BPS Thrust Vector Testing

Head over to Twitter to find out more on Joes’s landing legs and grid fin design!

Video Caption: After building a ground-up simulation of the vehicle’s behavior under thrust, I re-tuned the stability algorithm to the inertia I calculated from the results of a bifilar pendulum test. The calculation was incorrect, due to an extra set of parentheses used, and the algorithm was then tuned to the incorrect vehicle inertia. The calculated inertia was much smaller than it should have been, so the simulation predicted a vehicle requiring less control authority, hence the loose oscillation during the test. The error was found soon after.

Video Caption: Once the error in the inertia calculation of the Series B Hold Down was found, a second bifilar pendulum test was conducted with newly added landing legs and grid fins to obtain an updated measurement. The vehicle was once again tuned in the simulation, the values were set in the flight software, and the test was conducted.
A slight oscillation can be seen during the test. The cause is unconfirmed, but is likely due to the following factors. A changing CG during the burn, a slightly loose TVC mount due to ascent and landing motors being loaded, or inconsistencies in the propellant causing small non-axial moments on the vehicle. There are other potential factors, but these are the most likely.
This test passes overall, and with a sufficiently accurate tuning(for the flight profile), focus will now be set on aerodynamic testing and flight software work.


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