Hi Guys,

Let me present my latest model, this time a smaller build: an RC Toyota FJ40. It started out as an experiment with motorization of my manual Toyota FJ40 alternate of the Ford Raptor set, but over time it grew to a fairly independent project. Interestingly the resulting model is simple but versatile one, that is buildable both with PF and PU electronics, basically with any kind of power source / controller.

I like the FJ40, especially the open version without a top and doors, something like this one, and I love this dark gray color:

Unfortunately, some key panels for making the hood were not available for a long time, so I did not start working on it, but in the meantime I though I'd do it in orange after the manual version. And luckily, the Peugeot hypercar was just announced recently in DBG, bringing the required panels, so now it will even be buildable in this color :)

So first I started thinking of a possible motorization. I started with PU electronics, but soon realized that PF motors could just work out better here, and since I was interested in testing and comparing them anyway, I gave it a go. For example for the steering, I wanted to test out the old PF servo's strength. In the end I built a PU version as well to make a comparison. Glad I did so, because I did get some interesting results!

Features:

- all wheel drive with 2-speed manual gearbox (2x L motor for drive, servo for steering), good speed and torque
- live axle suspension on both axles, 4-links + Panhard rod at the front, 2-links + Panhard rod at the back, soft articulation
- working steering wheel with good amount of turns
- openable doors, hood and trunk, foldable windshield
- removable and swappable doors, modular bodywork

Chassis

As often for off-roaders, I wanted to build a sturdy drivetrain with planetary hubs and new CV joints. After my Bronco build, the 'L motors on the floor with a gearbox in between' layout seemed like a good idea to use again, but this model was slightly smaller scale than the Bronco, requiring a shorter chassis. That's where the PF L motors started to come in mind, as the length of the PF L motors is only 7L, which is just perfect for sandwiching a gearbox between them as the length of the gearbox is also 7L, which is important if one wants to build only using new CV joints, because that length cannot be changed due to the fixed axle length of the CV joint. The 8L PU L motors can be hacked in, but then they would be in the way for the mounting points for the rear suspension links, so those have to be moved back 1 stud, which would result in slightly misaligned geometry (wrt the CV joint's pivot point). No big deal, but I like when things line up well :) Or the longer motors could be moved towards the front, but then would complicate things for the gear-train coupling them and going to the gearbox. Also, a big plus for the PF L motors is that they are about 30% faster than the PU L motors, hence when used with planetary hubs, they result in a more playable speed while still having plenty enough torque (for a model this size).

Second, the steering. I like linkage based steering for a live axle due to its simplicity and realism. The shape of the PF servo is just great for this kind of steering, it is possible to make its output low, but the whole motor is not too low to take space from other stuff. Furthermore as the PF servo has a rear output, it can be used to route it to a working steering wheel. Last, but not least, it really seems to me that the PF servo is quite a bit stronger than the PU L motor for steering. (At least, based on some testing, my guess is that none of the control software make full use of the total power of the PU L motor, but it can make use of the power of the PF servo; I guess the difference might be in the complexity of the control algorithm, as the PU L motor is not designed for servo function only). Anyway, as I have tested both options, the PF servo was able to steer under a complete build with bodywork while stopped on rough terrain and the front axle being flexed out, while the PU motor was lacking here..

The axles are 13 wide, similar to my previous builds, though they are getting more and more slim :) The front axle has a complete 4-link setup with an additional Panhard rod that is placed quite low and results in minimal sideways sway upon flex. The steering is via a linkage directly from the servo. The springs are placed fairly close to the middle, so it has a good amount of flex, about 2 studs at the wheel. The rear axle is a 2-link setup with positive caster, and an additional Panhard rod, also placed very low to minimize sideways movement, which would be bad for the drivetrain as it only has a single CV joint.

I think the resulting chassis is quite simple, clean and has good geometry. And it's not even over-crowded, so the build remains simple and gives room for other options such as using PU motors. So I built that version as well, sacrificing the perfect geometry in the rear, for the sake of comparison :)

Obviously, the functional steering wheel is lost in this case, as the PU L motor does not have a dual output.

Here's one more fun render of the inside

The battery goes simply into the trunk, which is big enough for any kind. I use it with a Buwizz 2 for PF (high mode) and Buwizz 3 for PU (80% motor power).

Bodywork

As I said the model started out from the manual version, which being an alternate build had lots of simplifications. Here I wanted to address them, making it more true to the real one. One key area was the nose and the hood, I definitely wanted to improve the grill / lights and make that iconic raise in the middle of the hood. At the same time I wanted to use a different technique to the versions of @rm8 or Madoca, so I went with a tile based one, trying to mix it smoothly with the technic beams and panels. I think they complement each other nicely, and the result is smooth. Also, the windshield was raised to be properly placed and this way it also became foldable, and it got a more realistic dashboard as well.

