Team 20, for as long as I’ve been involved with the team, has had over 100 students, and about 130 members altogether. As you’ve said, it’s awesome, but crazy.
What we’ve done, from my 4 years on the team, is had a set system of sub-teams, and a fall season dedicated to training new members. For this year and last year, sub-teams include an engineering side and a non-technical side, and students, starting this season, are required to partake in both.
For the Fall Season, we start around the end of September, and go till kickoff, teaching students the ins and outs of the sub-team. As an example, programming usually gets a lot of students (20-30 each year), and has different levels of fall projects to work on. New students are taught Java by our student sub-team leaders, while our older, more experienced leads, learn and implement robot code to our T-Shirt cannon and competition robots. Mentors tend to help wherever they feel most comfortable, and the Fall Season is almost completely student run.
For kickoff weekend, we divide into groups that contain members of all sub-teams (usually almost 10-15 groups, 7-10 students in each), and one or two student leaders. From there, each group gets a large piece of paper to write ideas and concepts on. After that, each student receives some sticky-notes, and comments on the ideas. Ones with the most sticky-notes are addressed by the full team, and we make our priority lists based on those.
For the rest of build, our members dwindle to about 20-30 per night, because our team doesn’t require people to come to every single meeting, but instead an hours requirement (40 hrs) (Many do a ton more). The people there can usually be assigned a task by a student lead, or can shadow an older member making a complicated part.
When we do have around 100 kids, on our required meeting days (Once a week), we swap between our technical and non-technical sub-teams for about an hour, who are prepared to have a large amount of incoming people for the day. Then, we can assign the most amount of people to different tasks, and teach more people than we could have if we just had one experienced member doing it.
At competitions, we run a scouting system with shifts, because we have around 20 kids who are interested, and are not otherwise occupied by pit crew, awards, or drive team. We often share data with smaller teams in exchange for some of the other team’s members taking shifts. Our mainly mechanical members, who aren’t yet pit crew, go around to help other teams build blockers, fix drivetrains, and generally, help out any smaller team that needs it.
The first step to getting your kids to stay and help is a defined leadership structure, so that they have a way to go to someone and ask what they can be doing to help. Training early on pays off, and team bonding activities (such as riding carousels in the mall together) are a good way to get to know the team better.