[MOC] Mini 42082 - Rough Terrain Crane

[Ngoc Nguyen]

 

CONCEPTION

42082 didn't really appear in my to-do MOCs until I saw the model by Akassin. It looks cool, but there are parts of it that I don't really like. Some parts like the mirrors are too flimsy by Lego standards, the undercarriage doesn't seem to be structurally sound, and the inclusion of the bidirectional gearboxes doesn't really make sense to me, among other things. My approach is that a model should be properly braced and stabilized, and there should be some adaptation regarding the scales. In other words, the features should fit the scale, and some features might work only in one scale and not another. To me, the bidirectional gearboxes work best when the model is motorized. If the model is not motorized, they only take up spaces that could have been used for other features. I think I can do a better job, so I decided to give it a try.

I would like to clarify that the statements above are only my personal preferences and approaches and are in no way criticisms of Akassin's model. On the contrary, I give credits to his model, because I developed mine based on the scale and some features set by that model. I don't have access to the Studio file of his model, but I was able to work backwards some features based on photos and started working on top of it. It is always easier to improve upon some existing thing than to develop that thing from scratch, and I'm standing on the shoulders of someone to build my creation.

 

UNDERCARRIAGE DEVELOPMENT

The first thing I did is to get rid of the 2 bidrectional switches in the middle, and make the functions manual through direct drive. In the original model, there are four functions: outriggers, superstructure rotation, 4 wheel steering, 4 wheel drive.

 

For four wheel steering and four wheel drive, I use the universal joints and the Ford Mustang rims, so that there is space for the U joints and the pivoting points. That's why the rims can only be in metallic gray and not red.

The superstructure rotation is driven directly through the red axle connector and a worm gear meshed with a 20z gear.

The outriggers are driven by one knob in the back. It drives one long drivetrain that has worm gears in the back and the front. In the original model, the switch for the outriggers is on the other side, next to the stairs. But to me it's more intuitive when the knob rotates in the same direction as the function that it controls. Therefore, I put the drive train for the outriggers to the back and makes it controllable through a black 12z gear.

At this point, I encountered a problem. I had an unused right side where the control for the outriggers is set up in the original model, and a relatively empty space of 7 x 7 x 3 modules in the middle. The space is not completely empty, as there are 3 drivetrains run through it: steering axle, drive axle, outriggers axle. Regardless, the space can definitely be used for something more interesting.

And in the end, I did come up with something! What is that new thing? Stay tuned to find out. And it's not just for the suspense. I was stuck on this extra thing for a very long time, so I worked on the superstructure in the mean time.

 

SUPERSTRUCTURE DEVELOPMENT + EXTRA FUNCTION NUMBER 1

I also got rid of the 3 switches and the mode switch in the superstructure. I also use a single linear actuator instead of two mini LAs, because a single thick cylinder resembles the set up in the real crane, and using two mini LAs take up more space than needed.

Since there is more space in the back, something else could be added in addition to the original 3 functions in the superstructure: winch, crane lift, crane extension. Not to mention, since the functions are all direct drive, there will be 3 knobs for 3 functions. Two knobs on one side, and one knob on the other side. That's not symmetrical. I prefer symmetrical structures. 

So I did some researches into what else can be added to the crane, and what I got was:

A tiltable cabin! Squeezing that function into such a tight space is not easy, but I finally did it. Originally I wanted the function to work on a worm gear, but there is no space, so in the end it uses a simple linkage and the cabin is kept in place due to friction.

 

EXTRA FUNCTION NUMBER 2

Sooner or later I'd have to confront the inevitable problem: What addition function should I put into the undercarriage? I know it's not anything significant, and the model works fine with the four functions, but it didn't feel right. I wanted to get to the furthest limit of what can be squeezed in that 7x7x3 area.

My first thought was another steering mode or two. Since the turning angle is already small, front wheel steering only doesn't increase the value of the model. Not to mention, front wheel steering isn't as simple as it sounds. In reality, it's actually front wheel steering + steering lock for the rear axle, because you wouldnt want the rear axle to steer by itself while the front axle move. 

Therefore I decided to do crab steering only. The linkage solution in the mini 42054 doesn't work, so I have to design something based on axle and gears. The idea is that the drive axle will be connected directly to the front axle, while it will be connected to the steer axle of the rear axle through a gearbox.

