Test Stand Engineering Pt 3
Electronics are the last step of the process. Pretty much everything should have a manual override but I’m designing things in a way so that everything is operated by the computer, but should it malfunction I will have manual switches to trigger all the valves necessary. I used an Arduino, which is an inferior option to many others used, but I picked it because of its massive speed and convenience factor from an acquisition and implementation point of view. It took me under two days to wire everything from the design. The Arduino is connected to and reads data from 6 pressure transducers and two thermocouples. The 6 transducers give valuable data for flight configuration such as the amount of gas consumed, the chamber pressure and the injector pressure drop. The pressure drop data is necessary as it may allow me to fabricate calibrated orifices in lieu of venturis on the flight vehicle. Small as they may be, they mandate an extended engine bay which may be problematic so a calibrated orifice will likely do the trick on a characterized system as well as lead to a smaller pressure drop. The first of the thermocouples will be intentionally destroyed! It will be burned in the igniter and also serve as the harbinger of ignition. Once the igniter lights, the thermocouple will detect heat, report a voltage to the Arduino and that signal will then open the propellant valves, initiating main ignition. This serves so that the propellant valve is not opened unless the ignition is 100% confirmed. Then the entire igniter is burned in half a second along with the thermocouple and the ashes are flung out of the system. The pyro igniter is designed to be secured by small aluminum fingers or spiders, which render it removable only by melting the spider. This makes it impossible for the igniter to ever leave the engine should it fail in doing its job. The reason for this is that the igniter generates its own thrust and should it ignite in anywhere but the desired location it will cause an explosion. This type of igniter was developed by Ken and his friend Ray Goodson over many years and has been in use for many decades. Ken has physically sent me an igniter to use. Single use as they may be, I can get more. The other thermocouple is used to detect the temperature of the liquid oxygen at the venturi inlet as to calculate the dynamics of the fluid and give an accurate view of the mass flow.
Overall the test stand is a complex piece of engineering. I’d argue it is on par with and if not more complex than the rocket because it also serves a dual purpose of data collection. I’m proud of the skills I’ve learned from my mentor as this specifically was his specialty for many years and looking forward to the results. The amount of consideration that has gone into it is honestly quite massive but once built the stand can serve for many years with minimal changes from project to project. I’d like to eventually paint it, make it look nice and get it some permanent tanks but that is not a priority at the moment.