🚜 Skid-Steer Loader: step-by-step build

No steering at all: left motor, right motor — spin it round on the spot!

A skid-steer loader has no steering wheel. Its left wheels are driven by one motor and its right wheels by another. Both motors forwards: straight ahead. One forwards and one backwards: it spins round on the spot, skidding its tyres. On each side a row of three gears links the front and back wheels, so they always turn together. And the loader arms? You crank them up with a worm gear — it is so strong it holds the bucket up all by itself.

Level 4 of 5 (tricky)
About 65 minutes
25 steps, 76 parts
Powered by: Multi-motor
Series: Gearbox & Drivetrain Cars

What you will learn

Remote Control: Invisible light carries your commands to the model.
Idler Gears & Direction: A gear in the middle flips the direction back.
Drive Train: The chain of parts that carries power from the motor to the wheels.
Worm Gear: The Lock: A worm gear turns a gear super slowly — and never slips back.
Four-Wheel Drive: Power goes to both axles so all four wheels push.
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

🪖 RC Tank: Two motors, two tracks, one remote. Spin on the spot and climb over anything! (level 4 of 5, about 60 minutes, 27 steps)
🏗️ Worm-Gear Crane: Crank the worm gear to lift the boom — then let go. It stays up by itself! (level 3 of 5, about 30 minutes, 15 steps)

Parts you need

2 × Beam 13
16 × Black pin (grippy)
3 × Open frame 5×11
4 × Axle 6
5 × Axle 5
10 × Half bush
2 × Giant gear (40 teeth)
2 × Medium gear (24 teeth)
2 × Beam 9
4 × Big tyre wheel
1 × L motor
3 × Tiny gear (8 teeth)
2 × L-beam 3×5
1 × AAA battery box
1 × IR receiver
2 × Dark giant gear (40 teeth)
1 × M motor
1 × Bush
1 × Double cross block
1 × Axle 9
1 × Axle 8
2 × Axle 11
2 × Axle joiner
1 × Worm gear
1 × Hand crank
2 × Beam 15
2 × Cross block
1 × Speed remote

Steps

Right side: stand a 13-hole hull beam on its edge, push black pins into holes 3 and 7 (outside) and press a 5×11 frame onto them, lying long-ways — the tower.
Push 6-long axles through the front and back wheel holes, and a 5-long idler axle in between (4 holes from each). A yellow half bush on the inside end of the back axle.
A giant 40 gear on each wheel axle and a 24 on the idler. They mesh in a row: 40 · 24 · 40. A half bush on the front axle, next to its gear.
Slide a 9-hole outer beam onto the three axles and push on the two big wheels.
Right motor: black pins in holes 11 and 13 of the right hull beam, pointing inwards, and the L motor on them — output pointing right, 3 holes behind the back wheel.
A 5-long axle through the hull into the L motor with a tiny 8 gear on it, meshing with the back 40, and a half bush on the end.
Worm stand, right half: black pins in the 9th and 11th top holes of the right tower (outside) and a small L-beam on them inside, its short arm standing up at the 8th hole.
Radio pack: the AAA battery box…
…with the IR receiver pressed onto its front half, window side on the right.
Push black pins into the 3rd and 5th top holes of the right tower, pointing inwards, and hang the pack on them by the receiver's 2 back holes.
Left side: stand a 13-hole hull beam on its edge, push black pins into holes 7 and 11 (outside) and press a 5×11 frame onto them, lying long-ways — the tower.
Push 6-long axles through the front and back wheel holes, and a 5-long idler axle in between (4 holes from each). A yellow half bush on the inside end of the back axle.
A giant 40 gear on each wheel axle and a 24 on the idler. They mesh in a row: 40 · 24 · 40. A half bush on the front axle, next to its gear.
Slide a 9-hole outer beam onto the three axles and push on the two big wheels.
Left motor: black pins in holes 1 and 3 of the left hull beam, pointing inwards, and the M motor on them — output pointing left, 3 holes in front of the front wheel.
A 5-long axle through the hull into the M motor. Slide on a bush, a tiny 8 gear meshing with the front 40, and a half bush.
Worm stand, left half: black pins in the 6th and 8th top holes of the left tower (outside) and a small L-beam on them inside, short arm standing up at the 9th hole.
Hold a double cross block standing up next to the right small L-beam and push a 9-long axle from the outside through the right tower, the L-beam's corner and the block's bottom hole (it ends flush with the tower, so the loader arm can swing past it). Then an 8-long axle through the top of the L-beam and the block's top hole, with a yellow half bush on its outside end.
Slide the left side onto the two axles sticking out of the block: they go through its small L-beam and its tower. Lock the top axle with a half bush outside the left L-beam — now the two sides are clamped together and the worm stand can't nod.
Loader pivot: hold an axle joiner, a tiny 8 gear and another axle joiner in a row between the small L-beams and push an 11-long axle through the 11th top holes of both towers, the L-beams and all three. The joiners are spacers: they keep the 8 gear in the middle.
Slide a 5-long axle through the middle hole of the double cross block with a half bush and a worm gear right on top of the pivot 8 gear, and the crank on its back end, snug against the worm.
A half bush on the front end of the worm axle stops it sliding out. Loader: slide a 15-hole arm onto the right end of the pivot axle. Hold a cross block (round hole at the bottom) just inside the arm's front hole and push an 11-long axle through both.
Slide a second cross block onto the front axle, then the left arm onto the pivot axle and the front axle at the same time. Push a black pin into each cross block's round hole, pointing forwards.
Press a 5×11 frame onto the two pins, standing across — the bucket. It tips a little on the front axle, so it always scoops flat.
Wiring: receiver cable onto the battery box. Left motor → RED, right motor → BLUE. Grab the remote.

Play time

Set up a "building site" with toy bricks. Drive to a pile, crank the bucket down, push, crank it up and carry the load. Try spinning on the spot on carpet and on a smooth floor — where does it skid more easily?

Real-world inspiration

Skid-steer loaders like the Bobcat. https://en.wikipedia.org/wiki/Skid-steer_loader

Build next

🚧 Twin-Motor Dozer: Wide caterpillar tracks, one motor per track, and a blade that cranks up with a worm gear. (level 5 of 5, about 100 minutes, 33 steps)