[TC27] 3-Axle Mobile Crane

[Wiseman_2]

 

So, I’ve decided to give TC27 a bash, mostly just with the aim of finishing an entry (given that I failed to complete anything the last time I tried with TC25… for a MOC that ultimately ended up being fewer than 200 parts).

My original idea was for a 3 axle truck along the lines of 42070, but after some rough proof-of-concept builds proved that the concept I had in mind wasn’t going to work - not least because the tires just didn’t suit - I decided to pivot to my backup plan: a 3-axle mobile crane. I wasn’t quite sure how happy I was with the build’s progress until I had the cab built, so the carrier is already essentially complete.

 

 

The last large MOC I completed (not posted anywhere just yet) was a 7-axle mobile crane, also built using this wheel/tire combo. That one was of the ‘one motor/many functions’ variety, this one is going to be all manual, with some different features that I don’t normally see in mobile crane MOCs at this scale (I’m sure somebody will correct me if I’m wrong).

So far the carrier has the following functions:

• Steering on 1st and 3rd axles with working steering wheel, controlled from rear; the 3rd axle has reduced steering angle compared to 1st axle
• I6 engine driven by differential on 2nd axle, via a 4-speed gearbox controlled from the cab
• Suspension on all 3 axles
• Outrigger extend/retract
• Outrigger raise/lower

 

Some more photos of the carrier thus far:

 

Here you can see the suspension. It has quite a lot of travel, necessitating the slightly higher wheel arches.

 

The cab interior. The 3l axle with stud is the gearshift; in the back, the 16t gears run from the gearbox to the engine, while the 20t gears run to the steering wheel.

 

With outriggers deployed. Extension/retraction is controlled by the 12t gear behind the cab, while raising/lowering is controlled by the 12t above the right-hand wheel arch. The engine is also visible behind the cab.

 

And a shot of the bottom of the carrier. The gearbox was an idea I had later in the build, when I realized that there would be space for a single-layer, 4 speed gearbox underneath the cab; in bigger cranes, the cab normally sits lower, and so that space would be occupied, but here the cab sits a little higher and so the gearbox - and the drive for the steering wheel - can sit in that space without looking too obtrusive.

 

I'm still not sure on the colour scheme just yet. I’d like the whole crane to be blue, but the boom is going to have to be yellow as I don’t have the parts in blue. I may look at 60324 and go with something similar for the superstructure, rather than making the whole thing yellow.

[mooneyes]

Looking good, what's your plan for the crane boom?

 

[schraubedrin]

That's awesome, i get some serious 42009 vibes.

To understand correctly, the gear shift in the cab is for different "motor speeds", not related to a switch between functions?

[LegoTT]

Lovely ! We can't see, what does prevent the springs to pop out the 3L perpandicular beam witch it is attached to ?

[Ksen48]

This is a very cool mobile crane, will we get instructions for it? There are very few good mobile cranes in the series of techniques (except for official sets)..

[Wiseman_2]

On 8/18/2024 at 1:06 PM, mooneyes said:

Looking good, what's your plan for the crane boom?

 

I'm hoping to have a 3-stage boom; I have a previous design that's quite compact, but would maybe look too bulky for this scale with only a 3-axle crane. I'm using the curved 3x11 panels for the main section in yellow (the only colours I have of this part in the quantities needed are yellow and red).

On 8/18/2024 at 2:37 PM, schraubedrin said:

That's awesome, i get some serious 42009 vibes.

To understand correctly, the gear shift in the cab is for different "motor speeds", not related to a switch between functions?

Yes, it's to shift between 4 engine speeds. The four ratios (using Sariel's gear ratio calculator):

• 1st: 1:4.38
• 2nd: 1:2.62
• 3rd: 1:1.46
• 4th: 1.14:1

On 8/18/2024 at 8:56 PM, LegoTT said:

Lovely ! We can't see, what does prevent the springs to pop out the 3L perpandicular beam witch it is attached to ?

Hmm, thought I had a photo of the steered axles kicking around, apparently not... here's roughly how they're designed:

There is a 3x5 thin triangle and a 3x3 T-beam that connects the two perpendicular crossblocks to the red one, which in turn supports the steering shaft. It isn't perfect and is the 7th or 8th iteration, at which point I decided I just needed something that would work. 

On 8/19/2024 at 7:23 AM, Ksen48 said:

This is a very cool mobile crane, will we get instructions for it? There are very few good mobile cranes in the series of techniques (except for official sets)..

