Here is a chain in tube drivetrain that we designed in anticipation of using a chain in tube style drivetrain during the build season.
Gearboxes: Vexpro 3 CIM Ball Shifter 18 fps high 6 fps low
Tube: 1"X2"X0.100" Versaframe rails
Sprockets: 18t Vexpro sprocket with 1/2" hex bore
Drop: 1/16" drop in the middle and 1/16" raise on the sides so the chain would not be too close or too far away from the top or bottom of the inside of the tube.
Spacers: 3d printed for maximum accuracy. However some were too small to use without breaking but they ended up being so small we just left them off and it worked fine. We were also required to mill down the 2 center sprockets so they would fit in the tube right next to each other.
We were very pleased with how it ran. We had no problems with skipping teeth or derailing (with new chain) despite not having a tensioner.
One of the main downsides of chain in tube has always been it’s tedious assembly process. We found that gluing the center 2 sprockets together and then dropping the entire chain assembly with all 4 sprockets in at once and then adding the shafts and spacers through the bearing holes before the bearing went on worked well.
A very notable downside of chain in tube style drivetrains is that there is no room in the tube for bolts or rivets to attach to the top, this could involve some tedious workarounds for teams intending to attach their superstructure directly to the side drivetrains rails. We had to do a lot of math to determine where we could safely put bolts in the side of the drivetrain rail for the bumper mounts.