[MOC] RC Jeep Wrangler - 42129 alternate

[gyenesvi]

Hey Guys,

I'm back with my second alternate model of the Zetros set (42129). As you might remember from the presentation of my Unimog alternate, I was originally entertaining the thought of rebuilding the Zetros into a Jeep, but I passed since Tim has already built one. However, as I kept thinking of how I would do it, it became clear that I had quite different ideas in mind, and it was just too tempting to do it, so I gave it a go. Here I will write down the design process as that seemed to be something interesting for you guys in case of the Unimog as well, and I also prefer such presentations.

Features

- 3-link floating axle suspension with Panhard rod at the front
- simplified rear floating axle suspension with 2 links of limited degrees of freedom and a Panhard rod
- 2-speed gearbox with coupled RWD/AWD selector (hi gear is RWD, lo gear is AWD)
- smooth and highly colour consistent bodywork
- openable doors, bonnet and trunk
- detachable hardtop
- detailed interior with green accents, built seats
- detailed engine, snorkel, minor extras (roof rack, jerry can, fire extinguishers)

Here's a real 2-door model in dark grey color which I used as a visual reference:

 

I also used a blue print to roughly set the proportions in a 1:10 scale.

Bodywork

Interestingly, this model started out from the bodywork, which I don't do often. As a fan of Jeeps, I have long been wondering what the best ways are for replicating its characteristic details, such as the hood and the grill with Lego parts. My Willys Jeep (alternate of the Defender) uses system parts for the (flat) hood and a simple vertical grill, but I wanted to build one with technic panels as well, replicating the slanted surfaces. I have seen two major techniques, one with the long wing-shaped panels (such as the models of @Madoca 1977 and @rm8), and the other with the long curved panel, mainly the classic model of @Sheepo. Since this set has those curved panels in DBG, and the wheels are about the same size as on Sheepo's model, I was wondering if a similar front could be built from the set, especially the angled placement of the curved part, along with the downward slanting of the whole hood, which also needed to be openable. It turned out that with quite a few alterations here and there, the hood could be built, and even better, they could be built using a few large panels only, which makes it look more clean and uniform.. Some arches needed to be redesigned, and the whole became 2 studs narrower, but the proportions worked fine. Then I moved on to the front and the grill, where much more redesign was needed due to different parts available, but after a few iterations with increasing the width and height of the vertical 'bars', I found the one that fit nicely with the smaller lights in the set and the newer curved small panel extenders (and as far as I can tell, newer Jeeps has such bigger grill, so it seemed fine).

From there, I moved on to the sides. I knew it was critical to use the BDG panels carefully, because otherwise there would not be enough DBG beams to build the whole body, and I wanted a clean and colour consistent body. I quickly concluded that the doors can easily be built with the large panels, and the windows can also be built with the DBG connectors. The next critical point was to use the thinner long DBG panels in the rear part above the fenders. The difficulty was that they only left one possibility to mount the pieces of the fenders, so I had to use all those black angled beams there, and I had to build the fenders a bit wider so that I can actually connect the two ends to make it a stable piece. Fortunately, the wider fenders also made it possible to build the front ones from black beams at the same angle, even without more available angled beams using triangulation. The last critical piece was to use the small BDG panels in front of the doors, which just fit there tight. If I had to build that section from beams (as I started out), it would have cost too many beams and connecting them to the chassis would have been difficult as well, but the panel solved both problems (unfortunately, it has a drawback as well, which I will cover later).

The remaining DBG panels were used in the back, also allowing for an opening trunk. The last tricky part was the rear corners with the lights. I wanted to make them more rounded with the curved panel extenders, but they would have screwed up the proportions, so I just used a slightly curved system brick to give it some curvature. Also I managed to use the black arched beams to replicate the characteristic rear roll bars, and the black tubular parts to build the roll cage, along with the 15L flip-flop beams, which proved to be critical for mounting the roof. The many flat black panels of the set were enough to build the whole roof, along with the side windows in a way that the whole hardtop is detachable from the roll cage as a single piece.

Later, when it was more clear what parts remain, I also added the two bumpers, and even a nice snorkel and minimalistic roof racks were doable to give it more interesting details.

