🎛️ One Motor, Knob Steering: step-by-step build

The motor drives, YOU steer — turn the knob as you walk beside it.

Big toy supercars often have a secret steering knob, called "Hand of God" steering, so you can steer while it drives. This car has a motor for the back wheels and a knob for the front wheels. The motor sits on top of the battery box and turns the back axle with two giant 40 gears. The knob turns the pinion, the pinion slides the rack, and the front wheels steer.

• Level 3 of 5 (medium)
• About 40 minutes
• 21 steps, 57 parts
• Powered by: Motor
• Series: Gearbox & Drivetrain Cars

What you will learn

• Steering: Turning the front wheels makes a car follow a curve.
• Rack & Pinion Steering: A gear rolling on a straight rack slides it sideways.
• Drive Train: The chain of parts that carries power from the motor to the wheels.
• Gear Ratio: Fast or Slow: A big gear turning a small gear makes it spin faster.
• Switching Direction: Flip which way electricity flows and the motor spins backwards.
• 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.
• Triangles Are Strong: A triangle cannot be squished — a square can.

Build these first

• 🏎️ 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)
• 🔋 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 × Beam 15
• 10 × Black pin (grippy)
• 2 × Long pin-axle block
• 2 × L-beam 3×5
• 1 × Axle 11
• 2 × Giant gear (40 teeth)
• 4 × Yellow-hub wheel
• 4 × Bush
• 1 × AAA battery box
• 1 × M motor
• 1 × Direction switch
• 2 × Axle 4
• 5 × Half bush
• 1 × Beam 3
• 1 × Double cross block
• 2 × Axle 5
• 2 × Beam 9
• 4 × Grey pin (smooth)
• 2 × Steering arm
• 2 × Axle 3
• 1 × Gear rack
• 2 × Red axle-pin
• 1 × Knob wheel
• 1 × Tiny gear (8 teeth)
• 1 × Extension wire

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 (on the inside) and press a long pin-axle block onto them — a steering socket.
3. Right knob post: black pins in holes 5 and 7 (inside) and an L-beam 3×5 pressed onto them, its long arm standing up at hole 5.
4. Motor post: black pins in holes 12 and 14 (inside) and another L-beam, long arm standing up at hole 12. A black pin in its 2nd hole from the top, pointing inwards.
5. Push an 11-long axle through the last hole of the rail, put a giant 40 gear on it, outside the rail, and push the right back wheel on after it so the gear can't slide off. A grey bush on the inside, against the rail.
6. Power pack: take the AAA battery box.
7. Press the M motor across the back end of the box — its studs-holes underneath click onto the box's studs. Output pointing right.
8. Press the direction switch across the front end of the box.
9. Slide the power pack in from the left: the pin goes into the hole under the motor's orange output. Push a 4-long axle through the top of the post into the motor, then slide on a bush, a 40 gear — it meshes with the 40 on the back axle — and a half bush.
10. Slide the left rail onto the axle and a bush onto the axle outside it. A black pin in hole 5 (inside) and a 3-hole post standing on it — the left knob post.
11. Hold a double cross block standing up between the knob posts and push a 5-long axle through both posts' 3rd holes and its bottom hole. A 4-long axle through the right post's 5th hole, a yellow half bush and into its top hole.
12. Push a grey bush onto the end of the short top axle, outside the right post. Left steering socket: 2 black pins in holes 1 and 3 (inside) and a long pin-axle block.
13. Push on the left back wheel.
14. Steering module: lay a 9-hole beam flat and push a grey pin up through each end hole.
15. Put a steering arm on each grey pin and slide a short axle into each arm.
16. Push on the front wheels.
17. Grey pins in the arm ends, the red tie rod on top, and the gear rack on the tie rod, teeth up.
18. 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.
19. Slide a 5-long steering column through the round hole of the cross block. Push the knob onto the back end, snug against the block, and a half bush behind it.
20. On the front end: a half bush against the block, the pinion right on the rack, and another half bush to keep it there.
21. Wiring: plug the switch's cable onto the battery box, and stack the motor's plug on top of the switch (use the extension wire if it is too short).

Play time

Build a slalom with cups. Switch on, walk beside the car and steer it round the cups with the knob. Can you park it backwards between two books?

Real-world inspiration

"Hand of God" (HOG) steering on Technic supercars, e.g. the Onyx pull-back mini MOC. https://rebrickable.com/mocs/MOC-2622/ibessonov/onyx-pullback-mini/

Build next

• 🔄 Reverse-to-Turn Car: Only one motor — but it can still turn! Drive backwards and the wheels swing round. (level 4 of 5, about 50 minutes, 24 steps)
• 🎮 First RC Car (Servo): Your first remote-control car: one dial drives, the other dial steers. (level 4 of 5, about 50 minutes, 27 steps)