(My Guess) ..... I have fooled around a bit with compressed air and figure high pressure may not be necessary (50 to 90 psi might do it) .... needing a large volume of it (large storage tank) is the problem ..... which may be solved with a small aluminum tank at 2000 psi .

I am sure it would give at least one good spin-up .... problem is getting the 2000 psi tank filled again .... most industrial piston-type air compressors work hard just to get over 200 psi

Trivia ..... back in the 1970;s I painted a lot of aircraft for a local A&P ..... one day I saw him pumping up the oleo struts on a plane with an old refrigerator compressor .... he said it was the only thing he could find that would go higher than 200 psi .... took forever but it worked

Also: ... think of a balloon .... blow it up and it probably has less than 15 psi but let it go and it will shoot across the room so fast you cant see it .... but its storage capacity is small so flight only lasts a few seconds ... storage is the key I think

Spinning a rotor at the tip is easy (takes very little power) .... a person can use a little finger to easily push the tip .... but at the mast requires strongman torque ... in other words low pressure at the tip should work if we have sufficient volume in an onboard tank

if high pressure is not needed to spin the pneumatic motor we need to produce the gas with the help of a small RC command reactor