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Gas Thruster RCS Drone - Update

🕑 Added 2019-06-02 11:23:12 +0000 UTC

Comments

Zaak Beekman

Critical pressure ratio for air is 1.89. So 60 psi gauge = 413 kpa gauge = 514 kpa abs. 514/101 >> 1.89 so you should be able to use a de Laval nozzle successfully. The problem is that maximum allowable area of the choke point is determined by the mass flow rate provided by the rest of your plumbing (likely the valves are the culprit here). If you don't achieve sonically choked flow in the throat, then increasing the cross sectional area of the nozzle will decelerate the flow. At 60 PSI gauge pressure, and room temperature, the maximum throat area, in meters squared is Q / 1210 where Q is the mass flow rate in kg/s and 1210 has units of s / (kg m m). This was computed from the red equation here: https://www.grc.nasa.gov/www/k-12/airplane/mflchk.html

Tom Stanton

Exactly, I've setup the flight controller to output pitch and roll values, then I've done the 120 degree mixing and valve triggering in an arduino. They're are off the shelf valves, the same cheap valves Joe is using from amazon. I probably should have looked for lighter valves, but these are so cheap and can actuate in about 10ms.

U.S. Water Rockets

Are you using the thrusters in a configuration that mimics a tricopter? Also, are you using your own valves or something off-the-shelf? I experimented a few years ago with valves based on pneumatic landing gear actuator valves for R/C planes, and those were around 70g with a servo.

Tom Stanton

The main reason for 3 nozzles is to save weight, each vavle is 120g! Since there's no torque like on a drone, three points of thrust should be fine. Also with 4 nozzles, theres still the possibility that one nozzle has to produce all the correction thrust, if it tilts on the diagonal axis between pitch and roll.