Thanks, i got it sort of working !
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I got to make a component in the HydraActor BP, and send their coords and rot through BPI because referencing a HydraActor in the anim graph was causing “Accessed None blabla” issues. So i got it working the other way. Works pretty fine , but when docked, it keeps the last position, so i will have to make a “when hydra docked or disabled, ignore rigging” thing.
Got little funny problem also ^^
It happens even without Hydra. I think i is because it gets no HMD location so the rig goes crazy, but it’s working fine in the anim preview… If you have a quick fix it would be kind 
otherwise i’ll sort it out myself .
Thanks again