Technic

4x4 Mercedes-Benz Zetros Trial Truck

A big app-controlled off-roader that climbs like a champ but rolls slow.

4.3/5

Set 42129 · 2021

Pieces2,131

Minifigsn/a

Year2021

Set number42129

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The verdict

If you want a chunky remote-control Technic truck that actually crawls over real terrain, this LEGO® set delivers, and its climbing ability genuinely impresses.

The catch is the price, which is steep because the hub and four motors eat up roughly half of it. Grab it if you love app-controlled models and outdoor play, but if you want speed or pure value per piece, keep looking.

Best for: Technic fans who want an app-controlled off-roader to crawl over real terrain

The full review

What it is

The 42129 4x4 Mercedes-Benz Zetros Trial Truck is one of those Technic sets built entirely around its powertrain, and it's a proper motorised beast. You get a Bluetooth smart hub, three large motors and one medium motor, which makes it second only to the massive Liebherr 42100 for sheer number of electronics packed inside. The headline party trick is a remote-control differential lock, something Technic had never done before. When the truck loses traction, you tap the app and it sends constant power to all four wheels, which is exactly the kind of thing that makes off-road driving feel real rather than gimmicky.

The catch

Here's where you need to be honest with yourself about the money. This thing launched around 300 to 330 dollars, and a big chunk of that is the hub and the four motors rather than the plastic. Brickset's own reviewer was famously harsh, calling it a poor value example of what's gone wrong with Technic pricing, and that criticism sticks if you judge purely by parts per dollar. On top of that, once you get it moving it's genuinely slow, the turning circle is wide, and the steering can throw a wobbly and lock fully to one side until you recalibrate the motors through the app. Younger builders hoping for a speedy RC racer may lose interest fast.

Who it's for

So who's this for? If you love app-controlled models, enjoy taking your creations outside, and get a kick out of watching a truck crawl up a slope it has no business climbing, you'll have a great time with this one. The Control+ app even has an augmented reality mode that lets you peek at the mechanical systems without pulling the model apart, which is a lovely touch. But if you're chasing speed, a bargain price, or the most parts for your budget, this isn't the set for you. It's a specialist climber, and on that specific job it's better than a lot of reviewers gave it credit for. Community scores landed around 4.3 out of 5, which tells you plenty of owners came away happier than the harshest early reviews suggested.

The parts story

What the build is actually like, and the pieces worth knowing about.

The build splits neatly into two halves. First you assemble the functional guts, with Technic frames and liftarms wrapping around the motors and gears to form a sturdy powered platform that can take a beating. Then the second half is the fun dress-up stage, adding the cabin, the hood and the flatbed on top of all that machinery. Reviewers found it an easier and more enjoyable build than its wave-mate, the 42128 Heavy-duty Tow Truck, though do watch your gears, because one reviewer forgot a single bevel gear inside the new differential housing and had to rebuild an axle. At 2,131 pieces it's a meaty session without ever feeling like a slog.

For parts hunters there's real treasure here. The set introduced a brand new rubber tire with a herringbone tractor tread, roughly 81mm across, which the designer suggested is ideal for the front wheels of a classic two-size tractor. There's also a new deeper Technic steering CV joint large ball that fits three modules of axle length, giving builders more room to run driveshafts. On the recolour front, several pricey parts arrived in dark bluish gray, most notably the toggle joint, which had never been made in dark gray in the roughly 40 years since it first appeared. Fun bonus, the four short bars in here helped make that element cheap to order individually through Bricks and Pieces.

Fun facts

01The remote-control differential lock in this truck was the first time LEGO Technic had ever done that function, letting you send constant power to all four wheels when traction fails.
02With a smart hub plus four motors, it packs more electronics than almost any other Technic set, beaten only by the enormous 42100 Liebherr R 9800 excavator.
03The Control+ app includes an augmented reality mode that lets you explore the truck's inner mechanical systems on screen without ever taking the model apart.
04It introduced a new herringbone tractor tire and brought the humble toggle joint to dark bluish gray for the first time in around 40 years.