I finally got all the components talking correctly. The Raspberry Pi receives data from the RF transmitter and sends movement instructions via USB serial (angle and velocity) to the Arduino. The Arduino translates those instructions for each of the 3 motors. This happens BLAZINGLY FAST (and explaining what is happening will be a different post once I work out the kinks that I’m happily ignoring for the time being).
Here’s the first video I took of it actually working! IT’S ALIVE!
Please post any questions or post ideas!