I built this K'nex clock to while away quiet Sunday mornings at Glasgow Science Centre. It generated some interest among the visitors, who sometimes joined in. One morning, a very small boy wandered up and "helped" me for a little while. I showed him the parts of the clock - the hands, the pendulum, the escapement, and so on, and explained what they were for. He inspected it all with great care and then said: "Your Mum and Dad must be so proud of you".
Now K'nex is great stuff, but K'nex artefacts are not very photogenic. In fact they are downright confusing. So you may need to be content to take away the flavour of the clock rather than the exact details of how it works. The picture on the right shows the clock with the main parts labelled.
One thing that I was up against straight away was that we had no K'nex gears. I was happy enough for the "second" hand to move to rotate at the same speed as the shaft of the escape wheel, but I needed to gear the motion down to run the "minute" hand. Now you can make an 8-toothed "gear" out of ordinary K'nex pieces (a white connector and 8 green rods), that operates quite well as a bevel gear. To gear down the motion of the escape wheel shaft, I made a sort of folded-up planetary gear system. No doubt there's a name for such an arrangement. The somewhat blurry photograph on the right shows the details. The drive comes in on the black shaft at the left (which is split from the output shaft near the point marked x). The input shaft is fixed to the vertical gear wheel on the left. The output shaft is fixed to the centre of the planet-wheel assembly, and it passes through, and rotates freely within, the centre of the right-hand (fixed) gear wheel. As the input shaft turns, the planet-wheel assembly rolls around on the fixed wheel, at half the speed of the input shaft. Thus the output shaft rotates at half the speed of the input shaft. I had three such stages in succession, thus getting an 8:1 reduction.
The picture on the right shows the back of the clock. The reduction gear train is the mechanism sticking out with green and white gears. On the right of the clock are the two vertical shafts that take the drive to the hands. The further one (black) takes the motion of the escape wheel shaft directly up to the "second" hand. The other end of the escape wheel shaft drives the reduction gear train, and then, via the nearer vertical shaft (red) to the "minute" hand. With the gears at my disposal, I had to abandon traditional systems of time measurement, and instead use an octal system with 8 "seconds" in every "minute" and 8 "minutes" in every "hour". (An "hour" is one complete revolution of the "minute" hand - there was no "hour" hand.) The two hands rotated coaxially.
Did it work?
Yes, it did, in the sense that the pendulum swung, the escapement escaped, and the hands rotated at the correct relative speeds. However, it wouldn't have been much use for timekeeping, because it would run for only about 2 earth-minutes on one winding.
The picture on the right shows the escapement mechanism. The pendulum pivot is off the top of the picture, where the two partially visible slanting yellow rods converge.