My goal is to build some educational robot kits for kids and so I'd like to know if there are any LEGO sets that let you build almost anything or can you only can build the specific model that the package is designed for?
I am looking for general parts to build different sorts of robots but I do not mind about electronic parts (motors, boards, sensors, etc. as I can build or buy those), I'm really after mechanical parts (gears, axles, beams, etc.).
I do not want pay for moulding and prefer to use something like LEGO parts, but I am unsure which LEGO set will offer the most flexibility to build anything I want?
Also if there are other universal building products other than LEGO that I could use I would be happy to know.