Designing a Lego orrery
I've always been a fan of the Lego Technic series, especially those models that have gears and cranks and moving parts. But it seems that Lego is shifting the focus of the Technic series away from functional models, so I had to take matters into my own hands. I think an orrery is the perfect project to build out of Lego Technic parts as it makes for a cool display set and is functional at the same time.
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.
This inspired me to build my own orrery with the same spheres for the sun, earth and moon, but my own custom designed mechanism:
