[MOC] Zil 131 Trial Truck (Powered Up)

[gyenesvi]

 

Hi Eurobricks!

Here's yet another model that has been waiting to be presented for a while: a trial truck based on a specific Zil 131 (video). This one was built for the truck trial competition in the 2025 Buwizz camp. The rules stated it had to be using around 80 mm wheels, it had to have working steering wheel and working fake engine, and a proper cab with two realistic seats.

I definitely wanted to build a 6x6 truck, a larger scale version of my mini Zil 130. I wasn't specifically going for yet another Zil, rather something simple / solidly buildable in terms of bodywork / cab shape, and something with a long nose for good balance (I'm not fond of European style short nose trucks, as they are front heavy for trial). Then I found this trial truck online, and thought it looked good, especially liked the color; I have been wanting to build something green for a while.

 

Below I will share the design details, but first, here is what turned out of it:

This is a purely Powered Up version, but of course in the Buwizz competition it was powered by a Buwizz 3 unit, providing even more speed and torque.

 

Features:

• Live axle suspension, rear tandem bogie, high ground clearance
• 6x6 drivetrain, driven by 3x PU L motors
• PU L motor for steering, linkage based
• Powered by PU technic hub
• Functional steering wheel
• Working V6 fake engine

 

Suspension

It took many iterations to arrive at the final setup, I experimented a lot with possible suspensions and electronics layouts. I definitely wanted something with live axles, as I consider independent suspension for trucks unrealistic (except for that one truck that @Appie built on a similar scale based on a real vehicle, but extremely rare). Also, I wanted to try myself with an elaborate tandem bogie setup. Furthermore, one requirement for myself was good ground clearance, using portal hubs for good torque.

First I tried to use Attika's axles with slanted lower arms for good ground clearance, but they were just too wide (17 studs between steering pivots) for these wheels, and would have made the build disproportional. Then I started experimenting with an interesting idea to mount the planetary hubs only from the top. I knew from the start that I would not be using differentials (pointless for trial), so the core idea for a slim non-steered axle looked something like this, which allows for heaps of ground clearance:

The only problem was the front axle, until @Attika showed me his entry for last year, which employed a similar trick for the front axle, albeit on a smaller scale (62 mm wheels). The key idea is to have two solid steering racks (the two beams) that can hold the wheel hub from tilting. So I gave it a try to see if this could work on a larger scale as well. I added one mounting point for the planetary hubs on the top, and two solid steering racks that go around the diff a bit to avoid colliding with the gearing (note that everything needs to be above the racks to allow them sliding underneath), until I ended up with this, and it holds the hubs really well in place:

It has panhard rods on both ends to keep it stable, and a linkage for moving the steering rack.

At the rear, I also elaborated the design to accommodate the drivetrain and the suspension linkage. I moved the drivetrain higher (detailed below), and added linkage for the bogie setup. I found the below bogie setup in other MOCs, and thought it's really cool because not only does it connect the two rear axles, but it is also spring loaded, imitating a realistic leaf sprung bogie. It was perfect scale for the wheels in terms of spacing the rear axles. So the final setup for the rear axles looks like this.

 

Drivetrain

As for electronics, the Buwizz competition allowed both Buwizz and PF/PU motors, however, I found that Buwizz motors have a pretty bad shape to be integrated into a truck chassis, especially if a working fake engine is also required somewhere. So I settled for XL/L motors, thinking that the trial race is not about speed anyways. I planned to use PU system to be able to do fine speed control (speed servo feature).

My first idea for the drivetrain was to use 2 XL motors, resulting in a simple chassis railing build with the fake engine and the transmission to the axles in between the motors. The transmission for floating axles requires a lot of (longitudinal) space, especially for highly articulated axles where long CV joints are required that allow sliding of the driveshaft as the axle moves around. However, for some reason, my XL motors did not want to cooperate; right when I started testing, one of them broke down. I replaced it, and then another one gave in; kind of weird, not sure why. As I ran out of usable XL motors, I had to use L motors, which actually turned out to be better for building in, leaving more mounting points for the cab. Also, I discovered that then I could add a 3rd motor in the back for more power.

