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Ball Tank

August 5th, 2021 Leave a comment Go to comments

A tiny model of a round tank with drive and steering and remote control using Circuit Cubes.


Completion date: 05/08/2021
Power: electric (Circuit Cubes)
Remote control: Circuit Cubes
Dimensions: length 12 studs / width 10 studs / height 12 studs (not including guns)
Weight: 0.291 kg
Suspension: none
Propulsion: 2 x small Circuit Cubes motor geared 3:1
Motors: 2 x small Circuit Cubes motor

The tiny size of Circuit Cubes motors and central unit provides plenty of inspiration – so much, in fact, that within days of building my tiny RC rowboat using these, I’ve come up with yet another idea. The idea was inspired primarily by the US “Tumbleweed Tank” concept, although there was also the mysterious German Kugelpanzer tank (only one unit remains today and no documentation as to who built it and what for survives) and allegedly also a Soviet Sharotank, although this one appears to be a work of fiction.

The idea was simple: to build a ball-shaped tank using the 6x6x2 corner round bricks. Because these pieces limit diameter of any such vehicle to just 12 studs, using LEGO motors and power supplies was out of the question, so I have turned to Circuit Cubes instead. It has taken some work, especially because I needed to add the large weighted LEGO brick to move the vehicle’s center of gravity to the side (it it’s too close to the center, the vehicle would just rotate in place between the “wheels” instead of driving them). Eventually I was able to fit the Circuit Cubes central unit, two motors and the weighted brick inside a 4-studs-wide section whose diameter was just marginally smaller than the diameter of the “wheels”. And because the “wheels” were hollow inside, there was just enough room to fit the gear reduction inside them. The motors were strong enough to drive the model at 1:1 gear ratio or higher, but because the “wheels” were so close to each other, rotating them at high speeds made the steering impossibly hyper-sensitive.

The resulting vehicle proved a little tricky to control, but also immensely fun to play with. It had few details, I’ve only added two fake guns on the sides and one larger cannon on front, installed in an opening which also provided access to the Circuit Cubes’ central unit on/off switch.


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