🏎️ Ackermann Soapbox: step-by-step build

Real car steering: the inside front wheel turns more than the outside one, so the tyres never scrub!

When a car turns, the inside front wheel drives round a smaller circle than the outside wheel — so it must turn MORE. Clever Mr Ackermann solved this 200 years ago: give each front wheel a steering lever that points inwards, towards the back axle. Your Go-Kart had straight levers; this soapbox has angled ones, just like a real car. Build the front axle module first, bolt it on, add the angled levers, then roll the soapbox down a ramp and steer between the cones!

Level 3 of 5 (medium)
About 35 minutes
20 steps, 59 parts
Powered by: Push
Series: Gearbox & Drivetrain Cars

What you will learn

Ackermann Steering: The inside wheel turns more than the outside wheel.
Steering: Turning the front wheels makes a car follow a curve.
Rack & Pinion Steering: A gear rolling on a straight rack slides it sideways.

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)

Parts you need

3 × Beam 9
1 × Axle 12
2 × L-beam 2×4
2 × Blue long pin
6 × Bush
1 × Axle 8
10 × Black pin (grippy)
2 × L-beam 3×5
4 × Long pin-axle block
4 × Half bush
4 × Yellow-hub wheel
4 × Red axle-pin
1 × Beam 5
1 × Beam 11
4 × Grey pin (smooth)
2 × Steering arm
2 × Axle 5
2 × Cross block
1 × Gear rack
1 × Axle 7
1 × Tiny gear (8 teeth)
1 × Hand crank

Steps

Stand a 9-hole beam on its edge — the left side of the soapbox.
Push a 12-long axle through the last hole — the back axle. From the inside, slide a blue L-beam onto it (long leg up) and push a blue long pin through the L-beam's foot and the 8th hole of the side beam.
Slide a grey bush onto the back axle, right against the blue L-beam, then the second blue L-beam, and push a blue long pin through its foot.
Slide on the second 9-hole beam — over the back axle and the long pin — and push an 8-long cross axle through the 7th holes of both beams.
Push a black pin into the 6th hole of each side beam, on the outside. Slide an L-beam post onto each side: its foot goes over the pin, the cross axle and the long pin, its long leg stands up.
Push two black pins into each post, on the inside: the 3rd hole and the top hole.
Press a long pin-axle block standing up onto each pair of pins, and lock the cross axle with a half bush on each end.
Two bushes on each side of the back axle…
…and the back wheels.
Push a red axle-pin into the middle hole of each block, pointing forward, and press the red 5-hole dashboard beam onto both.
Front axle module: lay an 11-hole beam flat and push a grey pin up through each end hole — the kingpins.
Push a red axle-pin up into the 5th and 7th holes (axle end up) and put a long pin-axle block on each, lying along the car.
Slide the module in under the front of the soapbox, blocks between the side beams. Push black pins through the 1st and 3rd holes of both side beams into the blocks.
Put a steering arm on each grey kingpin, pointing straight back. Grey pins are smooth, so the arms swing.
Ackermann levers: hold a cross block inside each arm, pin hole pointing back, and push a 5-long axle in from the outside through the arm's corner and the block.
Push the front wheels onto the axles.
Push grey pins up into the pin holes of the two levers and lay the red 9-hole tie rod on them.
Lay the gear rack on the tie rod, teeth up.
Hold the tiny pinion gear on the rack with a grey bush behind it and a half bush in front of it, and slide the 7-long steering column through the dashboard, the bush, the pinion and the half bush.
Push a yellow half bush onto the back of the column, right against the dashboard, then the red crank — your steering wheel.

Play time

Make a ramp from a book and a board, put cups at the bottom as cones, and steer the soapbox between them. Then steer full lock and push it slowly in a circle — the front tyres roll without scrubbing.

Real-world inspiration

Ackermann steering geometry — https://en.wikipedia.org/wiki/Ackermann_steering_geometry ; LEGO crawler steering geometry notes — https://legocrawler.wordpress.com/2015/11/23/part-2-steering-geometry/