Based on the original rolling ball clock by Idle Tyme Corporation, this Lego version is a bit more amusing to watch — complete with an RCX 1.0 and external supply to obtain longtime stability. Four video clips after the jump.
The clock works by using steel balls to indicate the exact time. The bottom rail represents the hours. The middle and upper rails are used to represent the minutes. An electric motor scoops up a ball every minute. Every five minutes, the top rail will dump and deposit a ball on the second rail. Every hour, the upper and middle rails dump and one ball is transferred to the bottom rail to increment the hours.