Extremely Tiny Model Train Christmas Ornament

This project is a miniature model train and diorama designed to fit entirely inside a Christmas ornament. It combines 3D printed parts, simple electronics, and a small mechanical belt system that moves a magnet under the track, causing the train above to follow along.

Before starting, I highly recommend watching the build video to understand the overall design and where things are headed.

Explore the fusion files here(sorry its a mess!): https://a360.co/49g66Fe

Grain of Rice pictured, but not needed.

Mechanical and General Parts

1. 1 × Neodymium Magnet, 1/16" thick, 0.1" OD
2. https://www.mcmaster.com/5862K426/
3. 1 × Neodymium Magnet, 1/16" thick, 1/16" OD
4. https://www.mcmaster.com/5862K137/
5. (Get a bunch. They are very small and easy to lose.)
6. M2 × 10 mm plastic threading screws
7. M2 × 8 mm plastic threading screws
8. 3 × 8 × 4 mm bearings × 4
9. 1.5 mm belt, approximately 10.75 inches long
10. Right-angle geared DC motor
11. Tiny 0.6–0.8 mm stiff wire (I used leads from a capacitor)

Electronics

1. Adafruit Feather ESP32 V2
2. Adafruit Wireless LED Kit
3. DotStar LED strip, cut to 16 LEDs
4. Circuit board (PCB)
5. Link to the project PCB

Electrical Component BOM

Refer to the schematic for exact placement and orientation.

1. 1N4148W Diotec Semiconductor × 4
2. MBR230LSFT1G × 1
3. MF-USML300/12-2 × 4
4. 6-pin 2.54 mm screw terminal, Phoenix Contact 1725698 × 1
5. 2-pin 3.5 mm screw terminal, Phoenix Contact 1751248 × 2
6. 4-pin 2.54 mm screw terminal × 1
7. PJ-063AH barrel jack × 1
8. AOSP36326C MOSFET × 4
9. 220 Ω resistor, 0805 × 4
10. 10 kΩ resistor, 0805 × 4
11. 1 × 16 pin socket × 1
12. 1 × 12 pin socket × 1

GITHUB FOR DESIGN FILES - https://github.com/idlehandsdev/seanville-model-train

PCBWAY for PCBS - https://www.pcbway.com/project/shareproject/SeanVille_Tiny_Model_Train_Christmas_Ornament_Controller_4a13288b.html

Some of these parts are small and require a 0.2 mm nozzle.

MAKERWORLD LINK FOR FILES - https://makerworld.com/en/models/2161834-extremely-tiny-model-train-christmas-ornament#profileId-2343881

Required Prints

1. LED Hoop and Leg × 1
2. Legs × 2
3. Track Base Belt Guide × 1
4. Motor Clamp Half × 1
5. Idler Pulley 11 mm × 1
6. Idler Pulley 14 mm × 1
7. Idler Pulley 18.8 mm × 1
8. Idler Pulley 22 mm × 1
9. Drive Pulley × 1
10. LED Clip × 6
11. Tiny Train Engine × 1 - 0.06mm Layer height is recommended.

Optional Decorative Prints

Print as many or as few as you want.

1. Workshop
2. Trees_Three
3. House_Big
4. House_Small
5. Lake
6. Mountain

If you want to do multicolor prints, get the 3MF files.

Apply solder paste to the PCB.

Place all of the small surface-mount components and reflow the board using a reflow oven or hot plate.

Once reflowed, solder all through-hole components. Use the Fusion 360 CAD file as a reference for part placement and orientation.

Press the bearings into all four idler pulleys.

Mount the pulleys onto the Track Base Belt Guide using M2 plastic threading screws.

Press the drive pulley onto the DC motor shaft. Install the motor clamp to hold the motor in place. Take your time aligning the motor shaft so it lines up with the center of the Track Base Belt Guide before tightening everything down.

Route the belt around the drive pulley and all idlers.

Insert the larger of the two neodymium magnets into the track channel underneath the belt.

The magnet moves purely by friction as the belt slides over it. This magnet is what pulls the train along above the board.

Use double-sided tape to secure the DotStar LED strip to the underside of the hoop.

Install the 3D printed LED clips to help reinforce the adhesive.

Route the LED strip wires through the hole provided in the hoop.

Attach the completed circuit board to the bottom of the hoop.

Attach the legs to the circuit board. Before installing the final leg, insert the wireless LED coil. The legs and the slot are designed to hold it in place.

Connect all wiring from the LED coil and strip to the control board.

Before attaching the Track Base Belt Guide to the legs, connect the motor wires.

One wire goes to 5V and the other to GPIO12.

Carefully install the Track Base Belt Guide onto the legs.

This step can be a bit tricky due to the tight fit, the motor location, and the wireless LED coil underneath. Take your time.

The Engine needs a magnet installed that will be attracted to the magnet in the base. Use the 1/16" x 1/16" magnet(careful they're tiny!) and insert it in the bottom. Also take a piece of wire or the lead from a larger through hold capacitor and stick it into the smaller 0.8mm hole. Mine was just friction fit for both. Leave the wire stick out of the bottom no more than 0.5mm, gently use a file to shorten it if necessary. This will guide the train on the track as it drags behind.

Connect the LED strip to the screw terminals shown in the reference images.

This is a good time to upload the firmware and test the system.

Make sure to add your WiFi credentials to the firmware before uploading. The system uses WiFi to control different parts of the ornament. After uploading, the serial monitor will display the IP address you need to connect to.

Nothing will move or light up unless 5V power is supplied through the barrel jack or screw terminals. You will also need to install a jumper.

This is where you get to be creative.

Print trees, houses, buildings, mountains, or anything else you want. I used double-sided tape to secure everything to the base.

You can also place wireless LEDs inside the printed structures or design your own additions entirely.

Add a small wire and hang the ornament on your tree.

Power is left intentionally flexible, so you will need to get a bit creative with how you supply it.

These projects are always shared for free.

If you want to support future builds:

1. Subscribe to my YouTube Channel (Free!) - SeanHodgins on YouTube(Click Here!)
2. Check out the Patreon - SeanHodgins on Patreon

It directly helps make more projects like this possible.