Hi, if you want to use Arduino only and not wifi, I suggest that you look at the schematic for the Z70:https://www.thingiverse.com/thing:2146425 (it is one of the pictures).
However, it's not difficult to make a wifi-controlled locmotive using NodeMCU, you can find schematic and instruction on the Hectorrail 141 page: https://www.thingiverse.com/thing:2575667
The RC6 was a bit of a side-project, as it's a bit too big to really function well on the track. If you intend to print this one, be aware that you might need to experiment a bit with smaller wheels. It runs fine in wider curve radius, and works also with the narrow radius but it has trouble navigating the turnouts/switches. I've had plans to test smaller wheels for a long time but haven't had time to do that yet, and this locomotive is more a display piece.