Tiny helicopters can’t out-hover hummingbirds

The spinning blades of micro-helicopters are about as efficient at hovering as the average hummingbird, which have had more than 42 million years of natural selection to hone their energetically efficient flight.

That said, hummingbird wings can still generate lift more efficiently than the best micro-helicopter blades, according to a new analysis led by David Lentink, an assistant professor of mechanical engineering at Stanford University. The findings could lead to more powerful, bird-inspired robotic vehicles.

male Anna's hummingbird

“I think it’s nice that there are still a few things about hummingbirds that we don’t know,” says David Lentink. (Credit: John Florence/Flickr)

Black Hornet vs. hummingbird wings

The experiment involved spinning hummingbird wings—sourced from a pre-existing museum collection—of 12 different species on an apparatus designed to test the aerodynamics of helicopter blades.

The researchers used cameras to visualize airflow around the wings, and sensitive load cells to measure the drag and the lift force they exerted at different speeds and angles.

Lentink and his colleagues then replicated the experiment using the blades from a ProxDynamics Black Hornet autonomous microhelicopter. The Black Hornet is the most sophisticated microcopter available—the UK army uses it in Afghanistan—and it’s about the size of a hummingbird.

Even spinning like a helicopter, rather than flapping, the hummingbird wings excelled: If hummingbirds were able to spin their wings to hover, it would cost them roughly half as much energy as flapping.

The microcopter’s wings kept pace with the middle-of-the-pack hummingbird wings, but the topflight wings—those of Anna’s hummingbird, a species common throughout the West Coast—were still about 27 percent more efficient than engineered blades.

Hummingbirds still win

Hummingbirds acing the test didn’t particularly surprise Lentink—previous studies had indicated hummingbirds were incredibly efficient—but he was impressed with the helicopter.

“The technology is at the level of an ‘average Joe’ hummingbird,” Lentink says. “A helicopter is really the most efficient hovering device that we can build. The best hummingbirds are still better, but I think it’s amazing that we’re getting closer. It’s not easy to match their performance, but if we build better wings with better shapes, we might approximate hummingbirds.”

Based on the measurements of Anna’s hummingbirds, Lentink says there’s potential to improve microcopter rotor power by up to 27 percent.

The study appears in the Journal of the Royal Society: Interface.

Serious muscle

The high-fidelity experiment also provided an opportunity to refine previous rough estimates of muscle power. Lentink’s team learned that hummingbirds’ muscles produce a surprising 130 watts of energy per kilogram; the average for other birds, and across most vertebrates, is roughly 100 watts/kg.

Although the current study revealed several details of how a hummingbird hovers in one place, the birds still hold many secrets. For instance, Lentink says, we don’t know how hummingbirds maintain their flight in a strong gust, how they navigate through branches and other clutter, or how they change direction so quickly during aerial “dogfights.”

He also thinks great strides are possible from studying wing aspect ratios, the ratio of wing length to wing width. The aspect ratios of all the hummingbirds’ wings remarkably converged around 3.9. The aspect ratios of most wings used in aviation measure much higher—the Black Hornet’s aspect ratio was 4.7.

“I want to understand if aspect ratio is special, and whether the amount of variation has an effect on performance,” Lentink says. Understanding and replicating these abilities and characteristics could be a boon for robotics and will be the focus of future experiments.

“Those are the things we don’t know right now, and they could be incredibly useful. But I don’t mind it, actually,” Lentink says. “I think it’s nice that there are still a few things about hummingbirds that we don’t know.”

Source: Stanford

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To test TV ads, watch 16 people’s brainwaves

By analyzing the brainwaves of 16 people as they watched mainstream television, researchers were able to accurately predict the preferences of large TV audiences, up to 90 percent in the case of Super Bowl commercials.

“Alternative methods such as self-reports are fraught with problems as people conform their responses to their own values and expectations,” says Jacek Dmochowski, lead author of the paper and a postdoctoral fellow at City College of New York (CCNY) when the study was under way.

However, brain signals measured using electroencephalography (EEG) can, in principle, alleviate this shortcoming by providing immediate physiological responses immune to such self-biasing.

