So I learnt the Schmidt Coupling was created for NASA, interesting. I know these coupling require the input and output shafts be parallel but I still don't know how tolerant the couplings are to the small amounts of out of parallel which is inevitable in the real world. It seems like this would be a good coupling for drive shafts in the huge ships now plying the world's oceans where the very large rotating mass on both sides of the coupling make constant velocity important (or maybe just very precise alignment of the shafts is sufficient without the need for this coupling, I have no idea).
