The Bug 6x6, Rough Sand Trials

[Kamil]

All the best

[Bartybum]

Very nice! I love how the rear axle pair is sprung from the middle, it's mesmerizing watching it flex as it goes over hills

[Kamil]

On 11/27/2025 at 3:59 AM, Bartybum said:

Very nice! I love how the rear axle pair is sprung from the middle, it's mesmerizing watching it flex as it goes over hills

@Bartybum Thank you ! 

While building the rear bogie, I tried to maximize articulation at the rear axle. So I preserved the two red springs of the mid-axle (coming from the original design), then I added two softer and longer springs to the rear axle. This is good for articulation, brings visual as you mentioned, but I think these softer rear springs are also the main reason for some of the mid-axle stalls, as the rear axle can not put the necessary pressure on the terrain. I could use four red springs, or I could use four softer suspensions at the bogie. The first choice would limit articulation and not sure what would happen if I use four soft springs.     

Edited November 29, 2025 by Kamil

[Zerobricks]

Seems to work good, but I would recommend redesigning the rear axle so they are always parallel to the frame when travelling. This way the load between the rear axles is evenly distributed. In your current setup, the torque transfers all the load to your rear - most axle and the second axle doesn't do much.

[Bartybum]

1 hour ago, Zerobricks said:

redesigning the rear axle so they are always parallel to the frame when travelling.

But then it doesn't look as cool :3

[Kamil]

On 11/27/2025 at 12:55 PM, Zerobricks said:

Seems to work good, but I would recommend redesigning the rear axle so they are always parallel to the frame when travelling. This way the load between the rear axles is evenly distributed. In your current setup, the torque transfers all the load to your rear - most axle and the second axle doesn't do much.

 

On 11/27/2025 at 2:12 PM, Bartybum said:

But then it doesn't look as cool :3

Okay, @zerobricks , @Bartybum thanks both. I havent given the suspension details, and it is hard to see from previous video. Actually, the bogie is constructed by using double control arms on each side (the two light grey 16L technic links are visible from outside, the other two are hidden inside). These provide parallel movement of the two axles. If not, the CV axles come loose. However there is also some play here as I wanted flexibility. I have used most loose parts in building. When the rear axle is forced to the extremes, then another movement starts to happen. 

I have seen many videos about 6x6's, and there the mid axle loses contact with the ground while the vehicle is going through a flat surface to a steep incline transition. In this vehicle this was prevented to some degree. How? Well it comes from the mid-axle tilting from the original design. Hard to tell, so maybe an update video is better:

    

Edited November 29, 2025 by Kamil

[gyenesvi]

Nice to see that machine evolve :) That's an interesting suspension setup at the rear, I mean a bogie setup in a 6x6 can get somewhat complex, and that seems like kind of a simplification in some ways.

[Kamil]

15 hours ago, gyenesvi said:

Nice to see that machine evolve :) That's an interesting suspension setup at the rear, I mean a bogie setup in a 6x6 can get somewhat complex, and that seems like kind of a simplification in some ways.

@gyenesvi Thanks :)  I initially used two black 1x9 links (32293) instead of the inner dark grey beams between two axles in my first prototype. Those were looking far better, but I think there would be too much stress on these parts. Yes, the last version is built as simple as possible, to the minimum requirements for maintaining integrity during trials. It was also tried to be consistent with the overall structure of the original model you have created (less weight addition, don't make it look like it was added later etc.). 

I also thought about making the rear axle with independent suspension, but since the upper body, to which the suspension would be attached, was very thin, it would need to be reinforced. Plus the angle of the bottom control arms would be too steep etc.

My conclusion:

To be honest, this vehicle delivered more than I expected. I am also planning to tune the mid-axle suspensions to softer grade for giving better bouncing height to the stalled wheels. Of course this is not initially my MOC, it is grown from an existing platform. If I were to build a 6x6 from the beginning, I would follow more a bug's leg principles (like your front suspension design in Ultra 4 Buggy). 

All the best  

 

Edited November 29, 2025 by Kamil

[Kamil]

@bartybum 

@zerobricks

 

Update: This 6X6 vehicle behaves different on sand and solid surfaces. 

Video below shows the effect of replacing red springs of the mid-axle with the grey springs, overcoming solid obstacles, overcoming obstacles on sand (comparison), climbing a 39 degrees ramp, and the two speed of the vehicle on solid surface. 

All the best

Edited November 30, 2025 by Kamil

[Bartybum]

How come those links at the rear are bending so much in the video?

[Kamil]

On 12/1/2025 at 3:29 AM, Bartybum said:

How come those links at the rear are bending so much in the video?

@bartybum Hi, thanks !

If I get it right, you are asking this issue below (Pls note, my file size quota for this topic is limited):

Yes, that is also a part of the mentioned plays in the bogie. This happens when the vehicle is forced to extremes. Power comes, and the rear axle tends to rotate backwards. The  black beam inside the red circle is the only resistance to this rotation. While the axle is rotating, the black beam hits the 16 stud grey link. If the force is high enough, then black beam bends the grey link upwards. This action is limiting the axle from fully rotating. Another reason for bending is; the upper grey links and the lower control arms are too close to each other. I thought to mount the lower control arms into a lower position under the bogie. But, there stands the cv axle, and I had to mount it on a very low position. Then I would lose a lot of ground clearance.    

Negatives:

The rear axle loses some parallelism with the ground when the vehicle is forced to extremes.