The speed of L motors routed to planetary hubs would have been quite slow (like the Zetros), so I decided to add some up-gearing, as there was enough torque left in the system. This has more advantages besides speed. For one, it allows me to do the up-gearing inside the rear axles, resulting in only 12T gears being used at the bottom, giving the best ground clearance. Second it allowed me to offset the front and rear parts of the driveshaft, compacting it longitudinally and making the total wheelbase length shorter, which is good for trial, and also to use 12T gears at the bottom in the middle of the chassis and in the front axle as well. Also, it gave more ground clearance in front of and in between the rear axles. The final driveshaft and electronics layout looks like this, including the steering mechanism.

The complete chassis looks like this

 

Bodywork and interior

Finally, the bodywork is really simple, using large panels, no doors, to keep it solid, although the nose does have some tricky ways of attachment. I did however add a rollbar, as it looks more detailed and is still solid. Here are some renders and photos of the complete model.

More images available on my Bricksafe.

Building instructions available on Rebrickable.

Let me know how you like it!

Cheers,

Viktor

 

Edited December 8, 2025 by gyenesvi

[Krxlion]

I really like it, Viktor. I especially love the "no-lower" linkage function. If it works and improves the ground clearance. I think that your instruction is very beneficial for people on their journey in 6x6 off-road trucks. Moreover, from the many, many trucks out there, Zil is the one that catches my eye. I have a few questions, if I may:
1. What is that brick (3rd picture) in the center, under the back 15L LBG liftarm? It is located inside the standard technic frame. Looks like 3L flip-flop beam.
2. I am confused on how this steering works, but I guess, when I will buy instruction, I will know. :D

Again, great build: the body is great as well. You have included both a working engine and steering wheel, which is just icing on the cake. ;)

[N1K0L4]

Great model! Looks really good too

I like the solution for the axles, looks really sturdy with great ground clearance. Also clever trick for rear suspension, got some inspiration for my trail truck for next year ;)

How many motors does it have for drive? On some picture I see 2 on some 3.

I like that you made it drivable without the need for BuWizz electronics. How is the weight distribution for a heavy PU C+ battery that high? Is it top heavy?

 

[Appie]

Very nice truck. Works great and yay green 

Chassis looks solid, nice axles.

Slightly puzzled by the placement of the fake engine (under the hood would be normal for this truck no?) but I understand it might make the drivetrain for steering and drive more complex by having the steering motor and the fake engine swap places.

[gyenesvi]

3 hours ago, Krxlion said:

I really like it, Viktor. I especially love the "no-lower" linkage function. If it works and improves the ground clearance. I think that your instruction is very beneficial for people on their journey in 6x6 off-road trucks. Moreover, from the many, many trucks out there, Zil is the one that catches my eye. I have a few questions, if I may:

Glad you like it and you find my writeup useful!

3 hours ago, Krxlion said:

1. What is that brick (3rd picture) in the center, under the back 15L LBG liftarm? It is located inside the standard technic frame. Looks like 3L flip-flop beam.

It is this part, introduced recently, a useful connector:  I only used it in that prototype example, not needed for the final model.

3 hours ago, Krxlion said:

2. I am confused on how this steering works, but I guess, when I will buy instruction, I will know. :D

It's actually a pretty standard steering, solid axle, solid tie rods on both sides built from 11L flip-flop beam and connectors, moved through a 6L link directly from the motor and a servo horn.

1 hour ago, N1K0L4 said:

Great model! Looks really good too

Thank you!

1 hour ago, N1K0L4 said:

I like the solution for the axles, looks really sturdy with great ground clearance. Also clever trick for rear suspension, got some inspiration for my trail truck for next year ;)

I guess I'm making the competition harder for myself next year :D

1 hour ago, N1K0L4 said:

How many motors does it have for drive? On some picture I see 2 on some 3.

It has 3 motors, I've just hidden the left one on the breakout view to make the driveshaft in the middle visible.

1 hour ago, N1K0L4 said:

I like that you made it drivable without the need for BuWizz electronics. How is the weight distribution for a heavy PU C+ battery that high? Is it top heavy?

