Pebble Time hooked up to the Arduino. Arduino hooked up to the car.
We started on the Pebble side of things, making sure we could get an Android app to talk to the Pebble and the Pebble to talk to the Arduino. For the Android to Pebble communications, we used PebbleKit Android. For the Pebble to Arduino communications, we used the newly-revealed smartstraps with ArduinoPebbleSerial.
With that out of the way, we began hacking a $9 RC car from Walmart so that our Arduino could interface with the motors and controls directly. Thanks to a couple awesome Pebble hardware engineers, we were able to reverse-engineer the pins from the original board so we could know what they each controlled.
Close up view of all our connections.
Our repo contains all the files needed for both hardware and software (Android app, Pebble app, Arduino code).