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Monster Bug

December 15th, 2017 Leave a comment Go to comments

A VW Beetle-inspired monster truck. Features 4×4 drive, steering, live axle suspension and BuWizz unit for remote control and power supply.


Completion date: 15/12/2017
Power: electric (BuWizz)
Dimensions: length 36 studs / width 31 studs / height 26 studs
Weight: 1.611 kg
Suspension: live axles
Propulsion: 2 x PF XL motors geared 7.2:1
Motors: 2 x PF XL, 1 x PF Servo

This was a simple creation with a fairly convoluted origin story. A while ago I came across the photo below when browsing Internet, and I fell in love with the vehicle it shows. I was determined to turn it into a LEGO model. I’ve started by building a rear axle, but then I got the idea for building a Porsche 917K model and the axle I’ve built was a perfect fit for it. So I started building the Porsche, not having enough pieces to build a copy of this axle, and putting this project, originally called Volksrod, on hold. After a while I got impatient, as the progress on Porsche was slow and the axle didn’t seem to be coming back to the Volksrod anytime soon, so I’ve decided to simply go with a different chassis: a monster truck chassis that required a very different axle design.

After that change, my first step was to dust off my good old LEGO Power Puller tires. Then I’ve built two simple live axles suspended on two shock absorbers each and connected to the chassis via a power joint, in a typical crawler-like fashion. The front axle had a PF Servo motor integrated into it, and small vertical rollers near the top of the tires, which prevented the front tires from rubbing against the chassis when turning and negotiating obstacles. The Power Puller tires are extremely wide and thus can be a bit wobbly on obstacles, especially in a steered axle. The rear axle had no rollers, as I didn’t expect them to be needed there.

The model was deliberately kept dead simple, with two PF XL motors directly coupled to the driveshaft, without any transmission or a central differential. I have used a significant gear reduction, also in the wheel hubs, because the Power Puller tires have notoriously high rolling resistance and need plenty of torque to be used off-road. The simplicity of the build made it a perfect test bed for a BuWizz unit, with which it was both powered and controlled. The unit proved perfectly capable of powering two PF XL motors under plenty of continuous strain, also in cold weather, and I was unable to exhaust it despite using it almost exclusively in the “fast” setting (which meant slightly increased voltage). It also saved plenty of space, since it combined power supply and remote control. It worked flawlessly and ensured a remote control range comparable to that of the SBrick.

The model was fun to drive despite its simplicity. I particularly liked testing it on various challenging obstacles and driving it on a fresh show, which produced interesting sounds as the snow was being compressed by the giant tires. I have also appreciated this opportunity to make some nice stickers, and to use purple LEGO pieces – a color I’m very fond of and haven’t really gotten to use much so far.

Work in progress photos:

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