🪢 Belt-Drive Buggy: step-by-step build

No gears touching: a loop carries the power from the motor down to the wheels.

Gears have to touch to work. But what if the motor is far away from the wheels? Then you use a belt or a chain! On this buggy the motor sits up high, and a loop of track links wraps round two small track wheels — one on the motor, one on the back axle. Bikes, motorbikes and old cars do exactly this. With a rubber band on two belt wheels instead of the chain, the belt would even slip if the buggy gets stuck, like a safety clutch.

• Level 3 of 5 (medium)
• About 35 minutes
• 11 steps, 38 parts
• Powered by: Motor
• Series: Gearbox & Drivetrain Cars

What you will learn

• Pulleys & Belts: Wheels joined by a belt pass motion over a distance.
• 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.
• Friction: Friction is the rubbing force that slows things down.
• Switching Direction: Flip which way electricity flows and the motor spins backwards.
• Frames: A frame is a ready-made strong rectangle.

Build these first

• 🔋 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
• 2 × Black pin (grippy)
• 1 × M motor
• 1 × Axle 10
• 1 × Axle 12
• 2 × Small track wheel
• 4 × Yellow-hub wheel
• 1 × Axle 3
• 22 × Grey track link
• 1 × AAA battery box
• 1 × Direction switch

Steps

1. Stand a black 5×11 frame up on its long side — the left wall.
2. Push two black pins into the 7th and 9th holes of the wall's top bar, from the inside. Press the M motor's front onto them: the two holes beside its orange output take the pins, and the output lines up with the 8th hole.
3. Stand the second wall against the back of the motor, and push a 10-long axle through the front bottom corners and a 12-long axle through the back bottom corners (one hole further out on the left).
4. Slide a small track wheel onto the left end of the back axle, then push on the two back wheels. The wheel hubs grip the axle and keep the right wall from sliding off.
5. Push a 3-long axle through the 8th top hole into the motor's output, and slide the second small track wheel onto it.
6. Push on the two front wheels.
7. Clip 11 track links together and wrap them under the two track wheels.
8. Clip on the other 11 links to close the loop over the top.
9. Power pack: take the AAA battery box, studs up.
10. Press the direction switch onto the front half of its studs, lever on top.
11. Press the power pack up under the M motor: the motor's bottom clicks onto the back studs. Plug the switch cable into the battery box and the motor plug on top of the switch.

Play time

Switch on and let the buggy drive into a cushion. What happens to the chain? Now try it with a rubber band round two belt wheels instead: drive into the cushion again and watch the belt slip. Twist the band into a figure 8 — the buggy drives backwards!

Real-world inspiration

Chain-drive bicycles, belt-drive scooters and vintage belt-drive cars; LEGO Simple & Powered Machines pulley models. https://en.wikipedia.org/wiki/Belt_(mechanical) · https://education.lego.com/en-us/product-resources/machines-and-mechanisms/simple-and-powered-machines/building-instructions/