Variable Mirror Changes Shape Under Pressure

June 27, 2020 by Dan Maloney 10 Comments

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.

We’ve seen a couple of interesting efforts from [Huygens Optics] before, including this next-level spirit level. He’s not all about grinding glass, though — witness this investigation into discriminating metal detectors.

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What Does The Bat Say? Tune In With This Heterodyne Detector

June 27, 2020 by Sven Gregori 29 Comments

Bats are fascinating animals, and despite all the myth and creepiness surrounding them, they really remind one more of a drunk bird lost in the night sky than the blood-sucking creature they’re often made out to be. Of course, some really fall into that category, and unlike actual birds, bats don’t tend to grace us with their singsong — at least not in ways audible for us humans. But thanks to bat detectors, we can still pick up on it, and [Marcel] recently built a heterodyne bat detector himself.

Bat Detector in its enclosure — The bat detector (and an insight to the beauty of German language, where a bat is a *flutter mouse)*

The detector is made with a 555, an MCP6004 op amp, and a 4066 analog switch — along with a bunch of passives — and is neatly packed into a 3D-printed case with a potentiometer to set the volume and center frequency for the detection. The bat signal itself is picked up by a MEMS microphone with a frequency range [Marcel] found suitable for the task. His write-up also goes in all the mathematics details regarding heterodyning, and how each component plays into that. The resulting audio can be listened to through a headphone output, and after putting together an adapter, can also be recorded from his smartphone. A sample of how that sounds is added in his write-up, which you can also check out after the break.

In case you want to give it a try yourself, [Marcel] put all the design files and some LTSpice simulations on the project’s GitHub page. If you are curious about bat detectors in general and want to read more about them, follow [Pat Whetman] down that rabbit hole, or have a look at this one made in Python for something more software-focused.

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Slipping Sheets Map Multiple Bends In This Ingenious Flex Sensor

June 26, 2020 by Dan Maloney 23 Comments

When thoughts turn to measuring the degree to which something bends, it’s pretty likely that strain gauges or some kind of encoders on a linkage come to mind. Things could be much simpler in the world of flex measurement, though, if [Fereshteh Shahmiri] and [Paul H. Dietz]’s capacitive multi-bend flex sensor catches on.

This is one of those ideas that seems so obvious that you don’t know why it hasn’t been tried before. The basic idea is to leverage the geometry of layered materials that slip past each other when bent. Think of the way the pages of a hardbound book feather out when you open it, and you’ll get the idea. In the case of the ShArc (“Shift Arc”) sensor, the front and back covers of the book are flexible PCBs with a series of overlapping pads. Between these PCBs are a number of plain polyimide spacer strips. All the strips of the sensor are anchored at one end, and everything is held together with an elastic sleeve. As the ShArc is bent, the positions of the electrodes on the top and bottom layers shift relative to each other, changing the capacitance across them. From the capacitance measurements and the known position of each pad, a microcontroller can easily calculate the bend radius at each point and infer the curvature of the whole strip.

The video below shows how the ShArc works, as well as several applications for the technology. The obvious use as a flex sensor for the human hand is most impressive — it could vastly simplify [Will Cogley]’s biomimetic hand controller — but such sensors could be put to work in any system that bends. And as a bonus, it looks pretty simple to build one at home.

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Excercise Ball Makes A Passable Landing Gear

June 25, 2020 by Lewin Day 17 Comments

Exercise balls are great for many things, from amusing children to breaking everything in your living room, often in quick succession. After seeing some German WWII prototype aircraft with wild landing gear designs, the [FliteTest] crew decided to see whether they could use an exercise ball to build a plane ready for even the bumpiest of runways.

Comparisons to the Gee Bee R-1 abound in the video.

