The way I see it--
The team captain doesn't have to be the most knowledgeable, though could be. That's what the officers on your other subteams are for. The captain should be someone that the team, both mentors and members alike, respect and work well with. Our current team captain deemed the role a "friendly ankle-biter": be responsible, and make sure things are running smoothly. S/he should be involved in every aspect of the club, but not doing everything.
Ultimately, I think the team captain should inspire the members. Any captain that is strict and, even if justified, relentless about deadlines, behavior, and quality of work should not be captain. The captain should raise team morale and be understanding and approachable. As far as I'm concerned, if your captain won't sit down with a member and talk to them about issues totally unrelated to robotics (family, depression, relationships, etcetc), they don't have what it takes to be a stellar captain.
...that came out a lot more corny than I intended it to.
