[MOC] Rock Crawler Jesse Haines Moon Buggy with RC Electronics

[gyenesvi]

 

Hi Everyone!

This model is long overdue, it's been sitting on the self for a while, and I'm happy that I can finally present it to you! I've always liked proper rock crawler buggies for their extreme capabilities (both in real life and RC models), so I wanted to build one for a while. I believe some of the best ones are made by Jesse Haines, they are race proven, they look cool, so I decided to attempt to build one of those, with as good performance as possible, and this is the result. Let the video speak for itself!

 

Features

• Highly articulated 4-link live axles with fake portals
• RC electronics: Injora MB100 ESC, LiPo battery, RC transmitter/receiver
• Two buggy motors inside PF L motor housing for drive
• GeekServos for steering on both axles
• Low center of gravity, good weight distribution

 

Design process and details

For a real version to model, I quickly settled on the one raced by Jesse Haines for a while, and more recently by Dave Wong (although I just saw a few weeks ago on FB that the buggy is on sale now). Here's a good picture of it, and here is a very good video overview of it by Dave himself.

 

The main challenges of building it were the following:

• what electronics to use for proper precise control,
• how to build a the massive 4-link suspension and portal axles
• how to build a (small) light tubular looking body in a stable way

 

Axles and suspension

As usual, I started thinking from the axles, as those are the most critical part. Lego currently does not have good solution for portals (the existing ones have awful steering properties and also leave little room in the middle of the axle for mounting links and shock absorbers, so that was a definite no-go), but luckily @Attika's axle design comes to the rescue (mounting planetary hubs with slanted lower A-arms and driveshaft), as they raise the axle by one stud, contain a down-gearing by the portal hub, hence I call them fake portals.

Furthermore, I have previously used these axles in my Toyota Hilux Truggy with GeekServos mounted to the axles, and those seemed like the perfect option here (the real buggy's axles also have servos mounted directly on them): they provide a strong and precise solution, while still leaving some room for mounting the links. So I settled for RC electronics, along with the custom PF L motors that I have borrowed. However, the Toyota's axles used 9L links and 9L shock absorbers, and I knew those won't cut it here, simply they would not be long enough.

As for lego springs, their travel is quite limited for such large articulation, especially as it needs to be fixed far out on the axle, but I also faced another puzzle of the real buggies. At first I did not understand how is it possible that they sit very low, yet they can articulate sooo much. I realized, that those shocks are air filled (and adjustable) and what's probably happening is that they are very soft, so that they sit in almost completely, and the wheels mainly articulate downwards from the base position (instead of up, as usual). I thought this is kind of fortunate because it could be nicely modeled using long pneumatic cylinders, which have a lot of travel. My first attempt was to fill them with a bit of air, adding complete tubing with switches and a small pump to the model. However, the system was a bit complicated, always leaking some air and never really leveling up properly on all 4 wheels. So I decided to try and just get rid of the tubing and the air, and let the model sit completely on the cylinders and only articulate outwards, the cylinders only acting as dampers for the movement. And this worked surprisingly well, simplified the build substantially, so I kept it!

For the links, the only option was to build them from parts, but then, triangulation becomes more difficult due to needing to add degrees of freedom to their movement, which makes things clunky and collide with other parts. I experimented a bit with aggressive outward looking lower links, but it just did not fit nicely, so I just decided to keep the lower ones almost parallel (the mounting of the ball socket providing minimal outward direction), simplifying the mounting at the chassis end, and only triangulate the upper ones aggressively.

 

Drivetrain

In the real model, the motor is placed on the back, all the front is kept for legroom and visibility. The transmission is routed on the right, while the seat is on the left. So I aimed to keep this layout, I wanted to keep the space for the seat. The two L motors (with the buggy motors swapped into them, same I used for the Hilux) went to the rear, while the front was a good place for the battery to balance out the weight. The only slight difficulty was the routing of the driveshaft with the right gear ratio, in a way that it leaves room for the seat low enough. In the end, this is what worked:

The differential is locked in the form of a 12:20 gear ratio, leading to the planetary hubs. This way the final speed/torque ratio is very good because the model is very light compared to the Toyota. Furthermore, it's center of weight is very low, hence it is very stable.

