How does your club schedule crews?

Our club is considering changing the way we schedule the ground and flight
support crews ( tow, instructors, recorder, crew chief, assistant, etc.)
Would like to find out how your club schedules the volunteers who make it
work.
Some clubs have only the Director of Ops, Tow Pilot and IP scheduled -- all
others are volunteers/day flyers. Others have every position scheduled every
weekend day. Finally some do it all by a reservation system - with those who
volunteer a specific number of hours paying less in monthly dues than the
those who do not volunteer.

I would like to gather some details on this before we change our system.

While answers from European and UK clubs are appreciated - I am focused on
USA clubs - Thanks!