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BuWizz Catamaran

January 13th, 2020 Leave a comment Go to comments

Simple catamaran built to test out the new LEGO floating hulls from the 42105 set. Features two independently driven screws and an onboard camera.


Completion date: 12/01/2020
Power: electric (BuWizz)
Remote control: BuWizz
Dimensions: length 45 studs / width 26 studs / height 25 studs
Weight: 0.679 kg
Suspension: none
Propulsion: 2 x RC motor geared 1:1
Motors: 2 x RC motor

Ever since LEGO has released the 42105 Catamaran set, including the first floating hulls in a Technic set, I wanted to try these hulls out outdoors. This very simple model was built just for that.

The vessel consisted of two hulls connected by a simple frame holding up a single BuWizz unit and a camera. There was one LEGO RC motor at the back of each hull, driving a set of two 9L propellers with 1:1 gear ratio. I have used the vertical holes in the hulls to secure them from opening accidentally by putting a vertical beam through the holes and securing it on top and bottom so that it kept the upper and lower half of the hull together. My testing has shown that two hulls have little load capacity left after all the necessary elements were installed, so I’ve tried to keep the weight down, e.g. by using BuWizz unit for power and remote control and by using the smallest onboard camera I had. There was also a problem with the weight distribution: the catamaran was rear-heavy (I kept the RC motors at the back to simplify the drivetrain) and the rear part of the hulls tended to go below the waterline, especially when under thrust from propellers. To remedy this, I have added two LEGO pneumatic airtanks above and behind the propellers, acting as flotation devices. Even so, the vessel often seemed dangerously close to sinking – but I have to admit that the hulls stayed dry inside at all times.

When tested on a lake with minimal wind, the catamaran proved reasonably fast, stable and very agile. It certainly ranked as one of my best performing LEGO vessels ever. Still, it was evident that just two of these hulls are not enough for a serious RC vessel, and at least one more should be used to reduce the risk of sinking. It was also clear that the hulls would be more stable if they were a little longer – at their current length, they are very sensitive to weight distribution. As for the inverted bow of the hulls – a unique feature among the LEGO hulls – I haven’t observed any clear advantages or disadvantages of this design.


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