I remember my dad building the depth-finder/fish-finder. We always had it in the boat with us. Who knows if it ever really helped us find fish, but we sure had fun with it.
Side note - I really miss that you can barely buy RC car "kits" anymore. Everything now comes RTR (ready-to-run). And that takes most of the fun out of it, for me at least.
Beside traxxas, nearly all manufacturer propose kit, especially for high end rc car :)
For plane and quadcopter it’s way harder though :\ submarines is still a more open field though !
Then there’s the hydraulics model. None are in kit, which saddens me a lot. Maybe too dangerous for common folk (like building a tube amp)
Side note - I really miss that you can barely buy RC car "kits" anymore. Everything now comes RTR (ready-to-run). And that takes most of the fun out of it, for me at least.