def _display_controls(self):
        """
        Method to pretty print controls.
        """

        def print_command(char, info):
            char += " " * (10 - len(char))
            print("{}\t{}".format(char, info))

        print("")
        print_command("Keys", "Command")
        print_command("q", "reset simulation")
        print_command("spacebar", "toggle gripper (open/close)")
        print_command("w-a-s-d", "move arm horizontally in x-y plane")
        print_command("r-f", "move arm vertically")
        print_command("z-x", "rotate arm about x-axis")
        print_command("t-g", "rotate arm about y-axis")
        print_command("c-v", "rotate arm about z-axis")
        print_command("ESC", "quit")
        print("")
Method to pretty print controls.