Powerful/lightweight speaker 
Tuesday, January 16, 2007, 12:07 AM - Electronics
Several people (my dad and I among others) have been experimenting with engine sound generators for electric R/C airplanes. Those generators make the plane produce the sound of the real plane. With all the chatter about this topic, there is a need for a compact, lightweight, but powerful loudspeaker that can be mounted in an airplane. It needs to be powerful enough to be heard from the ground. The necessary power seems to be around 40 Watts.

Some of us have so far been using cheap 10cm speakers, such as the Visaton R10S-4 (4 Ohms, 20 Watts, 10cm diameter, 150 grams).

Interestingly, Blaupunkt seems to have a range of powerful and lightweight speakers, such as the THx 402: 10cm diameter, 40W continuous (120W peak), 4 Ohms. The magnet weight is 30 grams (not sure about the total weight).

The only problem is that it retails for $55 to $90 (compared to about $10 for the Visaton).



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United Hobbies: Real Cheap R/C Stuff direct from Hong-Kong 
Saturday, January 13, 2007, 02:49 PM - Flying Contraptions
United Hobbies is an on-line hobby store located in Hong-Kong that sells direct to customers around the world. They have all kinds of Chinese-made R/C stuff at unbelievably low prices. For example a complete helicopter with collective pitch is $101 (ready-to-fly, with radio). They have ultra-low price brushless outrunner motors, and LiPo batteries, e.g. a 3S 4100mAh pack for $52.



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ThrustPac: propeller-powered bike 
Friday, January 12, 2007, 11:13 PM - Misc TechnoToys
The ThrustPac is a backpack with a 4-stroke engine powering a ducted fan. The mid-range model features a 1.5HP, 35cc engine, can propel a bike at 40km/h, and costs about $900. The only problem is the loud noise, kinda like flying a 1/4 scale model airplane in the street....

Modern outrunner brushless electric motors are powerful enough to replace those noisy gas engines, and way more quiet. It should be possible to have a decent range with LiPo batteries.



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Foldable Indoor 3D biplane 
Friday, January 12, 2007, 12:14 AM - Flying Contraptions
This nice (but expensive) biplane kit is not made of Depron or any other kind of extruded closed-cell styrofoam, it's made entirely of carbon fiber rods and plastic foil. The plane can be taken apart and folded flat.

There is no aileron: the whole wing pivots. My experience with flat pivoting wings for small gliders has been a disaster. I suppose having a propeler blowing on the wings solves the brutal stalling behavior I have observed.



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Amazing Lego Car Factory 
Wednesday, January 10, 2007, 07:19 PM - Robotics
There is an amazing video of an automated car factory built with Lego Mindstorms on YouTube. The whole setup is huge. I couldn't count how many RCX bricks are used, but it seems like a lot. Unfortunately, there doesn't seem to be any other web site that describes the system.


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High Power LEDs for cheap 
Tuesday, January 9, 2007, 12:41 AM - Electronics
High-power LEDs have been available for some time, but most web stores have huge markups on the price. Lumiled Future Electronics sells them for (relatively) cheap. For example, their 3 Watt Luxeon III Stars are $3.50 to $4.50 depending on color.

Instructables has a tutorial on an RGB light controller that uses them.



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Buy a CNC machine from Sears 
Tuesday, January 9, 2007, 12:00 AM - Robotics
Are CNC machines becoming a consumer item? Sears now sells consumer-grade 3D CNC machine called the CompuCarve computer controlled- woodworking machine under its Craftsman brand. The machine sells for $1800. It looks more appropriate for shallow carving, engraving, and cutting thin sheets (the cutting depth is limited to 25mm). It can handle pieces up to 36cm wide, 12.5 cm thick, and almost any length.

Pretty soon, we are going to see low-price consumer-grade CNC machines coming out of the .... woodwork ;-)



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Programmable Roombas 
Monday, January 8, 2007, 09:06 PM - Robotics
Irobot announced the Irobot Create Programmable Roomba. It a version of the Roomba without the vacuum cleaner parts, with a payload bay, a "real" serial port, and an optional Atmel-based programmable micro-controller module that includes external sensor interfaces. The best thing: its' dirt cheap: $130 for the basic robot, $180 with the controller module, and $1000 for a 10-pack. There is an article about it at Robot Magazine.



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Cool VTOL concepts from WWII 
Sunday, January 7, 2007, 01:51 AM - Flying Contraptions
During WWII, German engineers came up with a bunch of interesting concepts for Vertical Takeoff and Landing aircrafts. They were never built, but they look pretty interesting.

The first one, proposed by Focke-Wulf, is another one of those flying pancakes with a circular wing and co-axial contra-rotating rotors in the middle of the wing. There is a description (in French) here, and a few pictures of 3D models here.

The second plane called the Triebflugel, was also proposed by Focke-Wulf. It's a sort of helicopter/plane hybrid, with three ¨wings¨ that rotate around the fuselage, serving as a rotor. The rotor is powered by ramjets placed at the tips. A description (in French), with pictures (worth 1000 words in any language you like) is available here.

The idea of ramjets-powered rotors was used in various helicopters, such as that one at the Seattle Museum of Flight. A similar concept (with rockets instead of ramjets) was revived in the late 90´s by the Roton corporation as a way to launch payload into space. A prototype was built and flown, but the company folded in 2001.

While those ideas have largely been abandoned for full-size airplanes, it might be possible to build R/C models of those things.



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Kyosho Manoi Robot Competition 
Saturday, January 6, 2007, 11:40 PM - Robotics
There is astory at Robot Magazine on the recent Kyosho Athlete Humanoid Cup. Most competitors use the Kyosho Manoi humanoid robot. The article has lots of pictures and a nice video.



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More Flying Pancakes 
Saturday, January 6, 2007, 03:44 PM - Flying Contraptions
Speaking of flying pancakes, this reminds me of the Chance-Vought V-173 / XF5U-1 "Flying Flapjack". The plane was was proposed in the mid-30's and first flown in 1942. It featured two large contra-rotating props, which allowed to fly at very low speed and very high angle of attack, very much like our radio-controled Drenalyns. Low-aspect ratio wings are generally inefficient, because of the drag induced by the vortex at the tip, but the props turn in the opposite direction, thereby reducing the effect of the vortex.

More details and pictures are available here, here, and here.




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Flying Pancakes 
Friday, January 5, 2007, 10:59 PM - Flying Contraptions
Speaking of flying saucers and the Coanda effect, I am reminded of the Avrocar. This was a Canadian R&D project in the 50's, which was later funded by the US. The idea was to develop a VTOL flying saucer, but the prototype never managed to fly higher above 1 meter altitude (using the ground effect).


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R/C VTOL flying saucer uses Coanda Effect 
Friday, January 5, 2007, 03:23 PM - Flying Contraptions
Speaking of the Coanda effect, back in January 2006, an English inventor named Geoff Hatton built a very cool R/C flying saucer based on the Coanda effect. He apparently demonstrated a prototype to the UK defense ministry (see video here). The latest prototype is 91cm in diameter and 5.45kg. He calls it the GFS (Geoff's Flying Saucer).

French unusual flying contraption enthusiast Jean-Louis Naudin built several models inspired by the GFS. Unlike Hatton's succint GFS web site, Naudin's site has lots of pictures and videos. Naudin is a creative and skilled tinkerer, and it's too bad that his site is littered with pseudo-science, which does nothing to help his credibility.



Several years ago, my dad made an attempt to build an electric flying saucer (not using the Coanda Effect), but never managed to make it fly in a controlable fashion. The wide-body Coanda trick with slats is a good solution.



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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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