[TC22] Compact Mobile Crane

[2GodBDGlory]

So, for this contest I decided I would build a Mobile Crane of some sort, because it has similarities to the boxy cars I'm used to building, and also has a fairly convenient shape for the volume constraints. At first I thought I would be building a fairly standard crane, probably with six wheels. I planned on using Corvette wheels, but since I only have four of them, I thought I might have to do something weird, like put Model Team wheels on one of the sides. As I looked for inspiration, though, I found a compact-looking mobile crane with only four wheels, which fit my supplies better, so I decided to take inspiration from the Liebherr LTM 1040-2.1

The planned features are:

• Two-stage extending boom
• Lifting boom
• Winch
• Outrigger extension
• Outrigger lowering
• 4-wheel steering
• Superstructure rotation

and possibly if I have room:

• 4WD and a micro I-6 piston engine
• Live axle suspension

Another design goal is to have all the controls manually operated from the chassis--I would like to have all the controls for similar functions in a similar location, and I feel like having controls on the superstructure will result in the boom swaying around as the control knobs are twisted. However, I've got three functions in the superstructure, and we all know how impractical it is to get three functions through one, so I thought of an unusual idea that might help here. It would essentially be a distribution gearbox placed inside of the turntable, switching between functions in the upper half, but with the switch being controlled from the bottom. The plan is to base it off of the 24/16T differential. The 16T side will constantly be driven from the bottom, but with provision to allow the differential carrier to slide up and down a stud. The 24T side, though, will engage different gears depending on whether the carrier is in the upper or lower position, causing it to operate different functions. We'll see how that turns out...

I started by developing a design for a two-stage boom based on the gear rack housing parts:

I really liked the design--stuff just fit nicely, and the grooves on the insides of the panels were perfect to help locate the red part as it extended. However, as I began to look at scaling the crane, I realized that in order to build the largest possible crane that would be within the rules, I'd be using 56mm balloon tires, and that if I did that, I'd need to have a far, far bigger boom. This crane seems to have a disproportionately large boom! My planned dimensions for the crane are 13 studs wide, 16 studs tall, and 48 studs long, and my boom is currently sitting at exactly 48!

Boom contracted

The boom is extended by that 3L worm gear driving a set of 4L racks

It is driven through these gears. I'll have to put some kind of pivot in still.

It extends really tall!

This is the how the middle segment is constructed

And this gives a glimpse of the pulley system needed to extend the smallest segment.

So far, I really like the boom, but I think the outriggers are going to have a really hard job keeping the crane upright with such a huge boom on such a small carrier!

Next I'll probably work on figuring out the details of the rest of the superstructure.

[TechnicRCRacer]

Looks like we have similar ideas! That boom sure is impressive, do you think it will be challenging to fit it on the superstructure within the size limit?

[2GodBDGlory]

13 minutes ago, TechnicRCRacer said:

Looks like we have similar ideas! That boom sure is impressive, do you think it will be challenging to fit it on the superstructure within the size limit?

I don't think fitting it will be too hard, though I'll have to watch the height limit. It is more or less in scale, so the other stuff will hopefully work out, but I think the biggest problem is going to be stability.

[johnnym]

Maybe you can put some weight bricks in the base and/or the superstructure in addition to outriggers. Not sure though if this will make a big difference.

[2GodBDGlory]

42 minutes ago, johnnym said:

Maybe you can put some weight bricks in the base and/or the superstructure in addition to outriggers. Not sure though if this will make a big difference.

Yeah, I've got two weight bricks, and I'm hoping to put them in. I'm sure they'll help, but unsure if it'll be enough.

[2GodBDGlory]

So, for this update I've added the rest of the functional parts of the superstructure (A cab and paneling can come later), as well as the connection to the chassis, and the manual control gearing for the winch, rotation, boom lifting, and boom extension have been added.

Here is the "hook." Because of a rather inefficient cable system, considerable weight was needed to keep it pulled all the way down. I started off with a simpler setup using just the magnets, which I figured would add weight without taking much space, and would give me a cool, unique way to operate it, by picking up metal things. That wasn't heavy enough, though, so I had to work in a weight brick, but I kept the magnets because while I may not need them for weight anymore, I still thought they were a fun idea.

