🐾 Twin-Spring 4×4: step-by-step build

Two spring engines — one for the front wheels, one for the back. All four wheels push!

Why stop at one spring engine? This 4×4 has two: one drives the back wheels and one drives the front wheels. With all four wheels pushing, it can climb ramps where the other racers just spin and slip. You will build each engine unit on its own, then join them with the long side beams — like a real car factory. Keep the weight in the middle so both axles grip!

  • Level 3 of 5 (medium)
  • About 35 minutes
  • 16 steps, 39 parts
  • Powered by: Pull-back
  • Series: Gearbox & Drivetrain Cars

What you will learn

  • Stored Energy: Energy can be saved up in a spring and let out later.
  • Mounting a Motor: A motor must be pinned tight, or it spins itself instead of your wheels.
  • Four-Wheel Drive: Power goes to both axles so all four wheels push.
  • Centre of Gravity: Keep the heavy stuff low and in the middle and your model won't tip.

Build these first

  • Pull-back Racer🏁 Pull-back Racer: Pull it back, let it go — ZOOM! A racer with a spring for an engine. (level 2 of 5, about 12 minutes, 10 steps)
  • 🔗 Driveshaft 4×4 Pusher: Turn one wheel and ALL FOUR wheels turn — a spinning driveshaft joins the axles! (level 2 of 5, about 20 minutes, 15 steps)

Parts you need

  • 2 × Pull-back motor
  • 3 × Axle 10
  • 20 × Black pin (grippy)
  • 4 × Beam 5
  • 2 × Beam 13
  • 4 × Yellow-hub wheel
  • 2 × L-beam 3×5
  • 2 × Half bush

Steps

  1. Rear unit: take a pull-back motor, long body pointing forwards, and push a 10-long axle through the cross hole at the bottom.
  2. The motor has a row of 5 holes along its bottom. Push a black pin half-way into the first and the last of them, from both sides.
  3. Press a green 5-hole beam onto the pins on each side.
  4. Push two more black pins into the 2nd and 3rd holes of each green beam, pointing out.
  5. Front unit: the second pull-back motor, long body pointing backwards, with a 10-long axle.
  6. Black pins half-way into the first and last bottom holes, from both sides.
  7. A green 5-hole beam on each side.
  8. Two black pins in the 2nd and 3rd holes of each green beam (counting from the motor axle), pointing out.
  9. Stand a 13-hole beam on its edge — the left side.
  10. Slide the rear unit sideways onto the beam: its two pins go into the 3rd and 4th holes.
  11. Slide the front unit on the same way: its pins go into the 10th and 11th holes.
  12. Press the right-hand 13-hole beam onto the four pins on the other side.
  13. Push on the four wheels.
  14. Roll cage: push black pins into the outside of the long beams, holes 8 and 9.
  15. Press an L-beam onto each pair, long leg standing up.
  16. Slide a 10-long axle through the tops — the roll bar — and lock it with half bushes.

Play time

Build a ramp from a book and a board. Pull the 4×4 back and race it up the ramp — then try the Pull-back Racer. Who makes it to the top?

Real-world inspiration

Rebrickable "4x4 Rally Truck" (pull-back 4WD) — https://rebrickable.com/mocs/MOC-23649/J_Svensk/4x4-rally-truck/ ; "Bat-Buggy with Pullback" (two motors) — https://rebrickable.com/mocs/MOC-33537/Bert83/technic-bat-buggy-with-pullback/