It would appear that the arena system is somewhat bugged, but I am not quite sure what the triggers for the bug are. Thankfully I was eventually able to trigger an arena battle. Here is how you do it.
It would seem that you need to use the "Quiet Alarm" in order to trigger the fights, but this wasn't working for me at all. I had 2 fighters setup on both platforms, but they weren't doing anything. They didn't even seem to be looking at each other.
I rang the quite bell and it went green. You can find the quiet bell in the Misc category for the cages. This appears to have been the trigger, but there was a very large delay in the time it took for the battle to actually trigger. I had intended to make a video of this, but the guys started fighting out of nowhere and I couldn't get them to stop.
I walked down to the arena door (on the right side of the pic) and when I had gotten there, the fight had started. Here are the steps to take.
- Build 2 arena platforms
- Assign settlers (or robot) to the platforms
- Build a quiet bell and activate it
- This will make the competitors fight.