> Recently got told by some founders doing a farming technology startup that nobody gets paid because "We don't even pay ourselves!", but if I would like to volunteer my time doing automation and robotics R&D, then that would be great.

So they are saying you should do slave-labor? I hope they expected to give you plenty of equity (which is cheap as the company is worthless as there is no money being made yet), otherwise it would be idiotic to expect people to work without compensation.