Kamil

I had another goal in mind when I did the above, I have slightly modified the Ultra 4 Buggy (designed by Victor Gyenes) into the Ultra 6 Buggy - The rear axle of the Ultra 4 Buggy is replicated and modified - A tandem style super flexible rear bogie is built - Red touches are added - Openable rear covers are added - Designed for low gear ratio of the Ultra 4 Buggy. High gear is usable but not recommended (may break parts if used without caution) - Oiling may be necessary for better performance

Thanks a lot ! It is well built, and I like its minimalist style. I think absence of a differential lock here did not seem to matter with this vehicle. Even if one wheel spins, the other three wheels provide traction. It is more energetic, more active, and far more easier to drive than official Zetros truck. Yes, this vehicle stalls with these 107x tires at the start of a hill at high gear in my video. Your observation is most likely correct. Although my batteries are 6 x 1.5V Duracell pack, they were also used in my last MB Zetros beast mode trials video before. So, these batteries may already have lost some of their power. It might be better to replace batteries, and take it to a faster riding outdoors terrain like you did before. All the best

This is the Lego 42129 unofficial C model (by Victor Gyenes) modified by 107x44R tractor tires. The tires are mounted in the reverse direction to provide shovel effect on dry and loose sand:

Hi, I disassembled the Zetros, found some wear and dirt on the parts due to these trials (everything was brand new before trials). Oiling is needed to prevent this wearing issue, maybe graphite grease...

Another issue on this leaked pic is written by another user in another platform (not sure to mention these names here). There says no suspension clearence exists between the front tire and the mentioned liftarm. So, the front axle must be a fixed one. I think, even it is fixed, there should be a visible clearence between them to appear normal to the eye.

@gyenesvi For sure, it's great that you have created at least three different vehicles while staying within the 42129 parts limit

@jundis thank you for info. @jundis Yes, I learned this by chance. I was building Zetros from computer screen, and realised my MB emblem holder pieces were different from the pdf instructions. That was weird being the same set having two different instruction files.

"The first leaked pics in 2021 were in 6x6 configuration, looked way better imho ;-)" @jundis I am not sure the leaked Zetros is fake or real (it also has some similarities with the red Zetros 6x6, released four yrs before 42129, which is posted above). I feel like I saw two XL engines in the leaked one. Okay, did the Lego CEO's told the builder "remove one axle, shorten the bed, change the two XL motors to L motors, then decrease speed of the truck?" I havent witnessed such a torture, from design to production, before. Something like designing a G63 6x6, and Multipla is coming out of the production line

@gyenesvi Absolutely, I leave it to the viewers to decide. Summary: To be honest, I never liked this set before buying. I would prefer to buy Lego technic G 500 set instead. There are issues that do not fit the overall scale of the truck. - The wheels are smaller than original, - The cabin roof is higher and wider than original, - The nose (engine cover) is shorter and wider than original, - The shape of the truck's nose doesn't seem very realistic either. I found this set for half a prize, it had unopened packaging, and I needed some parts of it for my new project. I built and played with this to satisfy my curiosity. My findings are: - This truck is too heavy (around 3.3 kg) and battery consumption is high. I have used three sets of 6x AA battery packs during my trials, - Some of its accesories come lose easily (like side mirror plates, fire extinguisher nozzles, snorkel and exhaust pipe) so precautions must be taken before using it outdoors or on sand, - Instead of using an app. controlled motorised diff. lock, two manual diff. lock controls (controlled by sticks from interior cabin if possible), and one app. controlled high-gear selector would be a better option, - It would be better to release this set as an expedition truck, instead of a trial truck, together with a rear cabin on the rear bed. Then its off-road capabilities would be reasonable on this basis. Here 94.3x38R Lego tires with black rims would be a better choice for this purpose, - As the truck is too heavy and slow, momentum can not be used as a driving force to overcome obstacles while climbing. Only full power and traction combination is helpful here, - Creating a flexible chassis, and gain more articulation via this chassis (cabin and rear bed can articulate in opposite directions as seen in off-road tests of these vehicles) would be fun to watch on Lego based Mercedes Zetros and Unimog vehicles, - This set is a good part source for app. controlled MOC's, - If I were the official Lego builder, I would create this truck chassis as a set (Mercedes-Benz Zetros 3643-S 6x4 Tractor Head). While having 6x4 drivetrain, I would build a front steering system with higher turning angle to match original Mercedes specs. I would leave the buyer free for what to build on the rear bed. Zetros 6x4 - Playing with the original set was challenging, it was barely playable. I think modifying this vehicle to the beast mode in video 4 was more fun to play with. Plus, the beast mode is 4-4.5 on the playability scale above. What do you think? Thank you Kamil