 I tried using the conventional gearbox switches, but it also has problems. One switch actually has 3 states, while I only need two states when the driving ring is engaged at either end. In the neutral state it's basically a front axle steering only and with an unlocked rear axle.

So I tried to use the orange wave selector, so that when one driving ring disengages from one steering mode, the other driving ring will engage in the other steering mode right away, and there's no neutral state. It all worked out perfectly. On Studio at least... When I built it with real bricks, the system doesn't work. When I turn the knob, the rear axle doesnt steer because of the cumulative slack of all the gears...

At this point I gave up on the crab steering mode. I decided to put a hand brake like the one in the Iveco Tipper that I worked on earlier. There's a switch on the drive train, one end is blocked, the other end meshes with a gear that is fixed. It works, but it feels like a cop out. I settled on that option, but I still feel uneasy with it.

It was not until last month that I went back to work on the undercarriage again, and made one last try with a certain new piece available only recently. And the crab steering FINALLY WORKED!

 

And that wraps up the development story of this model!

 

FUNCTION SHOWCASE

Functions:

- Four wheel drive
- Four wheel steering
- V-8 engine
- Outriggers
- Superstructure rotation
- Crane arm lift
- Crane arm extension
- Winch movement
- Winch lock

Details:
- Ladder from both sides
- Side compartment with a box for tools
- Mirrors in undercarriage and superstructure
- Outrigger pads
- Oil filter
- Counterweight
- Openable cabin door
- Fire extinguisher
- Max height 58cm

 

 

 

 

 

And of course, since this is a crane, there has to be a max height flex.

 

Instruction available at Rebrickable:

https://rebrickable.com/mocs/MOC-187137/nguyengiangoc/mini-42082-rough-terrain-crane/#details

 

P.S: This model has been planned to be released around this time, and the fact that there is TC27 going on is purely coincidental. I wasn't aware that TC27 will be around the 49.5 tyre. I decided not to use this model as a submission because that would be not fair and not fun. It's not fair because it took me 6 months to develop this, while TC27 only allows 3 months, and I already teased some parts of this in my Technic corner already. It's also not fun because the real fun is in solving the design challenges and squeezing things into constraints, while this model is a solved problem already, and as the boss said, contest is about fun. 

Edited January 16 by Ngoc Nguyen

[Jurss]

I think we had contest for minimising something, OK, but it seems, that this kind of thing fits also there, except, this thing then is lego licensed ;)

[Ngoc Nguyen]

2 hours ago, Jurss said:

this thing then is lego licensed ;)

What do you mean 

[Shiva]

Thumbs up tp this build.

[Ksen48]

Very cool version, I have long wanted a mobile crane in my collection, but I would like to find a small size and here it is! I'll try to see if the parts are needed or if I'll have to buy something in addition and I'll build it, but I'll make it in a different color.

[Timewhatistime]

Wow, I'm deeply impressed not only by shrinking but also by enhancing (two more functions, and simply by reasons of symmetry, hahaha  :-)   ) the original 42082.

What is the certain new piece which was crucious for the crab steering?

By the way, in the picture explaining the two steering modes there seem to be two different versions mashed up. Just look at the position of the gear selector (red 2 L axle connector) and the two thin 1x3 (or 3x3?) liftarms in its vicinity...

Edited June 20, 2024 by Timewhatistime

[Ngoc Nguyen]

29 minutes ago, Timewhatistime said:

What is the certain new piece which was crucious for the crab steering?

I'd like to keep it as well as the whole steering mechanism a secret for a while  But it's not hard to figure out. The inventory is on Rebrickable, and in the list there is only one part that is available only starting from this year.

30 minutes ago, Timewhatistime said:

By the way, in the picture explaining the two steering modes there seem to be two different versions mashed up. Just look at the position of the gear selector (red 2 L axle connector) and the two thin 1x3 (or 3x3?) liftarms in its vicinity...

I think that's a rendering error. I just checked the model file and the image file, but there's no overlapping of anything.

2 hours ago, Shiva said:

Thumbs up tp this build.

 

2 hours ago, Ksen48 said:

Very cool version,

Thanks a lot for the compliments!

[Timewhatistime]

There is no overlapping, right. However, the parts I mentioned are swapped: They are located in a certain position in one image, and they are changed in the other image.

[Ngoc Nguyen]

2 minutes ago, Timewhatistime said:

There is no overlapping, right. However, the parts I mentioned are swapped: They are located in a certain position in one image, and they are changed in the other image.

