When 42055 Bucket Wheel Excavator was revealed at the toy fairs at the beginning of the year it understandably caused much excitement among Technic fans given that it is the largest Technic set ever in terms of part count -- just short of 4000 -- and dimensions.
Having now built it, I can confirm that it is indeed an impressive machine, but it's really pushing the limits of what is possible with the Technic system and one motor...
Unlike the other three large Technic sets released this summer, this one is not based on a real-life machine. Its design is certainly influenced by real BWEs but it looks nothing like any that I have been able to find pictures of. Take a look at some images yourself and see if you can fine one.
Packaging and parts
I won't bore you with pictures of the box but will point out the alternative model which is a rather cool mobile aggregate processing plant. I believe you feed 'rocks' into the top hopper and they come out one end or the other depending on their size and I am told it's fun to watch. I have not built it because instructions are not yet available on LEGO.com but I probably will.
There are just two new parts in the set: the bucket (6145856) and the 1/4 circle gear piece (6151167) which you can clearly see in the pictures below.
Instructions are provided in a single 550-page book with construction split over 669 steps. Thankfully parts are in numbered bags. I know some people relish the additional challenge that having all 4000 pieces to sift through would provide but I am not one of them!
First to be constructed is the truck which is very similar in design to last year's 42035 Mining Truck. This one has a revised cab and front, and no engine, but the unloading mechanism, operated by twisting the black gear on the side, is the same.
The chassis/underframe of the excavator is constructed next. The first four of fourteen 1/4 circle gear racks are mounted on the base to allow the body to rotate. The gear in the centre of the circle drives the tracks.
There's some complicated gearing buried inside which links the tracks, the rotation of the body and the lower conveyer belt via the three vertical axles on the left to the upper body assembly.
After 225 steps and about 3.5 hours of building the chassis and lower part of the body are complete.
Next to be added is the lower conveyer belt.
Bags numbered six builds the business end of the machine and this is the most time consuming of the eight bags, taking around 1.5 hours.
Following on from that, the rear end of the digging arm is constructed which includes the control panel/gear box. Here you can see the innards before they are hidden by the top panel.
Now, by this point the model has become so big that it no longer fits on my regular photography table so I was unable to take more photos until I had something bigger. The following pictures are therefore taken with different lighting in a different 'studio' and to be honest I am not that happy with them but hopefully they will serve to illustrate the finished model.
However, we still have not finished construction... At the end of bags #7 the model is functionally complete and can be tested and I urge you to do so because if there is any debugging to be done it will be more easily achieved now.
Bags #8 add the cab, bodywork, walkways, lights and other cosmetic details. Overall, the build time for the entire model is around 7 hours.
The completed model
It's massive! The arm is 75cm long. It stands 45cm high. It's 28 cm wide. There are a lot of nice finishing touches: the walkways, handrails, lights, ladders and so on which enhance its appearance considerably.
It's somewhat front-heavy so there is a bit of a tilt on the body which results in the vertical frame not being exactly vertical. It doesn't seem to interfere with operation though.
It's a long satisfying build and the finished model looks great, but how does it operate? Unfortunately this is where it's a bit of a let down.
The machine is powered by a single large PF motor mounted at the end of the arm. Operation is fairly simple: the middle gearbox lever switches between rotating the bucket wheel and the body on its axis or moving the machine forward/back. When you have selected one or the other, you can then choose forwards or backwards movement (right lever below) or clockwise or anticlockwise rotation (left lever) of the body. Whichever you choose, the bucket wheel always rotates in the same direction.
You can't go forwards and rotate the bucket wheel at the same time which is a shame.
The bucket wheel rotates at something like 6 RPM; forwards/backwards movement of the machine is probably something like 10cm a minute, i.e. it's very slow. I don't suppose real BWEs exactly race across the quarry though, so it's probably realistic.Given the weight of the machine it's a wonder the motor can move it at all. Also, it needs fresh batteries. Anything less than full power from the motor will result in nothing much happening at all.
