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Comment by navane | Hacker News Reader

Reminds me of the self balancing train that rode on a single, small rail track. Project got cancelled because the double rail system was already well established.

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Note that reaction wheels do not make use of gyroscopic torque (which balances these monorails). They are different control mechanisms. Altho both use spinning wheels.

More info: https://en.wikipedia.org/wiki/Control_moment_gyroscope

The gyroscopic action of the cube's momentum wheels must make the control algorithms quite entertaining.

Details for the curious: https://en.wikipedia.org/wiki/Gyro_monorail https://www.youtube.com/watch?v=kUYzuAJeg3M

Isn't it more likely that idea got abandoned because a failure of the balancing system would be catastrophic?

+ intensive in terms of energy usage + needed a second gyro to feel like you are standing in a flat environment.

As a sibling of yours pointed out above, the train worked with CMGs, their energy usage seems not too much:

"CMGs are also far more power efficient. For a few hundred watts and about 100 kg of mass, large CMGs have produced thousands of newton meters of torque. A reaction wheel of similar capability would require megawatts of power."

Iirc the second gyro is necessary to ensure the train doesn't course correct itself right off the rail in the case of a curve? Coupled together to make the "correct" side more responsive for any given direction? Dunno.

you would also need a gyro in each train car, so that doesn't help

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