code: def update (self):
          
          delta_velocity = Vector.null()
          target_position = self.target.get_position()
          sprite_position = self.sprite.get_position()
  
          desired_direction = target_position - sprite_position
  
          if 0.0 == self.los or desired_direction.magnitude <= self.los:
              try:
                  desired_normal = desired_direction.normal
              except NullVectorError:
                  desired_normal = Vector.null()
              desired_velocity = desired_normal * self.sprite.get_max_speed()
              delta_velocity = desired_velocity - self.sprite.get_velocity()
  
          self.last_delta_velocity = delta_velocity
          return delta_velocity, self.power
docs: Calculate what the desired change in velocity is. 
          delta_velocity = acceleration * delta_time
          Time will be dealt with by the sprite.