This a rover platform that you can assemble choosing among many blocks that fit in the same mounting points, so you can adapt the design to what ever fits your needs the better.

NOTE: You can find the main page of the project, with the index of related links and articles here. 

I thought it to be as symmetric as possible, allowing you to reuse many parts in different spots, for example, the front and back shells have the same mounting points, allowing you to print the Shell - RPi Camera for the front, and the Shell - Blank for the back part. Unless you want a camera in the back too. You could also print the Shell - Switch for the back, to control the power source of your rover.. Your imagination is the limit.

I am designing this in Sketchup, these files will be uploaded too, in case you want to design custom blocks yourself.

In this video, you can see in detail how to mount a track frame (One side of the robot)
NOTE: Please let me know if you find issues on any of the parts, and if you would like me to create a specific block for any hardware you think could be useful.

Files description

InnerTrackFrame - DCMotor v0.3.stl

It is the block that holds this kind of DC motor.
You need 4 of them.

CenterTrackFrame v0.3.stl

Is the block used to hold two InnerTrackFrames together
You need 2 of them.

OuterTrackFrame v0.3 .stl

This block locks into the CenterTrackFrame and covers a wheel
You need 4 of them.

Shell - Blank v0.2.stl

This block locks into the InnerTrackFrames. It is the front and/or back of the rover
You need 2 Shell blocks of any type.

Shell - Switch v0.1.stl

This block locks into the InnerTrackFrames. It is the front and/or back of the rover
It is design to host this kind of switch, to control the power of your rover
You need 2 Shell blocks of any type.

Shell - RPi Camerav0.3.stl

This block locks into the InnerTrackFrames. It is the front and/or back of the rover
It is design to host a Raspberry pi camera module
You need 2 Shell blocks of any type.

Shell - RPi Camera Support v0.3.stl

This block locks inside the Shell - RPi Camera
You only need it if you are also printing the Shell - RPi Camera.

Track v0.1.stl

This block is one link of the track chain.
You need print 27 per side (54 in total)

Cog - Drive v0.1.stl

This block is what moves the track
You need 4 of them.

Spindle - DC Motor v0.3.stl

This is what links a motor to its Cog
You need 1 per each InnerTrackFrame - DCMotor you have (so 4 in total)
Cover - Blank - v3.stlThis block acts as base or cap (top or bottom) of your rover
You need 2 Cover blocks of your choice.

Notes:

The settings depend on the part you are printing.

Cog should be printed with Support, and I printed it also with brim, but just because the support was not sticking to the bed. If you dont have this problem, then you don't need the brim (but print it with support)
Shell: I printed without supports, and with 0.3 mm resolution
InnerTrackFrame: No supports, 0.3 mm resolution
CenterTrackFrame: No supports, 0.3 mm resolution
OuterTrackFrame: No supports, 0.3 mm resolution
Tracks: No support, 0.2mm resolution

Post-Printing
To assemble this rover you will need the some M3 Screws. I bought mine from here. I used M3x10, but you can use something a little shorter too. I did not use nuts, but if you could, if you find the screw is not fasten enough

InnerTrackFrame Mounting point
These blocks support the motors, and act as main chassis for the rover. Right now I designed one for a 6v DC motor, but I'm planning to create another based on a standard continuos rotation servo like these.

InnerTrackTrame - DC Motor
his block is design to support the common no name yellow dc geared motor. You can find them here in aliexpress.

Shell Mounting point
The Shells are the front and back of the rover. You can choose the shell block that fits your need the better. Here is the list of shells that exist right now:

Shell - Blank
As the name says, this is a basic shell, you could use this if you don't want your rover to have holes you will not use.
Shell - Raspberry Pi Cam
This Shell was design to accommodate a Raspberry Pi camera, if you are planning to use one, you can use this block to fit it in the front of your rover. You can find the camera here

Shell - Switch
This Shell was design to accommodate a switch so you can turn on/off your rover without using the main area for the electronics. The hole has 7mm, and was designed for the switch you can find here.

Cover Mounting point
The Covers are the top and bottom of the rover. You can choose the cover block that fits your need the better. Here is the list of covers that exist right now:

Cover - Blank
As the name says, this is a basic cover block, you could use this if you don't want your rover to have holes you will not use.