The big concept is -
Go aerodynamically unstable at apogee
Deploy a nice big parachute before hitting ground
Electronics and logic make this possible
From there, tons of options and possibilities remain. The typical setup in bigger rockets is to have a coupler between main tube and payload that houses all the electronics, shear pins to hold it onto body tubes until charges fire, use a small parachute out the body tube at apogee, and big one goes up in payload for deployment at 500 or 800 feet. The coupler becomes a third airframe component known as an avionics bay, and everything inside is dedicated to how and when the other components are blown off via black powder charge.
Another common possibility, especially with medium sized rockets and new builders, is to let the motor charge do the first step, let the parachute hang out but bundled up, and use electronics to fully release it. Another advantage of this technique is that you can modify any kit with a payload bay for this, in other words you do not need significant changes to have multiple separation points. You could also have a small parachute or even a streamer deployed alongside the bundled parachute. A cable cutter is a simple device to sever a zip tie or otherwise release something to allow the main parachute to fully deploy. The electronics go directly into the payload bay, and a lead is run out to the cable cutter. No dedicated avionics bay is needed.
Thousands of combinations of these ideas are possible. Share what you try and how well each works!
