Hi Folks,

Finally, after a long design time on this one, I can show you my latest alternate build out of the Volvo Hauler (set 42114). I had long been thinking what to build out of this set, because as I was slow (busy with other sets) my first idea (the grader) was taken by others. Afterwards I had some crazy dump truck ideas, but convinced myself that yet another dump truck is not such an ingenious idea, and I finally got a hint for a tow truck. That sounded like a nice idea, because the functionality seemed to match the Control+ profile nicely, the extra function being the towing arm. So the search began for something real to model, and I quickly converged on Ford F350/F550 models as inspiration.

Features

• Rear wheel drive with 3-speed automatic gearbox
• Pendular suspension with torsion bars on both axles
• Working inline 6-cylinder engine
• Towing arm with two-stage motion: fold and lift
• Openable doors, hood
• Interior with seats and dashboard

Design process

The design of this model started from the looks / body work. I found a few variations on the below Ford F550 and similar F350 models, and thought this could be doable from the parts, especially because the big fenders can be used in the front, and the rear one could have been built with the curved panels, and the overall shape is fairly blocky that could be done with all the big flat panels (I could make use of surprisingly many of the trapezoid ones). I designed the cab, the hood and front grille mainly (I could even throw in the stickered mirror plates as headligths), and it started taking shape nicely.

 

After that I started with the internals. My goal was to build it with suspension to make it more challenging, to retain the 3-speed gearbox of the original, and to be able to implement some kind of a towing arm. Also, I was sure there would be plenty of space for an interior.

As for suspension, the parts would only allow some kind of pendular axles, but to make them both pendular, I needed some actual damper. Learning from Egor's Dakar truck alternate build, I decided to go with torsion bars. Starting with the front axle, however, I realized a problematic point: it will be hard to make the wheels turn and articulate without getting stuck in the fenders; there would be only one chance; by keeping the scrub radius as little as possible, so regular use of portal wheel hubs were out of the question. I could have built it without using the portal hubs, but I did not want to have these large wheels simply attached to an axle, so I decided to try and make the front axle with the portal hubs turned flat (I knew there's no chance to make them driven anyway, not enough joints for that). I think that my alternate is the only one with suspended and steered axle that uses the fender parts as fenders..

The next problem was the steering mechanism. After some sketching, I realized that I can't just put the servo on the axle, because then the chassis rails have to become wider to allow the servo to tilt, and the wheels would simply get stuck in the chassis upon steering / articulation (even though the truck is wide, the wheels take much space). So I had to make the servo stationary, which was also favorable because it would hopefully leave more space for a working fake engine above. After a lot of juggling (some workable options ruled out because of too short cable length) I came up with the following configuration, in which steering is though a tight linkage, that allows the axle to tilt without introducing any bump steer (the linkage tilts exactly where the pendular axle does). Here, the servo is stationary, and the axle is mounted to it in the middle of the O frame and in front as well, while the steering linkage is behind the axle, and the torsion bar of the suspension is in front of it. As for mounting the wheel hubs, it was doable, though it's not my strongest build (held by 3/4 and half pins), but it does the job okay. It even has Ackermann geometry. The rear axle was really simple compared to the front, just a regular driven pendular axle, with some torsion bars attached.

Next up was the middle of the chassis, with the gearbox and drivetrain. This proved to be the most challenging part, to fit it into a rigid framing, while also having the output for the towing arm in the right position. I had to alter the gearbox layout w.r.t. the one in the Volvo, as the Volvo has both its drive output and the dumper output somewhere in the middle, while I had to arrive more towards the back, all while keeping the logic of the layout essentially the same, so that the same Control+ profile can work with it. After a series of redesigns, the final chassis became quite compact and solid, with a nice structure.

I could finally start adding the fake engine and some support structure to make the chassis and the body meet, and also make some internals. The many O frames helped a lot.

 

And last but not least, the towing arm.

At first I tried kind of a conventional setup with the linear actuators lifting the arm from the bottom, but that had two problems. First, as the actuators are pretty long, the space was really tight for them. Second, that would have only allowed me to lift the arm, but not unfold it (the first idea was to make unfolding manual). But I did not like this design, and started to think about moving the actuators out to the end of the arm and make them perform the folding of the arm (at this point I thought it's not so necessary for the arm to lift). But then I realized that by mounting the upper end of the linear actuators to a linkage, I could make it perform two motions at once :) But which motion would get priority and what would decide that? The answer was pretty simple: gravity will solve it; the movement that requires the least resistance will be performed.

