With the Arduino you could make the robot more autonomous. You could add some sensors that would detect that it was against the wall of the tunnel and adjust track speed to keep it parallel. Or that could detect some distance from the wall and use it to guide the robot straight and parallel but ofset from the wall for each pas down the duct. You could add sensors to detect where ridge in the pile of sand is and adjust the robots position to keep too much sand from dumping off the side of the blade that is in the area that has already been cleaned. If you did something like that then your RC link would be more of a guidance and override rather than CONTROL.