[MOC] Small scale modular 4x4 RC pickup truck

[AutoBacon]

Greetings. I would like to present my first completed model; a small-scale remote-controlled pickup truck.

Featuring 4x4 drive, 3-Link suspension front & rear, 7-stud wide axles, no old-style CVs, and a fully modular body/chassis.

I had a few goals with this project;

• Produce the smallest possible scale 4x4 whilst retaining realistic proportions
• Use as few parts as possible
• System body for detail and smoothness

This project began as a test platform for an improved 7-stud wide driven front axle design taken from my WIP KrAZ project I started last year. I wasn't happy with the unreliability of old cv joints, and weak rubber-sprung axles, so I embarked on a quest to fix these issues.

I realized I could fit new CV joints after seeing @apachaihapachai's Terracotta Pickup Truck, this massively improved the load capacity and reliability, while making the overall package smaller, making me confident the axle was now strong enough to support a brick-built body. Next was the suspension, I needed real springs instead of 45590 rubber pieces. After some pondering, I discovered that I could take springs out of regular shock absorbers, and keep them in place with ball joint pins. The suspension now had great support and range of motion.

 

I made the rear axle with as few parts as possible, it flexes a little but it is strong enough to handle a small model such as this one. I wanted to keep it as simple as possible to keep the level of bulk to a minimum. Below is the final chassis. Because the axles are only 2 studs high, the chassis can be nice and low, while still giving one stud of vertical suspension compliance.

What I found with really small models, is the motors tend to get put in strange places and often become structurally integral in order to keep the model small. To keep with the ethos of this build, I wanted the drive and steering motors to be concealed within the chassis rails, while also being easily removable, and using the fewest gears possible. The result is a drive motor/transfer case with an integrated steering motor. It is mounted directly to the chassis with just 4 pins.

The model is powered by a MouldKing battery mounted in the cargo bed, feeding power to the L motor for drive, and Cada micro motor for steering. The final drive geared down 1.67:1 from the motor, and with a total weight of about 650g, this gives a good mixture of torque and speed. The Cada micro motor is slow enough that it can be used to directly drive the steering rack, as long as you have a proportional controller.

As well as the suspension solution, there are a couple of modified parts; namely a shortened suspension arm with tow ball for the rear axle, and a 2L half-thick liftarm to improve the front drive input shaft rigidity.

 

Regarding the body design, I decided to try using the new wheel arches from the Camero set. I hoped these pieces could result in a body that wasn't outrageously heavy but still had a good level of detail. I needed to keep the design simple as this is the first time I've created a body, I don't usually get past the chassis in my builds. The proportions and style of the design were based loosely on a 70s Chevy k20, although the arches are a little too big. I ended up liking how the side panels could be removed completely in one piece each, and the rest of the body plugged into the chassis with 2 pins per section for easy removal.

 

Anyway, thanks for reading, any feedback regarding the build/presentation is welcome.

 

Check out the video for a closer look and to see its capabilities with some outdoor driving.

 

[Aurorasaurus]

can you show the shortened towball liftarm? im very impressed with the scale and functionality, it reminds me of paaves pickup truck a bit.

[2GodBDGlory]

Very impressive! The body looks great, and the performance is really impressive too! I like seeing the possibilities of that micro-motor. Great idea for the suspension, too! I did something somewhat similar on my recent Geo Tracker MOC, but that could have been another option!

Also, is there any trick for getting the spring over the ball? I just gave it a shot and couldn't get it to work, even using tools, but then maybe I have a different spring variant

[gyenesvi]

Oh man, I love this. So many interesting solutions in there!

And I thought my 9-wide axles I'm working on were small :) Though it's a tad bit larger scale. I love how light-weight your axles are, this solution for the new CV joints seems quite promising, and the spring solution is interesting too, so I'd also be interested in how it can be mounted.

And then the chassis itself is so realistic, simple and low! The motor transfer case and steering motor combo is genious! Again, realistic placement.

Why is the shortened suspension arm at the rear needed? Just to give space for the steering motor?

