After designing the pookkalam and the hex, I decided to build a clock. I had already designed several rotational systems incorporating a Hoberman-inspired mechanism, but instead of random movements, I wanted to give them a purpose. The idea was to create a clock with three concentric rings: the innermost ring for seconds, the middle for minutes, and the outermost for hours.
Kinetic Clock
Concentric three-ring planetary carrier timekeeping mechanism driven by a single mechanical actuator.
Synchronized planetary carrier gear train and concentric linkage simulation
Each of these rings acts as an independent planetary carrier. This is a major upgrade from my pookkalam design, where the planets were stationary. In this clock, the planets actually work as carriers, driving the mechanism around the circle. Because of this, the clock doesn't have traditional hands. Instead, it relies on rotating discs with different gears for the hours, minutes, and seconds. One specific gear on each ring is color-coded to act as the "hand," and its position tells the time.
I wanted to drive the entire mechanism with a single actuator. While it would have been much easier to just use three individual motors, I was determined to make it purely mechanical—don't ask me why, I just really wanted the challenge. My plan was to add expanding and contracting links directly onto the planetary carriers tracking the time.
The concept was straightforward, but the execution was an incredibly fun puzzle. Because the system is so complex, the first step was sketching out the entire gear train. Connecting the individual planetary carriers to achieve the exact gear ratios was highly rewarding. By the end of it, I had gotten really good at calculating planetary gear systems and defining the precise RPM for every component.
However, once the design was finished, I wasn't fully satisfied. I realized that to accurately hit those precise gear ratios, I actually need a high-reduction gearbox, like a cycloidal drive or a strain wave gear. So, that’s exactly what I’m working on now.