I think this technique is called "tele-launching." I used it a lot in my
Tele-Coaster map. It is a series of those launches set up in a loop.
One thing I would add is that if you rotate the high receiver teleporter to face straight down, the player's momentum when they walk into the first teleporter won't matter. Any extra momentum will send them straight down, which is where they're going anyway. That way they hit the bottom teleporter every time.