Fig. 9
From: Structure analysis in an octocopter using piezoelectric sensors and machine learning
Comparison of the power spectrum of the voltage signals generated by the piezo sensors MFC1-MFC8 for (a) the intact state of the motor M1 for the grounded UAV (b) failure state of the motor M1 by 60% damage for the grounded UAV (c) the intact state of the motor M1 for the flying UAV (d) failure state of the motor M1 by 60% damage for the flying UAV.