@gyenesvi Okay, thank you, good to talk about this. Mine is an observation, not based on technical knowledge (or maybe not knowing like a mechanical engineer/mechanic etc.). In my video, diff. lock = on means engaged, on the phone control app. the button is at up position. “Off” means diff. lock is disengaged, and the button is at 0 position. Let me explain the operation step by step, while giving the exact moments in one of the video scenes of the last video. - At 18:33, I started the truck while diff. lock = on mode (I do so in all of my trials). - At 18:42, wheels start slipping, truck stops while at maximum throttle (truck is stuck). I release throttle. - At 18:48, I disengage the diff. lock (deep click is heard), bring it to off (zero position). - At 18:50, at full throttle, the front wheel starts turning faster, and the truck has moved few cm. - At 18:59, front wheel spins fast, and truck stops again. I engage diff. lock, deep click is heard. - At 19:00 the truck starts moving again. I would be grateful for a technical explanation for this. Coming to tires, okay, I see now. Thanks in advance

My last video on being the angel of Lego 42129 Zetros. The beast mode (Thanks to Viktor Gyenes for his suggestion for adding more articulation): Video includes: LEGO 42129 MB Zetros, with bigger wheels, outdoor trials: 1. The beast did not like sand trials 2. Outdoor climbing = Good performance 3. Outdoor tree root trials : Good performance 4. Outdoor rooftop ceramic tiles trials = Good performance (forward only) 5. Outdoor dirt trials = Acceptable performance 6. Outdoor dirt downhill trials = Good performance 6. Night driving, diff. lock on/off traction transfer trials = Good performance Cheers

@gyenesvi Thank you for introducing me your cute little kitty. I really missed it within my searches. I wish I could build it for learning more. For sure, I will try to PS: The original tires matches the overall scale this time.

gyenesvi thank you for the suggestion. For sure the red springs are too stiff for the rear axle of the vehicle. I have replaced them with softer grey springs. Now suspension became softer and gives more articulation. However, the real Unimogs and Zetroses also have a flexible chassis. The front cabin and the rear bed articulates in opposite directions while off-roading. This vehicle is far from this ability. The articulation I have added may seem insufficient to you (it wont be like the one used in the x-treme off-roader), but I think it is better compared to the original (see video Part 3 below). I have also added 107x44R tractor tires to the back axle. I recorded more videos for making the Lego Zetros, the ultimate beast (:-D) outdoor trials. On that video, I have discovered a hidden function of the diff. lock while trying to climb. The diff. lock transfers more power to rear axle or front axle. If the rear is stuck, it is possible to transfer traction to front axle. I have planned to merge these videos as Part 4, I need days to edit all. LEGO 42129 MB Zetros, with bigger wheels, foundry sand trials (Part 3): Is this set playable or not? Cheers

Yes, I have seen this video previously, thank you for posting it here. I am not sure this comparison is right, Zetros and other vehicles may be different classes. Zetros is a safety concerned commercial set (no buwizz motors etc.) for 12+ customers. It has more finished exterior shell than others, so it is heavier and slower than others too. I wish it had two manual diff. locks, and a high gear, but not available here. Maybe they always leave incomplete functions in a commercial set, so we have to go and buy new ones to complete it. I would compare Zetros with some of these more finished MOC's below: Sariel's pug proof MAZ-535 8x8 truck (having more finished exterior): The "Zetros Killer": Or, maybe this Unimog: Or a similar Zetros: To me, Lego Zetros is more a Unimog than a Zetros. It is more a rock crawler than a trial truck. Here, I want to stay on the "playability" scale. To avoid misunderstanding, I give my Lego off-road playability scale here: 12 points: 10 Points: 7 Points: The three trucks on Sariel's comparison video above 3 Points: Lego Zetros original 3.2 Points: Lego Zetros with bigger tires My new aim here is to upgrade Lego Zetros into rank 4 by adding few modifications to increase playability of the vehicle. Thank you

@jundis That is a good question. When I first seen this set, I immidiately thought something is wrong with it. I realized that the wheels are out of scale. The proof is here: In addition to looking closer to scale, these bigger tires are handsome, increase speed of the truck, give better ground clearence, and their specs differ on different terrain types. For example, you are right for loose sand conditions. However, it does not matter on wetted stable sand. I have videos on preparation (part 2, part 3 etc.) so the answers may remain in them. I will try to add them here in my new posts. Thanks in advance. This is my second video on Lego Zetros foundry sand trials. Performances of three different Lego wheels were compared in it. Dry and wetted stable sand surfaces were obtained.