Team 1619 also used a chain-in-tube drivetrain with great success this year, and we were surprised by how easy it was to manufacture and assemble. It was put together using custom sprockets, bicycle chain, and hex shafts to serve as the axles. Since one of the axles was the output shaft of the gearbox, only three sprockets and two runs of chain per side of the drivetrain were required.
We started with our sprockets, which we machined ourselves to allow the use of bicycle chain, which was both lighter and stronger than the other solutions we had explored in the past. The ability to control the offset between sets of teeth on the sprocket (since we were making them ourselves) and the spacers holding the sprockets in the tubing meant we could control the position of the runs of chain within the tubing to still allow us to through-bolt into the chassis where the chain was located. It was just a matter of designing the sprockets and spacers so that the center of the tubing was unoccupied by chain.
The chain itself was quite simple in that we simply bought bicycle chain and then removed links to make it the correct length before adding the master link to create a loop of chain.
The assembly was the part that nobody was looking forward to at first, since we had to put all of it together inside of 2.5x1.25 aluminum tubing that had solid walls without "windows" removed to see inside other than the slots for the bearings that held the axles. Due to this, we actually put together the runs of chain outside the frame by holding one sprocket, then dangling the first chain from it, then cradling the second sprocket in the first chain, then dangling the second chain with the third sprocket cradled inside. We then took the whole assembly, still held by the first sprocket, and gently lowered it inside of the tubing until the top sprocket was visible in the hole for the first axle. It was then a simple matter of inserting the axle to hold the top sprocket in place, then "capturing" the dangling sprockets by inserting their respective axles. The assembly process is the same one described by Abhishek that 624 used.
Provided that you can reach high enough to insert the assembly into the open end of the tubing on your drivetrain (we had to stand on a stood to accomplish this), it is a method that is both quick and easy for installing a chain drive inside of tubing. The downside to this method is that it does require precision machining capabilities if you want to retain the ability to through-bolt in the center of the tubing (so that you can ensure the proper offset to the chain inside the tubing) for the sprockets and spaces, as well as the ability to machine out the bearing slots for your axles in the tubing in the correct location. In the future I would assume that we're likely to use a similar solution due to the positive experience we had with it this year, provided that it continues to be an advantageous solution for our overall game strategy.
If anyone has any specific questions about our drivetrain, feel free to shoot me a message and I'd be happy to provide more details. A powerpoint presentation with CAD models on a similar drivetrain design (which was our fall project last year) can be found
HERE for those who are interested.