Stonehenge uses a CrustCrawler Smart Arm and a Parallax Propeller chip to display the current time. All the digits needed to display the time are located on cards positioned in a semi-circle around the left and right sides of the arm. The time itself is displayed in front of the arm. This gives the clock a "Stonehenge" like appearance. There are a total of 14 cards. Each card has two digits with one on each side. The software planner determines which card and which side is needed to display the time and then sends the necessary movement commands to the arm.
Most of the project was constructed from foam board purchased from the local office supply store. The cards are 1 ¾ by 4 inches. Embedded in the bottom of each card are two Neodymium magnets. The magnets snap to heads of 4-40 screws that are mounted in the base. The magnet/screw scheme compensates for any small amount of error that inevitably occurs when gripping and moving the cards around.
Below is a short video showing Stonehenge in action.
The video shows a time update from 12:09 to 12:10. It demonstrates all the basic movements needed to display the time. If you watch carefully you can see it execute the following movements.
Put Card in Display
Get Card from Display
Put Card in Storage
Get Card from Storage
Since the update can be slow for large changes (over a minute) the software will compenstate by advancing the time display as needed.
If you want to build your own version, Stonehenge will appear in the next issue of Robot Magazine due out on September 15th.
For another offbeat robot check out RoboStool - It's funiture On-Demand. If you want more practical robot you should take a look at RoboCam a telepresence robot which can be used for security and elder care.