I still dont understand where or what exactly you're referring to. Can you highlight or circle that part?

[Timewhatistime]

So, once again:

I am talking about the image explaining the two steering modes.

There are three columns of renders. I am talking about the middle column.

This middle column consists of three small images: The upper one (1) shows the steering mode which turns both axles in different direktionn (for smaller turing circle). The second one (2) shows how the red 2L axle connector is turned. The one at the bottom (3) shows the crab steering mode.

I am talking about the parts directly left from the 3x3 biscuit part: red bush on some kind if axle; two thin 1x3 liftarms. You indicated these parts with a straight white arrow in (1) and (3), respectively.

In (1) and (2) they are arranged in the same way; in (3) they seem to have changed their places.

Edited June 20, 2024 by Timewhatistime

[Timewhatistime]

For anybody who doesn't like this kind of riddles about a well-kept secret:

The crucial part must be the grey knob gear with 45 degree offset, appearing in the 42167 garbage truck for the first time.

[Ngoc Nguyen]

5 hours ago, Timewhatistime said:

a well-kept secret:

I've never said it's well kept 

 

6 hours ago, Timewhatistime said:

In (1) and (2) they are arranged in the same way; in (3) they seem to have changed their places.

Yeah the red bush is supposed to be the indicator of the steering mode. If it's in the left position, the steering mode is counter steering. If it's in the right position, the steering mode is crab steering. You change the steering mode by turning the 1x2 axle connector in red in front of the 3x3 biscuit liftarm. And the bush moves back and forth between those two positions when you rotate the red connector.

 

 

Edited June 21, 2024 by Ngoc Nguyen

[Paul B Technic]

Well done, great result.

[Timewhatistime]

Ah, now I see. Thanks. I was confused by the artificial shadows in the rendered images. After your explanation, I could identify them as mere shadows.

Edited June 21, 2024 by Timewhatistime

[Ngoc Nguyen]

There's another detail that I managed to replicate but forgot to mention. It's very trivial, but it increases the realism of the model.

Rough Terrain Cranes usually have high ground clearance because they need to travel in rough terrains. The clearance is visible in the gap from the ground to the chassis between the wheels. The gap is like a half of the height of the wheel.

 

In my model. I also tried to keep that clearance in my model. It is obviously impossible to have that clearance right at the axles due to the differentials, and at the outriggers as well, but I wanna keep the clearance in the space between the wheels. That means less space for the steering mode mechanism, which compounds the difficulty in designing the crab steering and the mode switch. But I succeeded in the end. You can see the 3 stud clearance between the two axles.

[Timewhatistime]

Maybe the changing between counter steering and crab steering is achieved by a kind of Baker valve gear, which is described in the "most challenging mechanism" thread?

I could imagine this would deliver some good results and could be implemented in the 7x3x3 space. So, the red bush would indicate the position of the controllable pivot. 

 

On 3/15/2024 at 9:00 PM, Stereo said:

Baker valve gear.  Kinematically it's doable, the problems are downsizing it to something that would fit in a MOC, making it sturdy enough to transmit any force, and having enough travel to actuate a pneumatic switch.  To a lesser extent it was difficult to figure out how it even works, from 100 year old scanned documents.

 

 

[Ngoc Nguyen]

3 hours ago, Timewhatistime said:

Maybe the changing between counter steering and crab steering is achieved by a kind of Baker valve gear, which is described in the "most challenging mechanism" thread?

It's not that complicated 

[karmadrome]

Fantastic build, fantastic presentation!

 

[Ngoc Nguyen]

9 minutes ago, karmadrome said:

Fantastic build, fantastic presentation!

 

Thanks a lot!

[Aleh]

Wow, you did a great job with all these renders! 

[Ngoc Nguyen]

8 minutes ago, Aleh said:

Wow, you did a great job with all these renders! 

Thanks a lot!

[Ngoc Nguyen]

Anyway, here's some food for Technic thought, chicken soup for gearhead soul!

 

The front half and the rear half are separate modules. Each module has an interface of 6 pin holes.  Between the two modules exists 7x7x3 (or 7x7x4 depending on your perspective) space. Inside that space is a mechanism that shifts between counter steering and crab steering. How does the mechanism work?  (Of course there are axles going through the pin holes but I already hid them all away, because the lengths are clues as well)

If you're desperate, the answer is only 5 EUR away. 

[Ngoc Nguyen]

So, how does the steering work?

