Chordata motion capture dancer and 3D model

A Motion Capture System For Everyone

September 24, 2018 by Steven Dufresne 23 Comments

[Chordata] is making a motion capture system for everyone to build and so far the results are impressive, enough to have been a finalist in the Hackaday Human Computer Interface Challenge. It started a few years ago as one person’s desire to capture a digital performance of a dancer on a stage and has grown into a community of contributors. The board files and software have just been released as alpha along with some instructions for making it work, though more detailed documentation is on the way.

Fifteen sensor boards, called K-Ceptors, are attached to various points on the body, each containing an LSM9DS1 IMU (Inertial Measurement Unit). The K-Ceptors are wired together while still allowing plenty of freedom to move around. Communication is via I2C to a Raspberry Pi. The Pi then sends the collected data over WiFi to a desktop machine. As you move around, a 3D model of a human figure follows in realtime, displayed on the desktop’s screen using Blender, a popular, free 3D modeling software. Of course, you can do something else with the data if you want, perhaps make a robot move? Check out the overview and the performance by a clearly experienced dancer putting the system through its paces in the video below.

As a side note, the latest log entry on their Hackaday.io page points out that whenever changes are made to the K-Ceptor board, fifteen of them need to be made in order to try it out. To help with that, they show the testbed they made for troubleshooting boards as soon as they come out of the oven.

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Serpentine: multi-purpose hand gesture sensor

There Are Multiple Ways To Gesture With This Serpentine Sensor

September 22, 2018 by Steven Dufresne 2 Comments

Serpentine is a gesture sensor that’s the equivalent of a membrane potentiometer, flex and stretch sensor, and more. It’s self-powering and can be used in wearable hacks such as the necklace shown in the banner image though we’re thinking more along the lines of the lanyard for Hackaday conference badges, adding one more level of hackability. It’s a great way to send signals without anyone else knowing you’re doing it and it’s easy to make.

Serpentine is the core of a research project by a group of researchers including [fereshteh] of Georgia Tech, Atlanta. The sensor is a tube made of a silicone rubber and PDMS (a silicone elastomer) core with a copper coil wrapped around it, followed by more of the silicone mix, a coil of silver-coated nylon thread, and a final layer of the silicone mix. Full instructions for making it are on their Hackaday.io page.

There are three general interactions you can have with the tube-shaped sensor: radial, longitudinal, and tangential. Doing various combinations of these three results in a surprising variety of gestures such as tap, press, slide, twist, stretch, bend, and rotate. Those gestures result in signals across the copper and silver-coated nylon electrodes. The signals pass through an amplifier circuit which uses WiFi to send them on to a laptop where signal processing distinguishes between the gestures. It recognizes the different ones with around 90% accuracy. The video below demonstrates the training step followed by testing.

Serpentine works as a result of the triboelectric nanogenerator (TENG) phenomenon, a mix of the triboelectric effect and electrostatic induction but fabrics can be made which use other effects too. One example is this fabric keyboard and theremin which works in part using the piezoelectric effect.

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555 Timer Robots Will Rule The World

September 21, 2018 by Steven Dufresne 21 Comments

A running joke we see in the comments by Hackaday readers whenever a project includes an Arduino or Raspberry Pi that seems like overkill is to proclaim that “I could have done it with a 555 timer!” That’s especially the case if the project amounts to a blinking light or anything which oscillates. Well [Danko Bertović] has made a whole robot out of a 555 timer circuit in his latest Volos Projects video.

Okay, it’s really a dead bug circuit in the shape of a robot but it does have blinking lights. We also like how the base is the battery, though some unevenness under it seems to make the whole thing a bit unstable as you can see in the video below. There are also a few parts which are cosmetic only. But it’s cute, it’s a 555 timer circuit, and it’s shaped like a robot. That all makes it a win.

We do wonder how it can be taken further. After all, a walk cycle is a sort of oscillation so the 555 timer circuit could run some servo motors or at least some piezoelectric feet. Ideas anyone?

On the other hand, if you’re looking for a dead bug circuit which belongs in a fine arts museum then you need look no further than The Clock.

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Fixing An IBM 1401 Computer To Get It Printing Again

September 20, 2018 by Steven Dufresne 10 Comments

The IBM 1401 is a classic computer which IBM marketed throughout the 1960s, late enough for it to have used transistors rather than vacuum tubes, which is probably a good thing for this story. For small businesses, it was often used as their main data processing machine along with the 1403 printer. For larger businesses with mainframes, the 1401 was used to handle the slower peripherals such as that 1403 printer as well as card readers.

The Computer History Museum in Mountain View, CA has two working 1401s as well as at least one 1403 printer, and recently whenever the printer printed out a line, the computer would report a “print check” error. [Ken Shirriff] was among those who found and fixed the problem and he wrote up a detailed blog entry which takes us from the first test done to narrow down the problem, through IBM’s original logic diagrams, until finally yanking out the suspect board and finding the culprit, a germanium transistor which likely failed due to corrosion and an emitter wire that doesn’t look solidly connected. How do they know that? In the typical [Ken]-and-company style which we love, they opened up the transistor and looked at it under a microscope. We get the feeling that if they could have dug even deeper then they would have.

