[MOC] Small 4-axle mobile crane - finished!

[ludov]

See this post for pictures of final result 

 

 

After having put a number of projects on the back burner due to being too lacking skills and/or parts, I figured I should try to build something a) smaller, b) simpler and c) using (mostly) parts I already have. I decided on a small-scale mobile crane, based on the 49.2 mm wheels. I also decided I should start a WIP topic to get feedback and stay motivated to finish (or abandon ship if it turns into a disaster ).

I first did some prototyping of the undercarriage in LDD:

I'm fairly happy with the prototype, although I'm not fully convinced about the styling of the engine compartment. It looks a bit untidy, but I'm not certain on how to change that without resorting to system bricks. Any advice?

 

This being a WIP topic, I also started building, of course. I violated point (c) above a bit, since it turned out I don't have all the parts, but most is there:

So far so good, except the steering long is really poor:

(Bricksafe is cropping the image for some reason: find the full picture here.) You can see that the fat tires and the pivot offset in combination with the close spacing does not allow a lot of space for the wheels to turn. I could space the wheels one stud more, but I think that doesn't look right:

Upper is the current spacing, lower is one stud more. What do you think, form or function?

Edited November 11, 2018 by Ludo Visser
finished!

[M_longer]

49 minutes ago, Ludo Visser said:

What do you think, form or function?

Something in the middle, I think that it could be possible to change spacing to half stud.

[Aventador2004]

Very nice, thought of something like this before.

[jwarner]

Are you planning on putting a working fake engine in the compartment?

[Jurss]

Good start, I like smaller builds.

[ludov]

8 hours ago, M_longer said:

Something in the middle, I think that it could be possible to change spacing to half stud.

This is a good idea. I can use this part to create the half-stud offset quite easily:

Didn't think of that. I'd need to order them though, since I only have two of them, so I'll first prototype it in LDD.

2 hours ago, jwarner said:

Are you planning on putting a working fake engine in the compartment?

Yes, there's room for a small V8 engine. I prototyped something in LDD, but I'd first need to build it to see if it will work properly.

 

Thanks for all the comments! 

[andythenorth]

9 hours ago, Ludo Visser said:

What do you think, form or function?

False dichotomy, prioritise both  

In the pictures, steering angle looks ok, but hard to tell without actually swooshing the truck 

[Jeroen Ottens]

Interesting, will follow this one

For the steering radius, have you considered using a 4-linkage system with a virtual pivot point (like I used on my orange Ford Focus)? This gives a near perfect steering behaviour of the wheels and keeps them in a very small space. It will be tight though to get it all in 7 studs width and I don't know if it is easy to add the different steeringangles.

The engine area is looking cluttered indeed. Can you put a panel on it's long side (maybe using a 3x7 panel) with a beam under it. It willl give a bit of a taper, but it will look much cleaner I think.

[1gor]

14 hours ago, Ludo Visser said:

What do you think, form or function?

Usually compromise, but at the end first impression is what you see, and what I see is interesting small scale Crane project 

[Erik Leppen]

Interesting start. I like this scale (and subject matter, of course). Interesting where this will be going. Especially curious to how you will be doing the outriggers. You're off to a good start already.

 

About the engine compartment. Personally I think the problem with it is twofold. 1. beam stacking, and 2. the panels pointing upwards and sticking out at the top. I would suggest to place the panels horizontally. And maybe use the longer 7x3x2 panels instead of the 5x3x2 you used here.

 

About the steering and wheel spacing. I think you could add tighter steering with the same tire spacing, if you're willing to give up the different steering angles per axle. The problem seems to be not the wheels touching the wheels, but the wheels touching that long steering arm of the second axle. So one possible solution would be to make that steering arm shorter. Another option would be to do that, and add 12:20 gearing to make the front axle steer more. Or use an 1L steering arm instead of 2L for the front axle, although that would increase the torque/friction on the steering drivetrain (but maybe on this scale this would be still acceptable).

 

Anyhow, interesting project. :)

[ludov]

Thanks for all the feedback, very helpful!

3 hours ago, Erik Leppen said:

About the steering and wheel spacing. I think you could add tighter steering with the same tire spacing, if you're willing to give up the different steering angles per axle. The problem seems to be not the wheels touching the wheels, but the wheels touching that long steering arm of the second axle. So one possible solution would be to make that steering arm shorter. Another option would be to do that, and add 12:20 gearing to make the front axle steer more. Or use an 1L steering arm instead of 2L for the front axle, although that would increase the torque/friction on the steering drivetrain (but maybe on this scale this would be still acceptable).

This is a good observation. I like the different steering angles, so I'd like to keep it. I'm afraid that using a 1L steering arm will restrict the motion just as much as it is now...

I'm still trying to figure out the crab steering that you added to your 5-axle crane  (the topic just resurfaced earlier today). I still have much to learn.

