Mack Magma

I consider myself a LEGO purist. I do not cut parts, paint them, and I do very little with custom stickers. But I confess, I’m bending my purist tendencies as of late with all the great custom tire options available. After getting these RC4WD tires, it was time to build another trial truck.

The full gallery may be found on Flickr.

When I build a trial truck, start with three questions: What functions will it have, how many Power Functions receivers will that require, and how many battery boxes will be needed in what placement. Using these decisions I draw up a basic sketch of Power Functions part placement, and I get to work. This truck would have steering, a 2x PF L motor drive, and a two speed transmission. As with other trucks I make, I started with the axles first. The axles were simple as they required no additional functions. Both front and rear have a knob gear in then center, then a 12t to 20t reduction, and a final 8t to 24t reduction in a portal axle setup. The front as a simple steering setup, and the steering universal joints between the first and second gear reduction.

Both axles are strung together with a frame that houses the suspension and electronics. Both axles have pendular suspension, and are linked together with liftarms front to rear. It is a system that is simple, and incredibly effective. A PF M motor is placed in the front to power the steering, and another M motor sits beside it to power the transmission. Two PF IR receivers and two rechargeable battery boxes are placed with one on each side of the chassis. Both PF L motors are mounted side by side in sliding housing in the rear of the chassis. Each motor drives a set of 12t and 16t gear. These separate axles combine to either a 20t or 24t center mounted gear. When both engines are connected 12t to 24t gear, an overall 10:1 ratio is achieved. When both engines are connected to the 16t to 20t gear, an overall 1:6.25 ratio is achieved. With the power of the L motors, this gives a good low ration, and an appropriate high ratio.

As this was a quicker build, I did not spend too much time on the bodywork. A simple flat bed was installed, and the cab is sparse. I selected a simple America style cab from this design idea to build in blue. The grille is big and square, and the rest of the cab generally follows the idea. Both the cab and the bed can be simple removed.

The truck has plenty of power, and the transmission worked without error. The steering was easily controllable. The larger tires gripped very well, as they are soft with big knobs. They were a little taller than LEGO’s tires, and combined with the softer sidewalls, made the truck a little less secure in its footing. But the truck did not roll over easily, and the soft tires made it grip the ground well. I will be using these tires again.

Until the next MOC, happy building.

Mini Mack Cabover

Sometimes I need to build something small to refresh my mind. This was the result of stepping away from other projects for a while, and spending a couple of hours on something small.

The full gallery may be found on

Recently I wondered if I could build something like LEGO set 8065; a small truck with one function. I liked the little roll off dumpster idea, and I see plenty of the Mack version around here. I had a couple of hours, so I thought, let’s see what I can build. The single function of the truck is the roll off feature. A worm gear moves the arm up and down, and the little hook catches a bar on the dumpster.

The rest of the truck is build on liftarms and connectors. The truck is 8 studs wide, and the space between the two rear axles is 4.5 studs. These two measurements made the chassis more challenging than it should have been. I built a simple cab, and added a little bumper, and the truck was done.

The truck works well. It only does one thing, so it should. It was fun to do a quick little build, and make something small and simple. Until something more substantial…

Happy Building!

Unimog U90

About 3 months ago I purchased a set of four Fischertechnik tires from After seeing a review of them by RM8, I reached out to him, and he mailed me a set. After a little time, I finally have something to show with them.

Unimog U90

After playing with a number of ideas, I decided to do another Unimog. It’s easy to motivate myself to build a vehicle I love. This time, I wanted to do the unloved U90 (418) version. It was not a terribly successful version, as many find the hood…not one of the best. But few people have built this version, so I was up for it. I put to to a vote on Eurobricks, and the decision was to build it in green. Off I went.

The scale required a 27 stud wheelbase and a 19 stud width. I built the front and rear axles and tied them together. Through a couple of edits, I finally added the suspension and figured out how to get portal axles into the truck. The Power Functions XL motor was mounted just over and in front of the rear axle driving power to all four wheels. The Servo motor was placed directly ahead of the XL for the front axle steering. I added a four cylinder fake engine over the front axle. The rechargeable battery box was placed over the rear axle.

Unimog U90 Driveline

The suspension is a live axle setup, with four hard shock absorbers at each corner. Each wheel has about 2 studs of travel. Not much for a Unimog, but enough for a 418. At this point I started a draft of the cab, and a draft of the bed. At this point the truck had an identity crisis. Move forward with green or find another option.

Unimog U90 Bed Tilt

Building LEGO Technic with green is not the easiest. The color lacks 1×5 and 1×11 beams. Both of the these parts would be needed for the bed and the cab. I could make some things work for the 1×11 in the hood, but there was no other option (read, inexpensive option) for the 1x5s needed for the bed. I toyed with other colors for the bodywork; orange, white, blue, yellow. None of them had the right pop I was looking for. Other than the orange, but, as other have said, orange has been done too many times. Then it dawned on me, “why not use plates?” I had my solution. With one bricklink order, I was done.

The truck drives well, and is easily controllable. The front portal axle can use a little strengthening, so serious trial abilities are lacking with this truck. Both the bed and the cab can be easily removed. I ran out of space for a ram to elevate the bed, but it can tilt three ways. I was pleased with how the truck turned out. It looks great. The driveline coule use some improvements, so I will make those improvements on the next truck.