↩️ Reverse-Gear Truck: step-by-step build

The motor only spins one way — the gear lever decides forwards or backwards!

Switch the truck on and the motor spins… always the same way. So how can it reverse? With a gearbox! In FORWARD the driving ring grabs the 24 clutch gear, which turns the giant 40 gear on the lay shaft. In REVERSE the ring grabs the 16 clutch gear instead — and that path has one extra "idler" gear sneaking in between. Every extra gear flips the direction, so the truck backs up. Real cars have exactly this reverse idler!

• Level 4 of 5 (tricky)
• About 55 minutes
• 18 steps, 52 parts
• Powered by: Motor
• Series: Gearbox & Drivetrain Cars

What you will learn

• Reverse Gear: An extra idler gear flips the direction.
• Idler Gears & Direction: A gear in the middle flips the direction back.
• Clutch & Driving Ring: A part that connects or disconnects a gear from its axle.
• Gearbox: A box of gear pairs where you choose which pair works.
• Gear Ratio: Fast or Slow: A big gear turning a small gear makes it spin faster.
• 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.
• Electric Circuits: Electricity flows from the battery, through the motor, and back.

Build these first

• ⚙️ Clutch-Gear 2-Speed Car: Push the gear lever and a driving ring grabs a different gear: 1st climbs, 2nd races! (level 3 of 5, about 45 minutes, 18 steps)

Parts you need

• 2 × Beam 15
• 2 × Axle 12
• 10 × Bush
• 2 × Medium gear (24 teeth)
• 1 × Axle 5
• 1 × Giant gear (40 teeth)
• 2 × Small gear (16 teeth)
• 1 × Axle 3
• 1 × Half bush
• 1 × Axle 6
• 1 × Clutch gear (24 teeth)
• 1 × Driving ring
• 1 × Clutch gear (16 teeth)
• 1 × Gear shifter
• 6 × Black pin (grippy)
• 1 × M motor
• 1 × AA battery box
• 8 × Blue long pin
• 4 × Beam 9
• 4 × Big tyre wheel
• 1 × LED lights

Steps

1. Stand a 15-hole beam on its edge — the right side of the ladder chassis.
2. Push a 12-long axle through the first hole (front axle) and the last hole (rear axle).
3. Slide a bush, a 24 gear and another bush onto the rear axle, so the gear sits right in the middle.
4. Lay shaft: a 5-long axle through the 12th hole, with the giant 40, a 24 and a 16 gear on it.
5. Slide the left side beam onto all three axles and a bush onto the front and rear axles, right against it — now the beam and the gears can't slide off.
6. Reverse idler: hold a 16 gear between the beams at the 10th hole and push a 3-long axle through the right beam into it. Slide a half bush onto the outside end so the axle can't fall out.
7. Input shaft: hold the 24 clutch gear, the driving ring and the 16 clutch gear in a row between the beams at the 8th hole, and push a 6-long axle through the right beam, all three and the left beam.
8. Clip the gear shifter onto the driving ring.
9. Push black pins into the 7th and 9th holes of the left beam, from the outside. Press the M motor's front onto them: the round holes beside its orange output take the pins, and the output slides onto the input shaft.
10. Two bushes on the right end of the front axle and a second one on the left end.
11. The same on the rear axle.
12. Battery pack: take the AA battery box.
13. Push blue long pins into the two lowest holes of both end flaps, pointing right.
14. …and the same on the other side, pointing left.
15. Press a 9-hole post onto each pair of pins, hanging down. Two pins each, so the posts can't swing.
16. Lower the battery pack over the gearbox so the posts slide down outside the side beams. Push a black pin through the bottom hole of each post into the side beam (holes 3 and 13). Plug the motor into the box and set its slide switch ONE way — from now on you drive with the gear lever.
17. Push on the four big truck wheels.
18. Push the two LED lights into the 2nd and 4th holes of the front right post — headlights!

Play time

Switch on with the lever in the middle: the motor runs, the truck waits. Push the lever to FORWARD and drive to a wall, then pull it to REVERSE and back away — without ever touching the switch. Forward is a bit slower but stronger (24 → 40).

Real-world inspiration

The reverse idler gear in manual gearboxes. https://en.wikipedia.org/wiki/Manual_transmission#Reverse_gear