Inspired by Tearloch's OTM Tracker, I decided to built a Brandt Power Unit on a Western Star chassis.
The Brandt Power Units are used as MOW vehicles on many railroads in North America, and are used as locomotives on some shortlines around the world. They are capable of pulling up to 10 loaded train cars or 25 empty cars.
I've included an M motor in the truck. It is slow and can't negotiate curves, but it is strong! It was able to pull a ~15 car Santa Fe that couldn't pull itself.
Western Star Brandt Power Unit by Ricecracker., on Flickr
And here's a breakdown shot of the cab.
Cab Breakdown by Ricecracker., on Flickr