A different take on the compound planetary gearbox. This time, we use split sun gears, synchronize the ring and planet gears. One sun gear will be fixed to the threaded shaft of the potentiometer (or some kind of tuning capacitor), the other to the knurled dial. The input will be the outer ring.
This might be useful for Arduino analog inputs or ham radio tuning.
By stretching the rules and circumventing the R=S+2P constraint, many possible gear ratios up to 100:1 are possible from the usual planetary arrangement. The provided sample is 16:1, which should be practical given tolerance, backlash and Arduino sampling resolution.
Note: The customizer will not take just any values. Several constraints must be satisfied. I have compiled a sample of possible combinations in this google sheet. I'll post a writeup of the mathematics at some stage, but it is contained within the scad source.
Also note that there should be a one-layer gap between the sun gears after slicing so that they are able to be separated after printing. A default layer height of 0.2mm is adjustable in the customizer if necessary. Otherwise it should print in place fully assembled. Better to over-extrude slightly so that the gears stick together initially but can still be cracked apart cleanly - this will help reduce backlash. You don't want the gears to rattle straight off the printer, they will loosen up fairly quickly as the gears are worn in.
A decorative cover plate could also be glued on to the ring gear if desired.
I don't seem to have any suitable potentiometers on hand, so I'm waiting for some to arrive before testing this design (it's all theoretical at this point). We'll need a decent threaded length on the shaft. 18mm guitar pots seem to be a good size.