Here's a photo of the two platforms. On the right is the Tamiya tank platform (Tracked Vehicle Chassis kit) with the Tamiya Universal Plate and the Tamiya L/R Independent 4 speed Double Gearbox.
Previously, I had mounted the Arduino Uno and the Arduino Motor Shield on the Tamiya platform, along with a couple of 9V batteries in parallel. I'd then program the Arduino to drive the tank via the motor shield with a preset list of commands (forward, rotate left, rotate right, reverse, etc.).
When I later bought the Raspberry Pi, I thought of using the Raspberry Pi as the brains of the robot, with its larger memory potentially allowing more programming flexibility than is available on the Arduino as well as the fact that the RPi is an actual computer (if a small, cheap, and low-powered one) as opposed to a micro controller, like the Arduino. In order to do this, I needed a bigger platform to accommodate the additional parts.
So, on the left is my current robot. It uses a Sainsmart 4WD aluminum robot platform. The right and left side motors are connected in parallel on each side, so the four wheels aren't really independent. I use 6 AA batteries to provide the motor power. At the front of the robot (right, in the photo) is the Arduino Uno (mounted by standoffs to the top plate), an Arduino motor shield, and a wireless SD shield, on which is mounted a Radio Shack ultrasonic distance sensor.
At the end of the robot (left, in the photo), on a small platform attached by standoffs attached to the top plate, is the Raspberry Pi (model B) and Mophie Juicepack battery pack for iPhone that I use to power the Raspberry Pi. The RPi also has an Edimax USB WiFi adapter and a Raspberry Pi Camera Module, mounted in a case that is mechanically attached to the wireless SD shield on the Arduino stack. The RPi assembly is strapped with a velcro strap to the raised platform. The battery pack feeds power to the RPi via a USB-micro-USB cable, and the RPi talks to the Arduino Uno via a USB cable, rather than the GPIO RPi pins to the Arduino pins that several other people use.
I'll go into more detail later on the assembly and programming of this robot. For now, it's not autonomous.
However, as of this evening, I was able to sit at my MacBook Pro and use the WiFi network to drive the robot around my house by moving a little and then viewing the camera image after subsequent moves to see where the robot was located. So that was fun.