Can you show more details of the front axle? Where is that 2L half liftarm needed?

The bodywork is beautiful and simple enough construction for a mixed technic/system build. I am tempted to buy the Camaro set for all those black/dark red pieces and those new fenders. I just saw it yesterday for 20% off for black friday.. Though I'm afraid that those wheel arches only work with 50mm wheels for the steered wheel, 56 tractor tires would already be too big for them I guess. Oh wait, you said you are using 56mm tyres, right? That's good news.. can the tyres hit the fenders when steered and articulated?

And finally great performance. Only thing I could not decide is the suspension softness, sometimes it does not seem to flex enough, sometimes it does seem to do well. I guess it's because the springs are at the end of the axles, and a bit too hard for the weight, but that's a typical problem even with soft lego springs for live axles. Or maybe it flexes to the max and hits the chassis rails? There's only half a stud space under there, right?

Great work!

Edited November 22, 2023 by gyenesvi

[Andman]

Great work. It reminds of the SCX24.

[keymaker]

I really like solution used in front and rear axle, the minimalism which is behind it. Also rims from Camaro plus RC tires, size 54 or 56mm, right? Great addition to overall very nice look.

Edited November 22, 2023 by keymaker

[Alex Ilea]

Phenomenal build! I do agree with @Andman, they are lookalike. It is impressive that managed to make such a small model and to still manage to make it look prettyand perform really nicely for the scale.

This must be the nicest and most realistic mini crawler that we have. Could you share the digital file of it please?

The only thing I don't like is that you used custom parts, as I don't believe them to absolutely necessary and I believe that a 100% lego version would be possible. The mini angular motor could be used for steering also. 

Congratulations on the build!

[Jurss]

Pretty good frankenstein.

[AutoBacon]

I'm glad you guys like it! I have created a Studio file that contains the fully assembled model and its constituent components, as shown in the render.

The file is in my bricksafe folder for the model, which also contains 4 custom parts that you might have to stick in your AppData\Local\Stud.io\CustomParts folder.

(the other two parts - one is a 3 stud flip flop beam that Cada makes, and the other is a 3 stud female CV which Studio does not have yet)

https://bricksafe.com/pages/autobacon/compact-drivensteered-axle-designs/4x4

 

 

8 hours ago, Alex Ilea said:

Phenomenal build! I do agree with @Andman, they are lookalike. It is impressive that managed to make such a small model and to still manage to make it look prettyand perform really nicely for the scale.

This must be the nicest and most realistic mini crawler that we have. Could you share the digital file of it please?

The only thing I don't like is that you used custom parts, as I don't believe them to absolutely necessary and I believe that a 100% lego version would be possible. The mini angular motor could be used for steering also. 

Congratulations on the build!

Thank you for the positivity! Regarding electronics, I don't currently own any powered-up components, but if I get my hands on a 88009 2 Port hub, angular motor, and an L motor I may try to adapt the model to make it 'more Lego'. I'd like to try using the angular motor as a servo with a pushrod steering setup like Paave used, instead of rack and pinion, I think It could end up being more compact.

 

9 hours ago, keymaker said:

I really like solution used in front and rear axle, the minimalism which is behind it. Also rims from Camaro plus RC tires, size 54 or 56mm, right? Great addition to overall very nice look.

From the pioneer in quality small-scale RC Lego, thank you :D The tires are 56mm, yes, and also a lot narrower to better suit the scale.

 

9 hours ago, Andman said:

Great work. It reminds of the SCX24.

Thanks, 1/24 scale crawlers were my main inspiration, I wonder with a lightweight body how close Lego could get to real RC in 1/24, especially when using RC tires.

 

10 hours ago, gyenesvi said:

Oh man, I love this. So many interesting solutions in there!

And I thought my 9-wide axles I'm working on were small :) Though it's a tad bit larger scale. I love how light-weight your axles are, this solution for the new CV joints seems quite promising, and the spring solution is interesting too, so I'd also be interested in how it can be mounted.

