Here is a Tiny Trak CAT D6 dozer, it is a vintage character model and is not a scale model, great fun little dozer, servo drive, based on the long lego track, although no doubt other systems could be used if you have a favorite, its built in the same way other tiny traks are built, it uses 8 high power magnets to hold top to bottom, ( one hic i found is that the holes dont line perfectly top to bottom, as i wanted the bottom magnets to protrude slightly and help a solid location , so i did over drill the holes for the first few mm) also i found it pretty tough work getting all my supports out, so keep the supports as weak as you can, the blade servo is using a small airplane linkage, to take rotary input to linear. otherwise have fun with it. i printed it in black PLA, and then gave it just a few light coats of Toolstation plant yellow, to try and make that vintage type look. the blade has two long 3mm bolts, drilled and screwed through the chassis wall, just drill the hole to leave enough space for your servo sticking out the front and its servo horn