🛻 Bouncy Monster Truck: step-by-step build

Four big wheels on four springy shock absorbers. Boing, boing!

Monster trucks drive over rocks, logs and even other cars! To do that, every wheel needs its own suspension. Each wheel sits on a swing arm that can move up and down, and a shock absorber pushes it back to the ground. The front has soft yellow springs, the back has hard red springs for carrying heavy loads. You will build the strong box chassis first, then four wheel units, then bolt on the springs.

Level 4 of 5 (tricky)
About 45 minutes
29 steps, 75 parts
Powered by: Push
Series: Starter Builds

What you will learn

Suspension & Springs: Springs let wheels bounce over bumps while the body stays calm.
Pins: Grippy or Smooth: Pins join beams together — some hold tight, some let things swing.
Frames: A frame is a ready-made strong rectangle.
Centre of Gravity: Keep the heavy stuff low and in the middle and your model won't tip.
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)
🛒 Push Buggy: A sturdy buggy with a push bar held up by super-strong triangles. (level 2 of 5, about 15 minutes, 12 steps)

Parts you need

2 × Beam 15
3 × Open frame 5×7
20 × Black pin (grippy)
2 × Beam 7
2 × Beam 11
4 × Axle 6
4 × Bush
3 × Double cross block
4 × Cross block
2 × Axle 5
4 × Blue long pin
2 × Soft spring
2 × Hard spring
4 × Beam 5
4 × Axle 4
8 × Half bush
4 × Big tyre wheel
1 × Open frame 5×11

Steps

Stand a 15-hole beam on its edge — the lower left chassis rail.
Stand a 5×7 frame up on the inside of the rail at the front, and pin its bottom edge to holes 6 and 8 of the rail.
At the back, push a black pin into hole 12 and stand a 7-hole post on it.
Hold the 11-hole top rail against the outside of the frame and the post, push a 6-long axle through the top rail into the frame, and another into the post. Then push a black pin through the rail's 6th hole into the frame, so the rail can't slide off the axles.
Push a 6-long axle through the middle hole of the frame's side and of the post, and slide a bush onto the middle of each axle.
On the outside, slide a double cross block standing up onto the ends of the two front axles, and another onto the two back axles.
Slide a cross block onto the middle of each top axle: the front one with its free hole pointing up and forwards, the back one up and backwards.
Slide the second 5×7 frame onto the front axles and a second 7-hole post onto the back axles. Lock them on with a bush on the end of each middle axle.
Pin the lower right rail onto the bottom of the frame and the post.
Slide the right top rail onto the ends of the two top axles, and pin its 6th hole to the frame too.
Cab mount: hold a double cross block between the rails at the front and a cross block on each side of it, then push a 5-long axle through the 2nd hole of both rails and all three blocks.
Push a second 5-long axle through the 4th hole of both rails, the frames and the double cross block.
Push a blue long pin into holes 7 and 9 of each lower rail, pointing outwards. The swing arms will hinge on these.
Hang the two yellow (soft) shock absorbers from the top rails at the front: a black pin through the 3rd hole of each top rail into the shock's top hole.
Hang the two red (hard) shock absorbers at the back the same way, from the 9th hole of each top rail.
Front-left wheel unit: a 5-hole swing arm with a short axle in its end hole. Slide a half bush onto the inside end so the axle can't fall out, and push a black pin into the 3rd hole, sticking out on the inside.
On the outside end: a half bush as a spacer, then a big wheel.
Push the front-left wheel unit onto its long pin — the pin in the swing arm goes into the bottom hole of the shock absorber.
Front-right wheel unit: a 5-hole swing arm with a short axle in its end hole. Slide a half bush onto the inside end so the axle can't fall out, and push a black pin into the 3rd hole, sticking out on the inside.
On the outside end: a half bush as a spacer, then a big wheel.
Push the front-right wheel unit onto its long pin — the pin in the swing arm goes into the bottom hole of the shock absorber.
Rear-left wheel unit: a 5-hole swing arm with a short axle in its end hole. Slide a half bush onto the inside end so the axle can't fall out, and push a black pin into the 3rd hole, sticking out on the inside.
On the outside end: a half bush as a spacer, then a big wheel.
Push the rear-left wheel unit onto its long pin — the pin in the swing arm goes into the bottom hole of the shock absorber.
Rear-right wheel unit: a 5-hole swing arm with a short axle in its end hole. Slide a half bush onto the inside end so the axle can't fall out, and push a black pin into the 3rd hole, sticking out on the inside.
On the outside end: a half bush as a spacer, then a big wheel.
Push the rear-right wheel unit onto its long pin — the pin in the swing arm goes into the bottom hole of the shock absorber.
Push a black pin up into the free hole of each top cross block, then lay the 5×11 frame flat on top so its end holes click onto the pins — the truck bed.
Push a black pin into the top hole of each front cross block, pointing forward, and press the red 5×7 cab frame onto both pins — the 2nd and 4th holes of its bottom edge. Two pins keep the cab from tipping.

Play time

Drive the truck over a pile of books. Push down on one corner and let go — boing! Which springs are softer, front or back?

Build next

🏆 Independent Rally Car: Every wheel on its own springy arm, a differential, universal joints and Ackermann steering. (level 5 of 5, about 90 minutes, 47 steps)