A recently reported The 2018 Year In Review of Aerospace America has reported ARRC's research in hybrid rocket propulsion using cheap and simple ball valve for precise throttling of H2O2/plastic hybrid rocket engine.
The report is basically correct, but with a mistake that we are using H2O2, not N2O for this technology.
Our throttlable hybrid rocket engine applies H2O2 and plastic as fuel and oxidizer respectively. A typical hot-fire video clip can be found at https://www.facebook.com/ARRCRocket/videos/1288540024624534/
And we are currently scaling it up to 120-150 kgf and apply it to the HTTP-3A rocket for the TVC purpose.
More development activities will be released as time goes on.