Henri Coanda, inventor of the Thermojet 
Friday, January 5, 2007, 02:42 PM - Flying Contraptions
Henri Coanda (1886-1971) was a Romanian inventor, aerodynamicist, and father of the jet aircraft, who studied at Supaero in Paris, and lived his adult life in France. He is well known for the Coanda effect, also known as "boundary layer attachment": the tendency of fluid to follow the contour of a convex surface, rather than go in straight line. He studied this effect after the crash-and-burn failure of his 1910 Thermojet powered airplane.

The Thermojet, (or moto-reacteur in French) is a predecessor of the jet engine, which uses an air compressor (e.g. a ducted fan) powered by a conventional piston engine, followed by a combustion chamber in which fuel is injected, causing the hot gases to exit the exhaust nozzle at high speed. This is the same idea as the after-burner for electric ducted fan that we talked about before.


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Cheap LiPo batteries at MaxAmps 
Friday, January 5, 2007, 02:53 AM - Flying Contraptions
MaxAmps has cheap LiPo battery packs, for example they have 3000mAh 3S 11.1V pack for 75 bucks. which can do 20C (60Aamps) constant, 30C (90Amps) sustained, and 50C (150Amps) burst. It even comes with a choice of connectors (including Dean Ultra), a cell balancing connector, and an optinal 300 charge cycle warranty. They have 10,000mAh cells up to 15C constant / 30C burst.

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Secret Life of Machines videos 
Thursday, January 4, 2007, 10:46 PM - Misc TechnoToys
Videos of the British TV documentary series The Secret Life of Machines are available on Google Video. I particularly like the one on the fax machine..
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The history of outrunner brushless motors 
Thursday, January 4, 2007, 12:03 AM - Flying Contraptions
Outrunner brushless motors are now widely used for model airplanes. Their main advantage is the ability to generate huge torques at reasonable RPM. The trick is to have different numbers of coils in the stator and magnets in the rotor, such that every time the magnetic field goes around one turn, the rotor rotates by a fraction of a turn. This has the same effect as a gearbox with the same ratio.

Some in the electro-magnetic machine community call this "Vernier machines".

The first time I heard about brushless outrunners, it came from Germany and was called an LRK motor. As it turns out, LRK are the initials of the people who proposed to apply the Vernier idea to model airplane propulsion (Christian Lucas, Ludwig Retzbach and Emil Kuerfuss). Retzbach published an article in the German magazine Elektro Modell in April 2000 which explained what they called the "Torquemax LRK" concept and started the whole thing. A few companies soon provided kits, such as Torcman and Flyware.

Naturally, the idea wasn't new. Such outrunner Vernier machines were used for CD-ROM motors and brushless fans for years. Apprently, the Vernier idea can be traced back to a 1991 article by P. Zielinski, K. Schoepp from the Institute of Electrical Machine Systems at the Technical University of Wroclaw in Poland entitles THREE-PHASE LOW-SPEED PERMANENT MAGNET
SYNCHRONOUS MACHINES. There is a related articles by Weh H., Hoffman H., Landrath J.: "New permanent magnet excited synchronous machine with high efficiency at low speeds" Proc. of the ICEM, 1988, pp.35-40.

this page has lots of links to animations that demonstrate the operation of brushless motors.
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Meta-EWI: enhanced electronic wind instrument 
Wednesday, January 3, 2007, 02:33 AM - Misc Music
Thomas Enrique from the University of Lisbon, is presenting his Meta-EWI (enhanced electronic wind instrument) at Dorkbot NYC tonight. As a fan of electronic wind instruments (Yamaha WX-5, and EZ-TP), I couldn't miss that. Electronic Wind Instruments generally have keys, a breath pressure sensor, and a lip pressure sensor. I have always though that more sensors would make the instrument more "personnal". I remember talking about this topic many years ago with David Wessel, director of Center for New Music and Audio Technologies at UC Berkeley. David says that musicians such as John Coltrane and Miles Davis can be recognized after only a few notes because the sound of their instrument is very special. The conformation of the mouth cavity of the player, the rigidity of the lips and other factors, give a personnal "voice" to wind instruments such as saxophones and trumpet. How could we reproduce this with electronic wind instruments?
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Tim Thompson: uber-geek-artist 
Tuesday, January 2, 2007, 12:42 PM - Misc Music
I stumbled again on the web site of my old pal Tim Thompson (a.k.a. "tjt"). Tim is a hacker and musician (I seem to run into a lot of those people). We met in the late 80's when we were both at Bell Labs in Holmdel, NJ (Tim did some work on our handwriting recognition systems). In the mid 80's, he founded the notorious Mostly Midi Mailing List, in which (mostly AT&T) geek/musisians would exchange tips and ideas about Midi and electronic music. He wrote the ultra cool KeyKit (formerly Keynote) Midi sequencer and composition software, which had a interpreted language front-end (as well as a GUI), and such things as Markov Model for generating melodies (he is a fan of algorithmic composition). Tim is now in California, and seems to be having fun with unusual Music controllers of his own design, real-time video processing, Burning Man contraptions, and such.
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ISS and Space Shuttle in front of the Sun 
Friday, December 29, 2006, 09:59 AM - Misc TechnoToys
Astrophotographer Thierry Legault took this amazing picture of the International Space Station and the shuttle Atlantis passing in front of the sun. The exposure was so short (1/8000s) that atmospheric disturbances did not have time to blurr the image. You can see all the details of the ISS, and the tail of the space shuttle from 550Km away!

