[MOC] Willys Jeep RC (42110 + 42129 dual alternate)

[gyenesvi]

 

Hello Folks!

Recently I have revisited a previous MOC of mine, the Willys Jeep alternate of the Defender. By adding the Zetros set's parts into the mix, I have built an RC version of it, so now I'd like to share the design of it.

Features

- all wheel drive with two drivetrain options: off-road with planetary wheel hubs, slower gearing, possibly locked differentials and off-road wheels, and street variant with faster gearing and street wheels
- floating axle suspension with imitated leaf springs with extra links and Panhard rods for stability
- linkage based steering and connected functional steering wheel
- remote controlled two-speed gearbox, functional gearstick as indicator
- openable hood, foldable windshield, removable soft top, clean interior, jerry can and spare wheel

Goals

This build has been in the back of my head ever since the building of the manual version, however I wanted to make a proper RC version, completely rebuilding the internals instead of just throwing a few motors in here and there. In particular I wanted to keep the spirit of the original. I set the following goals (besides keeping the body intact):

- keep the original's suspension which is live axles with 'imitated' leaf springs. At the same time, make the axles narrower if possible as the manual version is a bit too wide. That meant some constraints on how the axles can be linked to the chassis.

- keep the AWD drivetrain including some form of simplified gearbox, preferably an RC one

- keep the functional steering wheel

- keep the interior clean of motors, gears and batteries. This means that the available space is much less than it seems because the car is open and the interior is fully visible

- use better wheels than what the Defender set has to offer, something that better matches an off-roader

A further dilemma was whether to use planetary wheel hubs in the motorization or not. On one hand it seems natural because it's an off-roader, on the other hand many builds with those hubs come out too slow, but I also wanted a playable speed. It's not a rock crawler after all.

The resolution of all these constraints is nicely solved by the Zetros set. It has enough electronics for the complete motorization, including an RC gearbox, and drivetrain components like the planetary hubs and heavy-duty diffs and CV joints. Furthermore, it has off-road wheels that are the same size as those of the Defender, so match the scale. And also some it's regular parts are a useful addition (interestingly I discovered that the Zetros uses the same color coding for parts as the Defender, probably because they have the same designer, so in the end I had more of the same parts in the same color). Furthermore I decided to try and make it work with the official Zetros profile of the Control+ app.

Layout of the electronics

I started with laying out the placement of the drivetrain and the electronics. Luckily, the the length of the Willys was just perfect to fit in the drivetrain with double CV-joints going to the axles, and a two-speed gearbox in the middle, so I concluded that the gearbox is probably possible. The big question was how to place all the motors and the battery. I figured that there are only two meaningful possibilities to place the battery: at the front under the hood or at the back as cargo or under the rear seats (the middle is not possible if I want a gearbox or even just a clean interior as the floor is so low). If I put it under the hood that would have left me with only awkward motor placements (either on the back, or under the seats, but because of the RC gearbox, the would have had to be placed too far out with a gear-train cutting the chassis structure), so the battery in the back - motors at the front seemed like a better idea. For the steering I also considered two options: on axle or off axle servo. I did not like the on-axle variant though as then it would have collided with the drive motors placed above the axle under the hood. Also, making a functional steering wheel seemed easier if the servo is off the axle. For that case, there were also two options; linkage based or joints based routing. A joints based routing would have probably required to place the steering motor somewhere in the floor, which would have collided with the gearbox/drivetrain, so I rather experimented with a linkage based one, which was something I wanted to try for a while to see how it actually performs. So the key was whether it's possible to somehow place 2 drive motors and one steering motor all under the hood and route both the drivetrain and the steering. Sandwiching the steering motor between the drive motors with an offset seemed like a possibility. This way the steering motor was low enough for linking the steering, but not too low to collide with the axle, while the drive motors could be comfortably placed higher to give way to the chassis frame itself. And later this even enabled good gearing options towards the gearbox.

Drivetrain options

The next thing was to decide on the gearing. The mix of Defender and Zetros components available gave me an interesting possibility: it seemed that both a slow, off-road drivetrain (using planetary hubs) and a faster drivetrain (using vanilla hubs) are buildable from the available parts. Also, two types of differentials are available in the two sets, so what I did is I coupled the planetary hubs with the older (faster 20:28) diffs, and the vanilla hubs with the heavy duty diffs (12:28). This way, the off-road setup is faster than in case of the Zetros, and the vanilla setup is more powerful than with old diffs. To further enhance the situation, the gearing from the motors towards the gearbox is also adapted: in case of planetary axles, it is built with a slight up-gearing (20:16), and in case of vanilla axles, it is built with a slight down gearing (16:20). The gearbox itself is 1:1 in low gear and 20:12 in high gear. These speeds turned out to be quite playable, both fast enough and powerful enough where needed. A further advantage of matching the planetary hubs with old diffs is that those diffs can be simply built locked, which is useful for actual off-roading at least in the rear axle. To top it up, the off-road axle can take the Zetros wheels, while the vanilla axle can take the Defender wheels, hence I named this the 'street' version. Note that as the Defender rims are deeper, these axles need to be built 2 studs wider to get the same actual looks.

