No really a Spirit specific question, but is there anyone who grounds the ECS/Servo negative wire to the frame? Some web sites advise doing it to prevent RX/flybarless controller reboots(or worse damage) and some are against it and advice to use silicone lubrication on the tail belt.

This depends mainly on helicopter.
Some older helicopters required a proper grounding. Some more recent does not need it at all, because it is built in in the frame or at least belt is made from material that does not produce so big static discharges.
Generally it is not needed, but in a rare cases even grounded model might cause problems. For example if tail boom has a lot of powder from the belt inside already.

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Spirit System developer