Off Road Knuckleboom Truck


It was time for another truck! Free instructions can be found at Rebrickable.

I have been building a lot of tractors and construction vehicles lately. I love building them as they offer a lot of movement and features. But it was time to build another truck. LEGO truck MOCs are beginning to coalesce around the “Mack Anthem standard” which is a 15 module wide truck in about 1:20 scale. Many MOCs are being designed in this scale as it is a good playable size, and fits the scale of some of the more recent LEGO trucks that have been released. I wanted to offer another truck in this scale, with some fun playable features.

I started with a chassis that uses a simple pendular suspension on the rear axle, which is damped by 2×1 rubber connectors. The rear axle drives a simple I3 fake engine under the cab through a two speed transmission. The transmission changeover is on the right side of the truck. Front steering is controlled though the HOG light on the top of the cab.

I have found a simple way to add a three way tipper bed in my trucks, and I have used it many times before. A mini linear actuator moves simple linkage under the bed that can pivot in three different directions. Each corner of the bed has a removable axle that allows control for which way the bed tiles. But in the past the control for this tipping function was in a tricky place to reach, so I wanted to route the control to the top of the cab. I managed to add this right next to steering light. I used a top pivot design on the bed sides and rear, locked by a 3/4 pin on the bottom.

Finally, I added a crane, and since I had a little space left over, two stabilizing outriggers. The outriggers are a simple two link design that are controlled with a worm gear mechanism. The crane is a little more complicated. It is mounted on a small turntable with a rotation control on the left side of the truck. The first lift mini linear actuator is controlled by the third HOG on the top of the cab. The second lift stage is controlled by another mini linear actuator. Finally, the third stage has an extending boom that allows the reach of the crane to extend a little more. The crane can lift some; not a lot, particularly when the boom is fully extended. By removing the three HOG knobs, the cab tips to show the engine. Also, both doors open.

I loved the way this trucks looks. The beefy tires, and the cabover design give the truck presence and look of toughness. The crane was a lot of fun to play with even if it could be a little stiffer. However, this may be the last time I use this three way tipper design. I am happy I moved the control to the top of the cab, but the linkage does not have the power it needs at the start of the tip. I will have to come up with something better for the next truck.

Stay tuned, and happy building until then.

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