Here is the bottom view of the carrier part under the superstructure. The middle rear knob runs boom lift and extension through the gearbox, while the left and right ones control superstructure slewing and the winch.

Here is the boom raised. The linear actuator positioning was a bit odd, but I didn't think I could route drive to have rear-mounted actuators like on most mobile crane models I've seen. This seems to work fine, though. Note the boom mounted on small turntables, and the winch in the middle. I would have liked to do a more typical winch, but space was super tight--the boom rests directly on top of the spool. The small spool seems to be working fine, though, because I'm using compact dental floss instead of regular string that would fill the spool too fast. This works nicely, especially since I don't have any normal string long enough anyways.

I also got in the function I think most interesting, the two-output distribution gearbox with both outputs above the turntable, and the shifting control below it.

Spoiler

The working principle can be seen in this mock-up (Imagine a turntable in the middle, and the two sides not locked together otherwise):

The 24/16T differential housing I was planning to use wouldn't work, since in one position the 24T side would lock in the turntable's mount, but this set of 20T clutch gears locked together by a transmission driving ring worked well enough. A simple 2L beam on the bottom pressed up against the lower 20T gear to shift up into the other position, and a spring-loaded beam on the top forced it back down when that 2L beam got out of the way.

Position 1

Position 2

Position 1

Position 2

Occasionally I'm getting skipping from one of my bevel-gear connections when trying to extend the boom, but overall everything is working pretty well, so I'll be able to venture into some other stuff on the chassis for my next update.

[Jundis]

I'm baffled that this will fit in the geometric limits of this contest, whoa!

I am really looking forward to this, the string guidance via the selector switch is really neat ;-)

[2GodBDGlory]

4 hours ago, Jundis said:

I'm baffled that this will fit in the geometric limits of this contest, whoa!

I am really looking forward to this, the string guidance via the selector switch is really neat ;-)

Yeah, I think the size of the boom is somewhat overkill, and will cause the model to be very cramped in other areas, but I think I can get it all to fit in the limit. It kind of doesn't feel like I'm building a mini vehicle, though, it feels more like a full-size model in a smaller space.

[2GodBDGlory]

Update time!

As you can see, I've just about finished the mechanical parts of the chassis, with the only thing I expect to add being a steering wheel in the cab hooked up to the wheels. (HOG wouldn't work well on the top thanks to the boom, and I think despair is the correct response to trying to route it to the back)

Here I've got the boom lifted and rotated 180 degrees.

Control knobs: Both the far left and far right ones run the outriggers for symmetry, the middle one runs boom lift and extension through the gearbox, the middle-left one runs the winch, and the middle-right one slews the superstructure. Also note the outrigger legs in the retracted position (They flop outside of my 13-stud width, because of a necessary half-stud offset in the geometry forcing them out, but they can easily be pushed into compliance, so I don't think they'll cause me volume issues.)

Outriggers extended: I didn't have space for independent leg extension and lowering, and the simple 4-bar linkage type lowering and extending from the crane used in many official sets would have looked too minimal for such a long boom, so eventually I came up with this super compact setup that uses extra linkages to pull the legs down in the same motion. It's based on having friction with the black 10L axle on the left and the LBG 9L axle on the right extend, which forces the extension to pull down the legs. The time at which the legs lower is somewhat random because of variations in friction, but all four legs extend and lower easily in one motion, which is pretty cool. Obviously, these legs provide little to no support...

Bottom view: It's really cramped. I've also got the wheels at a half-stud offset, aiming to have only a half-stud of ground clearance, allowing the half-studish protrusion of 12T gear on the top of my boom to fit within my 16 stud limit.

Overall, it's getting strange proportionally. As I said, I scaled this to use 56mm balloon tires, but I realized that if I used those, they would be sticking up above the turntable, preventing it from rotating. In the end, these tires were the biggest I could fit. 

I think my issue with scale is that while the boom is the correct length for my planned dimensions, by the time I added the two-stage extension, it had become too large vertically, forcing everything below it to be squished down.

