Update: I finished miniaturizing my circuits. Had some custom PCBs made (by jlcpcb.com) and got everything tucked into the body shell nicely.
Here's a video of my first run with everything 100% functional. My son was cracking me up with his reactions to it. 
Major features:
- Controllable over WiFi
- Tachometer and speed control
- Smoke system
- LED directional lights
- Digital sounds
The speed control does a really good job of keeping constant speed on curves and up the hills. It speeds up a bit going down my 4% grade hill though. The controller/motor are getting set down to the minimum possible power that won't stop the engine, but even at that amount, gravity takes over and causes some acceleration. If I let the PID controller go any lower, it would jerk to a stop though. The only real solution would be lower gears in the trucks.
I'm releasing the firmware open-source: https://github.com/joelwetzel/MQTT-Locomotive I don't expect anyone else to ever build one - it's quite a project - but if anyone is curious... have fun! I'll probably post the PCB and wiring diagrams at some point too.
