Capacitors soldered to the motor. Without such RC filter this cheap brushed motor creates so much electric noise that microcontroller goes mad (especially hardware interrupts are affected).
Motors, wheel encoders, bumper switches, and a battery case installed.
An Arduino board and a solderless breadboard installed on a SparkFun's Holder. I made additional holes in the holder for fastening it to the robot's upper deck. I also made a hole in a small plastic pole in the lower right of the holder's Arduino slot for fastening Arduino board with a small screw (visible just above the Arduino's DC power jack).
before installation of microcontroller board. M3x10 hexagonal standoffs (4 brass hexagonal poles) turned out to be ideal for installation of the SparkFun's Holder - they fit into grooves on the underside of the holder board holding it parallel to the robot's deck. 2 Photocells, a Pan and Tilt kit, an IR receiver, and a power switch are installed at the front of the platform.
Arduino board, Adafruit Motor shield, and solderless breadboard as a single unit attached to the robot. On top of the main battery holder sits another holder (attached with violet rubber bands) for 9V battery providing Arduino with power.
Adafruit Motor shield on top of the Arduino board.
Sensors at the front: IR receiver, Ultrasonic Range Finder (on top of the Pan and Tilt kit), Photocells, IR proximity sensor, Bumper switches
Sensors wired to the MCU, only whiskers are missing