Hey, I'm working on a project to build a drone which is powered through air jets. The drone needs a valve control system which can control the flow rate (hence the thrust) going to each nozzle in order to adjust it's altitude and stabilty. I need to set up a circuit which can electronically control a valve to alter the flow rate of air (coming from a constant pressure supply - 85psig). The system is to be used to control the flow rate of air in order to control the thrust output from a nozzle. I have been looking into proportional solenoid valves (i.e. http://www.smcpartbuilder.com/categories/cat/127096) where the valve position is altered by controlling the supplied current. My worry with these kind of valves is that they won't be accurate/repeatable enough or precise enough to provide the level of air flow control that I require. My plan had been to map the valve position to the output thrust to allow control of the thrust however in order to gain precise control of the flow would I require a system involving a mass flow rate controller? (something like this: http://proportionair.com/electronic-flow-controls/medium-flow-control/) My experience with pneumatic systems is very limited and I wonder if anyone has any suggestions for a system which could do what I need?