Here is the core of the complete chassis:

 

Bodywork and interior

As for the rest of the chassis and bodywork, this time I kept it simple and stable, didn't aim for complexly angled tubular structures, just decided to use beams and the paneling itself as the main structural elements, and throw a few angled parts (like those F1 suspension arms) mainly for enhancing the looks. The seat itself is a detailed one (borrowed from my previous rock bouncer), and there's minimal cockpit design with steering wheel and gear stick, but the other half of the cockpit is occupied by the transmitter and wiring, while the ESC is on top of the drive motors for easy access to turn it on. Actually, the usable space is quite small compared to the overall size, because, well, it's all about the huge wheels.

 

And finally some more photos as well in its natural environment:

 

More pictures are on my Bricksafe. The Studio model is available on Rebrickable.

Let me know what you think!

Cheers!

Viktor

Edited November 22, 2025 by gyenesvi

[msk6003]

Suspension idea is very good!

[N1K0L4]

4 hours ago, gyenesvi said:

As for lego springs, their travel is quite limited for such large articulation, especially as it needs to be fixed far out on the axle, but I also faced another puzzle of the real buggies. At first I did not understand how is it possible that they sit very low, yet they can articulate sooo much. I realized, that those shocks are air filled (and adjustable) and what's probably happening is that they are very soft, so that they sit in almost completely, and the wheels mainly articulate downwards from the base position (instead of up, as usual). I thought this is kind of fortunate because it could be nicely modeled using long pneumatic cylinders, which have a lot of travel. My first attempt was to fill them with a bit of air, adding complete tubing with switches and a small pump to the model. However, the system was a bit complicated, always leaking some air and never really leveling up properly on all 4 wheels. So I decided to try and just get rid of the tubing and the air, and let the model sit completely on the cylinders and only articulate outwards, the cylinders only acting as dampers for the movement. And this worked surprisingly well, simplified the build substantially, so I kept it!

Very interesting idea for the suspension, and it works very well! It could be said it works as a damped pendular axle I think? Also, do you think adding some springs on the chassis end of the links could improve it by helping the wheels to go down faster, while still having the same travel because of the leverage?

All in all I'm impressed by the performance. How much are the RC tires helping it actually?

[2GodBDGlory]

Nice work! That suspension design is really interesting. Do I understand correctly that there are no springs involved, and it just relies on the weight of the axle to cause it to articulate down?

[gyenesvi]

18 hours ago, msk6003 said:

Suspension idea is very good!

16 hours ago, N1K0L4 said:

Very interesting idea for the suspension, and it works very well!

16 hours ago, 2GodBDGlory said:

Nice work! That suspension design is really interesting.

Thanks guys, glad you all point out the suspension, as that's the main technical novelty :)

16 hours ago, 2GodBDGlory said:

Do I understand correctly that there are no springs involved, and it just relies on the weight of the axle to cause it to articulate down?

16 hours ago, N1K0L4 said:

It could be said it works as a damped pendular axle I think? Also, do you think adding some springs on the chassis end of the links could improve it by helping the wheels to go down faster, while still having the same travel because of the leverage?

So yeah, there are no springs involved, and only the weight of the axles pulls it down. In theory, small springs could be added to the base of the lower links (though the space to add them is very limited due to the upper links), that could make it more responsive in terms of pushing the wheels down, but the surprising finding is that it is not really needed, as I tested it with air in the cylinders first. I think one problem either with air in the cylinders or with additional springs is that it also effects all wheels, not just the one being hung in the air. So in a situation when the model hang on the rock, if there was a spring, true that it would push the wheel in the air down, but on the other side, the same amount of spring force would be pushing the model sitting on the other wheel upwards, so the end result would not necessarily be better. So in the end, simplicity decides in my case.

