This invention is a robot that can move vertical on a string. Unlike in the film "Mission Impossible" our string acrobat can also move sideways. That is why we have used it to clean the window sill. It moves along the window sill sideways, detecting the end of the window with the light sensor (it is a daytime worker). It moves horizontally in a settable height in one direction and closely to the sill into the other, indiscriminately pushing everything from the window sill.

The height close to the window sill is controlled by the touch sensor, the upper height is controlled by the ultrasonic sensor.

The robot works on a single rope, and functions much like a block and tackle. If the rope is shortened or lengthened, the robot moves sideways, likewise when moving sideways, it also moves up and down. Putting the movement stuff into our own blocks caused the PC program to crash now and then, so we did not build advanced programs. We were thinking of one that only cleans the sill when there is something on it. At the moment the robot just moves in a rectangle across the window.

Outlook: Our ultimate dream application for this robot is of course window cleaning. If we get it to work properly, we are prepared to buy one Mindstorm per window.