Jarvis....the weapon will be mounted on 2 bearings that are mounted onto a solid bar that will go right through the robot and into flanges on the outer chassis where they will be keyed and grubscrewed. the same on the inner side of the chassis.....about 8 inches of keyed bar in total....flanges will be welded to chassis. I hope that will be enough to stop the twist you suggest but in all honesty i dont know how it will perform as its not been done before. The bar is hollow 50mm OD with 15mm wall. If it fails i will just redo it stronger.