[REVIEW] 42055 Bucket Wheel Excavator

[Blakbird]

42055 - BUCKET WHEEL EXCAVATOR

INTRODUCTION

I never thought LEGO would make a bucket wheel excavator (BWE). First of all, the vast majority of Earth's population have no idea what it is (excepting the Germans). Secondly, such a model would have to be scaled around a bucket and therefore would be enormous even if made at the smallest possible scale. It just didn't seem likely, yet here it is.

Bucket wheel excavators are among the largest pieces of mobile equipment ever created by humans. Whereas a standard hydraulic excavator removes material one bucket at a time and must empty each load individually, a BWE removes material continuously and transfers it via a complex series of conveyors to a fleet of waiting trucks. These machines are used in open pit mining to remove the over-burden: the loose soil and rock on top of the seam of target material. They excavate not downward, but forward. The machine is placed below grade, and then slews across a wall of material to bring the grade down to the level of the machine. Although they may have on-board hydraulics, these machines are electric and are tethered to the power grid via a cable large enough to run a small city. Though technically mobile, the machines move rarely and slowly and doing so is a major operation. They are constructed on-site at the mine since it is impossible to move them over long distances.

Only the Germans have a unit large enough to describe the amount of material these machines remove: the scheisse-tonne. The LEGO model happens to include several scheisse-tonnes of overburden for your pit mining enjoyment.

All BWEs share a common feature of a rotating bucket wheel, usually with at least 16 buckets. After that, the designs vary considerably. The largest and most familiar type of BWE is the gantry type. This type uses tall gantry booms and cables to support the bucket wheel arm.

Set 42055 is clearly not intended to be a gantry type BWE, but seems modeled after a C-frame type like the Sandvik PE100. Even so there are clear differences. Whereas the LEGO model has the counterweight on the opposite end of the bucket wheel arm, the real BWE has the counterweight much lower for greater stability. Given the structural limitations of LEGO, this seems like a reasonable compromise.

Although there has never been an official LEGO Technic model of a BWE before, the topic is not unknown among AFOLs. A couple of examples are shown below. The first, from Holger Matthes, is a gantry type built from traditional studded Technic.

The second model by Desert752 uses studless building. Both models have many more parts and motors than 42055.

SET INFORMATION

Set Number: 42055

# of Parts: 3927

Main Model Weight: 3.5 kg

Main Model Size: 83cm x 40cm x 30cm

THE BOX

This is a big box, roughly the same size as the UCS star destroyer and death star boxes. Unlike those boxes though, it does not have a cover that lifts off. Instead it has a top flap which shows the functions with a huge picture. The box opens to either end.

Front

Back

Front flap

CONTENTS OF THE BOX

Instructions

The instruction book is a massive brick nearly the size of the Porsche manual. It has 552 pages, 72 steps in the truck, 669 steps in the main model (not including callout steps). The manual is reasonably protected in a snug plastic bag along with the stickers but no cardboard. Mine was in good shape.

Stickers

There is an ample sticker sheet with all of these used for the main model. Quality is typical.

Bags

The parts are split into 8 sets of numbered bags which nearly fill the box. Some large bags contain smaller bags.

3x bags numbered 1

4x bags numbered 2

3x bags numbered 3

5x bags numbered 4

2x bags numbered 5

9x bags numbered 6

3x bags numbered 7

3x bags numbered 8

HIGHLIGHTED PARTS

This set is a smorgasbord of parts, and not just because of the total part count. There are a huge number of useful and/or rare parts here including:

• 53x 5x7 frame
  
• 22x red 16-tooth idler gears
  
• 19x 20-tooth bevel idler gears
  
• 24x 90deg corner pin connectors
  

The biggest obstacle to a model like this is the slew ring. The turntables in the LEGO parts palette were simply too small and weak to support a large overturning moment, so custom solutions were always required. LEGO has finally solved that problem with some new parts. These giant parts can be used as ring gears (like in the bucket wheel) or as huge turntable (like in the slew ring). 14 of them are included in the model.

When four quarter segments are connected together, you get a complete circle with 140 teeth.

There are also 8 new buckets. The 3 hole attachment along the back of the bucket was needed for this model.

THE BUILD

Bag 1 - The Truck

The build begins with the mining dump truck in white. There is nothing special to say here except to note that it is NOT the same as the 42035 yellow truck. Although the scale and subject matter are the same, this truck does not have a moving engine.

There are also a pile of rocks included for the BWE to dump into the truck.

Bag 2 - The Carrier

The second portion of the build is the main structure of the carrier. As you might expect, this needs to be really strong to support such a huge model. Looking at the picture, you can see that the entire thickness is supported with 5x7 frames making this thing a real brick. The corners are reinforced with 3x5L liftarms and 11L double angled liftarms. This assembly is mostly structural; the only moving parts here are the axles to drive the sprockets.