I think this model is going to be more on the over-engineered side than I expected, so I don't see it being competitive in the contest, but it's still fun and I want to finish it. I guess in theory I might finish in time to throw together a second model to submit instead, but then I'd actually have to find something else eligible that I have interest in building!

[2GodBDGlory]

Here's my final update!

Since the last time around, all I've added functionally is connecting the steering wheel in the cab to the wheels, but I made a few other tweaks, such as getting rid of the weight brick on the hook, as well as the pulley for the hook, and adding the larger-diameter worm gear to the boom extension to keep it from skipping. Aesthetically, I added the main cab and the operator cab, some lights, and red highlights. Below here I'll just give a normal MOC presentation, rather than a WIP one:

------------------------------------------------------------

Here is my entry for Eurobricks contest TC22, a compact mobile crane. In order to be within the 10,000 cubic stud limit, this MOC was made to a 13 stud width, 48 stud length, and 16 stud height, for a total of 9984 cubic studs.

Spoiler

Functionality includes:

• Steering from steering wheel in cab
• Outriggers that extend and lower using a rear control knob (actually two knobs hard-coupled together for convenience and symmetry)
• Rotating superstructure via rear knob
• Winch via rear knob
• Lifting boom via rear knob
• Two-stage extending boom via rear knob
• Two-output distribution gearbox for boom lift and extension, controlled from one knob and one selector on the chassis, with two outputs on the superstructure.
• Magnetic "hook"

Most of the functions were quite straightforward, but three deserve extra mention.

1. Boom extension. This was the first time I had tried making a two-stage extending boom, so it wasn't perfect, but it was still quite cool. A large-diameter worm gear run off a crank ran a long string of 1x4 gear racks to extend the middle segment of the boom (4x3 studs), while two pulley systems caused the end segment of the boom to simultaneously extend out of the middle one, allowing the boom to extend to a little less than three times its original length. With such a large boom on such a small crane, it looked pretty impressive when extended. Sadly, there was too much friction to extend it effectively from the main knob, and while one could extend it by hand by pushing on a different gear, it would take an immensely long time.
2. Outriggers: The outriggers had to be very compact to fit within the size limitations for the contest. In the end, they were based on two 13L gear racks pressed against each other and connected with gears so they would extend together. Furthermore, the legs were attached to them on a pivot connected to a transverse axle. When the legs reached nearly full extension, this axle would be forced to catch and pull the leg down, allowing for both to be controlled from the same knob. The legs weren't especially stable, but they did help keep the crane stable despite the very long boom.
3. Distribution gearbox: The unusual distribution gearbox was developed in order to allow all three superstructure functions (winch, boom extension, and boom lift) to be controlled from the chassis. The winch was driven by a central axle through the turntable from its own knob, but the other two functions used the gearbox. It was shifted with a small lever on the side of the crane, and would push a setup of a transmission driving ring with a 20T clutch gear on each side up and down. In all cases, this assembly was driven from a single knob on the chassis, but depending on whether it was up or down, it would drive different functions on the superstructure. Because the shift lever could only push the gear assembly up and not down, there was a rubber-band loaded lever on the top to force the gears down when the shift lever got out of its way.

Mock-up. Imagine the two sides as connected only by a large turntable.

WIP model shifting

 

Overall, I think the model had fairly impressive and interesting functions, and looked decent in my eyes. It definitely had its shortcomings, such as the inability of the boom to rotate while lifted, the extreme difficulty of extending the boom (unless you resorted to an external motor), and the weak chassis (the cab would sometimes scrape the ground.) I don't have ambitions of beating the far more experienced builders in the contest, but I'm glad to have participated, and gone outside my comfort zone a bit.

More images at:

https://bricksafe.com/pages/2GodBDGlory/compact-mobile-crane

Edited April 30, 2022 by 2GodBDGlory
Added bounding box images

[Thirdwigg]

Well done with all the features! There is so much packed into this MOC, which is becoming a bit of a trend with you @2GodBDGlory. The proportions are a little wonky to me, but it must be the price to pay for that huge boom!