Remember what I said about testing after bags #7? I did just that and found that the bucket wheel barely moved and kept juddering. It was perhaps not surprising given that the single motor is driving two conveyers, the huge great bucket wheel (which is driven via the upper conveyer) and rotating the body as well. There was just too much friction in the system which was causing the two white slip gears (that you can see in the picture of the open gearbox above) to continually slip rather than drive the output axle.
It's entirely possible that I was not careful enough during construction and mounted gears or connectors too tightly thus causing too much friction but if I -- a Technic veteran with 20+ years experience -- can do that, what hope do kids have of building it any better?
The solution was to replace the slip gears with regular ones, the two large grey gears at the top of the picture immediately above. Now the bucket wheel moves more smoothly, but still not perhaps as smoothly as I would like. Of course, should the mechanism jam or stall for whatever reason the lack of slip gears in the drive chain puts the motor at risk of damage but given they are a commodity item I am not too worried about that.
The arm and thus the bucket wheel can be raised and lowered manually using the black gear on the side of the body which you can see below.
You can also see in this picture the three axles that transfer power from the upper part of the machine to the lower part. They are connected using 'slip axles' which means it is easy to disconnect them for testing purposes.
One of the cleverest aspects of the machine's operation concerns the lower conveyer belt. The exit from the belt would usually be placed above an awaiting truck to collect the rocks. But, if you have enabled arm rotation, the lower conveyer would rotate as well resulting in the the rocks missing the truck.
To solve this problem it is possible to lock the lower conveyer belt so that it remains stationary even as the arm rotates which keeps it in position above the truck. This feature is enabled using the gearbox lever at the back: push it forwards or back to lock it. There's a lot of slack though, and I think the arm has to be in a particular place relative to the body for it to work properly but when it does, it is a great feature and one that Sariel demonstrates in his video (see below).
One thing I have not mentioned yet is the effectiveness of the machine to pick up the 'rocks' (1x1 round bricks and 2x2 dome bricks) and transport them through itself. Unfortunately, it's virtually impossible to get the buckets to pick up 'rocks' from the ground and you will see why if you watch Sariel's video. Once rocks are in a bucket though, the machine works well although it does occasionally get jammed up causing it to grind to a halt.
The bucket drops the rocks down the chute onto the conveyer which transports them along the arm. A hinged 'door' prevents them from falling out the end.
The roof of the cab can be lifted but the seats are too small for a minifigure to sit on them.
Unfortunately, I have to say, I am disappointed with its operation. It's a huge, heavy, complex and impressive-looking model, and given that it's powered by a single motor positioned right up in the back of the arm it's perhaps a wonder that it works at all.
But, it's virtually impossible to automatically 'dig up' rocks so much of the play value is lost as a result. The bucket wheel's motion, on my model at least, is a bit juddery, which can perhaps be explained by my lack of care when building but more likely because it is being driven via the conveyer belt and dozens of gears.
It's a great set to build and to behold but its operation lets it down a bit. Also, its size -- while impressive -- will make it difficult for many people, myself included, to display. It's not something you could take into work and put on your desk, for example!
I am therefore not able to wholeheartedly recommend this set: Personally I think it's pushing the boundaries of what's possible with Technic, particularly the Power Functions system, a bit too far and the model has suffered as a result.
Die-hard Technic fans will want it regardless but if you are on the fence or have limited funds, there are much better Technic sets released this year that I would buy before this one.
This is definitely a set that benefits from a video review so I encourage you to watch Sariel's. You can skip past the unboxing and construction to 17m 30s to see the machine in operation.
Watching it again now, I see that Sariel's wheel judders a bit too, so it's not just me...
Have you built it? What do you think? Does yours work okay? Let us know in the comments.
Thanks to the LEGO community team for providing the set for review. The review is an expression of my own opinions and not those of the LEGO Group.