You will also need 16 nuts (3mm) for the battery contacts, some wire, 8 AA batteries and a pair of 600 RPM DC motors batteryspace.com/dcmotorhightorquemini12vdcgearmotor 600rpmforhobbyproject.aspx.

Print out the following:

4 x axel-end.stl
2 x axel-gear.stl
4 x axel-spacer.stl
4 x axel.stl
8 x axelholder.stl
2 x battery.stl
4 x elbow.stl
2 x motorholder.stl
1 x pcb-holder-mirror.stl
1 x pcb-holder.stl
12 x plus.stl
16 x short-axel.stl
32 x tank-tread-1-single.stl
32 x tank-tread-2-single.stl
8 x wheel.stl
4 x worm-end.stl
2 x worm-gear.stl
2 x wormholder-mirror.stl
2 x wormholder.stl

Assemble as depicted in tank.stl or tank.blend. You will find that the motors need to be mounted to the motor holders PRIOR to assembly or you won't be able to bolt them in. The battery holders should be wired up prior to mounting as well.

Build the PCB github.com/NBitWonder/DCMotorController and mount it to the pcb holders.

Add some wiring to connect the PCB to the batteries and motors and then figure out how to control the darn thing with that last-generation ipod or smartphone you've got laying around collecting dust...