[WILD MOC] LEGO Half Abnormal 4x4 Paleolithic Extender

[Kamil]

LEGO Half Abnormal 4x4 Paleolithic Extender V1.0

*** (See the specifications of the vehicle below - it is at 10th post) ***

 

After my previous trials with 4x4 and 6x6 Legos, I was planning to build this:

Sbarro Windhawk

https://www.6-wheel-drive.org/vehicles/sbarro.html

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Later, I discovered this creature by chance:

Hydraulic extending Rock Buggy

https://www.youtube.com/watch?v=dbPYj7Zd_vk&t=22s

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Then this one popped out:

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So I decided to combine last two to solve the problem of Lego vehicles sinking into the sand:

All the best

 

Edited 2 hours ago by Kamil

[2GodBDGlory]

That's a pretty wild concept! I'd love to see some more of the technical details. What kind of mechanism are you using for the extension?

Also, how does the suspension with those dampened shock absorbers work? I've thought about using them a few times, but the dampening seems like it would be too annoying on extension

[Kamil]

On 3/25/2026 at 6:47 PM, 2GodBDGlory said:

That's a pretty wild concept! I'd love to see some more of the technical details. What kind of mechanism are you using for the extension?

Also, how does the suspension with those dampened shock absorbers work? I've thought about using them a few times, but the dampening seems like it would be too annoying on extension

Thank you ! 

I am planning to share technical data whenever ready, some photography is still undergoing. This vehicle is constructed in modular style, and all four blocks, including the cabin,  can be separated under one minute. Then I hope to show the extension mechanism separately. As a clue, all crane like extensions have not worked here because they could not provide sufficient attachment points. In my design 3+3=6 links are available on each side (front and rear).   

I can talk about suspension. Sadly the one in the video is my C plan. My A plan was 2 springs + 1 air cylinder (damper) combination. That was working perfectly well. It was bouncing like a real Traxxas RC Baja. Soft compression and slowly recovering decompression was available. When I added second battery box and the cabin, the vehicle lost ground clearence.  I added two more springs, have not worked either. So I preferred two air cylinders as a C plan. These have enough travel while carry more load compared to the spring.  

PS. Sadly not all the air cylinders have same character in my collection, so I can't give a standard answer. I have selected the softest ones. The vehicle still has extreme articulation. Extending mechanism also allows a lot of torsional twisting.  Finally, the pivot points, and angles of these suspensions play a great role, the ones on the suspension arms are closer to the mid body, this softens. 

Best wishes

Edited March 28 by Kamil

[Kamil]

Hi, 

Testing is ongoing to see what this vehicle can do.

Here:

Down driving from 155, 235 and 387 mm high steps is introduced. Some horrific roll forward accidents also included in the video:

All the best

[Jundis]

This is really an insane concept. Never thought  this would work actually :D

[Kamil]

12 hours ago, Jundis said:

This is really an insane concept. Never thought  this would work actually :D

Thank you !

I honestly couldn't have imagined it would be this much. Because the vehicle I was inspired mostly (hydraulic extending rock buggy above) is designed to be effective on high rock walls. However, showing where else this vehicle's extension ability could be effective requires a bit of research. 

Due to the rain in my area, I haven't been able to experiment outdoors, and on rocky terrain yet. I'm curious to see how it will perform there. 

Edited March 29 by Kamil

[Kamil]

Outdoor trials of the Half Abnormal is ready. Extending ability also working on fine gravel and wet stones.:

 

[gyenesvi]

That's a weirdly interesting concept :)

[Kamil]

11 hours ago, gyenesvi said:

That's a weirdly interesting concept :)

Almost, near, a family sedan :)

Specs. are under preparation, and planned to be shared whenever possible. 

All the best

[Kamil]

Half Abnormal 4x4 Paleolithic Extender V 1.0

(@techbricks5300 called this as a “stretchy buggy”)

 

 

 

 

This is an experimental vehicle capable of extending and retracting its arch like chassis in two directions. Thus it has a variable wheelbase. Continuous extraction and retraction movements recovers the vehicle from some of the stuck positions, increasing the ability to navigate through rough and loose terrain for the given Lego tractor tires. The main goal here is to create a playful RC vehicle. Trying to navigate through complex terrain by using this multi-functional vehicle sometimes requires a lot of thinking and calculating. This makes it a fun tool for having a playful time. This vehicle is tried to be constructed with minimal weight to ensure that the vehicle is capable of climbing steep hills.