If you’re unfamiliar with the work of this team who maintain the machines at the museum, you’ll want to read up on how they recently got a 1401 to run FORTRAN II code.

DIY Falcon Heavy 2nd stage test flight of BPS.space

Rocket Science With The Other SpaceX

September 18, 2018 by Steven Dufresne 29 Comments

When you say that something’s not rocket science you mean that it’s not as hard to understand or do as it may seem. The implication is that rocket science is something which is hard and best left to the likes of SpaceX or NASA. But that’s not the hacker spirit.

[Joe Barnard] recently had an unsuccessful flight of his Falcon Heavy’s second stage and gives a very clear explanation of what went wrong using those two simple concepts along with the thrust, which in this case is just the force applied to the moment arm.

And no, you didn’t miss a big happening with SpaceX. His Falcon Heavy is a homebrew one using model rocket solid boosters. Mind you, it is a little more advanced than that as he’s implemented thrust vectoring by controlling the engine’s direction using servo motors.

And therein lies the problem. The second stage’s inertia is so small and the moment arm so short that even a small misalignment in the thrust vectoring results in a big effect on the moment arm causing the vehicle to deviate from the desired path. You can see this in the first video below. Another issue he discusses is the high drag, but we’ll leave that to the second video below which contains his explanation and some chart analysis.

So yeah, maybe rocket science is rocket science. But there’s no better way to get your feet wet then to get out there and get building.

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Wind-Blaster: Haptic Feedback That’ll Make You Recoil

September 16, 2018 by Steven Dufresne 8 Comments

A big challenge in the VR world is getting haptic feedback no matter where you are. That’s not so much of a problem when you’re sitting in a chair, the hardware can be attached to the chair or to something near you, what’s referred to as grounded force-feedback. But with VR, we’ve gotten used to at least moving around a room. How then do you feel the recoil of a gun, the pressure against a shield, the inertia of a sword slicing through the air, or the pulsations of magic sword emitting lightning?

A team of researchers at the [MAKinteract Lab] at KAIST, a university in South Korea, have come up with a small device which straps to your wrist and provides all those types of feedback. It’s called the Wind-Blaster and consists of two ducted propellers which can provide up to 1.5N of force. Both propellers are mounted on servos, and with the help of an IMU, the propellers are oriented as needed. An Arduino doing PWM controls the motor speeds.

Fire a VR shotgun and the propellers quickly spin up to 33,000 RPM for just 250 ms, giving your lower arm a quick backward tug, providing the feel of a recoiling gun. Swing a VR sword through the air and the propellers rotate at 33,000 RPM for 400 ms and then linearly decelerate to a stop in 300 ms. Making the propellers move asynchronously with respect to each other causes rotation torque on your arm for a pulsating feeling for the magic lightning-emitting sword. A connected PC runs the games using the Unity game engine. As with drones, there is noise at around 41 dB but the user’s headphones block it out. Watch it in action in the videos below.

Here on Hackaday, we’ve covered few more ungrounded haptic feedback systems. There’s one which responds to light, another which lets you feel textures, and a glove which gets feedback as it controls a robotic gripper.

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Testing Lithium Ceramic Batteries (LCBs)

September 15, 2018 by Steven Dufresne 29 Comments

Affordable solid-state batteries large enough for cell phones and drones have been promised for a long time but seem to always be a few years away from production. In this case, Taiwan based Prologium sent [GreatScott] samples of their Lithium Ceramic batteries (LCBs) to test, and even though they’re not yet commercial products, who are we to refuse a peek at what they’ve been up to? They sent him two types, flexible ones (FLCBs) and higher capacity stiff ones (PLCBs).

The FLCBs were rated at 100 mAh and just 2 C, both small values but still useful for wearables, especially given their flexibility. Doing some destructive testing, he managed to keep an LED lit while flexing the battery and cutting away at it with tin snips.

Switching to the thicker 7.31 Wh PLCB, he measured and weighed it to get an energy density of 258 Wh/L and a specific energy of 118 Wh/kg, only about 2/3rds and 1/2 that of his LiPo and lithium-ion batteries. Repeating the destructive tests with these ones, the LED turned off and smoke appeared while cutting and hammering a nail through, likely due to the shorts caused by the electrically conductive tin snips and nail. But once the snips and nail were moved away, the smoke stopped and the LED lit up again. Overcharging and short-circuiting the batteries both caused the solder connecting the wires to them to melt but nothing else happened. Rapidly discharging through a resistor only resulted in a gradual voltage drop. Clearly, these batteries are much safer than their LiPo and lithium ion counterparts. That safety and their flexibility seem to be their current main selling points should they become available for us hackers. Check out his tests in the video below.

Meanwhile, we’ll have to be content with the occasional tantalizing report from the labs such as this one from MIT of a long battery life and another from one of the co-inventors of the lithium-ion battery which uses a glass electrolyte.

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