When I enter an arrangement where there is nothing developed I generally have a contract put together in which I get equal ownership of the resulting software, and that that ownership is vested on the same timetable as all other owners. As I look at a pure equity arrangement as me being the technical guy, I am doing all the other guys a huge favor. As a technical person you need to look at these arrangements in that manner. I am not necessarily saying be a jerk about it, but all things tallied you will be taking the most amount of risk on as the developer, as you put the lions share of the work in up front.
Once you start to look at this arrangements as you doing the other guys a favor then arguing your fair position becomes a whole lot easier. The thing to remember is that you can go out and build any idea, you could be working on your own and taking 100% of the equity, model that in your mind in these situations, if you view it as they are not letting you in on their idea (which are worth little), but rather you are, letting them in on your equity by taking their idea over your own, it sets the stage for negotiating, up-front to not get in the situation you experienced.
Unfortunately clueless founders are on the rise again, I have had a recent rash of dealing with them, where these hipsters are going to change the world with a dumb idea and all they need is some of those tech guys to whip it up for them. The good news is that they become easier and easier to spot once you have had one or two dealings with the type. In doing so you start to only loose a week or so instead of spending months of your life on what amounts to nothing.
Finally what I personally do when a deal or start-up I have been working on falls through is I go back to freelancing to built up my reserve to take another swing. It helps me recharge, learn some new things and see what the rest of the industry is doing.