I need to build a mechanism that moves a pin to release a payload from a drone. The drone is very small (150 grams) and the payload will be very light, something like 2 or 3 grams. I can't use any digital circuit, battery... it has to be purely mechanical and light.
At first I was thinking about a hook that I would attach to my drone and when I make a very strong movement sideways the hook would release and drop the payload, but I couldn't find a good design to work reliably.
Then I thought about creating a mechanism just like a timer: after 30 seconds it would move a pin. The way I thought about it, would be like a small balloon with a tiny hole releasing air, and when it's completely empty it would become small/shorter and would pull a pin. But having a balloon hanging in a drone would not be good (it would become a kite even using a small balloon).
Still using the timer idea I thought about folding a paper, when you fold a paper and release it, you will see that slowly it tries to get back to the original position... maybe attaching a string to the paper and make it pull a pin while it's trying to get back to the original position... but I think that must be a better way.
So I ask you: is there some way to build a "timer" (it does not need to be precise) that after sometime it can move a pin?