13 hours ago, Jeroen Ottens said:

For the steering radius, have you considered using a 4-linkage system with a virtual pivot point (like I used on my orange Ford Focus)? This gives a near perfect steering behaviour of the wheels and keeps them in a very small space. It will be tight though to get it all in 7 studs width and I don't know if it is easy to add the different steeringangles.

I've played around with that when I saw it in a build from @Erik Leppen (http://www.erikleppen.nl/lego/bouwinstructies/vrachtwagens/enforcer.php). His approach would allow to implement different steering angles also by longer arms, but it seems (at least, from this picture) that alignment is a bit of an issue (the wheels show some toe-in/out due to the steering links not being "in system"). I will probably try again in a future build when I'm more confident in my building, but for now I think that increasing the spacing by half a stud (as suggested by @M_longer) is the best way to not overcomplicate things :

(From top to bottom: 6, 6.5 and 7 studs spacing)

I think it looks nice; will try building it to see how it looks "in the brick".

 

13 hours ago, Jeroen Ottens said:

The engine area is looking cluttered indeed. Can you put a panel on it's long side (maybe using a 3x7 panel) with a beam under it. It willl give a bit of a taper, but it will look much cleaner I think.

 

4 hours ago, Erik Leppen said:

About the engine compartment. Personally I think the problem with it is twofold. 1. beam stacking, and 2. the panels pointing upwards and sticking out at the top. I would suggest to place the panels horizontally. And maybe use the longer 7x3x2 panels instead of the 5x3x2 you used here.

I don't know how I missed the 3x7 panel (assuming you mean this one). Finding panels in LDD is always a challenge for me   It seems a perfect fit. I'll try to rework the engine compartment with this panel. Thanks for the tip!

[Didumos69]

It's admirable how you try to build at such a small scale and (mainly) with parts you already have. The undercarriage and cabin are looking good already and I think the 6.5 stud axle spacing seems to be the best option. Good luck!

Edited March 7, 2018 by Didumos69

[Erik Leppen]

15 hours ago, Ludo Visser said:

I don't know how I missed the 3x7 panel (assuming you mean this one). Finding panels in LDD is always a challenge for me   It seems a perfect fit. I'll try to rework the engine compartment with this panel. Thanks for the tip!

Which is why I would advise to always build with real bricks, alongside your digital design. Especially when doing bodywork. (I think digital building is better suited for designing geartrains, functions and complex structures rather than bodywork.) You don't forget a panel if it's right in front of you in your panels bin :)

[Ivan_M]

I would suggest to use 7L rack for 1st and 4th axle and 7L liftarm with 1x4 rack for axles 2&3. The axles 1&4 would steer with 12t bewel, axles 2&3 with 8t pinion. You will get different steering angle this way and perfectly aligned wheels as well (as opposed to 12:20 reduction).

I'm looking forward to your result!

[ludov]

Time for a much overdue update...

I considered @Ivan_M's suggestion, but it took too much vertical space, so I went for @M_longer's suggestion of making the spacing the axles 6.5 studs. In the end though, I had to rebuild the entire frame. Removing the horizontal 7M beams that were holding axle 2 and 4 meant losing some connection points and it took me a while to work around that. Of course, as I was doing that, I found a lot of other things that could be improved as while, which made me take even longer. But the result was worth it:

Look at that steering lock 

I also redesigned the bodywork as per @Jeroen Ottens suggestion using the 3x7 panel and a beam. It looks really good, I think:

Next steps:

1. Order a few steering parts from Bricklink, as I don't have enough of them. Maybe also some panels, since the yellow ones I have are from the 42009 Mobile Crane MkII, which means most of them have stickers on them and I don't know how easy they'll come off...
2. Disassemble my Claas set to get some much needed parts
3. Finish the undercarriage
4. Start with thinking of the actual crane...

Comments welcome! 

[doug72]

26 minutes ago, Ludo Visser said:

 

1. Order a few steering parts from Bricklink, as I don't have enough of them. Maybe also some panels, since the yellow ones I have are from the 42009 Mobile Crane MkII, which means most of them have stickers on them and I don't know how easy they'll come off..

Comments welcome! 

To remove stickers use a the edge of a sharp blade to lift a sticker corner enough to grip with fingers then s l o w l y ease it free. Go to fast will break them. Warming them slightly helps. I have transferred some several times this way.

[Aventador2004]

Good to see progress, I am finishing my mobile crane, so I hope to see this finished!

[jwarner]

2 hours ago, Aventador2004 said:

Good to see progress, I am finishing my mobile crane, so I hope to see this finished!

Same here. Guess we all had the same idea

[Aventador2004]

14 hours ago, jwarner said:

Same here. Guess we all had the same idea

Cool. Best of luck Ludo!

[Erik Leppen]

Interesting update, Ludo. I think the decision to go for 6.5 stud offset works very well. The wheel spacing is not at all distracting, which is a good thing. I really like your "internals" photo, it shows what a dense build this is. I really like these smaller but tightly packed models.