Good that you asked, as I forgot one trick :) So, for one, I am using Phondly LiPo battery insert (9V), which is lighter than having 6x AA batteries (like half the weight). Second, the Zetros tires are weighted with some extra lego tires inside (another trick from Attika, he used the same trick this year at the competition). That makes the model quite well grounded, even on steeper slopes.

1 hour ago, Appie said:

Very nice truck. Works great and yay green 

Glad you like the color choice, this basic color is so rare nowadays..

1 hour ago, Appie said:

Slightly puzzled by the placement of the fake engine (under the hood would be normal for this truck no?) but I understand it might make the drivetrain for steering and drive more complex by having the steering motor and the fake engine swap places.

It's exactly as you say, it would have been more realistic swapped, but then there's no way to route them around each other (at least not without introducing a lot of steering lag due to a bunch of gears). Plus then I could not have added a 3rd drive motor.

[Zerobricks]

Well done, great idea with having the steering links stabilize the hubs, so you can skip the lower control arms. I did something like that but with normal hubs and yes, it requires a very strong steering rack to minimize the slack and to resist the torque. Nice idea using the small fake engine cams with half pins too!

Edited December 8, 2025 by Zerobricks

[TLCB]

Featured at

The Lego Car Blog

[2GodBDGlory]

Nicely thought out as usual! That is an interesting trick for the front axle

[vascolp]

That's a very nice truck with lots of nice tricks!

What software did you use to drive it?

If you have a Lego Remote handset, it looks like perfect to be controlled by RemoteBlaBla.

[gyenesvi]

6 hours ago, Zerobricks said:

Well done, great idea with having the steering links stabilize the hubs, so you can skip the lower control arms. I did something like that but with normal hubs and yes, it requires a very strong steering rack to minimize the slack and to resist the torque. Nice idea using the small fake engine cams with half pins too!

Thanks, glad to hear you also used this trick before, I haven't seen it yet!

The engine cams work nicely with half pins as well, I used the pins to reduce friction that would have resulted from using the proper piston pieces that come with this cam. Also, the 4-way connector is a must here, without it I could not have built this compact V6 engine (that's why it has inline-3 in the video, as at the time I did not have that connector).

Thank you @TLCB!

5 hours ago, 2GodBDGlory said:

Nicely thought out as usual! That is an interesting trick for the front axle

3 hours ago, vascolp said:

That's a very nice truck with lots of nice tricks!

Thanks!

3 hours ago, vascolp said:

What software did you use to drive it?

If you have a Lego Remote handset, it looks like perfect to be controlled by RemoteBlaBla.

I used PyBricks with an Xbox controller, was fairly easy to set it up. I am using the speed servo function for precise driving speed, and also proportional steering is important here, so the remote handset with non-proportional buttons would not be enough for it.

[vascolp]

6 hours ago, gyenesvi said:

I used PyBricks with an Xbox controller, was fairly easy to set it up. I am using the speed servo function for precise driving speed, and also proportional steering is important here, so the remote handset with non-proportional buttons would not be enough for it.

Yes that´s better. RemoteBlaBla for XBox has been always on my mind... but no time...

[mdemerchant]

Wow, great performance on the rocks.  I never would have expected that front axle concept to be strong enough in a million years but clearly it works great and is a clever trick.

[AutoBacon]

This looks amazing, love the colour choice. Would be great to see it in some custom RC tyres too!

[gyenesvi]

On 12/10/2025 at 3:41 AM, mdemerchant said:

Wow, great performance on the rocks.  I never would have expected that front axle concept to be strong enough in a million years but clearly it works great and is a clever trick.

Thanks, indeed, I was also skeptical in the beginning, but it turned out to be great, sometimes it's worth experimenting with tricky stuff.

10 hours ago, AutoBacon said:

This looks amazing, love the colour choice. Would be great to see it in some custom RC tyres too!

Thank you, glad you like the color :) I'd also like to have some RC tire at 80-82 mm size, but I never really found any great ones that fit 43mm lego rims. Best I have is these Injora ones, but only 4 and does not look that great either.