The people I know that do cutting-edge research mostly do it because it's fun. That might be hard to imagine, but if you have great (government-funded) local hackerspaces where you can meet others, talk to them and built stuff together, it becomes a viable free-time activity. For example, I can schedule a Prusa (FDM) / Form (SLA) / Fuse (SLS) print job remotely and then quickly walk there to pick it up. If I need custom sheet metal or wood, I'll bring a USB stick with the DXF and then walk. That kind of infrastructure massively cuts down on iteration times. Plus it's great to get feedback in-person by other tinkerers when you pick things up.
That's all good and well, but the very time you would try to start selling your tinkering, or, God forbid, hire somebody - that's where the hell begins.
Being a self-employed is a living hell in Germany, as well as receiving any money outside of employment. Esp. if money are small (but > than hobby money, 500 euro iirc) and don't justify the hurdle of dealing with Finanzamt, tax pre-payment, possible regulations with upfront Formulars etc.