And then the chassis itself is so realistic, simple and low! The motor transfer case and steering motor combo is genious! Again, realistic placement.

Why is the shortened suspension arm at the rear needed? Just to give space for the steering motor?

Can you show more details of the front axle? Where is that 2L half liftarm needed?

The bodywork is beautiful and simple enough construction for a mixed technic/system build. I am tempted to buy the Camaro set for all those black/dark red pieces and those new fenders. I just saw it yesterday for 20% off for black friday.. Though I'm afraid that those wheel arches only work with 50mm wheels for the steered wheel, 56 tractor tires would already be too big for them I guess. Oh wait, you said you are using 56mm tyres, right? That's good news.. can the tyres hit the fenders when steered and articulated?

And finally great performance. Only thing I could not decide is the suspension softness, sometimes it does not seem to flex enough, sometimes it does seem to do well. I guess it's because the springs are at the end of the axles, and a bit too hard for the weight, but that's a typical problem even with soft lego springs for live axles. Or maybe it flexes to the max and hits the chassis rails? There's only half a stud space under there, right?

Great work!

I'm glad you love it :D Thank you. To answer your comments;

The shortened arm means the end of the liftarm lines up with the chassis flip-flop beam hole, and you are right, it couldn't be any longer because the steering motor is directly in front of it.

Yes, the tires are 56mm, and at the current ride height, they don't rub anywhere in the steering/suspension travel range. This is due to the relatively narrow width compared to 56mm tractor tires, as well as the wheel arch pieces themselves being very thin at the bottom. I think this tire size is the limit of what this fender allows.

In terms of suspension, I did play around with weights. Soft springs couldn't really support the body and would allow for too much chassis roll under load, they did give the most flex because once one side of the axle hits the frame, the limit is now how much the opposite spring can stretch. Hard springs didn't really give much flex for crawling. In the end, I got some old medium-weight springs from bricklink, and they seem to be a good middle ground. I think what you are describing in the video is caused by the rearward weight distribution due to the battery position, meaning the model has a bias towards rear suspension flex, and sometimes the front has more to give, it's especially noticeable when the rear axle is loaded. But I do agree with what you are saying. Also something to consider is how small the model is compared to those muddy obstacles, which are nowhere near proportional hehe :D

I think before I walk away from this build I might try an alternate build to optimize it for crawling; a super lightweight body, lower the shock towers by a stud for longer travel, and use soft springs for the best flex. Perhaps a simple cabover-style trial truck or a Willy's Jeep.

Below you can see the 2L thin liftarm, which acts to counter the downward force when driving forward. Without it, the input shaft mount rolls downwards along the axis drawn with the thick red line. This doesn't cause the gear to slip but the flex means the front and rear axles go out of sync when the front wheels get stopped by an obstacle, as if the front drive axle was connected by a spring to the transfer case.

 

14 hours ago, 2GodBDGlory said:

Very impressive! The body looks great, and the performance is really impressive too! I like seeing the possibilities of that micro-motor. Great idea for the suspension, too! I did something somewhat similar on my recent Geo Tracker MOC, but that could have been another option!

Also, is there any trick for getting the spring over the ball? I just gave it a shot and couldn't get it to work, even using tools, but then maybe I have a different spring variant

Thanks! I too was pleasantly surprised by the performance with only a single motor! For spring mounting, the spring strength didn't matter too much, I just used my nails to pull down the densely coiled end over the ball joint. It is helpful to put the ball joint in a long liftarm to help hold onto it.

 

16 hours ago, Aurorasaurus said:

can you show the shortened towball liftarm? im very impressed with the scale and functionality, it reminds me of paaves pickup truck a bit.

Thank you! Regarding the liftarm, there isn't much to show really, I just used a blade to shorten it by a stud and then carefully cut the rough edges away. You can see it in the close-up of the rolling chassis in the video :D

 

[gyenesvi]

27 minutes ago, AutoBacon said:

Below you can see the 2L thin liftarm, which acts to counter the downward force when driving forward. Without it, the input shaft mount rolls downwards along the axis drawn with the thick red line. This doesn't cause the gear to slip but the flex means the front and rear axles go out of sync when the front wheels get stopped by an obstacle, as if the front drive axle was connected by a spring to the transfer case.

