Here is a great way to recycle cardboard and use some creativity to make your own train engine. The fun thing is that you can make additions, add more features, add wagons, and extend the track and so on. In this instructable, we will see how the motorized engine can be made.

Supplies

Cardboard from packaging boxes (corrugated type)
Sharp scalpel or a paper cutter of your choice
Glue gun
A compass to draw the circles of 2 different diameters to make the wheel
Toothpicks/Skewer sticks
Dual shaft BO motor
Some wires and a switch to connect the BO motor
9V battery with a connector

Step 1: Making the Wheels

Cut 2 sets of cardboard circles
Use strips of cardboard and a circular object that matches one set of circles to make circular rings
Sandwich the cardboard ring of step 2 with a cardboard circle carefully
Carefully, using toothpicks attach 2 wheels to a BO motor
Use a toothpicks and straw bit to make a axle.
My engine uses 4 pairs of wheels, if needed you can also add 6 pairs

Step 2: The Motorized Mechanism

Use cardboard pieces to join the motor with the wheels
The images above are self-explanatory
This step is optional (recommended if you wish to used curved tracks) to allow smooth turning of the engine, I have added toothpick pegs in the motorized and non-motorized set of wheels
Use a rectangular cardboard piece fix the wheels using a rectangular piece of cardboard and attach the pegs securely using cardboard bits
Connect the motor wires to 9V battery with a snap on connector and a switch in between

Customize battery case!

In this project I have made use of recycled 18650 Li-ion rechargeable battery from a laptop battery pack. Initially, I tried to use an appropriate battery case for it but to allow easy replacement, I have used 2 magnetic screws and 2 small neodymium magnets to act as battery connectors.

Step 3: Engine Body

First we start with building the springs and other accessories. Do note, these are optional, but add to your engine's detailing.
I used a wire and rolled into a spring then attached them to undercarriage with the glue gun
Finally, you can design your engine body. I have used a freight engine model here
Color it with your favorite colors
Use bits of skewer sticks to design the railings
I have added a sliding feature in the engine to easily replace the batteries

Step 4: Making the Tracks

Here, I will show to how to build a basic straight tracks:

Cut long strips of cardboard as shown in the images
Make you own cardboard template to space the tracks evenly and glue the tracks equidistantly
You can use sellotape to join the track pieces
Finally, you are ready to test run you train engine.

Step 5: Get Set Go!

You can watch this video to see the quick steps and see the engine in action.