 

However, from the render, I do feel the proportions are slightly "off" though. After looking at it for a while, I think the reason is that the cabin is pretty big and sits pretty low to the ground. The ground clearence is rather bad. I understand that you need all room you have in the chassis, but maybe you can increase the "visual" ground clearance by raising the bottom of the cabin? By making the cabin 8 studs tall instaed of 9? What would happen if you were to raise the entire bottom half of the cabin, but keep the roof at the current level? (so, the windscreen will then be one stud lower) And then work from there? Although it could be that if you do that, the outriggers will look weird, because they are also low to the tround, and probably can't so easily be raised.

 

Speaking of which... how do your outriggers work? Do you have any pictures of those?

[1gor]

Nice update 

[LvdH]

8 hours ago, Erik Leppen said:

Speaking of which... how do your outriggers work? Do you have any pictures of those?

It looks like a worm gear is behind the 8 tooths, and I think the exhaust stacks and red bushes at the rese lower them. I see a black gear housing at the exhausts so that seems like it to me. 

[ludov]

21 hours ago, Erik Leppen said:

Interesting update, Ludo. I think the decision to go for 6.5 stud offset works very well. The wheel spacing is not at all distracting, which is a good thing. I really like your "internals" photo, it shows what a dense build this is. I really like these smaller but tightly packed models.

 

However, from the render, I do feel the proportions are slightly "off" though. After looking at it for a while, I think the reason is that the cabin is pretty big and sits pretty low to the ground. The ground clearence is rather bad. I understand that you need all room you have in the chassis, but maybe you can increase the "visual" ground clearance by raising the bottom of the cabin? By making the cabin 8 studs tall instaed of 9? What would happen if you were to raise the entire bottom half of the cabin, but keep the roof at the current level? (so, the windscreen will then be one stud lower) And then work from there? Although it could be that if you do that, the outriggers will look weird, because they are also low to the tround, and probably can't so easily be raised.

 

Speaking of which... how do your outriggers work? Do you have any pictures of those?

Thanks! You're right about the cabin: the other day I was playing around in LDD trying to fit some seats in, when I realized it's too tall. The windshield is at least a stud too high with respect to the rest. I will try to fix that; should be fairly easy without having to redesign everything.

You asked about the outriggers before, and I forgot to answer: they're really simple... The current implementation has the outriggers extend outwards just by pulling on them by hand. They gear rack rolls on the 8-tooth gear that you see sticking out in the front. It turns on a friction pin, not connected to anything else since there's no space left in the bottom part of the frame. The lowering of the outriggers is done with the mechanism that's on the Arocs and also on 8053. Indeed via the red bushes.

13 hours ago, LvdH said:

It looks like a worm gear is behind the 8 tooths, and I think the exhaust stacks and red bushes at the rese lower them. I see a black gear housing at the exhausts so that seems like it to me. 

You're giving me way too much building credit   On the bike earlier today I was thinking though that I can maybe swap the gear rack upside down and maybe have an axle running through the upper part of the frame somewhere so that at least left and right are in sync, perhaps controlled via a gear or something. The exhaust stacks are for the steering; left and right are linked since there will be a boom in the middle.

[ludov]

I got sidetracked and built a new type of outrigger:

It's one stud higher and one stud thicker than the other design, but it allows to be controlled from a central control, if i can manage to squeeze it in somehow... I foresee a v3.0 of the chassis... I hope I'm not being too ambitious here...

[ludov]

Update time! It's not that I've been sitting still... just rebuilding the chassis about a dozen times.

After @LvdH's guess at how the outriggers extended, I was determined to actually incorporate at mechanism to extend all of them in unison, instead of manually as in the previous version. Of course, there was no room for that, so I soon decided to ditch the chassis. I had a couple of tries at designing new outriggers with the idea of then building a chassis around those. I finally settled on this design, which is strong enough to lift the crane up (for now at least):

Internally it looks like this:

The toothed bar 8M is supposed to sit on the two 1x1 round plates, but LDD won't let me due to the 3M beam that is supposed to hold it in place. This makes me doubt if it is a legal construction. In reality it fits, although if I put a 1x8 plate under the toothed bar, instead of the 2 round plates, it gets stuck. What do you guys think? Acceptable or not? Other suggestions to keep the outrigger in place (replacing the 3M beam)?

 

The gearbox around the outriggers is fairly compact, although on this scale everything appears big:

Routing the axle that is going to connect the front outriggers with the back ones (black, barely visible in the center of the turntable) was a real pain, but I managed.

In order to fit the outrigger gearboxes, I had to turn the steering mechanisms around. This had all kinds of implications for the chassis, as you might see here:

The core of the chassis is 3M "thick" in order to support the rather segmented lowest layer...

I'm curious to hear your opinions on the outriggers!