Gearbox

After being satisfied with the rough bodywork, I started designing the functional parts, which I also wanted to put emphasis on, since that's what technic is all about. However, since my Unimog alternate was about the suspension, this time I wanted to focus more on the RC gearbox and build a less articulated suspension which takes less space. I have been tinkering with the idea of a coupled 2-speed gearbox and a central diff-lock for a while (and @Pattspatt also teased me about it), but I never managed to design a compact one, where the drive motors are also placed conveniently. When I looked up a Jeep Wrangler drivetrain, I found this image, which was particularly interesting for me because of the front wheel drive that can be decoupled. Being offset to the side, I thought this could actually be nicely reproduced with lego clutch gears (something similar I already did with my Willys Jeep alternate, not knowing that it's done similarly in real life).

After a lot of juggling with the placement of the motors and the gearbox components, I came up with this quite compact drivetrain setup with the gearbox inside the 11x7 frames, which not only includes the drive motors, but the steering motor too (later on that as well). The key ideas regarding the overall chassis structure are the following. First, I use a simplified (limited degrees of freedom) rear suspension, which requires only one CV joint, which makes the rear part of the drivetrain shorter, making more space for the gearbox, which is placed a bit to the back. Second, I placed the motors to the front of the middle section, and use the back of the motors as the mounting point for the front lower suspension links. Thus, the motors play a major structural role in the chassis. Here is the central part:

And here is the whole drivetrain without the motors and the frames:

As you can see, the rear part is short, and the front is offset to the side, and can just be routed between the drive motors, under the steering motor. Another interesting thing about it, is that it actually has two shafts (yellow axles at the front) coming from the two drive motors (but they are coupled by the red gear in the middle), and one of the shafts powers the 2-speed gearbox, that then goes to the rear axle, and the other shaft powers the the front axle, so the front axle drive does not pass through the gearbox, as it's only active in low gear. The orange selector switches both the gearbox and the RWD/AWD switch at the same time, activating the front of the drive train when low gear is selected.

As with my Unimog, the placement of the gearbox motor was again difficult, as a lot of additional elements (end stoppers, clutch gear protection, down-gearing) need to be placed, so the gearbox motor had to be routed out to the trunk.

Suspension

As I outlined above, the rear suspension is a somewhat simplified live axle. I saw this trick first in @nico71's Ford F150 alternate, but builds of @rm8 use it as well. It is like a ball-joint based suspension, but without the ball-joint as support that prevents the axle from rotating forward/backward. In case of non-motorized models or smaller RC ones with less powerful motors, the joint itself is enough to keep the axle from rotating, but it was not enough in this case (the coupled motors could just rip apart the driveshaft), so I had to fix it explicitly. I opted for a suspension link that does not let the axle rotate forward on the far end, only tilt sideways (not using towball pins, just regular axles). This setup provides strong enough support to prevent the torque from ripping the driveshaft apart. A Panhard rod further stabilizes the axle to prevent sideways movement. Unfortunately, it's still not as solid as a ball-joint would be, and does not relieve all friction from the driveshaft.

On the front, I used a similar 3-link suspension as the Unimog, but I had to move the Panhard rod behind the axle as the space was even less in the front, and managed to move the springs further in, giving it a softer and longer travel. It actually came out too articulated and had to be limited, as the wheels hit the fenders. Also, I used a better steering geometry than the Unimog (no anti-Ackermann geometry), and the max steering angle became very good, too good actually, as the wheels hit the bodywork at max angle, and can get stuck in it, so I limited the angle a bit, but is still better than the Zetros (the limiters are just half pins, which can be taken out to get a lot of steering angle, at the cost of risking the front wheel getting stuck in the body at max angle and max articulation, but work pretty good on flat surface).

So the suspension is not bad actually, limited a bit by the bodywork, but the model still drives around quite okay on real terrain.

Also, I wanted to experiment with a different steering setup, not placing the steering motor onto the axle. As said above, I found it a nice place between the drive motors, and using the CV joints there was just enough space to route it to the axle. It works okay, however, the two joints already introduce some lag in the steering, which is most noticeable when trying to automatically return to center, it does not center totally. But it's still okay and can be controlled with fine adjustments.

Interior

As the seats in the Zetros set were too small for this scale I needed to build bigger ones. Since I did not want to use the green beams on the outside, I used them as accents on the inside, they were enough to build seats and to be used in the middle console. I entertained the idea of making the steering wheel functional, since the steering motor is not on the axle, but there was not enough space to route it to the steering wheel, and furthermore, the curved panels used as a dashboard just block the way, and otherwise they are important structural elements that hold the front and the sides, so I did not want to alter them.

The battery is placed between the B columns, as there was no other convenient place, and there it's easily accessible. The seats can be folded forward, to give room for replacing the batteries.