“Our findings show that these immediate responses are in fact closely tied to the subsequent behavior of the general population,” he adds. The findings appear in Nature Communications.

Lucas Parra, professor of biomedical engineering at CCNY and the paper’s senior author explains that, “when two people watch a movie, their brains respond similarly—but only if the video is engaging. Popular shows and commercials draw our attention and make our brainwaves very reliable; the audience is always ‘in-sync.’”

Brainwaves and tweets

In the study, participants watched scenes from “The Walking Dead” TV show and several commercials from the 2012 and 2013 Super Bowls. EEG electrodes on their heads captured brain activity.

The reliability of the recorded neural activity was then compared to audience reactions in the general population using publicly available social media data provided by the Harmony Institute and ratings from USA Today’s Super Bowl Ad Meter.

“Brain activity among our participants watching ‘The Walking Dead’ predicted 40 percent of the associated Twitter traffic,” says Parra. “When brainwaves were in agreement, the number of tweets tended to increase.” Brainwaves also predicted 60 percent of the Nielsen ratings that measure the size of a TV audience.

The study was even more accurate (90 percent) when comparing preferences for Super Bowl ads. For instance, researchers saw very similar brainwaves from their participants as they watched a 2012 Budweiser commercial that featured a beer-fetching dog.

The general public voted the ad as their second favorite that year. The study found little agreement in the brain activity among participants when watching a GoDaddy commercial featuring a kissing couple. It was among the worst rated ads in 2012.

How the brain responds

The CCNY researchers collaborated with Matthew Bezdek and Eric Schumacher from Georgia Tech to identify which brain regions are involved and explain the underlying mechanisms.

Using functional magnetic resonance imaging (fMRI), they found evidence that brainwaves for engaging ads could be driven by activity in visual, auditory, and attention brain areas.

“Interesting ads may draw our attention and cause deeper sensory processing of the content,” says Bezdek, a postdoctoral researcher at Georgia Tech’s School of Psychology.

Apart from applications to marketing and film, Parra is investigating whether this measure of attentional draw can be used to diagnose neurological disorders such as attention deficit disorder or mild cognitive decline.

Another potential application is to predict the effectiveness of online educational videos by measuring how engaging they are.

Source: Georgia Tech

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transportation • Re: Thinking of getting a new ride …. carbon edition

I definitely agree on the fit of it. I have gone through the process once before, but that was 3 years ago when i got my current bike. I will most likely do it again, as it is worth the extra time. Also, my plan is to run either 25 or 28. Im done with 23 at high pressure. It seems that most manufactures have caught on to this and most bikes allow up to a 28 (some go to 32) so I will probably go as big as i can. I did ride some 28′s @ ~85 and the ride was substantially dampened. However, when i started hammering on it uphill I felt like I was about to roll the tire off.

As far as the shapes and the speed thing, I agree that there really isnt an absolute proven method to correlate the marketing numbers (compliance/stiffness) and how it feels. Although it is amazing how much different each frame feels. My goal is to start with going through some frames and getting a feel for them, and then get the fine tuning from there. I figure that I will be able to narrow my choices based on too stiff/too plush/too ‘buzzy’/etc. Right now, when I hit a bump, I can feel it rattle all the way up my spine. It was obvious that comfort was not a priority on the SLC01. I plan to head out and ride some of these soon, so I will post my initial impressions of them.

general design discussion • Re: Bike Design Project

Rough crowd, I enjoyed all the projects and digging through the process. The final bikes are beautifully built and there are a lot of great features that would appeal to me as a consumer (granted I’m a 20-30 something designer hipster, but at least they know their market).

I’m not a bike guy so maybe I’m not educated enough to see what’s so glaring insulting to the bike gods about these, but I think there’s more than enough room for this type of exploration. I appreciate the fact that these aren’t just renderings but ridable prototypes, I think it’s cool that they are influenced by people not necessarily imbedded in the bike world but built in collaboration with people who are.

Human’s are curious and diverse, this idea that there’s nothing new under the sun so let’s all just stop what we’re doing and use the same stuff is unrealistic in my opinion.