Your diagram has both packs in parallel. Everything running from 5S. This is the safest solution.

You can run split voltages as wired in the below diagram but things are likely to go wrong. Splitting the supply in this manner is not recommend (and parts may go pop).

diagram.png

The way to achieve what you want is to run both motor controllers from one pack and use the second pack to boost the supply for the weapon controller. This can work, but you do need to be careful with your wiring.

diagram2.png

Complicating the electrics may lead to more problems than it is worth.