Summary Another little tracked robot, inspired by Ktronics (https://www.thingiverse.com/thing:14599) and Geir (https://www.thingiverse.com/thing:8740). You'll need to print 6 of the wheels, 2 of the sprockets and 2 of the sideplates for the basic assembly, plus 2 of the battery mounts and one of the arduino/9110 holders if you choose to use them. Purchased items are the motors (about $3), belts ($8), threaded rods and nuts ($5), bearings($2), and the battery ($20) and electronics($4). Some of my early versions of this tank had issues with the belts running off the wheels and jamming the motors, but the little flanges on the wheels and sprockets seem to have fixed that. You could put another pair of plates on the outside of the wheels, like is shown in the "one_side_assembly" .stl file, but my current version works OK with just the inboard plates as shown in the photo BILL OF MATERIALS: This thing uses 2 of these cheap little geared motors (http://www.ebay.com/itm/Smart-Car-Robots-Plastic-Gear-Motor-For-Intelligent-DC-3V-6V-Robot-1-48-/191941830108?hash=item2cb09fe5dc:g:OKEAAOSwMtxXqUG2) and these 94 tooth timing belts for tracks (https://www.amazon.com/gp/product/B00NWG9AK0/ref=oh_aui_detailpage_o06_s00?ie=UTF8&psc=1). Battery is a 12V Li-ion (http://www.ebay.com/itm/6800mAh-DC-12V-Super-Rechargeable-Li-ion-Battery-Pack-for-12V-Devices-HBJ12680-/261975779618?nma=true&si=nC%252F3liHzllJ4wGbTZkS0mDeSaGY%253D&orig_cvip=true&rt=nc&_trksid=p2047675.l2557) which is probably overkill since these motors are designed to run on 3 to 6 volts. It really scoots, though! You could probably run it on 6 AA batteries and save a few bucks. The axles are 6" 5/16 threaded rods I bought at Lowe's. You could use 8mm rod without modification to the design if you're in a place where metric is more common than it is here in Texas. The wheels use 8mm skateboard bearings. I've mounted an Arduino Nano and a L9110 H-bridge (http://www.ebay.com/itm/H-bridge-Stepper-Motor-Dual-DC-Motor-Driver-Controller-Board-L9110S-For-Arduino-/161308004962?hash=item258eb4d262:g:OaMAAOSwXeJXdeF9). The arduino holder is adapted from cimo's customizable thing (https://www.thingiverse.com/thing:1381358/#files). I plan to put an array of ultrasonic sensors on it to make it autonomous, but i haven't gotten that for yet. Print Settings Printer: Prusa clone from JG Aurora Resolution: .2mm Infill: 20% Notes: Printed in PLA at 205 degrees C.