Another area of improvement is the doors. I wanted to make the doors visually separate and clean, which also resulted in a properly detachable and swappable construction similar to that of @rm8 / Madoca. Other areas of improvement are the rear fenders built using slopes and the curved rear corner, but that's just the same technique used by others before me. I also made the trunk open in a different direction than the manual one. And I changed the roll-bar to match the one on the image above.

Custom tires

This model was also ideal for testing my new RC tires I bought recently thanks to @HorcikDesigns. They are the same size (76mm) as the lego buggy tires, and they fit the rim nicely, and the material is also okay I think for the very cheap price. All-in-all the model is fun to play with, it has good amount of speed and torque. In fact, the only problem is that it is too light-weight and the drivetrain has enough power to spin all wheels under it quite easily even on rocky terrain. I was running it with locked rear differentials and open front ones.

You can find many more images in my Bricksafe gallery.

Building instructions are available on Rebrickable.

Let me know how you like it!

Cheers,

Viktor

Edited May 7, 20231 yr by gyenesvi

That turned out amazing! Great Job!

 

I had noted the lacking power in the PU motors but found that using them through the BrickController 2 App improved performance quite a bit. I have a PU-L motor set in servo as my steer motor in my Rover and it does quite well with the large 94.3x37mm tires. 

That looks amazing, nice one!

Well done, this is amazing.

A great model indeed! I personally prefer PF version since It uses the benefit of motor shapes! The body seems to fit the chassis very nicely without causing extreme load on it! Well done!

Thanks guys!

On 4/27/2023 at 3:52 PM, TexasEngineer454 said:

I had noted the lacking power in the PU motors but found that using them through the BrickController 2 App improved performance quite a bit. I have a PU-L motor set in servo as my steer motor in my Rover and it does quite well with the large 94.3x37mm tires. 

Indeed it feels a bit better with BC app, but I think it is a big difference to use these motors with rack based steering vs linkage based steering, because the way the link lengths need to be set up vs the gear size, the link based steering may require 2-3x more power (simple physiscs). With gear rack based steering it also works fine for me, but it is simpler and more realistic with linkage based steering for live axles.

Simple amazing! Great job!

I think wheels needs some more clearance above to avoid worst road scenarios ;)

Edited May 1, 20231 yr by RedWolfwere

On 5/1/2023 at 7:35 PM, RedWolfwere said:

Simple amazing! Great job!

I think wheels needs some more clearance above to avoid worst road scenarios ;)

Thanks! Yeah, the rear clearance is a bit small for the articulation, but with the custom tires it does not matter, it does not get stuck in the fender even when it touches it (the lego buggy tire can get stuck a bit unfortunately). But I did not want to change that part because it's clean and simple this way, plus the real one does not seem to have more clearance either.

I used to read to my favourite EB topics twice, so I did with FJ40 . I have a question about the suspension geometry this time. I wonder why front and rear axles differs so much in the number of links. At the front you have 4-link setup with additional Panhard rods, while at the rear only 2 links with a Panhard rod. Does an additional Panhard rod limits the suspension flex at the front? Does the rear axle have any unwanted side-to-side wobbling?

On 5/5/2023 at 8:56 PM, Daniel-99 said:

I used to read to my favourite EB topics twice, so I did with FJ40 . I have a question about the suspension geometry this time. I wonder why front and rear axles differs so much in the number of links. At the front you have 4-link setup with additional Panhard rods, while at the rear only 2 links with a Panhard rod. Does an additional Panhard rod limits the suspension flex at the front? Does the rear axle have any unwanted side-to-side wobbling?

Thanks for the good questions! There are a couple of reasons for the difference, mainly to make the rear one space efficient. The key limiting factor is the CV joint in the drivetrain, the length of that is fixed. With this setup on the rear, it is enough to have only 1 CV joint, while in the front it has 2 CV joints, saving 3 studs of space longitudinally. The single U-joint results in a positive caster for the rear axle, which is acceptable, but in the front it would mean a large negative caster, which would be bad, both for the suspension and the steering geometry. So in the rear as the axle is not parallel to the chassis and the caster changes upon articulation, you cannot have two more links. This setup is like the lego ball-joint setup, but without the ball-joint itself, as that would take up too much space to fit in due to its limited connections. In the front, you must have a proper 4-link suspension to have good geometry, and also to allow linkage based steering. The Panhard rods don't limit the flex, they are designed to be as low as possible to also not result in side-to side movement or bump steering (it is parallel to the steering link). In the rear it is actually essential to minimize the side-to-side wobbling, because of the single CV-joint setup, that cannot follow side-to-side movement, and side-to-side movement would put friction on the driveshaft. I think however that this setup only works well in a smaller, lighter build, and at slower speeds I guess. For bigger heavier models you'd have more space longitudinally and you could add another CV-joint to the rear as well.

You can see more images of similar axles in my other thread about the different small chassis variations, they share the same concept.

Another good property of this rear setup is that the springs are positioned much lower than in the front, that keeps the rear bed clean, where the battery hub needs to be placed (which can be a problem for bigger battery hubs like the Technic one), otherwise the springs would end up colliding with it.

Wow, looks nice and solid, like it's not even MOC.