I was thinking:A turret is in high demand. How about a giant, fast, powerful cross-bow looking thing.

Sounds OP, right? How about it requires a robot to aim and shoot it on a swivel. If you kill the robot, another runs over and takes its place, and you can kill that one too. Or... you can take it and completely dominate.

No-One has posted in 2 days!

Yes indeed add this just not that fast and give it limited movement so the human doesn't try to shoot us

It would be cool if the ballista/cannon shot the robots on the arena.