The engine details are just some imaginary ones built from the remaining parts (nothing working). But the snorkel tubing continues on the inside :)

Here is the whole chassis with the interior:

And here are a few more renders and photos of the complete model, but much more is available on Bricksafe.

Building instructions are available on Rebrickable.

Let me know how you like it!

Cheers,

Viktor

 

Edited November 26, 2021 by gyenesvi

[iLego]

Did not yet get a chance to look at the video, but just had to comment. Fantastic MOC !! It looks awesome and has very nice functionality.

And your detailed thoughts on the design process are most appreciated !

[Void_S]

7 hours ago, gyenesvi said:

Another interesting thing about it, is that it actually has two shafts (yellow axles at the front) coming from the two drive motors (but they are coupled by the red gear in the middle)

So, it means that with some minor parts replacement it could be turned in a kind of 9398/41999/42099 "Lego-AWD" scheme with per-axle motors.
I have no intention to do it at all but just wanted to notice this interesting fact. 

[Didumos69]

Very nice B model! I like your style. You really put in the extra mile in getting the best out of an existing set, where others seem to rush things to a finish.

[Jurss]

Really good!

[agrof]

I have to say, top quality B-model! 

Edited November 26, 2021 by agrof

[ninoguba]

You are really good at designing alternate models!

[Celeri]

C-models are definitely better than the A-model for this set!

Congrats @gyenesvi !

[gyenesvi]

18 hours ago, iLego said:

Did not yet get a chance to look at the video, but just had to comment. Fantastic MOC !! It looks awesome and has very nice functionality.

And your detailed thoughts on the design process are most appreciated !

Thanks, glad that the design process was useful!

12 hours ago, Void_S said:

So, it means that with some minor parts replacement it could be turned in a kind of 9398/41999/42099 "Lego-AWD" scheme with per-axle motors.
I have no intention to do it at all but just wanted to notice this interesting fact. 

Actually, if you take out the red gear from the middle that connects the two sides, in low gear, you immediately get that Lego-AWD scheme! If you replicate the 2-speed gearbox to the left side as well (just need to insert two more gears), then you'd even have it working in both hi and lo gear (obviously by losing the RWD/AWD switch). So in essence you'd only need one blue 20T clutch gear as extra part :)

9 hours ago, Didumos69 said:

Very nice B model! I like your style. You really put in the extra mile in getting the best out of an existing set, where others seem to rush things to a finish.

Thanks a lot, I really appreciate that. Indeed, I like to get the max out of the concept I have in mind for a certain build. Luckily, with an alternate build the resources are limited, so it does not take ages to finish a model :)

8 hours ago, Jurss said:

Really good!

5 hours ago, ninoguba said:

You are really good at designing alternate models!

Thank you all guys!

3 hours ago, Celeri said:

C-models are definitely better than the A-model for this set!

I am happy that there are so many nice alternates in this short amount of time already, it definitely helps make the set more popular!

[Daniel-99]

Great MOC and it drives well! ;-)

Also you have a cool and well-written story behind the build. I would warn readers that this story takes 3 cups of coffee to read through! But it is too interesting to skip!

The amount of care for the drive-train is astonishing! Probably im too stupid im building live axles but i did not understand if the rear axle has an articulation (it seems that both rear wheels could only move up and down simultaneously). Do you use an admissible wobbling of lego parts? 

Also i really like how you mentioned some other authors in your story... It is very good to see the story of wide-world development of RC lego technic models. 

P.S. It would be great to see your car on custom tires (85 / 90 mm)!

 

[SaperPL]

Great model, actually something that I would really see as a B-model for this set from Lego. There's barely anything to pick on with this model, the only weird thing is battery/hub placement, butt with hard-top on it's well disguised and again, since this is better for the ergonomics, I guess Lego would do things like this too.

The chassis is beautiful and I like the separate body with this modular approach. Great job!

[Daniel-99]

2 hours ago, SaperPL said:

Great model, actually something that I would really see as a B-model for this set from Lego. There's barely anything to pick on with this model, the only weird thing is battery/hub placement, butt with hard-top on it's well disguised and again, since this is better for the ergonomics, I guess Lego would do things like this too.

The chassis is beautiful and I like the separate body with this modular approach. Great job!

Yea, some B-models would be nice to have... But you know, that Lego B-models will not be as good as custom projects, just because Lego do not have thousands of Designers working on the same build ;-) As far as i can see, the market of Lego B-models going well nowadays, and it is very nice to see how people made projects with such a limited build-pallet, and this custom projects appears to be better than the original one!

