The Mellotron is probably the simplest musical instrument I ever modelled back in my 3D days.
That's a great little video, and who else said "Moody Blues" when she played using the flute setting at 6:35?
Mellotrons were a love/hate beast to most of the musicians who used them. Not too bad in the studio, when you could stop to fix something, but take them on the road where anything from a bit of buffeting just manoeuvring them onstage to the ambient temperature and humidity, could make them go out of wack, and you're talking an accident looking for somewhere to happen. This shows the complex process involved in playing just one note. Wheels, pulleys, springs, rollers. It was almost a mechanical synthesizer/sampler hybrid.
As I've hijacked (sorry) what is a YouTube-themed thread though, I'll leave the last word to Mr Wakeman.
I didn't used to need the internet, my wife knew everything.