Need help building drivetrain.

My team would like to see some building instructions for drivetrains, specifically, one that is within the competition width of 18" and has interior space for a mobile goal collection mechanism.
Where should we start?

This is probably the simplest and most efficient design you can use that fits your specific criteria
Link Here

Can I ask why you are unwilling to design your own? It may end up being not good, but making your own is the only way. The most small possible drive base will be six holes wide on each side. (Beyond that is possible however it is a little more advanced so I won’t describe it)

The best place to start is to have your team attempt designing a drive on their own. The drive is the most basic part of the robot; even the new team I’m mentoring this year that, has never touched a screwdriver, was able to build their own drive train. Asking for instructions will not get you anywhere and hurt you in the long run.

I recommend looking at robots like 8059a to get an idea of a simple and effective robot to attempt building. Also based on your user name, it seems like you are a teacher/mentor of your team. I would recommend they try to find a solution on their own and make their own forum accounts so they are able to learn more directly. My drivetrain’s normally start like this, but with omni wheels

And probably bigger.

I’m not against them designing their own; in fact that’s what they’ve been doing for the last two weeks, in addition to looking at some designs on youtube to get ideas. They’ve also had a little experience with their clawbot and super clawbot builds. At this point, they have an idea of the shape of the drivetrain they want but want to see different ways to map out the geartrains/chain and motors.

The hardest thing is visualizing a robot in your mind, and estimating how much space every subsystem will take up. When I was a freshman, things always turned out way bulkier than I expected. By my senior year, I have a pretty good idea of how everything will fit together, almost like a CAD model in my mind. It just takes experience, really. But, looking at others’ robots is a great way to get an idea, and there’s nothing wrong with that.

This video is done by theSTEMclass.
It is a great way to learn and find out how other teams’ build the drive train (or any other parts of the robots).
Maybe you can consider getting your team to do a detailed breakdown or dissection of other robots’ drive train. It will be the best way to learn.