I think this is a very satisfying mechanism to fidget with. It's not quite a planetary-gear system, because there isn't an outer ring gear, but the since it shifts between the astrological symbols for Mars and Venus, I'm going to call it these planetary gears anyway!
Turning the center dial causes the two planetary gears to spin around two stacked, concentric sun gears. One of the gear pairs has a 3:7 gear ratio, the other has a 1:3 gear ratio. So when the dial has been turned 135°, one of the planets has turned a full rotation minus 45°, and the other has turned a full rotation plus 45°. The end result, as you can see, produces the ♀ and ♂ symbols, and a nice continuum of other shapes while it moves.
I hope you print one, or a hundred! I've already had multiple (i.e., two) people ask if they could print and sell versions of the model. The answer is yes!! with some caveats:
Speaking of licenses, the pins used in this design are based on the classic pins by emmett (CC-BY-SA).
Print the following in a background color of your choice: base_gear, dial_frame, 15_tooth_gear, 18_tooth_gear. Depending on which base gear you choose, you may need to print the optional limiter_pegs. If you print the base gear for a hobby servo, be sure to print the dial frame for the hobby servo as well.
Print the following in a foreground color of your choice: center_dial, dial_pins.
If you printed one of the base pendants with holes for removable limiter pegs, now's a good time to test and see if they fit. These limiter pegs keep the dial frame from turning past the positions for ♀ or ♂.
Insert the long pin (the one that doesn't have a dial indicator on one side) into the center of the base gear. Line up the dial frame and snap it in place over the pin. If you are using the hobby servo base gear and dial frame, screw the dial frame into place with whatever screw came with the servo.
Look for a notch in the 15-tooth gear, on one side of the slot for the dial pin. This notch indicates which direction the dial should be inserted.
Slide the gear into place at one of the end positions, either ♀ or ♂. In the ♂ position, the gear should be lined up under the gear holder at the top of the model, and the notch should be pointing to the right. In the ♀ position, the gear should under the right-most gear holder, and the notch should be pointing to the left.
Whichever position you have the gear in, fix the gear in place by inserting the shorter dial pin.
The 18-tooth gear is symmetrical, so there's no notch to worry about aligning.
Slide the 18-tooth gear into place at one of the end positions, either ♀ or ♂. In the ♀ position, the gear should under the left-most gear holder, and the pin slot should be aligned so the dial will point to the to right. In the ♂ position, the gear should be lined up under the gear holder at to the right of the model, and the notch should be pointing upward.
Whichever position you have the gear in, fix the gear in place by inserting the taller dial pin.
The center dial has holes that line up with the notches in the top of the dial frame. This helps reduce play while turning the assembly.
Run a chain through holes at the top of the base to turn it into a wearable pendant, or write some code to move the servo-driven version throughout the day. I'm eager to see what people do with it!
The pins need some flex to work properly. I printed them in PLA. Pins printed in polycarbonate were too rigid and snapped instead of sliding into place.
If the dials scrape against each other while turning, check if they are fully seated in the gears. In this picture you can see the pin wall is bent inward, meaning it's not fully clicked into place:
For comparison, here is a pin that is fully clicked into place:
This happened to me because my black filament was overextruding pretty dramatically (which you may have noticed in the assembly photos!).
The author marked this model as their own original creation.