I found BV4213 on ebay back in early January. The 4WD dfrobot chasis has four discrete motors. All the commonly available Arduino motor shields only support two channels. The BV4213 is a solution to this. Each board is about 2.5cm square; it provides full PWM and directional motor control to two motors per board. You communicate with it using I2C. Using two of these boards, I have discrete control over all four motors and free up four pins on the primary Arudino (now a Mega…so it does not matter that much.)
A few days ago I finally got the test command on the BV4213 to return a test signal. It’s alive! Today I started writing direction and PWM commands to it. I have not yet figured out the behavior of PWM when you change its value. It seems to lag a bit. I’ll post some code when I get it cleaned up.