So I am working on a project. I need a drone (quadcopter) to ascend for 5 seconds, then cut off power to the drone, then let it stay in the air for as long as possible without power. My idea for allowing it to glide is to have some rubber bands attached to some parachute like material, and the rubber bands will be stretched and held in place by some pins. After 4 to 5 seconds, the pins will disengage, allowing the rubber bands to compress, expanding the parachute-like material. An image is included to illustrate what I mean.
The red lines illustrate the rubber bands. The black are the quadcopter arms. The blue circles are where the pins would be located. After the timer stops, the image on the right demonstrates the rubber band straightened, and the purple is the parachute area. There will be one parachute per rubber band, and each rubber band will have its own locking mechanism.
So what I want to figure out is how to design a mechanism that will retract a piston/pin after 4 to 5 seconds. I did some research on pneumatic cylinders, and I figured I could have pressurized air entering the cylinders with air leaving the system slowly until the piston disengages the rubber band. There would be some measuring to get the required air pressure needed to have the pistons last 5 seconds, but these cylinders are too expensive and too long for this application. Then, I read the post linked at the bottom of this post, and I think the mag-locks would be great, but I have only found them in rectangular forms; none of them have the geometry needed for this, so I figured I could have the mag-lock attached to the bottom of the drone, and the mag-lock would pull pins that were attached to springs that are attached to the top of the drone; when the mag-lock deactivates, the pins would retract, allowing the rubber band to disengage.
However, I am having issues with finding timers that are suitable for my task. Kitchen timers don't work well when it comes down to setting them for 5-seconds. I want to know if you guys have any ideas regarding getting a timer that would be well suited for this task and if you guys have any suggestions as to how I could improve the design of the parachute mechanism I have planned.
Post mentioning mag-locks: Is there a device like this?