Laser power system keeps UAVs flying indefinitely

Drone technology is driving the aerospace industry as companies trip over each other trying to develop the next big thing. Here’s a good example of what we’re talking about. Lasers can no be used to keep a UAV in the air indefinitely. The trick is to add an array of photovoltaic cells specifically tuned to an IR laser’s wavelength. A ground system then directs a high-intensity laser beam onto the aircraft’s cell array to transfer energy while in flight.

After the break you can catch a video from a trade show where a Lockheed Martin employee describes the successful testing of such a system. But there’s a lot more information available in the white paper (PDF) which Laser Motive has released. They’re the folks behind the technology who have teamed up with LM to implement the system. The laser unit on the ground can track a UAV visually, but there is also a method of using GPS coordinates to do so in the case of overcast skies.

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Testing 30 brands of batteries

Batteries come packaged in bright blister packs emblazoned with vague guarantees such as “45% more pictures” and “five times longer lasting.” During his internship at BitBox this summer, [Thomas] decided to put those statements to the test. He tested thirty brands of batteries on a homebrew rig to find the batteries with the most power and the most bang for your buck.

The hardware [Thomas] used an STM32 microcontroller to perform two different tests: a high drain and a low drain condition. For the high drain, 1000 mA were sucked out of the batteries until the voltage reached 0.8 V. For the low drain, 200 mA were used. Data including milliwatt-hours, milliamp-hours, joules, voltage, current, power, and effective load resistance were all logged for both conditions for all 30 batteries.

Generalizing the results for both low and high drain conditions, lithium batteries were better than alkaline, which were both better than zinc AA cells. Perhaps unsurprisingly, batteries marketed as ‘long life’ and ‘extended power’ were the worst batteries for the money, but a brand-name battery – the Kodak Xtralife cells – were actually the best value for the money.

Ugly upgrade keeps the tunes playing longer

[Sam] picked up a Sansa Clip audio player to listen to some tunes while working on projects. He liked the fact that he could run the Rockbox alternative firmware on the device, but thought the 15 hour battery life needed some improving. He swapped out the stock cell with a larger Lithium cell for a long life of 50-60 hours. It’s an upgrade fom 300 mAh to 1100 mAh, but as you can see, the size of the replacement made for some interesting case modification.

The battery swap required more than just taking one battery out and putting in the other. [Sam] is using a cellphone battery as the replacement and he didn’t want to have issues with the internal circuitry. He took the cell out of its plastic enclosure, removing the circuit board in the process. That PCB is the charging circuit, which he replaced with the one from the stock battery. After insulating the cell with a layer of Kapton tape he soldered it to the MP3 player and did his best to adhere all the parts to each other.

Sure, its ugly, but that makes it right at home on the work bench.

Passion Fruit acquire laser defenses

Apparently being overrun by ripe Passion Fruit is a problem if you live in Hawaii. [Ryan K's] solution to the situation was to use his extra fruit to power a laser. In an experiment that would make [Walter White] proud, [Ryan] gathered everyday supplies to form a battery based on the fruit.

He used some galvanized bolts as the source of zinc. It forms one pole of each cell, with a thin copper tube as the other pole. Each cell is rather weak, but when combined with others it makes a respectable battery. We’ve seen acidic fruit used to power LEDs, but [Ryan] wanted to do a little more. He built a circuit that would store electricity until he had enough potential to power an LED diode. After the break you can see a four second clip of the fruit wielding its new laser defense system.

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Arduino voltage measurement tricks

We think it’s a great learning experience to tear back the veil of abstraction and learn a bit more about the hardware found on an Arduino board. This project is a great example. [Scott Daniels] takes a look at the other voltage measurement options available to AVR chips used by Arduino.

If you’ve used the analogRead() function then you’ve already measured a voltage using the Arduino. But do you know what is going on behind the scenes to make this happen? The Analog to Digital converter on the AVR chip is being used to measure an incoming voltage by comparing it to a known voltage reference. That reference is by default the supply voltage line for the chip. This should be 5V but will only be as accurate as the regulator supplying it. [Scott] looks at the other voltage references that may be used. An external reference can be used by adding hardware, but that’s not the focus of his article. Instead he looks at using the 1.1V internal reference. He’s written some short example code that let’s you measure the incoming line voltage based on that internal reference. This is a very handy trick that can let you detect when the chips is running from a battery and how much juice is left in the cell.

Convert a speaker to a battery-powered amplifying party box

[Matt the Gamer] loved his pair of Minimus 7 bookshelf speakers. That is until a tragic hacking accident burned out the driver and left him with a speaker-shaped paper weight. But the defunct audio hardware has been given new life as a single portable powered speaker. Now he can grab it and go, knowing that it contains everything he needs to play back audio from a phone or iPod.

The most surprising part of the build is the battery. [Matt] went with a sealed lead-acid battery. It just barely fits through the hole for the larger speaker, and provides 12V with 1.2 mAh of capacity. He uses an 18V laptop power supply when charging the battery. The PSU is just the source, his own circuit board handles the charging via an LM317 voltage regulator. Also on the board is an amplifier built around a TDA2003A chip. He added a back panel which hosts connections for the charger and the audio input. Two switches allow the speaker to be turned on and off, and select between battery mode and charging mode. As a final touch he added a power indicator LED to the front, and a drawer pull as a carrying handle.

Fauxrarri is the PPPRS Champion

The Power Racing Series (PPPRS) is an electric vehicle competition with a $500 price ceiling. This is Fauxarri, the 2012 Champion. It was built by members of Sector67, a Madison, WI hackerspace. To our delight, they’ve posted an expose on the how the thing was built.

It should come as no surprise that the guys behind the advance electric racer aren’t doing this sort of thing for the first time. A couple of them were involved in Formula Hybrid Racing at the University of Wisconsin. That experience shows in the custom motor controller built as an Arduino shield. It includes control over acceleration rate, throttle response, and regenerative braking. But you can’t get by on a controller alone. The motors they used are some special electric garden tractor motors to which they added their own water cooling system.

If you want to get a good look at how fast and powerful this thing is head on over to the post about the KC leg of PPPRS (it’s the one towing a second vehicle and still passing the competition by).