This is the smallest printable tracked base I was able to print reliably.It is designed as two independent mirrored halves, each one hosting it's reduction gearing, motor, etc.The only vitamins you need are motors and 4mm threaded rods, the rest is all printed or filament.The motors are the round type found in most CD-ROM/DVD-ROM drives to close/open the tray, so get your old drives and find a matching pair :) Important: keep the small screws keeping the motor in place you will need them.It's all designed in Blender so you get the .blend file for now, I'll add stl's at a later point.You'll find two layers in the .blend file on the first you will find an assembled half, on the seconds you will find all parts laid out and grouped for printing.They are arranged as I have printed them on my Prusa, feel free to rearange for your size.To print as select a part group, export to STL, netfabb the STL, slice.I have a 0.35 nozzle and printed them at 0.25 mm getting a theoretical layer width of 0.39 (as indicated by Slic3r). As I have setup the gear distances based on these facts and by measuring the actual gears, well YMMV.There are more gears laid out than you'll need, print them all. This is due to their real small sizes so if you print smaller quantities they will not print very well.I used 20 mm/s perimeters, 10 mm/s small perimeters, 40mm/s infill at 180 degrees to print the gears (first layer at 185).For the case 40 mm/s perimeters, 20 small perimeter, 60 infill 185/195 degrees.As pins for the small gears I used 1.75 mm filament pieces, you should be safe with anything smaller or equal to 2mm. Same is used for connecting the track links.You will need about three track links sets printed as I have them laid out or two if you add more rows, for each side 30 links are needed.I have used soft PLA for my tracks but they should be fine with normal PLA too.For the output gear and track pulleys I used 4mm threaded rod and (embedded ) nuts, this make sure everything stays in place. This is still a WIP though I'm pretty happy with it for now.Cheers!Update! Added stl files.So to print you will need (so far):1 x case_side_1.stl 1 x case_side_2.stl 4 x drive_wheel.stl 4 x idler_wheels.stl 2 x gear_set.stl 64 x track_link.stlVitamins:2 x 125mm 4mm threaded rod 2 x 45mm 4mm threaded rod 2 x cdrom motors (mine are Mitsumi R-14 1425) 26 x 4 mm nuts I think that's it ...UPDATE: Due to changes in all Slic3r version after 0.72b the gears will not slice with newer versions. It turns out 0.72b has a "bug" allowing the gears to slice, I disagree but I'm not a developer. Interestingly enough Cura slices them without trouble ... So for the gears to print properly use Slic3r 0.72b or Cura. I'm marking this one as done as no further development will happen on this design. Added pictures of the final working tank :) Youtube later ...