value in user_set_speeds.items()
              if value
          }
          if axis_max_speeds:
              self._driver.set_axis_max_speed(axis_max_speeds)
          if combined_speed:
              self._driver.set_speed(combined_speed)
docs: Set the speeds (mm/sec) of the robot
  
          Parameters
          ----------
          combined_speed : number specifying a combined-axes speed
          <axis> : key/value pair, specifying the maximum speed of that axis
  
          Examples
          ---------
  
          >>> from opentrons import robot # doctest: +SKIP
          >>> robot.reset() # doctest: +SKIP
          >>> robot.head_speed(combined_speed=400) # doctest: +SKIP
          #  sets the head speed to 400 mm/sec or the axis max per axis
          >>> robot.head_speed(x=400, y=200) # doctest: +SKIP
          # sets max speeds of X and Y