The 4 red pins with bushing will be used to attach the superstructure.

Bag 3 - The Treads

The third bag builds the tread assemblies. These are two identical assemblies (rather than mirrored). I was a little surprised to see the black tread links here given that the conveyor uses DBG links. There is no suspension.

Then the two tread assemblies are connected to the carrier, completing it. I was worried about the use of bevel gears in what is sure to be a highly loaded drive assembly, but the use of a gearbox bracket prevents slippage.

Bag 4 - The Slew Ring

The bottom of the superstructure is build next and sits atop the slew ring. There is a LOT going on here as you can see from this plan view. The only function that passes through the slew ring is main drive, but the smaller turntable also passes the power for the output conveyor. A few DBG wedge belt wheels can be seen positioned circumferentially. These ride on the slew ring to support the imbalance of the superstructure.

The assembly is then connected to the carrier along with the linear actuators used for tilting the main arm. The three vertical axles seen in the front will receive power from the arm.

Now the support towers have been started as well as the mechanism to control the angle of the output conveyor. Another 180 degrees worth of ring gears are used to support it and are concentric with the main slew ring. A pair (upper and lower) of standard size turntables are used to center the superstructure while the slew ring supports the weight and moment.

Bag 5 - The Output Conveyor

The relatively simple bag 5 is the output conveyor. It is just some sprockets, supports, treads, and a wall.

This is suspended at a fixed elevated angle above the upper turntable, and a chute above it funnels the rock and earth from the main conveyor to the output conveyor. This is centered so that it works regardless of which direction the output is facing.

Bag 6 - The Bucket Wheel

Bag 6 represents by far the major portion of the build and makes up the main digging arm. We start with the support for the bucket wheel including the chute that funnels the material from the bucket to the conveyor. It is important that there be no gaps so parts can't into the mechanism and jam it.

The bucket wheel itself is pretty simple. It uses 8 ring gear segments and 8 buckets.

After the bucket wheel is attached, you can see the 6 pairs of 12-tooth double bevels gears which center and support it held by a radial spiderweb of structure.

Now the main conveyor is built and a lot of structural reinforcement is added. This arm is cantilever a long way from the main frame, so it needs to be stiff not only in bending but also in torsion. The 5x7 frames and diagonal members you see help a lot with this.

Here is a view of the completed bag 6 arm (bag 7 will build the back of it). The yellow axle protruding is used to drive the conveyor.

Bag 7 - The Counterweight

The back of the arm contains the counterweight. Why make it a boring inert mass when you can use batteries and a gearbox for weight instead?! The gearbox here is pretty intricate and is explained further later on. A single XL motor drives all functions and has plenty of power. At the stage shown, the gears are all present but nothing is supported yet.

Now a bunch of structure has been added to properly support the gears. This view is from the bottom of the gearbox.

After the gearbox counterweight is attached to the front of the arm you have a very long, but very rigid, beam assembly. The panels and labels for the switches effectively hide the awesomeness of the gearbox. I kind of wish the panels were transparent.

The completed arm in a perspective view.

Now the arm is attached to the main frame via a pair of small turntables about which it pivots. Then the top of the frame is added. The model may look complete at this point, but there are still a lot of aesthetic details to add.

Bag 8 - The Operator Areas

Box 8 adds the details needed for a human (or minifig) to actually operate such a beast. This includes railings, ladders, and the operator's cabin.

This is what the model might look like to a mini figure for scale. Note however, that this model is much smaller than minifig scale.

HOW DOES IT WORK?

OK, we've built this thing and we know that it's huge, but what about the functions? Does it work, and how does it work? Is it just a big monster that doesn't do much? Hopefully this picture will answer that last question in the negative. There is in fact a lot going on here.

In case you couldn't figure it all out from just looking at that cutaway, let's look at a color coded animation. This breaks the functions apart to make them more understandable. Blue is motor drive, orange is inside the gearbox, yellow is main drive, green is conveyors and bucket wheel, and red is rotation.

Let's dig in further. Here is a view of just the gearbox, but it is still too hard to understand without some colors. You can see the 3 white clutch gears which are used to protect the gearbox from stalling.

That's better. Blue is the motor drive. The XL motor is geared down 5:1 at the point that it rotates the center blue driving ring. If no driving rings are engages, nothing turns except for the blue parts. The center driving ring can engage either the orange or the green parts. The orange parts and internal to the gearbox and don't drive anything directly. The two orange driving rings rotate in opposite directions. The yellow driving ring outputs to the main drive, and can make the model go either forward or reverse depending on which direction is engaged. Note that the main drive is VERY slow, but I think this is probably scale accurate. Even if you desired the model to go faster, I wouldn't recommend trying to get any more power down that long gear train.