I am not sure to call this vehicle as a “rock crawler” because I could not manage to find a suitable parcour to test it yet. Maybe a cross RC, or a rough terrain buggy for now…

Specifications:

4x4 drive (independent front and rear axles).

All locked differentials. These can also be converted into open differentials (It may require quite a bit of disassembly and reassembly). Locked ones are better for the purpose.

Long double wishbone suspension arms are used providing extreme articulation. The springs and damper shock absorbers are connected to the upper wishbones from the pivot points located near the center. Two long springs and two damper shock absorbers were connected to each suspension arm. This combination is minimal for balancing the weight of the vehicle. This suspension system provides slow shock absorbing and a delayed rebounce.

Ackerman geometry: This feature is available on both axles.

Positive caster: This vehicle has a positive caster angle at the front axle. The rear axle is nearly straight up.

Motors and control boxes:

There are five functional motors in this vehicle. 

Front drive: 1 XL Powered Up motor for front drive, vertically mounted. The motor drives a 20 tooth double bevel technic gear. This gear drives a 62821 techic gear differential (diff. is locked).   

Rear drive: 1 XL Powered Up motor for rear drive, vertically mounted. The motor drives a 20 tooth double bevel gear. This gear drives a 62821 techic gear differential (diff. is locked).

Front steering: 1 L Powered Up vertically mounted motor, driving 12 tooth double bevel technic gear. This gear drives a Lego technic gear rack. This motor also serves as a structural part of the chassis connection. Hoping, it never breaks 

Rear steering: 1 Power Functions vertically mounted servo motor, 12 tooth double bevel technic gear. This gear drives a Lego technic gear rack.

Chassis extending/retracting: The chassis is built in Venetian Bridge over Venetian Canal type . This design enables to increase ground clearance by 10 mm when extended. When the vehicle is stuck on a bump in the retracted mode, vehicle can overcome this bump by extending the chassis. Venetian arch style is also helpful in overcoming steep downhills. 1 Power Functions L motor drives the chassis. Then driving 3x 8 tooth technic gear to 3x 24 tooth clutch gears. The axle of the clutches splits for front and rear of the chassis. Then these axles drive 12 tooth bevels to 20 tooth bevels. Finally, these 20 tooth bevels drive 12 tooth double bevels and the technic gear racks. It is a series of gear reduction.

Powered Up battery box: This vehicle uses one box for front & rear drives plus front steering.

Power Functions battery box: This vehicle uses one PF battery box for rear servo steering and chassis extension/retraction.

IR receiver: This vehicle contains 1 Power functions IR receiver. A cap is added on it to protect from sunlight when played outdoors. Despite this it may sometimes be difficult to target the connection.

Remote control center: This remote control center is designed to accept two phone types. Lego 42099 type control is enabled via smartphones. The bottom section contains two PF remote controllers. Left side is used for fine steering (red gear) and extending/retracting (black gear). Right side is used for fast steering and centering (red gear knob) and fast extending/retracting (black stick). In practical, left steering and right extending controls are more practical to use.  

Cabin: A very lightweight roll bar frame was constructed to dissipate energy. It is disintegrated when roll over happens. 

Tires: Standard Lego 107x44R tractor tires.

Driver: A representative driving figure was inserted into the cabin.

Grille: An orange funny mouth with tongue out, sucking air type, eye-catching grille is used to indicate what this black vehicle is doing at the trial. This grille is also designed to dissipate energy in case of a rollover.

Modular structure: All four components of this vehicle including front and rear axle modules, central extending/retracting chassis and cabin are all separable within a very short time. This enables easy fixes if needed. See video below:

 

 

Weight: This vehicle weights 2.150 kg (My target weight limit while building was 2 kg. This limit is exceeded slightly due to some reinforcements, and by adding the driver figure)

Overall dimensions:

Length:   525 mm (Retracted), 640 mm (Extended)

Width: 296 mm

Height: 255 mm (Retracted), 265 mm (Extended)

Wheelbase: 400 mm (Retracted), 504 mm (Extended)

 

Retracted chassis (comparison with Lego 42099 X-treme Off-roader):

 

Extended chassis (comparison with Lego 42099 X-treme Off-roader):

Pros & cons:

This vehicle can overcome some stuck positions of previous Legos on loose sand and gravel by performing a wild cat movement (extend – dig – retract – dig) of the chassis. (see videos Part 1 and 3 above). The vehicle can jump down from high steps by extending itself (see video Part 2 above). Extreme articulation capability without using a turntable on the chassis is another feature (pls see the articulation video below).  Here, entire body of the vehicle is acting as a big torsion bar.