Can't promise anything I'm afraid, I did used to replicate my builds in LDD but time is a very precious resource these days! I will see how the final build ends up.

[steph77]

Hello,

Great start. IMHO, the 4 speeds gearbox is a bit too much, but the rest of the build looks pretty well build.

Serious entry so far.

S.

[NV Lego technic]

I don't think there's ever any excessive functions, as long as they are realistic and don't compromise reliability or interior.

[CK28]

This is looking lovely! It just breathes technic from all sides with the suspension, gearbox and gears and axles running everywhere! I am a big fan of the outriggers there are just perfect for this scale / size!

[mooneyes]

Looking forward to seeing it!

Shame about the colour though.

  On 8/18/2024 at 1:06 PM, mooneyes said:

Looking good, what's your plan for the crane boom?

 

I'm hoping to have a 3-stage boom; I have a previous design that's quite compact, but would maybe look too bulky for this scale with only a 3-axle crane. I'm using the curved 3x11 panels for the main section in yellow (the only colours I have of this part in the quantities needed are yellow and red).

[Wiseman_2]

One last update as the build is now essentially complete (I'm on mobile so hopefully the formatting isn't screwed up):

 

After much testing I managed to get a 3 stage boom that fits neatly into a 5x5 cross section (plus some sticky-out bits to support) and works without error, extending to a maximum length of about 108 studs. I'm quite happy with the yellow contrast against the blue as well.

Boom extension and the winch both use ratchets and friction brakes instead of worm gears, which makes them much faster and more satisfying to operate. The XL LA for raising the boom and the boom extension are controlled from the right hand side of the superstructure, while the winch is controlled from just behind the superstructure cab.

I basically have no time left for any more building at this point. I'm going to try get some better photos taken on Sunday when lighting in my apartment will hopefully be better...

[NV Lego technic]

The blue and yellow are great together indeed! It's really impressive that you managed to squeeze a 3 stage boom in a 5 x 5 space!

[Wiseman_2]

Final photos all done now. Ideally I would have taken it over to my brother's (he has a great setup for Lego), but in this case my desk will have to suffice as a backdrop.

And some additional photos:

The outriggers, if not extended outwards, are capable of lifting the entire crane off the ground:

 

More photos can be found on my Flickr.

 

[Erik Leppen]

This thing is great. A worthy successor of 8460, I would say, which is my favorite studded set. It just seems to have everything, and i also really like the color scheme. It even seems to have suspension and a gearbox? And the crane has a considerable reach, nice!

This basically puts 42009 to shame 

[bruh]

I LOVE this. Would you have instructions by any chance? I would seriously love to at least build the boom. How did you make the third stage extend?

[Combustible ice]

I'm surprised to have so many functions packed in such a small space.

[Wiseman_2]

On 9/2/2024 at 9:45 AM, Erik Leppen said:

This thing is great. A worthy successor of 8460, I would say, which is my favorite studded set. It just seems to have everything, and i also really like the color scheme. It even seems to have suspension and a gearbox? And the crane has a considerable reach, nice!

This basically puts 42009 to shame 

Thanks! Incidentally, 8460 is my favourite studded set too, and one of only two from that era I still keep on display. It does indeed have suspension and a gearbox - when doing some research on mobile cranes for the build, I noted many have much more interesting features that don't normally ever get replicated in Lego cranes (normally being reserved for sets like the Mercedes G500), like selectable drive axles, diff locks, hi/lo range gearboxes and so on. I couldn't fit all that in at this scale but I could at least make it more interesting than the norm.

 

On 9/3/2024 at 12:15 AM, bruh said:

I LOVE this. Would you have instructions by any chance? I would seriously love to at least build the boom. How did you make the third stage extend?

I don't have instructions I'm afraid, I've never actually made them before. I'm on a bit of a break from building for now while I reorganize my parts collection, maybe I could trial some for the boom on its own...

The third stage extends using a cable-return (I'm not sure on the technical name for it, if there is one). A single piece of Lego string is attached at the top of the yellow outer boom, which then threads down through the second stage to the base of the third stage, and back up onto the top end of the outer yellow boom. As the second stage extends, it pulls the string up and extends the third stage. That probably doesn't describe it very well, this photo might help:

You can hopefully see the black thread that I'm talking about, it's similar to what's used in 42009.

[bruh]

Haha! I am also in the middle of resorting/ cataloging my collection!

ok, I think I get the idea. How much weight can the string withstand? Won't it just collapse back into the second segment?