"Designing a Lego orrery."
Apparently the orrery was built 2 years ago but this article explaining how it was built was only written last month.
"An orrery is a scientific instrument that models the motion of the celestial bodies. These are typically the orbital period and the period of the rotation around the axis of a body. For example, the time it takes the moon to travel around the earth once is ~27 times the time it takes the earth to rotate around it's own axis (a day). This relation is accurately modelled in an orrery. However, the orrery does not model distances or the relative sizes of the celestial bodies."
I'll admit to skipping to the video right away and the video is oddly mesmerizing. Then went back to read about how it was built.
"I experimented with 3D printing custom fixtures to put Lego gears in, but eventually moved on to building an orrery out of Lego parts only."
"I used Bricklink Studio to make a digital model of my orrery. During the design process, I switched back and forth between buildig with physical parts and designing digitally."
"In my orrery, one rotation of the crank corresponds to one day. So to get the main arm to rotate once every 365.25 days, it needs to be connected to the crank using a gear sequence with a transmission ratio that is as close as possible to 365.25."
"The gear ratio of a gear sequence is the product of the fractions of tooth numbers for each pair of gears in the sequence."
"To find a sequence of Lego gears, there are some additional constraints. Most importantly, we are limited by the gears that Lego actually makes."
If you're building anything with gears, what may be of particular interest to you is the tool he made for finding optimal gear ratios. It will use the prime factorizaton of the gear ratio you want and the gears available and find a combination that gives you the exact ratio you want if possible, and if it's not possible, it will find a close approximation. If you're not using Lego gears you can replace the Lego gear numbers with whatever you have available.
