def head_speed(
            self, combined_speed=None,
            x=None, y=None, z=None, a=None, b=None, c=None):
        """
        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
        """
        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)
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