 

 

 

The place to mount the second battery box was hardly found. This also brings a lot of extra weight and presses the back axle down more. Thanks to the two XL motors capable of handling this extra weight.

If this Powered Up control had a low-speed cruise control mode, then one would focus on rear steering more, and control this vehicle faster.

I really like the rear Power Functions servo motor steering best. It can be turned gradually by using small indexes, it stays where it is left, and back to center whenever red button is pressed. I would use this for the front steering if it had a more powerful receiver. Despite the cap on the IR receiver, it is sometimes difficult to target the connection.

The remote control center contains two large toothed red gears from 1970's. This enables one finger control while controlling from upper screen. 

This vehicle must be handled from both axles. If handled from mid chassis, one reduction gear may come loose due to flexing of the extender. I wish Lego had free telescopic axles having a diameter of 1 stud. This would fix the problem. Or, it can be a custom build. This issue never happened while cruising. I am still looking forward for a better solution.  

The Ackerman geometry sometimes causes excessive strain on the rear wheels due to Lego tolerances, the inner tire steers excessively inward, although I limited it from that. But it doesn't hinder the vehicle's operation, and it corrects itself.

All gears and sleds are oiled by using silicone based treadmill oil. This is what I have learned from my previous topics in Eurobricks.

This vehicle is big in scale, and has a long wheelbase, so it must be carried in a suitcase.  

A Lego tripod is also included:

Best wishes

Edited April 15 by Kamil
Improving the text

[2GodBDGlory]

I like the use of those old red gears on the controller!

[Kamil]

4 hours ago, 2GodBDGlory said:

I like the use of those old red gears on the controller!

Thanks, yes, these could be used for bogie type steering in 1970's (like Fageol Cargoliner, it has bogie type steering). These gears are my favorite, so strong, so handsome, they even have a metal spring inside axle hub. Gear clicks to the axle and do not slide while working, so deeply thought analogue !   Mines come from the wheel hubs of set 392. 

[Shiva]

Impressive :)

[Kamil]

On 4/7/2026 at 7:51 PM, Shiva said:

Impressive :)

Thank you !

On 3/25/2026 at 6:47 PM, 2GodBDGlory said:

Also, how does the suspension with those dampened shock absorbers work? I've thought about using them a few times, but the dampening seems like it would be too annoying on extension

Let me show the suspension shortly on the vehicle. Here soft bounce and slow recovery is clearly seen. The suspensions correct themselves while moving. This character has some advantages and disadvantages. I would prefer to use one air damper on each wheel if it was possible:

Another short vid. comes for the defective air cylinder. The slow one is absolutely wrong for Half Abnormal but the fast one is acceptable:

In my opinion, if these air cylinders is to be used, then one of them on each wheel can be modified to work faster (see pic. below). Either open the bottom snap fit part by using fine watchmen screwdrivers and take out the diaphragm, in case it is possible, or drill 0.5-1 mm holes to the tube (top and bottom). These would minimise air resistance and the part would act as a spring not a damper. I have 10 total cylinders and 8 of them are used in Half Abnormal. As this part is rarely found, I will not prefer to modify mines at this time. Oiling the inside air cylinder can be another try.   

I would also love to test the shock absorbers came with Lego 8420, bike with rear suspension (48912c01), however, I have lost all my hope of finding four 8420 sets in my next three lives :)

This is the articulation video for this suspension setup:

All the best

Edited April 9 by Kamil

[2GodBDGlory]

Cool, thanks for the detail on that! I'd agree that the speed for the unmodified ones is definitely too slow, but modification does look pretty easy if one wanted to go that route!

[Kamil]

On 4/9/2026 at 10:54 PM, Kamil said:

48

On 4/10/2026 at 6:41 PM, 2GodBDGlory said:

Cool, thanks for the detail on that! I'd agree that the speed for the unmodified ones is definitely too slow, but modification does look pretty easy if one wanted to go that route!

