Lego 42108 – Mobile Crane

Lego 42108 – Mobile Crane is not motorized, not licensed and for this reason, it was very reasonably priced. It has lots of play features and it looks wonderful as a display set, especially when its boom is raised and extended.

There are 1292 pieces in this set. As you can see most of the set consists of pins as usual. We have lots of short axels and some gears for the boom itself and base of the boom.

This set is very similar to 42009, and they can be mismatched easily. This set is newer but not motorized. 42009 is an older model but it is a motorized set. 42009 has a higher piece count and it’s a more complex and more expensive set.

Building

The build is done in 3 stages. In the first stage, you build all the chassis. In the second stage, you build the base of the boom and driver’s cabin. In the 3rd stage, you complete the boom.

Stage 1

The all-wheel steering mechanism is complete at this stage. This set doesn’t have any differential and suspension but the all-wheel-drive mechanism and steering build are interesting.

You start by building the crane’s chassis using technic frames and building a long axle in the middle that extends from the front of the crane to the back. This axle will later be connected to the steering mechanism.

The all-wheel steering mechanism is built so that the front and rear wheels turn opposite to each other. This mechanism allows a smaller turn radius at a lower speed. I have found the best explanation of why rear wheels turn in the opposite direction here. Small gear and a “gear rack” are used to steer each wheel pair’s wheels. A simple connection technique makes the back and front wheels turn in opposite directions.

Steering is done by using one of the signal lights on top of the crane’s cab. There are two nobs for the left and right sides of the driver’s cab. Obviously, they can’t put a single nob in the center because this is where the boom of the crane is located when the boom is not in use. In order to make both nobs (lights of the crane) operate the steering, 6 “bevel gears” and 3 “pin connector toggle joint smooth double with 2 pins” are used to convert and deliver turning of nobs to the middle axle.

There are 4 individually controlled outriggers. Rear outriggers are operated by turning a gear but front outriggers need to be pulled out. Especially back outriggers when extended lift the back wheels. Unfortunately, they are not strong enough to support the crane when the boom is fully extended to the side. Even a small load can cause the crane to flip. The building of outriggers is very clever and simple. When fully extended it locks, and if you apply force to the base of the outrigger, it doesn’t raise. You have to turn the nob to raise it.

Stage 2

In this stage, you mostly complete the body of the crane and build a 360-degree turning base for the boom. You build the base of the boom separately and attach it to the crane using 3L orange bushes. The base is connected to a large linear actuator. This actuator is later connected to the bottom center of the boom to raise and lower it. To make the base turn, a 60 tooth turntable is used.

Stage 3

In this stage, you build the boom. It is extendable using a nob. To extend it fully, you need to turn the nob for around 5 turns. First, you build the outer boom by using 8 curved technic panels. This makes the outer boom 4 technic panel long. Later you reinforce it using long beams. Later you build a long axle that lays all the way from the bottom of the boom to the top of the boom by connecting 11L axles. This axle will carry the turning of the nob from the bottom of the boom to the top and there it will be used to push out the inner part of the boom by using a small 12 tooth bevel gear and a 20 tooth blue bevel gear. 12 tooth bevel gear and 20 tooth bevel gear are connected perpendicular to each other and this way 20 tooth gear pushes the inner part of the boom using the racks connected to it.

Play Features of “Mobile Crane”

All the features are manually operated and fun to control. There is a dummy load for testing your crane. The dummy load is only 20gr.

• All-wheel steering, done using any of the signal lights mounted on the driver’s cab.
• Crane can be turned by hand 360 degrees.
• The boom can be raised and lowered using a nob. You can lock it using a lever.
• The Boom extension can be deployed using a nob. You can also lock it using a lever.
• Back outriggers can be operated with a gear. Outriggers really lift the entire crane off the ground.
• Front outriggers can be operated manually using your hand.

Missing Features

We can’t expect every feature from the 1292 pieces set, but here are the things we think would add value to this set;

• Suspension and differentials
• Opening and closing the doors

Speed Build

If you are interested, you can watch a speed build video of Lego 42108 Mobile Crane on our Youtube channel: