Some quick answers:
- Horizontal pistons - Correct, they push the stack onto scoring platforms.
- Vertical piston - Pushes on a pulley to act as a break.
- Blue circles - These are not sensors but the back side of the pulley shafts. There are three pulleys on the back side of the board that the belt wraps through.
As for racking, we are concerned. Our hope is that the overall design is stiff enough and our lift belt straight enough that it does not rack. Unfortunately there is not a great way to test this without building it so we're gonna charge ahead!
Here's some progress picks as of last night:
http://imgur.com/a/bUKq0