Converting from a freelancer to a co-founder. Is this the definition of risk/reward?

I have a salaried day job, but nights/weekend I've been working on a really engaging project for the past few months. I know one of the two co-founders personally and was brought on as a freelancer. So far it's been great - we have a good working relationship and they have compensated me well for my time. They're bootstrapping everything out of pocket.

We're close to wrapping up our original contract. We have a few clauses in there for support, ongoing work, etc. My original idea was to charge them for these line items.

I've been the only developer on the project this whole time and I have come to love the code and I really believe in the product. I want to keep working on this project and I want to have more ownership of it.

When the contract is up, I'm considering asking to be brought on as a co-founder. If I did that, I would expect to no longer be paid for my time until we are profitable, although I would also trade my time instead of helping them bootstrap it with cash.

What do you all think of this? Would you voluntarily stop payment in order to take some ownership of a project you like a lot? If so, what percentage of ownership would you look for? Is this the definition of risk/reward, or is it foolishness, assuming they might otherwise pay me for my time? I suppose this is basically the balance of having a day job vs. being an indie hacker. But it feels a little different because I already have the freedom as a freelancer.