Speaking of astrophotography, here is a list of the top 10 astronomy pictures of 2006, and here is a nice web site with several beautiful pictures of the sky (not necessarily astronomical).

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Math jokes 
Thursday, December 28, 2006, 09:23 PM - Misc TechnoToys
A couple random sites of Math jokes here, and here.

Example:
Q. Where do adders (a common snake in England) multiply?
A. When they are in logs.

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Big list of amateur telemetry/UAV web sites 
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OpenServo project 
Wednesday, December 27, 2006, 01:16 AM - Robotics
The OpenServo project proposes turn a cheap analog servo into a high-performance, programmable digital servo by replacing the circuit board with a custom board built around an Atmel AVR-8 micro-controller. The servo includes I2C control with position/force feeedback.
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ChRoMicro UAV auto-pilot project 
Wednesday, December 27, 2006, 01:06 AM - Robotics
The ChRoMicro helicopter autopilot project uses a Gumstix Connex board. The Gumstix are tiny computers running Linux that are built around a Freescale PXA255 ARM processor.

The software part of the ChRoMicro, called pxaRC, has its own web site. Other goodies include instructions and software to connect a CMOS camera to a Gumstix Connex board.

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F. Thobois's R/C Electronics Site in English 
Wednesday, December 27, 2006, 12:45 AM - Electronics
French author Francis Thobois has published numerous articles on how to build your own R/C set since the early 60's. His web sites has instructions for building receivers, transmitters, and various R/C-related circuits. Some of his pages have been translated into English.

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Magnetometer-based UAV auto-pilot 
Wednesday, December 27, 2006, 12:31 AM - Robotics
Apeliotes is an autu-pilot for UAV that uses a 3-axes magnetometer. This allows the UAV to measure its attitude using the Earth's magnetic field. Unlike gyro-based attitude estimations systems, magnetometers are not subject to drift.

This was a project conducted by Matthew Chave at University of Otago in New Zealand. The board is built around a Philips LPC-2129 microcontroler (with an ARM-7 processor core). The project report is available.

The project web site is being moved to www.uavdev.com, but the new site is still in construction.

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MicroPilot 28g UAV auto-pilot 
Wednesday, December 27, 2006, 12:14 AM - Robotics
MicroPilot sells a miniature auto-pilot for UAVs that weigh only 28 grams, on a 10x4 cm board that includes a GPS, Gyros, airspeed, and barometric altimeter. The price is not light: the cheapest model, the mp1028g, is
$1700, if you buy 100 of them.
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Donuts Models: the latest in European indoor R/C design 
Tuesday, December 26, 2006, 01:55 PM - Flying Contraptions
Donuts Models is a French manufacturer and reseller of R/C equipment for indoor and 3D flying.
Their Aito V2 indoor biplane is particularly succesful and popular. The specifications are: wingspan: 890mm, mass: 160-200g, wing loading 4.9-6.2 g/dm^2, motor: AXI 2204/54, 3 servos (6 gram type), battery: 500mAh 2-cell LiPo, prop: GWS 9x4.7. The website has a video of the plane in action, flown by Jerome Chambon.

Last summer, I met master pilot Philippe Noirault at his usual indoor flying spot in Pleslin (in Brittany, France), and took a picture of his Aito, as well as a couple of videos. The Aito is the plane of choice for Philippe and his friend Nicolas Fratti in F3P competitions.


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Huge Collection of Optical Illusions 
Tuesday, December 26, 2006, 01:27 AM - Misc TechnoToys
German vision scientist Michael Bach has a huge collection of amazing optical illusions. Well worth a (prolonged) look.

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