This is a Kinect project that could sell well if mass produced and it hints at many other possible applications. Can you believe it - a trashcan that catches your randomly  thrown rubbish?

This is an easy-to-understand application of the Kinect. Place a Kinect on a wall so that it can track the position of the trashcan and any projectiles you care to throw into the air. Provide some additional software to compute the trajectory and then just move the trashcan to the location where the projectile comes to earth.

Now watch the video and wonder why with all that technology why is there a typewriter producing all that waste paper:

The video shows the build process, but you really should consider what is involved in making this work. One of the first tasks for the early electronic computers was computing range tables for targeting big guns. The computation of where a projectile will fall is that complicated. In this case, though, we not only have to compute the landing spot but first we have to detect the 3D trajectory given a number of positions. In theory three should be enough to determine the parabola and the velocities. Then there is the small matter of getting the trashcan into position to catch the projectile - this is no small planning task.

So the final challenge is - can you think of a really useful application for this?

Having a robot that catches anything  you drop or throw should be useful, but in most cases there are simpler solutions. A game of catch comes to mind and if you scale it up what about a robot baseball player?

Any others?