This was a project that I have been working on for a few months on an off. The wheels are a little larger than 2 inches ind diameter. The are designed to be used on the Tamiya 3mm shaft gearboxes.
There are two versions of the .STL The one that ended in inches is the one I used for the 3d-print. The other one should be in millimeters. For some reason the file size is different.
The .STl files are large. Download the zip file not the .STL