Ask HN: How to calculate the salary of the working partner?

A friend of mine owns a chain of restaurants, and during a chat we came up with an idea for a software that we believe will drastically improve his HR management.

We decided to try to build a business out of it. His chain of restaurants will be the pilot, and once the software is working we will start selling to other restaurants.

We split the equity 50/50, but I am the only one working full time on it (I am the developer).

We are therefore trying to figure out a reasonable salary/compensation for my role as main developer/CEO.

My initial idea was to start with a base salary of $2500 + 10% of company revenues. So once we reach $50000 monthly in revenues the salary becomes $7500 monthly. So on and so forth.

Do you thinks this would be fair for both sides? Are there best practices regarding when and how to pay the working partner?

Any feedback is appreciated.