🚞 Cog Railway Climber: step-by-step build

A mountain train that grips a toothed rail — it climbs super steep ramps and never slides back.

Normal trains slip on steep hills: smooth wheels on smooth rails have hardly any grip. Mountain railways in Switzerland solved it with a toothed rail in the middle and a gear under the train that bites into it. Our loco has the same trick: a pinion gear walks along a line of racks. The motor drives it through a worm gear, and a worm gear can't be pushed backwards — so the train can stop halfway up and stay there!

Level 4 of 5 (tricky)
About 55 minutes
20 steps, 58 parts
Powered by: Motor
Series: Mechanical Wonders

What you will learn

Rack & Pinion Steering: A gear rolling on a straight rack slides it sideways.
Worm Gear: The Lock: A worm gear turns a gear super slowly — and never slips back.
Torque vs Speed: Slower gears are stronger gears.
Mounting a Motor: A motor must be pinned tight, or it spins itself instead of your wheels.
Plugging In: Power Functions: Battery box → (switch or receiver) → motor. Plugs stack like bricks.

Build these first

🏗️ Worm-Gear Crane: Crank the worm gear to lift the boom — then let go. It stays up by itself! (level 3 of 5, about 30 minutes, 15 steps)
🔋 Motor Buggy: Your first car that drives by itself — with a forwards/backwards switch and headlights! (level 3 of 5, about 30 minutes, 20 steps)

Parts you need

2 × Open frame 5×11
17 × Black pin (grippy)
2 × Beam 15
2 × Beam 7
4 × Beam 13
3 × Gear rack
2 × Tan gear rack
4 × Blue long pin
3 × Beam 3
2 × Axle 6
4 × Small white wheel
1 × Open frame 5×7
1 × Axle 7
1 × Small gear (16 teeth)
1 × Bush
1 × Medium gear (24 teeth)
3 × Half bush
1 × L motor
1 × Worm gear
1 × Axle 8
1 × AA battery box
1 × Extension wire

Steps

Lay a white 5×11 frame flat. This is the first half of the track bed.
Lay the second frame end to end with it. Push black pins up into hole 2 of the first frame's left edge and hole 3 of the second frame's left edge, and press a 15-hole rail flat onto them — it bridges the joint.
Push two more black pins down through the rail's 4th and 12th holes into the frames. Two pins in each frame: now the joint can't bend.
Right edge: pin a 15-hole rail flat from hole 9 of the first frame to the end of the second (pins in frame holes 9 and 3).
Fill the gaps: a 7-hole rail at the far end of the left edge…
…and a 7-hole rail at the near end of the right edge.
Push black pins up into the middle hole of both short ends of the first frame. Press a 13-hole beam flat onto the two pins (its 3rd and last holes), down the middle of the track — it sticks out 2 holes past the start.
Do the same on the second frame: two black pins in the middle holes of its short ends and a 13-hole beam flat on top (its 1st and 11th holes) — it sticks out 2 holes past the end.
Lay racks along the middle beams, teeth up, end to end with no gaps. Start at the 2nd hole of the long middle beam.
Add the last rack. Near buffer: push blue long pins down into the two holes of the long middle beam in front of the first rack, and press a red 3-hole beam flat onto them, overhanging the end.
Press a second red 3-hole beam on top of it. Far buffer: push blue long pins into the middle beam's 10th and 12th holes, just past the last rack, and press a red 3-hole beam flat onto them.
Loco: stand a 13-hole beam on its edge and push two 6-long axles through its 2nd and 12th holes.
Slide the second 13-hole beam onto the axles.
Put a small wheel on every axle end.
Motor frame: push a black pin into hole 9 of the right side beam and press the bottom-right corner of a 5×7 frame onto it, standing up.
Push a 7-long axle through hole 5 of both side beams and the frame's bottom-left corner, with the 16-tooth pinion in the middle, and slide a bush and the 24-tooth gear onto its right end. The axle is the frame's second joint.
Slide a half bush onto the axle end to keep the 24-tooth gear in place. Push 2 black pins into the 2nd and 4th holes of the frame's top row and press the L motor's side holes onto them, output pointing down.
Hold a half bush, the worm gear and another half bush in a stack next to the 24-tooth gear and push an 8-long axle up through all three into the motor.
Set the loco on the track from above so the pinion bites into the rack.
Control station: lay the AA battery box on its side, switch pointing away from the track, and push the 1st and 3rd holes of its end flap down onto the tops of the far buffer's two blue pins. Plug the long wire into the box and the motor.

Play time

Lean one end of the track on a pile of books and drive up. Stop halfway — does the train slide back? Add more books: how steep can it climb before the wheels lift off?

Real-world inspiration

Rack railways such as the Pilatus Railway and the Mount Washington Cog Railway — https://en.wikipedia.org/wiki/Rack_railway