 

[gyenesvi]

3 hours ago, Daniel-99 said:

Great MOC and it drives well! ;-)

Also you have a cool and well-written story behind the build. I would warn readers that this story takes 3 cups of coffee to read through! But it is too interesting to skip!

Thanks, glad you enjoyed it!

Quote

The amount of care for the drive-train is astonishing! Probably im too stupid im building live axles but i did not understand if the rear axle has an articulation (it seems that both rear wheels could only move up and down simultaneously). Do you use an admissible wobbling of lego parts?

Yes, the rear axle does have articulation, the two sides can move independently, it's not just a trailing arm, and not just the admissible wobbling of lego parts (but that helps too). The reason why it can articulate, is that because the links (olive green ones on the image) are mounted to the rear axle with a 5L brown axle with an end stop, on which the links themselves can rotate sideways (it's a bit hard to see on the image as it's dark, maybe I'll try to do a better render).

2 hours ago, SaperPL said:

Great model, actually something that I would really see as a B-model for this set from Lego. There's barely anything to pick on with this model, the only weird thing is battery/hub placement, butt with hard-top on it's well disguised and again, since this is better for the ergonomics, I guess Lego would do things like this too.

Thanks a lot! About the battery: originally I wanted it exactly as you say, but there were quite a few problems. The main one is that I had to place the gearbox motor into the trunk, as there was no place elsewhere and it also had to be routed into the gearbox. It's a pretty problematic issue in this set, because with this M motor for the gearbox, you have to insert first a 3x down-gearing, then a clutch for protection, and then and end stopper before you get to the orange shifter (if you want it to be safe and controllable with the stock app). Second, the rear suspension springs also take up space in the trunk, so the battery would have to be lifted too high. And there's another minor problem, that in the app, the battery's rotation sensor is configured in a standing position, so if you put it flat it will keep screaming that the model is tilted too much. So I gave it a try in the beginning but did not pursue this too much, just put it in a standing position, this way at least it also constitutes to the stability of the roof bar structure.

2 hours ago, SaperPL said:

The chassis is beautiful and I like the separate body with this modular approach. Great job!

It might have been misunderstand-able because of the render showcasing the bodywork, but unfortunately it's not the whole body that can be detached as one piece (I think that would require more connector parts to be able to build separately as a solid unit), just the hardtop (roof and rear windows). True that the bodywork is built in large modules (like the sides, fenders, tailgate, hood) but it's not like some of it can be easily detached and replaced (for example taking the doors off is not easy, but at least they are solid).

[gyenesvi]

20 hours ago, Daniel-99 said:

if the rear axle has an articulation

Here's a better render of the rear axle mounting, to show where it can pivot to tilt sideways. The other end of the olive green beam is attached to the chassis with a frictionless pin, so it also allows a bit of wobbling to help the free articulation.

[Daniel-99]

45 minutes ago, gyenesvi said:

Here's a better render of the rear axle mounting, to show where it can pivot to tilt sideways. The other end of the olive green beam is attached to the chassis with a frictionless pin, so it also allows a bit of wobbling to help the free articulation.

Wow! That is genius! I was not expecting to see such a solution! Great!

[thekoRngear]

I build the 42110 Willy's Jeep I becomes the fan of Gyenesvi. His works specially finishes and suspension system are pure class. Will seriously give a thought abt buying the 42129.

Edited November 29, 2021 by thekoRngear

[gyenesvi]

9 hours ago, thekoRngear said:

I build the 42110 defender I becomes the fan of Gyenesvi. His works specially finishes and suspension system are pure class. Will seriously give a thought abt buying the 42129.

Thanks, glad you like my builds! Indeed, I like to build suspensions.

[Zerobricks]

Impressive, really well done. Looks as good as an official set.

[gyenesvi]

4 hours ago, Zerobricks said:

Impressive, really well done. Looks as good as an official set.

Thanks :)

[alpinesman]

 

This will be my next MOC. He looks superb.

[gyenesvi]

Thanks, it will look nice alongside the Bruiser build :) And I think there's plenty of potential for adding extras if you have more parts available.

[alpinesman]

30 minutes ago, gyenesvi said:

Merci, ça ira bien avec la version Bruiser :) Et je pense qu'il y a beaucoup de potentiel pour ajouter des extras si vous avez plus de pièces disponibles.

 

Yes I have a lot in stock