Follow the steps below to build the robot. It will help to also skim the Bluefruit LE feather robot guide to see more pictures of assembling the robot chassis. There are a few small differences in the assembly of the Pi robot that will be noted below.
Start by screwing the DC motors to the back of the chassis (i.e. the end farther away from the angled front). Make sure the motors have the same orientation, with the side that the wire exits facing forward.
Next screw in the caster to the center mounting holes.
Assemble the wheels by stretching the tires onto the hubs, then push the wheel into place on the motor head and screw it in.
You can feed the DC motor wires up through the angled mounting slots in the chassis.
Flip the robot over so it stands on its wheels.
Cut out a small square of cardboard that's about the same size as the Raspberry Pi. This cardboard will protect the bottom of the Pi from touching the metal robot chassis and shorting out. It's very important to prevent the bottom of the Pi from touching the metal chassis or you could damage the Pi!
Screw the top plate standoffs into the mounting holes near the center of the chassis (flanking where the angled mounting slots meet).
Place the Pi on the cardboard and position it so the Pi's rear mounting holes (near the USB ports) are directly above the long mounting slot at the back of the chassis. Use the #4-40 machine screws and nuts to screw through the Pi and cardboard to securely hold the Pi in place.
If you aren't using Pi HAT standoffs to hold the motor HAT place a piece of electrical tape across the HDMI connector side of the Pi. This will help prevent the motor HAT from getting pushed down into the connectors and shorting out. If you are using the standoffs you can place them over the front mounting holes of the Pi (not shown).
Push the motor HAT into place on the Pi's GPIO connector. Screw down the standoffs if being used to hold the HAT.
Connect the DC motors to the motor HAT as shown to the left.
The left (or 'driver side' for US/right side of the road drivers) DC motor should be connected to port M1 on the motor HAT. The right (or 'passenger side') DC motor should be connected to port M2 on the motor HAT.
The black motor wire connects to the left screw terminal of the port, and the red motor wire connects to the right screw terminal of the port. The middle GND screw terminal is unused.
Connect the 4x AA battery pack red wire to the +/positive power screw terminal on the HAT, and the black wire to the -/negative power screw terminal.
Finish the robot by screwing the top plate firmly to the standoffs in the center. Use double sided foam tape or electrical tape to hold the 4xAA battery pack to the top plate, and the USB battery pack to the front of the robot.