Einstein's Clock

This is a project I started during my junior year in college. Between classes and working it took about a year to complete.

Basic Concept:
I found that with every clock, no matter how abstract the face is, the hands always move in perfect circles. This inspired me to create Einstein's clock. The basic idea was to design and build a clock where the hands do NOT move in perfect circles.

How it Works:
The minute hand is attached to the bicycle chain which follows an irregular path created by the randomly placed cogs of varying size. Through the clever use of a low RPM motor and gear ratios, the minute hand makes one complete rotation every hour. The hour hand of this clock is simply the cog in the middle. The hour cog/wheel/hand thing has 24 teeth (one for every hour of the day) which ratchets over one tooth every time the minute hand goes past.

What Makes it Einstein's:
Good ol' Einstein threw us all for a loop when he showed through relativity that time may not move at a constant speed. Due to the irregular shape of this clock, the minute hand can be pointing in one direction (signifying one time) and then 5 minutes later be pointing in the same direction (signifying the same time). Also, along some parts of the clock the minute hand moves relatively quickly, while along other parts the minute hand seems to barely move at all. The combination of these two effects gives the illusion that time is not moving linearly, hence Einstein's Clock.

Pictures and Development:
As you can see in the images below, the general shape remained the same while the orientation and the back board changed. The board in the center picture was cut out from the board in the first picture. It broke and so I made the board in the third picture. You can click on the images to see larger pictures.

 

Materials and Construction:
The original board was a 24"x24" piece of 1/2" plywood. After breaking that, I used two pieces of 9/32" plywood glued together. I glued two boards together so that I could mount the 1/4" motor plate flush with the face. The cogs were cannibalized from various bicycles and mounted on aluminum hubs. The cogs are attached to the board using T-nuts and 1/4" stainless steel socket head cap screws with nylon spacers holding the cogs away from the board. The chains are just cheap bike chains (318 links for the perimeter and 50 links for the motor circuit) and the motor is a 1-1/3 RPM, 115VAC induction gear motor. I used an induction motor because the RPM is based on line frequency (generally constant at 60Hz) rather than line voltage (Which varies from 110V to 120V).

If you want to calculate it out here are the numbers:
1-1/3 RPM motor
10/25 gear reduction
10/318 gear reduction

That comes out to a little over one rotation per hour, but the motor is a little slow, so it comes out almost perfect in reality. Detail images of the gear reduction and of the spring tensioner below: