Treehouse Elevator or Dumbwaiter

My kids wanted to take stuff up and down the treehouse constantly, and instead of watching them fall down a ladder with a bucket of rocks (really) I started working on a solution. The dumbwaiter is currently installed on a treehouse, but is appropriate in any venue where 3/4 inch EMT conduit would not be unsightly. The "car" is still a work in progress and will likely evolve. Right now it's just made of plywood with PVC (I think 1 inch) on the rails. There is potential improvements in the future to the car itself. Also pulling the ball chain (even with the approximate 4:1 mechanical advantage) is a little tough for young ones, so I'll probably add a crank at some point.

EDIT: I designed and printed the crank arm (see added STL file). Definitely an improvement and now even the 2 year old can bring things up and down.