🎮 First RC Car (Servo): step-by-step build

Your first remote-control car: one dial drives, the other dial steers.

Time for a real RC car! It has two motors with two different jobs. The M motor spins round and round to drive the back wheels. The Servo motor is different: it does not spin, it turns to a position and HOLDS it — like your hands on a steering wheel. The Servo turns the little pinion on the steering rack, so the front wheels steer. The IR receiver listens to the remote with invisible light: channel A (red) drives, channel B (blue) steers.

• Level 4 of 5 (tricky)
• About 50 minutes
• 27 steps, 65 parts
• Powered by: Motor
• Series: Gearbox & Drivetrain Cars

What you will learn

• Remote Control: Invisible light carries your commands to the model.
• Servo Motor: A motor that turns to an angle and holds it.
• Rack & Pinion Steering: A gear rolling on a straight rack slides it sideways.
• Steering: Turning the front wheels makes a car follow a curve.
• Drive Train: The chain of parts that carries power from the motor to the wheels.
• 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

• 🎛️ One Motor, Knob Steering: The motor drives, YOU steer — turn the knob as you walk beside it. (level 3 of 5, about 40 minutes, 21 steps)
• 🏎️ Steering Go-Kart: Turn the steering wheel and the front wheels really turn — just like a real car. (level 3 of 5, about 30 minutes, 25 steps)

Parts you need

• 2 × Beam 15
• 19 × Black pin (grippy)
• 2 × Long pin-axle block
• 6 × Beam 7
• 1 × Servo motor
• 1 × Blue long pin
• 1 × AAA battery box
• 1 × IR receiver
• 1 × M motor
• 3 × Bush
• 1 × Axle 7
• 1 × Giant gear (40 teeth)
• 1 × Axle 11
• 4 × Yellow-hub wheel
• 4 × Axle 3
• 1 × Medium gear (24 teeth)
• 2 × Half bush
• 2 × Beam 9
• 4 × Grey pin (smooth)
• 2 × Steering arm
• 1 × Gear rack
• 2 × Red axle-pin
• 1 × LED lights
• 1 × Tiny gear (8 teeth)
• 1 × Speed remote

Steps

1. Stand a 15-hole beam on its edge — the right chassis rail.
2. Push black pins into holes 1 and 3 of the rail (inside) and press a long pin-axle block onto them — a steering socket.
3. Right Servo post: a black pin in hole 5 (inside) and a 7-hole post standing on it. Push black pins into the post's 4th and 6th holes, pointing inwards.
4. Slide the Servo onto the two post pins from the left, orange output at the front. Then brace the post: a 7-hole beam from hole 8 of the rail up to the post's 5th hole, outside, with a black pin and a blue long pin.
5. Push black pins into the 2 back side holes on the right of the Servo, then press a 7-hole beam onto them — the receiver rail.
6. Power pack: take the AAA battery box.
7. Press the IR receiver onto the front half of the box, its tall dome side on the right.
8. Press the M motor across the back end of the box, output pointing right.
9. Push black pins into holes 5 and 7 of the receiver rail, pointing inwards.
10. Slide the power pack in from the left under the receiver rail: the 2 pins click into the 2 holes in the back of the receiver.
11. Push black pins into the Servo's 2 front side holes on the left and press the left Servo post onto them.
12. A black pin into the bottom hole of the left post, pointing out, and press the left rail onto it, lined up with the right rail.
13. Tie the rails together: hold 2 bushes between them at hole 7 and push a 7-long axle through the left rail, both bushes and the right rail.
14. Left steering socket: 2 black pins in holes 1 and 3 (inside) and a long pin-axle block.
15. Make the rails longer: black pins in holes 13 and 15 of the right rail (outside) and a 7-hole beam pressed on, sticking out at the back.
16. The same on the left rail.
17. Back axle: hold a giant 40 gear inside the right extension and a bush inside the left one, and push an 11-long axle through the last holes and both.
18. Push on the back wheels.
19. A 3-long axle into the M motor with a 24 gear on it — it meshes with the 40 on the back axle. A half bush on the end keeps the gear from sliding off.
20. Steering module: lay a 9-hole beam flat and push a grey pin up through each end hole.
21. Put a steering arm on each grey pin and slide a short axle into each arm.
22. Push on the front wheels.
23. Grey pins in the arm ends, the red tie rod on top, and the gear rack on the tie rod, teeth up.
24. Slide the steering module in under the front, then push 2 red axle-pins, axle end first, up through the 3rd hole from each end of its axle beam into the cross holes of the pin-axle blocks.
25. Headlights: push the two LED lights into the round holes left and right on the Servo's face.
26. A 3-long axle into the Servo's output, the pinion on it, right on the rack, and a half bush on the front end so the pinion can't slide off.
27. Wiring: receiver cable onto the battery box. M motor → RED (channel A), Servo → BLUE (channel B). Pick up the remote.

Play time

Drive a figure eight round two cups. Then try a very tight circle and listen: the solid back axle makes one tyre scrub. (The Diff-Lock Mud Truck fixes that!)

Real-world inspiration

LEGO Power Functions RC models like the 9398 4×4 Crawler and 42065 RC Tracked Racer. https://en.wikipedia.org/wiki/Lego_Power_Functions

Build next

• 🛵 Front-Drive Servo Trike: One front wheel does everything: its own motor drives it and the Servo swings it round. (level 4 of 5, about 50 minutes, 21 steps)
• 🔒 Diff-Lock Mud Truck: Stuck in the mud? Slide the diff lock and both wheels are forced to turn together! (level 4 of 5, about 60 minutes, 33 steps)