The CV joint connected to the rear axle comes near to its working limits.

Positives:

Very flexible bogie.

High sideways tilting.

The 16 stud grey links act as torsion bars for sideways tiltings of each axle.

The 16 stud grey links and the below control arms allow seesaw movement of the bogie.

The rear axle trying to rotate backwards means, the axle is doing its job, and playing its role for moving the vehicle on a steep ramp. 

High ground clearence

Lightweight equipment

All the best

Edited December 4, 2025 by Kamil

[Kamil]

Hi, 

A few changes have been made to the rear bogie of the 6x6 Bug. The lower control arms are lowered two studs below. The upper 16 stud links are doubled on each side. This gives less flexibility of the bogie but better sand performance. 

Negatives:

- Less flexibility so watching the bogie on action may be less entertaining than the old one. 

- Suspension travel of the mid axle is limited more, so it can not come down as much.

- 39 degrees ramp climbing has not worked with this redesign (not included in the video below).

- The bending issue discussed above still happens (not included in the video below). 

Positives:

- Better sand climbing performance.

- Better overcoming of solid obstacles. 

- Less mid axle stalls. 

- Better progress on rough terrain. 

Well, as this vehicle is powered by two Lego L motors, it may be a little unfair to add new weight to this bug by adding a more complex drivetrain. I think it gives optimal performance here:

All the best

Edited December 8, 2025 by Kamil

[vliet]

Hi Kamil,

Will there come instructions for this fantastic 6x6? I hope so 😉, I can't wait to build this great vehicle.

Greets,

Sander

[LEGO Train 12 Volts]

Beautiful model and impressive work areas!

[gyenesvi]

1 hour ago, vliet said:

Will there come instructions for this fantastic 6x6? I hope so 😉, I can't wait to build this great vehicle.

Well, if I understand correctly, it is based on this model of mine, by adding a 3rd axle and a longer tail, and using larger wheels, so with the help of some extra pictures of the 3rd axle, you should be able to build it already:

https://rebrickable.com/mocs/MOC-98177/gyenesvi/42129-c-model-ultra-4-buggy/#details

[Kamil]

3 hours ago, vliet said:

Hi Kamil,

Will there come instructions for this fantastic 6x6? I hope so 😉, I can't wait to build this great vehicle.

Greets,

Sander

Hi @vliet, thanks ! Exacly what @gyenesvi has said. I tried this rework of his Ultra 4 Buggy 4x4 without using any extra digital material. I may post all the unclear details about these modifications here. The details of the bogie, and the tail are easy. 

- You will need Lego 42129 MB Zetros parts mostly. 

- First build Ultra 4 Buggy (from the link provided by @gyenesvi)

- Replicate the rear axle of Ultra 4 Buggy as it is in the instructions (build a copy of the original rear axle).

- Connect two rear axles by using the four control arms. 

- Add tail with rear flexible suspension (actually it is lengthening of the original tail).

- Add six tractor tires.

- Add exhaust, and some touches if you like. 

Ready !

 

 

Edited December 7, 2025 by Kamil

[Kamil]

3 hours ago, LEGO Train 12 Volts said:

Beautiful model and impressive work areas!

Thank you, @gyenesvi's original 4x4 model plus some 6x6 modifications. 

[vliet]

Thank you both, Kamil and Gyenesvi, I have the 42129 and (more than) 6 tractor tyres. When I am correct you use the large motors for driving or did you upgrade them to XL motors? I will to build this soon, I will keep you both updated.

Greets, Sander

 

[Kamil]

38 minutes ago, vliet said:

Thank you both, Kamil and Gyenesvi, I have the 42129 and (more than) 6 tractor tyres. When I am correct you use the large motors for driving or did you upgrade them to XL motors? I will to build this soon, I will keep you both updated.

Greets, Sander

 

@vliet Hi Sander, power is coming from the two L motors from the Lego Zetros set. I think it would be better if you could insert XL's. But the original Ultra 4 Buggy is compact, and may need major changes on the initial design (not tried that).  

All the best

Edited December 7, 2025 by Kamil

[vliet]

Hi Kamil and Gyenesvi,

It needs some modifications but I managed to fit 2 XL motors, I also managed to keep the gear ratio the same. Off course there where some minor problems, but that is common when changing a well done design. I also want to change the colour, DBG is a little boring for such a nice vehicle.

Greets, Sander

 

[gyenesvi]

2 hours ago, vliet said:

It needs some modifications but I managed to fit 2 XL motors, I also managed to keep the gear ratio the same. Off course there where some minor problems, but that is common when changing a well done design. I also want to change the colour, DBG is a little boring for such a nice vehicle.

Glad you managed to modify it, enjoy fiddling with it!

[vliet]

I am trying to connect the 2 rear axles, there where some clear pictures here but they are replaced by the videos. The videos are nice but not very helpfull when building. Maybe Kamil can send me a PM with the photos or a link where I can find them.

 

[Kamil]

I have limited time at the moment, so I will try to post others later:

 

 

Hope it helps for now,

All the best

Edited December 9, 2025 by Kamil

[vliet]

Kamil, you can erase my PM, on my phone are the pictures a lot better than on my computer.

[Kamil]

4 minutes ago, vliet said:

Kamil, you can erase my PM, on my phone are the pictures a lot better than on my computer.

ævliet No problem, my busy days, maybe tomorrow I can upload all in their original resolutions :)