When I started this project, I chose nitrous oxide and HTPB for propellants. However, at the time there was no published data on regression rates for that propellant combination. So I started out with a small lab motor that is shown in the previous posts. It was a simple design, similar to motors used in high power rocketry with the exception that the case was 4130 steel instead of aluminum.
That motor turned out to be a good way to do many more things than simply collect regression data. Finding vendors, setting up data acquisition, and learning plumbing best practices are all non-trivial tasks. In keeping with the test a little, build a little philosophy, I find it much easier to incrementally add features as you go. Not worrying about all the features a motor (or any system for that matter) needs to have will often generate more progress than a "single step to solution". Or as my brother says, sometimes you need to just go build something even if you're not sure what it is.
In the intermediate time between when I started and now, a group at Stanford has started publishing data for nitrous oxide hybrid motors. You can read the first page of their papers here and here. Fortunately, their data and mine compares reasonably well as you can see in the chart.
Once I had reasonable regression data and a working test stand it was time to start building a flight worthy motor. However, before you design a motor you have to choose a vehicle architecture. A VTVL vehicle has a much different motor than a sounding rocket. I'll talk a little about motor applications in a future post.