Sliced using Cura 2.3.1, printed in PLA on an Ultimaker 2+ Extended and an Ultimaker 3 Extended at .1mm vertical resolution. Print "Knob and Axle.stl", "Chassis Left.stl", "Chassis Right.stl" and "Spring.stl" with 100% infill, the remaining components with 50% infill. Print two each of "Wheel Front.stl" and "Wheel Rear.stl", print one each of the remaining parts. Study "Assembly.stl", carefully noting the locations and positions of the various components as assembly proceeds. 1) Press "Gear Axle Rear.stl" onto "Axle Rear.stl". 2) Press "Gear Idler Small.stl" onto "Axle Gear Idler Small.stl". 3) Slide "Knob and Axle.stl" into "Chassis Right.stl", then press "Spring.stl" and "Pawl.stl" onto "Knob and Axle.stl". 4) Slide "Gear Pawl.stl" onto "Knob and Axle.stl". 5) Slide "Gear Spur.stl" onto the axle on "Chassis Right.stl". 6) Place the idler assembly ("Gear Idler Small.stl" and "Axle Gear Idler Small.stl") and rear axle assembly ("Axle Rear.stl" and "Gear Axle Rear.stl") into position in "Chassis Right.stl". 7) Press "Chassis Left.stl" onto "Chassis Right.stl". 8) Place the o-rings on the wheels. 9) Press one each of "Wheel Rear.stl" onto each end "Axle Rear.stl". 10) Position "Axle Front.stl" into the chassis assembly, the press one each of "Wheel Front.stl" onto each end of "Axle Front.stl". Hope you like it!