[Uber_hampster]

Estes engines arent the most reliable things in the world. If I were you, i would explore other, more precise engines. Through much experiance with rockets, I can tell you that they will not light all at once except for a freak accident, or u can wire in some voltage regulator that will apply the power all at once. My worst experiances were: a rocket took about 30 seconds to take off. I tsmoked for a while, the fizzeled out. A couple seconds later, the rocket took off. My other one is that once, the rocket just exploded on the pad(not James Bond boom, but tor the cardobard tube apart and set it on fire), and as any rocket enthusiast knows, half the tim, these things dont even light. Lastly, in elementry school, my friend tried making a rocket powered styrofoam skateboard, using a cluster of 4 engines. They did not all light at once, and it didnt do much anyway(except melt styrofoam).

One the subject of Co2 cartriges. They are efficent and reliable, the problem would be puncturing the cases (as already mentioned). I supose you could have some sort of swinging gate with a pin and spring, but that would take time, and might not work properly.