This is a model of mine based on the CAT D8. It has a drive system that integrates the outputs from two motors - one for collective and one for differential movement of the tracks - so it's guaranteed to drive in a straight line and much more precise and flexible to control than a model with one motor per track. It also incorporates suspension inspired by the real CAT dozer which gives it masses of grip and stability and is driven by the digital two channel remote as Lego's 8275 was, but one channel is spare for possible expansion.
I've managed to squeeze in a system for operating pneumatic cylinders remotely to control the blade (no custom parts are used), but I decided not to include a ripper because it doesn't add much play value in my opinion. Links for a four-point mount at the rear are included, so that could always be added though. The blade is shamelessly taken from 8275 with little modification, but the rest is entirely my own creation.
My intention from the start was to build something that Lego themselves might have produced - not the most super detailed MOC I possibly could, but a decent representation of what it's based on that functions well and leaves plenty of room for little tweaks and embellishment that make Lego models such fun even after you've finished the build from instructions. I've payed special attention to the drive system to make sure there are no weak spots where bits might move or flex and gears slip past each other once it's put under load - it is a bulldozer after all - and I'm happy to say it's very robust.
A YouTube of it in action can be found here
I'm currently working on a CAT 740 articulated dump truck with ejector bed in the same scale, which is power function driven with working chassis articulation and suspension system. The ejector bed I'm particularly pleased with - Lego just doesn't suit the tipping version :)
Happy building and thank you for your vote if you do, I really appreciate it!