Shell Motion Testing

Microcontroller Motion Testing

A microcontroller-based accelerometer unit was developed for testing shell motion during discharges. The unit consists of a microcontroller board, and accelerometer, and a real-time clock. The chosen microcontroller, the Adafruit Feather M0 Adalogger, saves files directly to a microSD card, and can be battery powered for remote operation. The accelerometer, an STMicroelectronics LIS3DH, is pre-mounted on the Adafruit LIS3DH Breakout board. The real-time clock is mounted to an Adafruit DS3231 RTC Breakout board.

To collect data with the accelerometer, a program was uploaded using the Arduino IDE to the microcontroller. The program collects data from each of the three accelerometer axes for one second at 1.6 kHz after receiving a trigger. To run the program, modified Adafruit LIS3DH libraries are needed rather than the standard library (.cpp and .h files). These modified libraries allow for burst reading of the data and enable a high-pass filter for the data, though it is possible this high-pass filter should be disabled if the frequencies of interest are attenuated, such as a 13 Hz response along the toroidal axis clearly visible from the first round of shell motion testing.

LTX motion data collected with microcontroller-based sensor. Two integrations are performed on data after being filtered with a 5th-order Butterworth filter with a pass band from 30 to 1000 rad/s.

Data is saved to the microSD card as a .txt file. This file is analyzed using LTX_data_read.m in MATLAB.