Self-assembling robot cubes and the electric grid

For years, the notion of modular, self-assembling cubes was an example of an idea that worked better as a conceptual model than as a functional design. Ryan Whitwam of ExtremeTech explains:

When studying modular robots, researchers often use the sliding-cube model. This is a simplified design concept where two cubes are connected face-to-face, but can also slide up and over each other without changing orientation. This model is useful for developing the algorithms that govern self-assembly, but building a working version of the model is surprisingly difficult.

Modular robots aren’t new, but real-world versions require complicated designs with a complex assortment of servos and they tend to be pretty limited in what they can do to very specific purpose-built tasks. Robotic cubes that can self-assemble in complex ways haven’t been an option.

John Romanishin, a researcher at MIT’s Computer Science and Artificial Intelligence Laboratory, thought it must be possible, and based on a design he’s been pursuing since 2011 he finally cracked the code. His breakthrough was to combine a suite of cleverly arranged magnets with a tiny, high-powered flywheel, all inside of a small cube. The flywheel, capable of up to 20,000 rpm, spins and then halts suddenly, its angular momentum is transferred to the cube itself, the cube is propelled into its new configuration, and the magnets secure it in the right location with the right alignment.

These two videos are worth watching if you’ve got a few minutes. In the first video, Romanishin and colleagues explain the principles of the system.

The second video shows off a bit more about how it works in practice.

In both videos you get a sense of just how sophisticated the action might be at some point, with multiple cubes operating independently to create or rearrange complex structures, much like ETH Zurich’s autonomous, self-improving quadrocopters.

Early hints at the potential for sophisticated, coordinated behavior by modular robots is exciting (if simultaneously disconcerting), but the flywheel technology on which it’s based – in contrast – is remarkable for its simplicity and efficiency. Flywheels, which are found in everything from toy cars to to reciprocating engine crankshafts to potter’s wheels, are essentially energy storage devices. Apply torque, store energy, and then release as needed. In modular cubes, that energy can be applied for the sake of propulsion. By using flywheel technology on the electric grid, it just so happens, allows you to store energy produced from a power plant elsewhere on the grid and release it when you need it, just like any other energy storage system.

On a grid dominated by coal, natural gas, and nuclear power generation, storage isn’t typically a major challenge because you can operate those generation plants to meet whatever the demand might be at that time. It’s an incredibly inefficient system because you have to invest an enormous amount of capital – power plants and transmission are expensive – in building enough capacity to cover all of your peak energy demand. It’s also inefficient because the type of power plants that can ramp up quickly to meet peaks in demand as they occur are particularly expensive to operate. It’s a stable system, but expensive, inefficient, and highly carbon intensive.

The growth in clean energy sources offer a way out: they have nominal carbon emissions, they are quickly approaching so-called “price parity” where the cost is competitive with the cost of fossil-based energy.

But clean energy sources like wind and solar don’t work the same way. For one thing, they are highly variable. Turbines turn when the wind blows and not otherwise, and solar panels convert solar energy into electricity only when the sun shines. In addition – and this is especially true with wind – they may not generate electricity during peak hours, precisely when the demand is highest.

Wind, especially, often blows the hardest at night when the demand for energy is at its lowest, and often doesn’t blow much at all during those hours of the day when demand peaks. Without large-scale storage systems, you can’t use the clean energy to offset dirty fuels. As we transform our energy system away from fossil fuels and toward clean energy generation, in other words, the importance of getting storage right, and of driving innovation in storage technology, is quickly escalating.

Thankfully, we’re seeing huge strides in storage technology. One example: Abengoa’s Solano solar thermal plant just began commercial operations last month, the largest parabolic trough concentrating solar power plant anywhere and the first in the U.S. to use a thermal energy storage system. Solar energy captured during the day is stored in the form of molten salt, enabling the plant to increase power supply in the even peak hours even as the amount of solar radiation dwindles.

Abengoa’s Solana concentrating solar project with thermal storage. (DOE photo)

Abengoa’s Solana concentrating solar project with thermal storage. (DOE photo)

Where do flywheels fit in? Flywheels are too expensive, at least for now, to store large amounts of energy for sustained use, and too industrial, as well, to work effectively in a residential context where a homeowner might want to pair her rooftop solar system with a storage system to provide electricity at night or on cloudy days. Beacon Power’s 20 MW flywheel array, for instance, involves ten shipping containers, each of which is surrounded by ten five-foot diameter cylinders. It might be a bit much for a backyard.

But unlike many storage technologies, flywheels can dispatch energy to the grid extremely quickly, fully ramping up in a matter of seconds. The organizations charged with maintaining the reliability of the grid, such as ISO-New England, already have to manage variability in demand and supply, including predictable changes like the increase in demand that soars when summer temperatures climb.

As the percentage of variable-supply clean energy sources on the grid grows – Vermont is aiming to meet 90% of its energy needs with renewable energy sources by 2050, for instance – this becomes a more complex problem, and storage systems that can dispatch almost instantaneously to balance the load will become even more important.

Ethan Zuckerman explains the “frequency regulation” problem really well:

The electrical grid is all about stability. The US grid provides power at 60 alternating cycles per second. When demand for power balances the amount of power being consumed, the grid remains stable at 60Hz, but if there’s an increased demand, the frequency will tend to creep downward. That’s a bad thing, as many electrical systems will fail in unpredictable ways if the frequencies drop below 59Hz or so. (Same goes for high frequencies, caused by generating more power than there’s demand for) … If lots of people get up during the NFL playoffs and microwave a plate of nachos, the demand for power spikes, and the frequency drops.

(Ethan deserves a hat tip, by the way, for his thoughtful framing of the flywheel/Beacon Power story in terms of of our difficulties with infrastructure innovation). A system that can provide 20 MW for 15 minutes – Beacon Power’s flywheel, for instance – is precisely what grid operators need for frequency regulation: a moderate amount of energy that can be dispatched instantly for a long enough period of time to bring other, slower-ramping energy supplies online (or for the spike to pass).

Flywheels aren’t the only option for doing this, incidentally. Isothermal compressed air energy storage shows some promise, as do supercapacitorssuperconducting magnetic energy storage systems, and other emerging technologies. But advances in flywheel technology are very much a part of the enormous disruption facing an industry that hasn’t changed much in its fundamental architecture for a century.

And perhaps flywheels, hidden inside modular self-assembling robotic cubes, will be part of the next major disruption. Maybe cubes with embedded photovoltaic cells that can self-assemble into whatever shape might be appropriate? Self-repairing solar assemblies on satellites or other extreme environments? Or maybe their role will be more straightforward: perhaps the cost and efficiency of flywheel systems will drop enough in the coming years to make them competitive for smaller storage or load balancing needs in community microgrids or even for individual homes.