If the green gears are engaged, they output to drive the conveyors and bucket wheel. The red driving ring can be engaged only if the red is already engaged. This controls the slewing and, like the orange gears, can reverse direction without reversing the direction of the motor. In fact, the battery box is blocked so the motor can only run one direction. Like the driving, the speed of the other functions is slow, but quite scale accurate.

This shows the system for main drive, not counting the gearbox. The power has to go a LONG way to get down to those threads. As you can see, it has to run concentrically through the turntable and there are a pile of idler gears used along with an additional 5:1 reduction for a total of 52.1:1 (there was an additional 20:16 in the orange gears). I found that it works surprisingly well with no trouble moving the model on a level surface.

The linear actuators for adjusting arm angle are as simple as it gets. I was surprised to see the the whole axle rotates even though it also supports weight. This is generally a bad idea, but in this case the arm is so well balanced that there is hardly any load here.

Next is the slewing function. Note how the 20 tooth idler gear is used to pass the torque past the arm pivot axis. After than, it is just a pile of spur gears used to get us over the fixed internal ring gear.

This shows the conveyor drive system. The sprocket for the main conveyor just tees off from the driveline. Note that the drive of the bucket wheel is actually powered by the tread links of the conveyor; there are no gears or axles running out the length of the arm. The main and output conveyors run off the same driveline so are always moving together. The gears for the output conveyor must pass through the upper turntable to allow the conveyor to pivot.

Here is a close-up of the bucket wheel. The greatest inefficiency in the model happens here. The black double gears don't just drive the wheel, they actually support it. This means that the upper gears in particular have a lot of weight on the teeth which causes a bunch of friction. A real BWE would support the wheel with bearings so the gears only carry torque. With that said, the bucket wheel still works fine. I have not had any trouble with it but it can be a bit jerky because of all the compliance in the system.

Finally, the output conveyor locking system is one of the more clever and unexpected functions in the model. The lower turntables rotates with the superstructure, and the upper turntable rotates with the output conveyor. If the driving ring is in neutral, then these turntables are independent and you can freely adjust the position of the output conveyor. If the right hand driving ring is engaged, then the conveyor is grounded to the superstructure and rotates with it. On the other hand, if the left hand driving ring is engaged then the upper and lower turntables are locked together and rotate in opposite directions. The effect of this is that position of the output conveyor remains fixed with respect to the ground while the superstructure slews. This is exactly what you want while loading a truck. Of course, there is plenty of backlash in the gears so it doesn't work perfectly, but it works well enough to demonstrate the idea.

SUMMARY

What can I say other than to utter lots of superlatives? This is the biggest Technic model ever in terms of dimensions and in terms of parts. It's complexity is right up there with the best, it works great, and it is a wonderful parts pack. Yes it costs a lot, but if you were starting a Technic collection from scratch this one model would provide everything you need for years of building (except, strangely, wheels).

The main con is that many people probably don't know what it is. This may be a positive depending on how much you like to fool your friends.

So just how big is it? It was hard to take a picture next to another big model, but I managed one with the Unimog.

DISCLAIMER

This set has been provided by the CEE Team of The LEGO Group. It's not my goal to promote this set. It's my goal to give you an honest opinion about it. Therefore, the opinion in this review is my own and is in no way linked to TLG.

[Imanol BB]

What an amazing work Black bird, a very deep and useful review of such big an amazing model, i love the picture of the Unimog along side the BWE, i now have clearly idea of the stunning size of this model, keep the good work .

[syclone]

Wonderful review!

Now the Unimog seems small

I noticed a small error, in the part after the mining truck you wrote "5c7 frames"

Edited August 26, 2016 by LXF

[suffocation]

Thanks for the terrific review, Blakbird. Your renders are out of this world!

Regarding the price, I managed to get it at a discount (due to slightly damaged box) for £130.00.

Edited August 26, 2016 by suffocation

[BusterHaus]

Very sweet renders as usual, they showcase the model well. The writeup is well done, too, although I would have liked a section for impressions or opinions (I know they were included within the text). Job well done.

Are you planning on reviewing the B model?

[Tommy Styrvoky]

Great review, any what gears are/aren't compatible with the new gear quadrants?

[dr_spock]

Thank you for the review. It would be nice to see the different prices for the set.

[lvassa]

Great review - and BTW, Australia uses these beasts to excavate its coal as well so there's good familiarity down under!.

[Blakbird]

Great review, any what gears are/aren't compatible with the new gear quadrants?