By the way, I would not say that it's like a pendular axle, because it has more degrees of freedom than a pendular one (which can only rotate around the middle), it's a proper floating axle capable of moving up and down as well as tilting.

16 hours ago, N1K0L4 said:

All in all I'm impressed by the performance. How much are the RC tires helping it actually?

I think these tires help pretty much, the are soft and sticky, designed for rocks, and of course, even with this, there are many situations when it can slip and spin out (obviously I cut those out from the video :D). Also, one disadvantage of lego tractor tires is that they are very edgy (while this one is rounded) and need more space, for example that can get caught up in the suspension links when steered to the maximum. Also, maybe the edgyness would provide less contact surface than the rounded tires have.

Edited November 23, 2025 by gyenesvi

[Kamil]

This model is a clear summary of your previous opinions about 42129's playability. Impressive job, thanks for sharing ! 

 

Edited November 24, 2025 by Kamil

[gyenesvi]

On 11/23/2025 at 10:13 PM, Kamil said:

This model is a clear summary of your previous opinions about 42129's playability. Impressive job, thanks for sharing ! 

Thanks, true that it fulfills (my) playability objectives, though I think that comparing this with the Zetros set would be kind of unfair, even if we factor out the question of electronics. This kind of car is built for very extreme off-roading, while a truck like Zetros is not exactly (even a trial version), so comparing their capabilities would be a bit unfair. So I guess what I mean is that even if the Zetros set was well executed in its class, this kind of car would easily beat it in terms of playability, simply due to the options it can provide due to its low weight, stability and extreme articulation, things that a Zetros will never have even if built really well.

But hopefully soon I can publish something that is more directly comparable to the Zetros, both in terms of its class and the electronics used.. :)

[Kamil]

23 hours ago, gyenesvi said:

Thanks, true that it fulfills (my) playability objectives, though I think that comparing this with the Zetros set would be kind of unfair, even if we factor out the question of electronics. This kind of car is built for very extreme off-roading, while a truck like Zetros is not exactly (even a trial version), so comparing their capabilities would be a bit unfair. So I guess what I mean is that even if the Zetros set was well executed in its class, this kind of car would easily beat it in terms of playability, simply due to the options it can provide due to its low weight, stability and extreme articulation, things that a Zetros will never have even if built really well.

But hopefully soon I can publish something that is more directly comparable to the Zetros, both in terms of its class and the electronics used.. :)

[PlasticGear]

It just looks so nice ! You made a fantastic job !

You made me want to build one

[lmdesigner42]

That is a truly impressive rock crawler with a novel suspension design, all of your years of experience building models like this have clearly paid off. Great work! The performance is so good, it makes me wonder what else could be done to make it better. Brushless motors??

[gyenesvi]

15 hours ago, lmdesigner42 said:

That is a truly impressive rock crawler with a novel suspension design, all of your years of experience building models like this have clearly paid off. Great work!

Thanks, glad you see me making progress :)

15 hours ago, lmdesigner42 said:

The performance is so good, it makes me wonder what else could be done to make it better. Brushless motors??

Well, I have been thinking exactly that :D My plan is to build a somewhat smaller, more compact version of this, using a brushless motor. For one, the brushless motor would take less space, as a single one is enough and no need to gear them together, at the same time would probably be even more powerful, and also more controllable at very low speeds. Second, one thing that could be improved a lot is the linkage for the suspension, because these links built from liftarms are bulky and have less degrees of freedom, so to make it possible to compact things, I have been experimenting with 3d printed links, and I successfully printed 11L links already, but even longer ones are possible if needed. Third, some custom springs for making it actually spring loaded while retaining the large amount of articulation.. So there's a lot to improve, and while it seems like a lot of custom parts, all of those would be parts that could in principle exist as generic lego parts.