In addition to talking to each team to get their permission to do research with them, I spent more time observing and brainstorming, trying to take advantage of the great opportunity being with so many teams right at the spot.
One lesson learned: I was concerned that if I had talked to the teams too early, it might be impolite to interrupt their work since some were still preparing their robots, so I waited for a while. And then some teams left early somehow that I was not able to catch 7 teams at the tournament. That was a big loss and I need to do it faster since I found that most of the teams were very helpful and nice.