One of the most important parts of any spacecraft is their attitude control system. This is the part which is responsible for keeping the craft pointed in the right direction something which is of the ultimate importance when you’re trying to do things like fine tuning manoeuvres or trying to monitor a specific part of the sky for an extended period of time. The most common of these kinds of systems are reaction control systems which typically use a hypergolic fuel (ignites on mixure, no external ignition source required) however they’re limited by the amount of fuel you can bring with you. Whilst there are many alternatives reaction wheels are the best in terms of weight, size and precision and they can make for cool systems like these:
Cubli isn’t the first reaction wheel controlled robot I’ve seen but it is most certainly the most elegant and precise. It’s also probably the best demonstration I’ve seen of how reaction wheels work, showing aptly how rotational momentum can be translated into an angular force on the objects that the reaction wheel is coupled to. Whilst most space craft won’t ever use the jumping and walking functions (that’s what station keeping boosters are for) the rest of the demonstrated capabilities are identical to what many modern space craft use.
As for uses for things like this on earth? Well there aren’t as many as there are out in space, mostly thanks to us having other means by which to stabilize and rotate things, but they do make for a cool technological demonstration.