The steering shaft and mechanism are tied into the structure of the undercarriage, so let's take a look through the whole structure.

Since I want the model to have 4x4 drive and 4 wheel steering, this is the most compact legal setup. I'm aware of more compact builds but they are not legal or structurally sound enough.

 

The reason the 28z differential is used is that the drive shaft is transmitted directly up from the driving bevel gear to the fake engine right above the rear wheel. There are 3 possible places to put the transmission: between the two axles, right in front of the rear axle, right behind the rear axle. Since the space between the two axles are for the two mode steering, and the space behind the rear axle is for the outriggers, the only possible place is right in front of the rear axle. That means the drive transmission has to bypass the steering axle, and the only combination that works is 28z differential meshing with a 12z gear, which meshes directly above with a clutch 20z gear.

 

In the photo above you can also see that on two sides are the drivetrains for outriggers and HOG steering knob. To accommodate space for the sideways movement at the two ends, the steering must use a 9L liftarm instead of a 7L gear rack. This setup also makes aligning the front and rear steering positions easier.

 

 

The outriggers are connected to each other through a horizontal axle. This setup is adopted from Akassin's model. On the left side the axle has an 8z gear that meshes with the worm gear to ensure the outriggers can be locked.

 

This is the how the drivetrain for outriggers look from above, for both axles. In order for the front and rear outriggers to rotate in the same direction, the meshing gear in the legs must be in the same relative position to the horizontal axle instead of in mirrored positions. That means they both have to be behind the driving 12z half gears, as highlighted in the photo.

 

You can also see the steering drivetrain has 2 CV joints. What are they for?

The logic of the steering mode is like this. Since the steering angle of each axle is very small, around 10 degree, there's no need for a front wheel steering only. Also, front wheel steering doesn't just involve the steering, it also requires locking the rear wheel steering, which increases the complexity of the problem. Therefore I only need two modes: counter steering and crab steering. In these two modes, the front wheel always steer. Therefore I made the HOG permanently connected to the front wheel steering, through the 3 8z gears in the front, as highlighted in the photo below.

 

Meanwhile, the steering shaft for the rear axle goes into the middle of the chassis, but is independent from the steering shaft of the front axle. On the axle, there is an 8z gear and a knob gear separated by 1 stud.

In the space between the two axles, there's a block called steering shift. It is 6L long and is build at the center of a 11L axle, so that there's an axle of 2.5L on each side. The space between the two axles is 7L wide, and since the steering shift needs to slide back and forth, it has to be 6L long only. 

 

The CV joints at both sides serve two purposes. First, since they have frictionless axle holders, they allow the steering shift to move back and forth. Second, since the frictionless axle holders is 1.5L deep, the steering shift can move by 1L in one direction while is still connected to the other direction by 0.5L. This setup allows transmission from HOG to front wheel steering is continuous; in other words the front axle always steer when the HOG is rotated.

When the steering shift is in the back position, the HOG shaft goes through 3 gears to reach the rear axle steer shaft, while in the front position, the HOG shaft goes through only 2 gears to reach the rear axle steer shaft, therefore driving the rear axle in the opposite direction. Thanks to the new 45 degree offset knob gear, both the HOG shaft and the rear steer shaft are parallel.

 

 

The steering shift has a fixed 8z gear so that a worm gear when rotated can push that gear along with the whole steering shift back and forth by 1L.

 

And that's how the two mode steering works. I'm very happy and proud that I can pull this off smoothly, especially in such a space that's not just small but is also restricted by many other factors. 

Edited September 3, 2024 by Ngoc Nguyen

[Timewhatistime]

Simply great!

It is a new principle, and it uses some features which have not been used for this purpose: the moving in the frictionless axle holders of the cv joints... and the usage of the 2L worm gear as miniature gear rack.

Nice!!!

 

There is an minor mistake in the description, but the image instantly clarifies it: On the steering shaft for the rear axle there is a 8z gear and a knob gear separated by 2 studs (not 1).

 

Question: Is the backlash (which results from 3 (or even 6) 8z gears) within an acceptable range?

Edited September 3, 2024 by Timewhatistime

[Ngoc Nguyen]

8 minutes ago, Timewhatistime said:

Question: Is the backlash (which results from 3 (or even 6) 8z gears) within an acceptable range?

There is virtually no backlash at all. The steering is very responsive. You can see it in action here at 0.37:

 

9 minutes ago, Timewhatistime said:

Simply great!

Thanks a lot!