All the technic gears have the same tooth profile so it should be compatible with any of the spur or double bevel gears including the turntables. Only bevel, worm, and rack gears would be excepted.

[motomatt]

This set is a smorgasbord of parts,

Fantastic review. You had me at "smorgasbord"... I'm leaning to get this just for the parts. With 53 of these I will add a new extension to my house.

[J_C]

Thank you for great review.

What is your opinion about too sensitive clutches (mentioned by Sariel in his review)?. I haven't seen BWE in real yet. I heard different opinions. Please share yours, thanks.

Edited August 26, 2016 by J_C

[Bering]

Definitely the best review around. Crisp pictures and great technical explanations.Thanks for your work.

Personally, i'm still not convinced to buy it. Too big to display and for the size just too little functions, which seem to suffer a lot (also for the B model). Comes not even close to much smaller sets like the 8043 (only 1100 parts, many functions and great playabilty).

I still see it as a statement (size & parts count) rather than a great (read flagworthy) set.It could have been the greatest set (in size and functions) but unfortunately to me the result is a missed chance and lame execution.

I hope some MOC's will convince me eventually. :-)

Edited August 26, 2016 by Bering

[Anio]

Note that a full yellow ring has 140 teeth, not 136.

What is opinion about too sensitive clutches

It works much better with regular 24t.

[hsky]

Very lovely made Review!

[Ngoc Nguyen]

Thanks Blakbird for the amazing review. Can you calculate the gear ratio from the motor to the conveyor belts, to the tracks, and to the slewing ring?

[Kristof]

Great review. I especially like the intro, which really puts the model into perspective :) Thanks!

[Erik Leppen]

Thanks Blakbird for the amazing review. Can you calculate the gear ratio from the motor to the conveyor belts, to the tracks, and to the slewing ring?

With all the pictures and renders, you could do this yourself :)

[Anio]

Thanks Blakbird for the amazing review. Can you calculate the gear ratio from the motor to the conveyor belts, to the tracks, and to the slewing ring?

Tracks : 125:3

Conveyor / Wheel : 35:1

Superstructure : 875:1

[N-4K0]

Great review Blakbird! Well written and informative

[Freekysch]

Awesome review ! Although I am not a big fan of this set I really enjoyed reading your review and seeing the detailed information about how this set worked.

[2LegoOrNot2Lego...]

Extremely thorough review...thanks for the effort!!!

[Andy D]

Excellent review! I had about decided to skip this set as just too large, but your review has me rethinking that decision. It looks like there are some interesting and perhaps educational subassemblies. So maybe I will rethink my decision and get this set.

Darn you for such a great review, now it looks like my credit card is going to take another hit.

Thanks again, this review was well worth waiting for,

Andy D

P.S. Is there anyway to freeze the color-coded distribution animation? Just when I start to study it, it changes. Thx.

Edited August 26, 2016 by Andy D

[KamalMYafi]

Great Review! But this render looks to 'shiny' (for me) and you had a 'typo' on the title. The title should be changed to "[REVIEW] 42055 Bucket Wheel Excavator", i think it need a space.

Edited August 26, 2016 by KamalMYafi

[Alasdair Ryan]

Great review,with cool renders.

Great Review! But this render looks to 'shiny' (for me) and you had a 'typo' on the title. The title should be changed to "[REVIEW] 42055 Bucket Wheel Excavator", i think it need a space.

Fixed.

[Blakbird]

I noticed a small error, in the part after the mining truck you wrote "5c7 frames"

Fixed.

Are you planning on reviewing the B model?

Eventually, but for now my fingers are still recovering from the build and I do not relish taking it apart. I think I would rather just buy another copy.

What is your opinion about too sensitive clutches (mentioned by Sariel in his review)?. I haven't seen BWE in real yet. I heard different opinions. Please share yours, thanks.

I didn't have any trouble with the clutch gears. They never slip and everything operates smoothly.

..........Too big to display and for the size just too little functions, which seem to suffer a lot (also for the B model) .......... missed chance and lame execution.

Can you be specific about your complaints? There are a LOT of functions and they are really well done. Not sure what the problem is.

Can you calculate the gear ratio from the motor to the conveyor belts, to the tracks, and to the slewing ring?

Yes.

P.S. Is there anyway to freeze the color-coded distribution animation? Just when I start to study it, it changes. Thx.

If you open the animation in Photoshop (or a similar program) you can view individual frames. You can also look at the other static pictures further down which show each system.

Great Review! But this render looks to 'shiny' (for me) and you had a 'typo' on the title.

Since I have to render 80 frames for the animated revolution, I use very low quality settings. It is just supposed to show you the model from every angle.