Thanks :)

Half Abnormal Update 1:

The split axles of the extender chassis are redesigned to avoid one gear detaching from the axle, in case the vehicle is carried by holding from the chassis center. A classical driveshaft for a very flexible chassis created this design flaw. Luckily I found and ordered new Lego cv joints to fix this problem. 

The problem:

 

 My new lego cv joint having a telescopic axle housing on one side:

 

Redesign with the new cv joints:

 

Video of the redesigned extender:

 

This redesign resulted in shifting the extender motor two studs back, and Powered Up battery box to shift one stud forward. I had enough free space for both:

 All the best

Edited April 16 by Kamil

[Kamil]

Half Abnormal Update 2

During my trials last weekend, the extender broke again. The image below shows that the left side of the extender chassis is not working on the rusty scrap iron pieces. The newly installed CV joints are separating under strain:

 

So, extender is redesigned again. Here entire motor-Powered Up assembly is moved one stud below to ensure the driving axles are not under strain in any conditions. Now, the angles of the driving axles and CV joints have decreased. The driving axles are better seated in their positions. Plus, two more reinforcing beams are added to provide more stable extender housing on each side of the vehicle. Hoping these beams will prevent separation of the extender housing elements during rising from the middle section of the extender. Photo below shows the redesigned extender:

Best wishes 

Edited April 21 by Kamil

[Kamil]

Half Abnormal Update 3

To resolve my doubts about the suspension, an experiment was conducted. One of the dual dampers was removed and replaced with a standard spring. Since this combination didn't fully support the vehicle's weight, a red spring was also added, which provides the same suspension travel over a short operating range (see fig. below):

 

Now, let's watch the result in the video below and discuss it further:

As seen in the video, this suspension setup shows good rebound. However, from an articulation perspective, it behaves like wood. Incoming ground level differences are reflected onto the chassis and rear suspension. It seems the original rear suspension responds better to articulation. Therefore, I will stick to the original suspension in future tests.

All the best

 

Edited April 26 by Kamil

[Kamil]

Half Abnormal Building Trials

Half Abnormal was constructed during two and a half months, few hours every day.

Eleven different variations of the front and rear driving modules were constructed. These two modules are identical in base design, however there exist some differences due to the servo motor type used, affecting the connections to the chassis. So, when I was building one variant front driving module, the rear module was also built at the same time. All design changes affected both modules. In the final modules, major design flaws such as gear skipping was eliminated. Placing the motors of driving modules into correct places was another issue. Their places should be adjusted in order not to interfere with the movements of the extender.    

Five different versions of the extender mechanism was built. After conducting primary trials by using the vehicle, it was found that the last accepted version still had some flaws to be redesigned. These were explained above. 

Also some changes were considered for placing battery boxes into suitable locations. 

 

The pictures below shows some of the design variations on Half Abnormal:

1. Driving Module Early Designs

Vertical driving motor / horizontal steering motor combination. I hadn't realised at the beginning that the steering motor could be brought inside vertically when I built this version. Here, steering motor occupies the space needed for the Powered Up battery box of the final design, not a good idea.

 

The two battery boxes were initially placed at both sides of the extender. This brought too much pressure on the extender. Moreover, these battery boxes weren't aesthetically pleasing. So the Power Functions battery box was removed to be on the rear driving module in the final design. This process resulted in a weirder look but a more fluid design rising from front to back (see early posts in this topic). 

 

2. Extender Mechanism Module Early Designs

The actuators that I own, or I can buy, and the Technic gear racks were shorter extenders for my purpose. So the very first extender design was standing a little higher at first. 

 

When it became clear that the first extender could not handle the load, some reinforcements were added.

 

Then a wider extender, with double racks on front and rear sides, was tried.

 

This design is applied and reinforced.

 

Finally I gave up with all the extender designs, and decided to build a perfect one. The result came out as the internal rack boxy extender. This new extender was working almost perfectly but lacked the internal thickness required to ensure the drive module connections were robust enough. As a result, I returned to the initial design back, and modified it further for the purpose. Here is the internal rack extender:

 

3. Result

Finally, the version shown in earlier posts above, in the trial videos, showed up.

Best wishes

Edited April 26 by Kamil