[2GodBDGlory]

20 hours ago, Thirdwigg said:

Well done with all the features! There is so much packed into this MOC, which is becoming a bit of a trend with you @2GodBDGlory. The proportions are a little wonky to me, but it must be the price to pay for that huge boom!

Thanks! I do like focusing on features. I'd agree that the proportions are odd, and I think you're right that it's the boom's fault. I believe its length is correctly scaled to the crane I was basing it on, but I never scaled the height of the boom part, and I'm assuming that in order to get the multi-stage setup inside, I had to exceed the height it should have had, cutting down on space below.

[Nazgarot]

I don't think the boom is to big compared to the real thing, but making it very square has made it look very dominating. If you could use the rounded panels it would look a lot less massive. 

https://www.bricklink.com/v2/catalog/catalogitem.page?P=11954#T=S&C=3&O={"color":3,"iconly":0}

 

Also the area between the cabin and the crane base looks kinda skinny... Might do it some good to beef up / cover up this area.

 

But I love the functionality! Really good work!

 

_ED_

Edited April 27, 2022 by Nazgarot

[2GodBDGlory]

1 hour ago, Nazgarot said:

I don't think the boom is to big compared to the real thing, but making it very square has made it look very dominating. If you could use the rounded panels it would look a lot less massive. 

https://www.bricklink.com/v2/catalog/catalogitem.page?P=11954#T=S&C=3&O={"color":3,"iconly":0}

 

Also the area between the cabin and the crane base looks kinda skinny... Might do it some good to beef up / cover up this area.

 

But I love the functionality! Really good work!

 

_ED_

Thanks for the feedback! You're right, those curved panels could have looked good. Unfortunately, I've only got two of that multi-hole type in black, and only one of the fewer-hole type in black, and I don't think I have enough in any other color either, so square it must be!

You're right about it looking skinny between the cab and the superstructure, but this was done intentionally. As pointed out in the video, when the boom is lifted, because of a poor pivot point location, the rear end of it sticks fairly far down, causing it to interfere with rotation at times because it will hit the top of the outrigger mechanism. Because the boom needs this extra space, I left it empty there to allow the boom to swing through that arc while raised up, but I don't recall ever actually doing that maneuver once it was finished! Perhaps it would have been better to use that space to reinforce my sagging cab and just rule out that option, but I'm probably not going to change anything at this point. (Too much trouble to take more pictures ) Good observations, though!

[GerritvdG]

I really like the functions, impressive! The distribution gearbox through the turntable is brilliant and is a step forward compared to the 8043 solution.

[Erik Leppen]

This has to be the model I least expected. Proportion-wise it looks a bit like a caricature, but it seems to be the most functional thing in existence. It totally doesn't feel "small" as the contest intended, but if it fits in the box, it counts. Though I must say everything about the model screams "I just wanted to fit as much in the box as possible" rather than "small-scale construction vehicle" ;) But oh well. I think it's quite the result because of this :)

Note that the model is 48 studs long, not the 44 that was claimed, meaning the volume is 48 x 13 x 16 = 9984. Still counts, and shows you really found the limit of what's possible :)

[2GodBDGlory]

1 hour ago, Erik Leppen said:

This has to be the model I least expected. Proportion-wise it looks a bit like a caricature, but it seems to be the most functional thing in existence. It totally doesn't feel "small" as the contest intended, but if it fits in the box, it counts. Though I must say everything about the model screams "I just wanted to fit as much in the box as possible" rather than "small-scale construction vehicle" ;) But oh well. I think it's quite the result because of this :)

Note that the model is 48 studs long, not the 44 that was claimed, meaning the volume is 48 x 13 x 16 = 9984. Still counts, and shows you really found the limit of what's possible :)

Yeah, I think you're right that I'm kind of stretching the limits of what the contest was meant to be, for better and for worse! Good catch about it being 48 studs long; I knew I designed it to be as big as possible, so I do recall thinking it odd that my final volume had that much leeway. I must have just miscounted at the end, so I'll fix that in the post. Thanks!

[LEGO Train 12 Volts]

Very cool, thanks for sharing the video!