[SmallHaul]

From wiki:

Advantages and disadvantages of the High Drive system

Among modern tractors, the high drive (elevated sprocket) design is unique to Caterpillar products. The concept originated in 1914 with Caterpillar predecessor C. L. Best Tractor's 30 Humpback; this tractor was discontinued a year later, and the only other tractor to use the concept until the D10's introduction was the Cletrac Model F, built between 1920 and 1922. The elevated sprocket eliminates the final drive system, which tended to break frequently. This elevated drive sprocket undercarriage was built in modular form. You can break down the tracks and then pull out the drive sprockets. From the back you can pull the transmission out because of the modular design. As the engine and drivetrain are mounted high in a traditional bulldozer, the half shafts from the differential exit above the drive sprocket, requiring a small gear on the end of the half shaft and another, larger one attached to the drive sprocket. The high-drive system eliminates the traditional final drive in favor of the planetary final drive, which is more effective at withstanding engine torque, since it spreads the forces over multiple gear teeth instead of a single tooth as in the traditional system. The disadvantage is that the track moves around one more sprocket, reducing track life. Caterpillar claims to have alleviated this with the SALT(Sealed and Lubricated Track), a permanently lubricated track system which was introduced on their track-type tractors in the early 1970s.

That will be cool to see a 1/50 rc dozer run.