Okay, thanks, I can see that now, so it's actually one axle hole and one pinhole that is needed there. And I think you forgot to mention the need of a custom 4.5L axle that holds it :) Though that does not seem to be required, a 5L would also work, it has space to stick out at the front.

27 minutes ago, AutoBacon said:

I'd like to try using the angular motor as a servo with a pushrod steering setup like Paave used, instead of rack and pinion, I think It could end up being more compact.

I guess you mean a linkage based steering like in a real car. I like to use that system a lot, and designed a few models with it. It's hard to get that one compact as well. One problem that you'll encounter is that the linkage needs to pass under the chassis rail and it even articulates together with the axle, so it typically needs quite a bit more space under the rail than the rack based. With the low railing like you have here, the only chance is to connect the linkage to the axle very low, and that can only be possibly achieved from the front (because from the back you have the drive shaft entering). So it will take more space towards the front, which can also be a problem. And also, at this short axle width, you can't even use existing 6L links or even 5L liftarms with towball socket, only short liftarms, that further complicate things and require more space.

To remedy all this, I recently came up with a design (well, others and even TLG used something like it in some small models), that could work out pretty well for your case. Instead of having a proper linkage, just push the steering rod around through some sliding servo-horn in a pinhole. Luckily, with a 7L flip flop beam as steering rod, the geometry works out quite well here, like this:

The red axle is at the same level as the chassis rail, it can pass under the drive motor and go to the servo directly. I haven't built it though, I don't know how firm it is. The part in the middle of the 7L flip-flop beam is not a pin, but has an axle to allow smooth rotation.

BTW, have you tested it with the tractor tires, as in the studio file? It looks pretty cool that way as well, I wonder if those tires work here, or alternatively, with the narrow tires, a bit wider axles could work as well, or maybe the fenders won't like that.

[AutoBacon]

12 hours ago, gyenesvi said:

To remedy all this, I recently came up with a design (well, others and even TLG used something like it in some small models), that could work out pretty well for your case. Instead of having a proper linkage, just push the steering rod around through some sliding servo-horn in a pinhole. Luckily, with a 7L flip flop beam as steering rod, the geometry works out quite well here, like this:

BTW, have you tested it with the tractor tires, as in the studio file? It looks pretty cool that way as well, I wonder if those tires work here, or alternatively, with the narrow tires, a bit wider axles could work as well, or maybe the fenders won't like that.

Interesting, thanks for the insight. I wonder now if a linkage system at this scale would offer significant improvements, it seems it would just put more stress on the motor and be less precise than a rack and pinion. I'll have to think about it and do some tests :D

I originally used the tractor tires before the RC4WD ones arrived, along with stiffer springs to mitigate wheel rub, and it is true it looks quite good the way they stick out from the body. I agree that perhaps 9 stud axles with custom tires would look pretty good and provide more stability. I'm thinking now that this kind of implies that the body I created is slightly too big, and could so with shrinking, to get the same effect, which would require the omission of the windscreen piece and the wheel arches, as they kind of set the 'minimum scale'.

I think I'll try scaling the axles up to 9 studs for the crawler version and trial linkage steering. See how that goes :D

Edited November 23, 2023 by AutoBacon

[nerdsforprez]

As others have said, great build.  I really enjoyed the video as well.  I could see the realism in this build as it dug in, climbed, etc.  Great choice of rims and tires, certainly added to the build.  Functioning looks great.  Right now I am in the middle of a large build, (not my own, other's MOC) but I can't forget these smaller builds.  In many ways they are superior to large builds in that they do not tax the limits of ABS as much, can offer superior functionality, and require thinking-outside-the-box to solve puzzles that require small spaces.  Job well done.  

[Appie]

What an awesome little nimble truck and the looks are perfect. Great video too.

In march I got a truck trial with the LUG with 56mm tyres, so this is great inspiration for that, thanks.