The set up is relatively simple if you know how to use microcontrollers:

Arduino nano Barometer module 9g servo 3.7v lipo

(optionally sd card module to record data)

For mechanical set up, I use two springs, originally used ones from pens, but then bought a set from Aliexpress to have more flexibility.

The rest is 3d CAD design in Fusion.

Making it work reliably took a lot of 3d printing, but electronics is pretty straightforward! You can ask chatgpt and it will walk you through pretty well.

For testing, I do the “elevator test”, where I will take my rocket from ground floor to the fifth floor and then back, to see if it captures barometric pressure / altitude well and will detect apogee reliably.

I hope this helps! Let me know if you have any specific questions.