Swell tynx for that... i have an idea.. of building a saucer using a fan for it to fly... and another 4 small fans to move it forward, backward and sidewards.. each 4 fans have their own sensors that when it sense it is going to hit something it would automaticaly turns the fan on to blow itself away from the object of collision and when it sense nothing it will turn the fan off, just like the principle of "obstacle avoiding robot" but the thing is i am not use to make programms for AT89S51 and AT89C51........