Robotime's mechanical engineering kits for adults are built around the ROKR line — laser-cut wooden puzzle kits where the finished piece isn't just a model but a working machine: a pinball table with a functioning plunger, a steam engine with a rotating flywheel and connecting rods, a marble run city that demonstrates real gravity and momentum, a music box that plays by plucking a steel comb with rotating gear pins. Every mechanism is visible once built, which is part of the appeal — you can see exactly how force transfers through the system, which makes the build feel like it teaches something rather than just fills time.
Source: https://www.robotimeonline.com/collections/mechanical-engineering-kits-for-adults