After correcting the BSC-ISI master model, I have installed filters (FF01) for the feedforward control from the HEPI (L4Cs read by the fourth ADC of the ISI model) to stage 1 of the ISI.

For the measurements and the filter design, no symmetrization filters were used on the HEPI L4C. Feedforward was implemented in the X, Y and Z directions. Coherence from HEPI to ISI is really low in the rotation DOFs.
In attachment, non calibrated amplitude spectra of the T240s (stage 1) and the GS13s (stage 2) are shown in two different configurations:
- RED: ISI Damped on both stages
- BLUE: ISI Damped on both stages and stage 0-1 actuators also fed by HEPI L4Cs - No Isolation on stage 2

Isolation is pretty good on both stages (with only stage 1 controlled).