On Track for Fun

There is not a child alive that has looked at their scale model toy cars without wondering what it would be like if they could actually drive them around. Some of those children grow up to be engineers, like YouTuber diorama111, so that they can finally find out. This Japan-based hardware hacker has a history of modifying scale model vehicles to add lights, motors, and all sorts of other fun things. But diorama111’s latest project may be the best one yet.

This project began with a TOMYTEC 1/150 scale Dual Mode Vehicle (model DMV-931). This is a model bus that can drive on both roads and model railroad tracks with its different sets of wheels. Well, it can drive on them if you are willing to give it a push, anyway, because the stock vehicle is just molded plastic without any actuators or other electronic components.

But diorama111 was determined to convert it into a remote-controlled car, so lots of tiny-scale fabrication work ensued. First, the plastic fixed front axle was removed. Bearings were added to the wheels before they were attached to a set of thin aluminum plates to create a steering mechanism. The rear axle was replaced with a metal rod that was attached to a series of gears driven by a tiny four millimeter diameter DC motor. Next, a 3.9 millimeter stepper motor was fitted into the vehicle to turn a feed screw, which in turn pulls on a rod that manipulates the steering mechanism.

A second stepper motor was used to lower the front rail wheels into place, which simultaneously moves the front road wheels up and out of contact with the surface below. This also causes the rear rail wheels to be deployed, yet the rear road wheels maintain contact with the surface below so that they can still be used for drive power.

To complete the build, an ATtiny3217 microcontroller and an RN4871U Bluetooth module were built into a small, onboard control system. A 55 mAh rechargeable LiPo battery supplies power, and some LEDs were added for headlights, turn signals, and brake lights. The wiring was all done with very fine 0.08 millimeter magnet wire.

A custom breadboard controller was created with a pair of analog joysticks for steering and speed control, as well as some switches for the lights. This controller communicates with the vehicle wirelessly via Bluetooth.

The bus was demonstrated zipping around a scaled-down roadway and train track. It seemed to be easily able to line itself up with the tracks and make the switch to rail mode at the click of a button. It was even demonstrated that the vehicle could be parallel parked — try squeezing a full-sized bus into that spot without a dent or two!

The work done by diorama111 is very delicate and skilled, so you might not be able to easily reproduce the work, but the video is very well done and worth a watch. Seeing the bus come together is a very enjoyable experience.