It is never really “for free”.
It appears free because machines, like perfect slaves, don’t ask to be paid for work.
They still need to be fed though, energy, iron, etc.
No matter how you turn it, it can’t be free. Meaning you can’t benefit from it without owning it or trading something.
Energy has become nearly free, though, as the space- and cost-efficiency of solar skyrockets. That's really not the problem here.
>They still need to be fed though, energy, iron, etc.
But just like humans can help each other, robots could help each other too. This includes digging up various resources, finding means of power generation etc..