The main reason I chose electronic control is that you want to be able to set the tidal volume, which means how far the piston moves. As far as I know you can only do that electronically, if you want to user to be able to change the tidal volume. I have seen some reciprocating mechanisms to drive a machine like this, but respiratory therapists advised us that user-selectable tidal volume is absolutely required, and documents like the MHRA emergency ventilator specification said the same thing. The other reason for electronic control is that electronics are extremely reliable and affordable nowadays. There is a risk of code bugs, but hardware failures of microcontrollers or pressure sensors and such are extremely rare. Stepper motors are likewise extremely reliable. Brushed DC motors are too, if you replace the brushes often enough, but there is some concern with the dust from the brushes combined with the pure oxygen these machines work with. I do think working on these machines and other creative viewpoints are still very valuable. Covid may appear to be nearing the end here in Europe, but the situation is still extremely dire elsewhere, and now respiratory virusses may also pop up. We really should be prepared next time.

Ah, answered the question a little later.

I think the most important point he made is to first figure out the requirements before you go building. With AirToAll we got to speak to some respiratory therapists, and there are tons of resources online about what a ventilator is supposed to do and why. It seems a bit silly to me to start building before you've figured out what the job even is.