The exercise ball created some constraints on the design, due to its weight and the large amount of drag it creates. To work around this, the design features a foamcore and carbon fibre construction to save weight. The exercise ball is placed front and center, serving as both the nose and landing gear of the aircraft. V-tails are used to place the rear control surfaces outside of the shadow of the ball, to help maintain control authority. Initial tests of the airframe showed handling problems. The team solved this by using a pair of gyro stabiliser boards of their own design, named Aura.

With the issues solved, the final aircraft is hilarious to behold. The huge, bouncing ball makes an excellent landing gear, able to launch off lumps and bumps and even skim over water. We’ve seen [FliteTest] get up to other escapades in the past, too. Video after the break.

[Thanks to Baldpower for the tip!]

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Building And Flying A Helicopter With A Virtual Swashplate

June 25, 2020 by Dan Maloney 33 Comments

They say that drummers make the best helicopter pilots, because to master the controls of rotary-wing aircraft, you really need to be able to do something different with each limb and still have all the motions coordinate with each other. The control complexity is due to the mechanical complexity of the swashplate, which translates control inputs into both collective and cyclical changes in the angle of attack of the rotor blades.

As [Tom Stanton] points out in his latest video, a swashplate isn’t always needed. Multicopters dispense with the need for one by differentially controlling four or more motors to provide roll, pitch, and yaw control. But thanks to a doctoral thesis he found, it’s also possible to control a traditional single-rotor helicopter by substituting flexible rotor hinges and precise motor speed control for the swashplate.

You only need to watch the slow-motion videos to see what’s happening: as the motor speed is varied within a single revolution, the tips of the hinged rotor blades lead and lag the main shaft in controlled sections of the cycle. The hinge is angled, which means the angle of attack of each rotor blade changes during each rotation — exactly what the swashplate normally accomplishes. As you can imagine, modulating the speed of a motor within a single revolution when it’s spinning at 3,000 RPM is no mean feat, and [Tom] goes into some detail on that in a follow-up video on his second channel.

It may not replace quadcopters anytime soon, but we really enjoyed the lesson in rotor-wing flight. [Tom] always does a great job of explaining things, whether it’s the Coandă effect or anti-lock brakes for a bike.

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Building A Scooter Exhaust From Scrap Metal

June 23, 2020 by Lewin Day 20 Comments

When a part on a vehicle fails, oftentimes the response is to fit a new one fresh out the box. However, sometimes, whether by necessity or simply for the love of it, it’s possible to handcraft a solution instead. [Samodel] does just that when whipping up a new exhaust for his scooter out of scrap metal.

It’s a great example of classic backyard metalworking techniques. The flange is recreated using a cardboard template rubbed on the exhaust port, with the residual oil leaving a clear impression. Hard work with a grinder and drill get things started, with an insane amount of filing to finish the piece off nicely. A properly tuned pipe is then sketched out on the computer, and a paper template created. These templates are cut out of an old fridge to create the main muffler section.

There’s plenty of other hacks, too – from quick and dirty pipe bends to handy sheet forming techniques. It’s not the first time we’ve seen great metalworking with scrap material, either. Video after the break.

[Thanks to BrendaEM for the tip]

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Voice-Command Chess Board Powered By Alexa

June 22, 2020 by Lewin Day 6 Comments

Talking to computers used to be reserved for Star Trek and those with overactive imaginations. Now, it’s a regular part of daily life. [CodersCafe] decided to put this technology to work in a chess robot, with the help of Amazon’s digital assistant.

The build relies on an Cartesian motion rig, built out of Lego Technics parts. The end effector is fitted with a magnet , fitted onto the Z-axis screw for engaging and disengaging with the pieces. A Mindstorms EV3 controller is used to run the show, hooked up over Bluetooth to an Amazon Echo. This allows the user to ask Alexa to move the pieces for the white player in natural language – by saying, for example, “move from B1 to C3”.

It’s a build that demonstrates how easy it is to create projects with advanced functionality by lacing together the correct off-the-shelf hardware. Other Cartesian-type motion platforms can make great chess robots, too. Video after the break.

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