I had some experience with this. - Define the % in different ranges. When the sales is less than X, you got them all. - The company may stop their effort on th

I had some experience with this. - Define the % in different ranges. When the sales is less than X, you got them all. - The company may stop their effort on this product. - You may disagree with the company. Maybe you should get a better % for yourself, if you want to take control. - You'd better to get an inital pay. It's, basically, co-found a project. You need value your self's work, the company's work, and the potetioal of this thing, etc.