Looney Clock

myminifactory

My submission to the mechanical clock competition. This clock is named after the Looney planetary gear arrangement, similar to this mechanism. UPDATE: This is a work in progress currently to get working reliably (when I get around to it). The clock is based on a complex planetary gearing mechanism composed of an input gear reduction stage, the rotating planetary gearing stage (green), which drives the output ring gears for the hours and minutes. It was originally intended to show the seconds (red hand) but due to a mistake I make in the gearing ratios this is not actually an accurate display of seconds; more like 100ish seconds per revolution, but I left it on for the looks. The green planet cage revolves once every 15 minutes. The outer gears on the cage mesh with three ring gears which have different numbers of teeth: 141 (stationary), 144 (hours ring) and 188 (minutes ring). The different numbers of teeth on the ring gears causes the hours and minutes ring gears turn at different rates as the green cage rotates around. The gear meshing on this initial design is not perfect and occasionally skips a tooth due to loose tolerances, I am currently working on improving the reliability. I didn't realise with the original printing of this clock, my printer calibration was way off. The X-axis was 1% larger than the Y-axis. This lead to printing very slight ovals instead of true circles which completely throws off the gear meshing since the teeth are only a couple of milimeters tall, so beware of this. This design is really pushing what can be made on a home printer since the gear teeth are quite small. The clock here is driven by an AC synchronous motor that runs at a fixed speed (5 RPM) using the power grid frequency. I didn't realise this original motor type I chose gets quite hot in use so I am looking at a replacement. If you want to print this design you will also need: 32x M3x8 countersunk screws, 2x 608zz bearings and a motor to drive it. I have added a lot of extra holes on the back if anyone wishes to add their own drive mechanism/motor. For those interested in the technical details, all three ring gears have the same base pitch, and yet are the same size despite having different numbers of teeth (usually impossible with normal gears). This is possible by using profile shifting, where the diameter of an involute gear can actually be increased or decreased while maintaining the same number of teeth and effective pitch for meshing with other gears. Usually only a small amount is added to adjust gear sizes, but here a large amount is used to make a 141 tooth and 188 tooth gear the same size. The meshing is not optimal, but ok for a low load scenario like this clock.