So it works as follows. When it's completely down, and the LAs start to extend, it is easier to fold the arm, as that's less weight. When the folding is finished and the folding part is blocked by the rest of the arm, then the LA cannot do anything else but lift the whole arm through the linkage, until completely extended. When lowering, the process gets reversed, because the weight of the whole arm is bigger, the whole thing lowers first, and when that's blocked, it cannot do anything else but unfold. The interesting part is that the raising changes if we put weight (a vehicle to tow) on it; then folding would require much more effort than lifting the whole arm, so in this case the LA will start lifting the vehicle. Exactly what's needed! All in all, at least there was some challenge in making this arm work in a playable and interesting manner, and I am quite satisfied with this simple solution, I'd even say I find it elegant :) And it looks good, like some solid machinery.

Being an alternate model, the parts were limited (lack of joints), and so the driveshaft routing the power to the linear actuators ended up being quite long and loose in the air (going from the base of the arm up to the LAs directly), which is not the most stable solution, even though it never failed for me. However, I designed the model such that there's an alternative output from the gearbox to the towing arm that can be used (moving the lower joint to be exactly in the pivot point of the arm) to build it more stable if one has an extra CV joint part available. Here is a way how the driveshaft could be routed inside the arm that makes it much less exposed in the air (older joints could also be used).

Here are some photos of the model in the wild. Of course I tried how it off-roads.. The performance is not great, it is obviously underpowered with the single XL motor, and while the suspension works okay, the bigger problem is that it is only RWD, and the tires slip quite easily and just spin under the vehicle, despite its weight.

Many more photos are available on my BrickSafe.

Building instructions are available on Rebrickable.

Let me know how you like it!

Cheers,

Viktor

Edited December 9, 20231 yr by gyenesvi

Heyhey, that lifting mechanism for the towing arm is a 10 out of 10! Great MOC!!!

Vety good; somehow simplicity (and beauty) of buggy overshadowed your wrecker a bit.

Like them both

Edited December 10, 20231 yr by 1gor

Wow, you sure put a lot of effort not only in the model itself, but the presentation, really top notch stuff, Viktor. The fact you managed to pull this off and even came up with a 2 in 1 mechanism for the tow is simply brilliant. Well done, it deserves a feature.

Frontpaged.

That wheel lift is simply genius! Love it.

That is very nice! Good all-around, but that lifting arm is definitely the highlight!

Absolutely ingenius!

I still don't get how the towing arm lifts itself just in the perfect sequence with its second (!!!) function... got to view your video some more times!

You really earned the frontpaging!

Your C model, looks better than the vehicle it is based on.

That towing is brilliant... two functions in a single setup!! Splendid model!

Edited December 8, 20231 yr by PlopiNinetySix

Thank you guys all for the praise. I'm really glad that you appreciate the mechanical aspect of it the most.

20 hours ago, Milan said:

Frontpaged.

Thanks a lot, really appreciate that!

17 hours ago, Timewhatistime said:

I still don't get how the towing arm lifts itself just in the perfect sequence with its second (!!!) function... got to view your video some more times!

It's really simple. Think about it like this: it could do both actions at the same time; the bottom end of the LA wants to fold the arm, while the top end wants to lift the whole arm when being extended. While it could do both, it only does the one that requires less force. So first it folds, but when that gets blocked (after it's folded all the way), it starts to lift. When lowering, it is reversed, because then the lowering of the whole requires less force, and when that's blocked, the unfolding comes.

Btw, I forgot that I wanted to add a zoomed in render of the steering linkage, I've inserted it above.

Edited December 9, 20231 yr by gyenesvi

What a cool truck! Especially the challenge to make a steering system without steering hubs :D

When under load, does to carrier lift up instead of folding in?

17 hours ago, Timewhatistime said:

I still don't get how the towing arm lifts itself just in the perfect sequence with its second (!!!) function... got to view your video some more times!

In the upcoming garbage truck, something similar is used for picking up the trash can.

Nice shaping and cool features!

Thanks again!

On 12/9/2023 at 11:21 AM, Jundis said:

When under load, does to carrier lift up instead of folding in?

Yes, because then that becomes the path of least resistance.

On 12/9/2023 at 11:21 AM, Jundis said:

In the upcoming garbage truck, something similar is used for picking up the trash can.

Yes, that's exactly the same general principle, but implemented with rotation instead of an LA.

Yes, it's quite clear how the sequential funtion is achieved.

The point I will have to examine in more detail is how the towing arm lifts itself. There are some cleverly mounted levers/linkages...

Edited December 12, 20231 yr by Timewhatistime

Superb work, awesome model presentation! 

That is a great MOC and I don't say this often :D.

19 hours ago, RedWolfwere said:

Superb work, awesome model presentation! 

19 hours ago, P6tu said:

That is a great MOC and I don't say this often :D.

Thanks guys, I appreciate it!