Static Test

A load cell previously developed for testing solid rocket motor performance was given an overhaul to provide more accurate results. High levels of hysteresis caused by friction in the linear bearings was eliminated by using rubber bushings, essentially adding a linear spring component to the system. The sampling rate was also increased to 25 Hz to better capture the response.


Load cell with circuit board and Bluetooth module.

The load cell uses a cantilever beam fitted with four strain gauges. An opamp boosts the signal which is measured by the on-board analogue to digital converter on an ATMega8 microcontroller. Readings are passed at 25 samples per second out over a Bluetooth serial adapter and recorded on a host laptop. The load cell was calibrated and set up for a static test using the solid fuel rocket motor revision 3.6 burning the experimental RNX propellant. The test is shown in the following video clip.



From the video the burn time was close to the nominal 5.6 seconds predicted by the mathematical model. Predicted thrust was 245N, but unfortunately the load cell data was not recorded due to a glitch the wireless link. Reasons for the Bluetooth link failure will be investigated and the test re-run.