The arrow should shoot out of the side with the arms. The arms don't move, they flex IRL. PTAL at how crossbows work for reference.

yes, but this is fantasy world?? and i think it look cooler this way :)

@raspberrypuppies its also autotargeting, i think a certain type of player with a medieval bias will still want it, kind of steampunk-retro

Auto targeting isn't as big of a deal because you can imagine someone/something in the turret base spinning it around. The backwards ballista mechanism physically doesn't work. It's like loading a gun and shooting out the back. Or pooping by putting your head in the toilet. It just doesn't make sense, in the factorio universe or in a historical setting.