See 4QD's website for lots of info on controllers and motors.
Top view with logic board removed. Notice nice chunky M8 (8mm) brass connectors. Mouse for scale. Base plate is 280mm long.
End view showing three ally bus bars. Larger ones are approx 6mm by 20mm - these are the ones that all the FETs are mounted on. Note the silicon sheet isolating them from the base plate/heatsink (9mm thick). Right hand is the positive supply rail, left is negative (for connecting to 12 of the FET legs) and centre is one of the motor outputs. Other motor output is at other end (centre bar is in two halves).
Side view (about half the length), showing some of the FETs, attached to the bus bars. One leg on each FET is bent up to connect to circuit board above. The other connects to adjacent bus bar. The third connection is presumably made by the connection the body of the FET to the bus bar. Total of 24 FETs - a lot of work!
The 300s baby brother, the 4QD-200-36. Don't need another 300, as we're using one for each motor now. Hopefully they won't be too imbalanced. Uses an identical top board to the 300, but with four FETs per leg of the H bridge, rather than six.