Gearbox

The gearbox itself is quite simple, but making it RC is not trivial with the medium PU motor of the Zetros set, as it needs many more components (first down-gearing, then a safety clutch, then physical limiters, besides the orange selector). Luckily it was not that hard to lay this all out flat on the floor under the middle console and the seats. Which left the space above the driving ring to the manual selector, that could this way be made functional to actually indicate the selected gear.

Chassis structure and axles

I wanted to keep the nice somewhat realistic chassis structure of the manual model. However, the frame had to be widened to make space for both the motors in the front and the battery in the back, and at the same time making the leaf spring attachment positions narrower to make room for the wheels in the narrower axle. As a result, routing of the functional steering wheel was the most difficult problem because both the motors and the main frame of the chassis is straight in its line, so I had to use a series of 4 U-joints to route it around the frame. At the same time, the whole suspension was stabilized compared to the manual version; both axles actually have two upper links as well and a further Panhard rod. The axles are somewhat different builds in case of the different hubs, and I had to make things such that the spring attachments are compatible with both axles, which also presented some complication and had quite limited the possibilities. The battery hub is lowered between the frame but can be easily taken out for replacing batteries. Furthermore it sits low enough not to obscure the internals too much, so I was able to build some rear seats on top of it that's only 1 stud higher than the manual version. 

 

Some shortcomings

Although I think the final chassis came out quite well, there are a couple details that I am not completely satisfied with. The main one is that due to the wide position of the springs (due to the space requirements of the motors and the battery), and the usage of hard springs, the suspension is too stiff for hard-core off-roading. The sets only have two soft springs, but even if they had four, it would not help; with soft springs the suspension just sags under the weight of the model. Doubled up soft springs would be optimal (in the front it's actually easy to install, but in the rear it would be quite problematic due to the shape of the planetary hubs). But I think it's an okay compromise, as the model still rides very well on tough terrain, just doesn't articulate that much. Another minor thing I could not fix is that the movement of the steering wheel is not that realistic, it was not possible to gear it up more. The root of the problem is that because of the linkage based steering, the servo range is not 90 degrees to start with, but rather around 35-40 degrees, and even though its doubled at the steering wheel, that's still not much. Anyway, at least the construction of the steering system is somewhat like in reality, from the steering wheel to the steering gearbox, then through the linkage to the tie rod.

Bodywork

The bodywork is the same as for the manual version. But I think it looks much better with the Zetros wheels. Here are some renders and photos with both axle/wheel variants and with/without the detachable soft top.

 

And finally, one of my favorite options; with the Zetros rims and the narrower axles it became possible to put on old 80mm diameter, narrower foam tires, which best match the real vehicle I think. And it's even not that bad at off-roading!

Many more photos are available on my Bricksafe page.

Building instructions are available on Rebrickable.

Let me know how you like it!

Cheers,

Viktor

[1963maniac]

Wow! That's cool!! I really like the old style tires on the last three pictures.

[JoKo]

It looks very clean. Very nice pictures!

I like the tractor tires better but old style looks nice as well.

 

[Zerobricks]

What a great combo model. If I see correctly the steering mechanism uses a simple linkage? Do you have more details about that?

[GerritvdG]

Well done, cool project to combine two sets into this! Thanks for the extensive description and for some reason I never realized that Medium Motor was used in the Zetros ...

[Thirdwigg]

Yeah, great job bringing these two sets together. The Zetros tires look much better too.

[gyenesvi]

Thank you guys!

22 hours ago, Zerobricks said:

If I see correctly the steering mechanism uses a simple linkage? Do you have more details about that?

Yes, that is a really simple linkage. Here is a render about its details. One of my goals was to test how a linkage based steering can work in a model of this scale. A few things about it. First, as you see here, the bottom of the servo horn is only 1/2 studs away from the tie rod. So if you push down the suspension, it cannot achieve its full 1 stud of travel given by the springs, only 1/2 studs. However, when the axle articulates, it sort of goes around the servo horn, so it is able to achieve its full 1 stud of articulation at the springs, so that is a good compromise I think, as articulation matters more. Second, the Panhard rod is parallel to the steering link, which minimizes bump steer. Although the movement range of the servo horn is about 35-40 degrees only, proportional steering still works fine with this PU motor, and even with the Control+ app because of the calibration finding the end points automatically. However, the system has a drawback; as the servo horn is 2 studs long, that decreases its leverage on the wheel hub, so the power of the steering system is weaker than in case of rack based steering with a 12T gear, which can be thought of roughly like a 1 stud long servo horn. So the power is halved compared to that, and that can be felt off-road. With all the weight of the model, it is too weak to steer in place on sticky rocks. But when the model is moving, it works fine as seen on the video. On flat surface, it can steer in place as well.

 

[Zerobricks]

Thank you for the detailed answer, seems like a good compromise indeed.