Thanks BOAC
I'm making an educated guess here. The Electric Harrier ORAC posted probably works like a Quadcopter ... which has a miniature gyro and speed controller on board. The default airborne state is stable/hovering flight. The pilot then controls pitch and bank by differential prop speeds ... or for a hover climb equal power to all props.
I still think true jet thrust vectoring is going to require some very clever engineering
Best ...
Coff.