Our design is based on a rail system from which the tennis ball hangs from a string. The gears at the top have a track system on them, and from this hangs the tennis ball.

One motor that we have controls the side-to-side movement of the track system, while another has the string tied to it. When this motor is turned one way, the string will wind around the pole/pinion and bring the ball up. When it goes the other way, the weight of the tennis ball will bring it down as it unwinds. However, since gravity is what brings it down and there is no gravity in space, you could use something that is stiff, such as a metal rod using hydraulics, so that it can be pushed down.

For ours, though, when raised, it cannot move back and forth without slack. To take care of that, we used a clothespin to act as a clip that will keep the ball stable. With the ball suspended, we can let out slack by unwinding the motor so that we can move it back and forth.

Although we cannot keep it moving for three seconds after we stop pushing it, we cannot see how this is needed, since it would be more important for it to stop quickly and on demand. Thank you for allowing us to participate in this competition.