The spectrum of DARM around 50 Hz seems to be composed by several small structures. It is known that at ~ 48 Hz there is a vertical resonance of FP payloads (involving the F7 crossbar). In order to investigate if some of those resonances are present in DARM, a noise injection has been performed.

Fig 1: noise has been injected on NI_MAR_Y_CORR and WI_MAR_Y CORR, at two different times. In figure, also the correction currently applied by the vertical damper is shown.

Fig 2: the effect on DARM of WI noise injection. The expected resonance is visible, but the projection of damper correction, obtained by this measurement, is quite low.

Fig 3: the same consideration is valid for NI noise injection. In this case the frequency of the crossbar resonance (48.3 Hz, already measured by the local sensor) is close, but not equal, to the frequency of one peak in the clean data (48.4 Hz). I would exclude that the NI crossbar resonance is the source of that peak. But the noise injection has excited one more peak (47.8 Hz), the origin of which is not known. It would be better to check if this structure can be more easily excited acting on the marionette in a different direction.

The work has to be continued injecting noise on NE and WE.