This design is a bit modular. It can be mobile robot chassis mechanical tank toy (no motors) motored tank toy mechanical buldozer motored buldozer. The [optional] tank palette is either a standard 7-8 speed bicycle chain or an o-ring of suitable size stretched to two wheels on one side. One o-ring for each wheel can also be used. The chassis is designed for the dimensions of geared DC mini motors which can be purchased from many sources. If it is going to be built as a pure mechanical toy, then the supplied extra axle parts can be built and used to fill places of the motors. There is a mechanism at the center of the chasis that enables us to tighten the chain without using an extra jockey wheel, by lengthening and shortening the entire chasis by turning a single screw. If you plan to build the wheels version then you might just glue the parts together. Or wrap two rubber bands around the chassis to keep parts together. the wheels are supplied in six different versions. One type is suitable for free rotation over the non motorized axles. And the other type is for being fixed to gear motor's shaft. And it can be tightened by a screw on it. Both of these are supplied in either tank palette, rubber ring or normal wheel versions which doesn'require a bicycle chain to be installed around them. Comments are welcome. https://www.youtube.com/watch?v=NfrQwK_K7No&feature=youtu.be