The round bottom of a proper wok is the key to a decent stir fry, but it also makes it hard to use on traditional Western stoves. That’s why many woks end up in a dark kitchen cabinet, unused and unloved. But wait; it turns out that the round bottom of a wok is the perfect shape for gathering something else — radio waves, specifically the 21-cm neutral hydrogen emissions coming from the heart of our galaxy.
Turning a wok into an entry-level radio telescope doesn’t appear to be all that hard, at least judging by what [Leo W.H. Fung] et al detail in their paper (PDF) on “WTH” or “Wok the Hydrogen.” Aside from the wok, which serves as the main reflector, you’ll need a bit of coaxial cable and some stiff copper wire to fashion a small dipole antenna and balun, plus some plastic tubing to support it at the focal point of the reflector. Measuring the wok’s shape and size, which in turn determines its focal point, is probably the hardest part of the build; luckily, the paper includes tips on doing just that. The authors address the controversy of parabolic versus spherical reflectors and arrive at the conclusion that for a radio telescope fashioned from a wok, it just doesn’t matter.
As for the signal processing chain, WTH holds few surprises. A Nooelec Sawbird+ H1 acts as preamp and filter for the 1420-MHz hydrogen line signal, which feeds into an RTL-SDR dongle. Careful attention is paid to proper grounding and shielding to keep the noise floor as low as possible. Mounting the antenna is a decidedly ad hoc affair, and aiming is as simple as eyeballing various stars near the center of the galactic plane — no need to complicate things.
Performance is pretty good: WTH measured the recession velocity of neutral hydrogen to within 20 km/s, which isn’t bad for something cobbled together from scrap. We’ve seen plenty of DIY hydrogen line observatories before, but WTH probably wins the “get on the air tonight” award.
Unless you’re in a carnival funhouse, mirrors are generally dead flat and kind of boring. Throw in some curves and things get interesting, especially when you can control the curve with a touch of your finger, as with this variable surface convex mirror.
The video below starts off with a long but useful review of conic constants and how planes transecting a cone can create circles, parabolas, or ellipses depending on the plane’s angle. As [Huygens Optics] explains, mirrors ground to each of these shapes have different properties, which makes it hard to build telescopes that work at astronomical and terrestrial distances. To make a mirror that works over a wide range of distances, [Huygens Optics] built a mirror from two pieces of glass bonded together to form a space between the front and rear surface. The front surface, ground to a spherical profile, can be deformed slightly by evacuating the plenum between the two surfaces with a syringe. Atmospheric pressure bends the thinner front surface slightly, changing the shape of the mirror.
[Huygens Optics] also built an interferometer to compare the variable mirror to a known spherical reference. The data from the interferometer was fed to a visualization package that produced maps of the surface shape, which you can easily see changing as the pressure inside the mirror changes. Alas, a deeper dive into the data showed the mirror to be less than perfect, but it’s fascinating to think that a mirror can flex enough to change from elliptical to almost parabolic with nothing more than a puff of air.
If ever any sci-fi robot form-factor made more sense than the Droideka of the Star Wars franchise, we’re not sure what it could be. Able to transform from a spheroid that rolls quickly onto the battlefield into a blaster-bristling tripodal walker, the Hollywood battle droid showed a lot of imagination and resulted in a remarkably feasible design. And now that basic design is demonstrated in a spherical quadrupedal robot that can transform from rolling to walking.
Intended as a proof of concept of a hybrid rolling-walking locomotion system, the QRoSS robot from Japan’s Chiba Institute of Technology is capable of some pretty amazing things already. Surrounded by a wire roll cage that’s independent of the robot’s legs, QRoSS is able to roll into position, unfurl its legs, and walk where it needs to go. Four independent legs make it sure-footed over rough terrain, with obvious applications in such fields as urban search and rescue; a hardened version could be tossed into a collapsed building or other dangerous environment and walk around to provide intelligence or render aid. The robot’s self-righting feature would be especially handy for that use case, and as you can see in the video below, it has a powered rolling mode that’s six times faster than its walking speed.
For a similar spherical transforming robot, be sure to check out the MorpHex robot with its hexapod design.
This odd-looking ball can automatically take a panoramic image whenever you throw it up into the air. Seriously, that’s then entire set of operating instructions for the device. Inside, a 3D printed frame hosts an array of 36 cellphone cameras, each capable of taking a two megapixel image. Also included is an accelerometer. When it senses the change in momentum associated with the apex of its vertical trajectory it snaps an image with all of the cameras at the same time. The result is a spherical image with no obstructions-like a tripod or other support mechanism. The images are automatically stitched together and displayed on a computer which allows the user to pan and zoom.
The whole story is told in the video after the break. The example images shown are quite good, although there are a few artifacts where the segments meet. Most notably, color variances between the images captured by different CCD modules. We’d image that this can be fixed automatically in software if a talented programmer were willing to put in the time. The thing about spherical photos is that methods using post processing to unwrap an image always have some distortion to them. With that in mind, we think the ball camera is as good a solution as we’ve seen.
[Ryubin’s] experiments with spherical video continue. This time around he’s using two cameras, both with fisheye lenses, to capture 360 degree by 360 degree video. The two cameras mount back to back and each record a 360 degree vertical view in a 180 degree horizontal range. By stitching the two recordings together and synchronizing them by comparing moving objects a seamless spherical video is produced.
He’s got one more trick up his sleeve with this setup. The tripod mount has a pivot point that allows the two cameras to shoot side-by-side instead of back-to-back. This produces a hemispherical video that is stereoscopic. That’s a pretty cheap way to make this type of 3D imaging compared to some of the CES offerings.