[MOC] Classic Dump Truck (INSTRUCTIONS AVAILABLE)

JLiu15 · October 10, 2022

A classic-style dump truck model with BuWizz. Features drive, steering, dumping, V6 piston engine, and working headlights and taillights.

Functions/features:

Drive
Steering
Dumping
Working headlights and taillights
Oscillating rear axle
Opening doors and hood
V6 piston engine

Instructions available on Rebrickable: https://rebrickable.com/mocs/MOC-125516/JLiu15/classic-dump-truck/#details

This model was originally conceived as a MOC I would make with the sets and parts I got at BrickFair VA. My initial plan was to make it in lime, as one of the sets I got was the 42138 Mustang and that one had most of the lime parts I would need. I have not made many lime MOCs due to not having that many lime pieces, so this felt like another good opportunity to make a lime MOC. However, I could not help but feel that green would be a strange color for a dump truck, so I then changed the cab color to red. My initial finished design in Stud.io had a red cab and dark bluish gray cargo hold. I also tried a white cab with black cargo hold and rims, but felt that an orange cab and black cargo hold with white rims and accents was the best color scheme to go with.

I decided to use BuWizz to control the model despite it not being made for speed - due to the smaller scale, it would be difficult to fit both a battery box and SBrick so using a BuWizz which has battery/control all in one unit was the best option. The model is built very compact - the drive and cargo hold elevation motors (both PF L motors) are placed side by side, and the PF Servo motor for steering is placed directly below the cab to leave room for the fake engine. Unfortunately, due to the small size of the model and the oscillating rear axle, there isn't much room for reinforcement (there's only one pair of beams going over the oscillating rear axle) so the chassis tends to bend. I was concerned that the chassis would bend too much as the cargo hold elevates due to the forces exerted on the end of the chassis, but fortunately it didn't seem to be much of an issue in the finished model.

As for the functionality, I decided to take advantage of BuWizz's 4 speed modes to adjust the power supplied to the motors and LEDs. While the model is not that big, it does pack quite a punch when driving in ludicrous mode. And because I'm not using the power-hungry RC motors, there's no issues with power cutting out. The LEDs are also brighter on fast and ludicrous modes, which I like. The oscillating rear axle worked very well on slightly rough terrain as seen in the video - the only downside is the ground clearance as the L motors for drive and dumping sit pretty low in the chassis. There weren't any issues with chassis reinforcement either despite my concerns. I was also concerned that the Servo motor being connected to the steering mechanism via a CV and U-joint would lead to excess play in the system (as the Servo motor is not placed directly next to the steering mechanism due to the space the fake engine takes up), but steering always functioned properly without any major issues. Overall, the small size of this model and the use of BuWizz made all the functions work very smoothly.

It did not take long for me to finish the virtual model in Stud.io and the building process is straightforward, but this MOC still turned out to take longer than anticipated. I ordered most of the parts I needed in a single Pick A Brick order so I can avoid buying from multiple Bricklink sellers, but because my order consisted of all "standard" parts, it took over a month for me to receive it. My order was also on "In Warehouse" status longer than usual. In retrospect I should have ordered all the parts for this model from Bricklink if I wanted to finish it earlier, but being able to order all my parts in a single order was definitely convenient.

Overall, while the functionality turned out pretty well for this model, it was still a project I felt that I started too hastily. I had to modify the virtual build several times (including three color changes) before starting the build IRL. A number of features had to be included (there's no interior due to the BuWizz unit taking up most of the interior space), but I am still happy about being able to include a fake engine at this scale. This was also my first MOC to use multiple pairs of PF LEDs - after getting one pair in late 2013 I always wanted to get a few more but never had a MOC where I thought of including multiple PF LEDs. Last summer I got a set of PF/WeDo elements from a friend which included two pairs of PF LEDs. This MOC felt like a good opportunity to use them as I used PF elements with no power-hungry RC motors. The amount of electronic elements in such a small model (3 motors and 3 pairs of LEDs) meant a lot of wiring to manage, but I was able to get the wires to all fit nicely inside the model.

Video: