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244 Articles

Lithium Ion Versus LiPoly In An Aeronautical Context

October 23, 2017 by 32 Comments

When it comes to lithium batteries, you basically have two types. LiPoly batteries usually come in pouches wrapped in heat shrink, whereas lithium ion cells are best represented by the ubiquitous cylindrical 18650 cells. Are there exceptions? Yes. Is that nomenclature technically correct? No, LiPoly cells are technically, ‘lithium ion polymer cells’, but we’ll just ignore the ‘ion’ in that name for now.

Lithium ion cells are found in millions of ground-based modes of transportation, and LiPoly cells are the standard for drones and RC aircraft. [Tom Stanton] wondered why that was, so he decided to test the energy density per mass of these battery chemistries, and what he found was very interesting.

The goal of [Tom]’s experiment was to test LiPoly against lithium ion batteries in the context of a remote-controlled aircraft. Since weight is what determines flight time, cutting even a few grams from an airframe can vastly extend the capabilities of an aircraft. The test articles for this experiment come in the form of a standard 1800 mAh LiPoly battery and four 18650 cells wired together as a 3000 mAh battery. Here’s where things get interesting: the LiPoly battery weighs 216 grams for an energy density of 0.14 Watt-hours per gram. The lithium ion battery weighs 202 grams for an energy density of 0.25 Watt-hours per gram. If you just look at the math, all drones are doing it wrong. 18650 cells appear to have a much higher energy density per mass than the usual LiPoly cells. How does that hold up in a real-world test, though?

Using his neat plane with 3D printed wing ribs as the testbed, [Tom] plugged in the batteries and flew around a field for the better part of an afternoon. The LiPo flew for 41.5 minutes, whereas the much more energy dense lithium ion battery flew for 36.5 minutes. What’s going on here?

While the lithium ion battery has a much higher capacity, the problem here is the internal resistance of each battery chemistry. The end voltage for the LiPo was a bit lower than the lithium ion battery, suggesting the 18650 cells can be run down a bit further than [Tom]’s test protocol allowed. After recharging each of these batteries and doing a bit of math, [Tom] found the lithium ion batteries can fly for about twice as long as their LiPo counterparts. That means an incredibly long test of flying a plane in a circle over a field; not fun, but we are looking forward to other people replicating this experiment.

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3D Printed Tyres Let You Drive On Water

October 14, 2017 by 28 Comments

[Jesus] apparently walked on water, without any tools at all. But when you’ve got a 3D printer handy, it makes sense to use it. [Simon] decided to use his to 3D print some tyres for his R/C car – with awesome results.

[Simon] started this project with a goal of driving on water. Initial experiments were promising – the first design of paddle tyres gave great traction in the sand and were capable of climbing some impressive slopes. However, once aimed at the water, the car quickly sank below the surface.

Returning to the drawing board armed with the advice of commenters, [Simon] made some changes. The paddle tyres were reprinted with larger paddles, and a more powerful R/C car selected as the test bed. On the second attempt, the car deftly skipped along the surface and was remarkably controllable as well! [Simon] has provided the files so you can make your own at home.

It’s a great example of a practical use for a 3D printer. Parts can readily be made for all manner of RC purposes, such as making your own servo adapters.

Video Streaming Like Your Raspberry Pi Depended On It

September 12, 2017 by 23 Comments

The Raspberry Pi is an incredibly versatile computing platform, particularly when it comes to embedded applications. They’re used in all kinds of security and monitoring projects to take still shots over time, or record video footage for later review. It’s remarkably easy to do, and there’s a wide variety of tools available to get the job done.

However, if you need live video with as little latency as possible, things get more difficult. I was building a remotely controlled vehicle that uses the cellular data network for communication. Minimizing latency was key to making the vehicle easy to drive. Thus I set sail for the nearest search engine and begun researching my problem.

My first approach to the challenge was the venerable VLC Media Player. Initial experiments were sadly fraught with issues. Getting the software to recognize the webcam plugged into my Pi Zero took forever, and when I did get eventually get the stream up and running, it was far too laggy to be useful. Streaming over WiFi and waving my hands in front of the camera showed I had a delay of at least two or three seconds. While I could have possibly optimized it further, I decided to move on and try to find something a little more lightweight.

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3D Printed Ribs For Not 3D Printed Planes

September 8, 2017 by 14 Comments

A few months ago, [Tom] built a few RC planes. The first was completely 3D printed, but the resulting print — and plane — came in a bit overweight, making it a terrible plane. The second plane was a VTOL tilt rotor, using aluminum box section for the wing spar. This plane was a lot of fun to fly, but again, a bit overweight and the airfoil was never quite right.

Obviously, there are improvements to be made in the field of 3D printed aeronautics, and [Tom]’s recent experiments with 3D printed ribs hit it out of the park.

If you’re unfamiliar, a wing spar is a very long member that goes from wingtip to wingtip, or from the fuselage to each wingtip, and effectively supports the entire weight of the plane. The ribs run perpendicular to the spar and provide support for the wing covering, whether it’s aluminum, foam board, or monokote.

For this build, [Tom] is relying on the old standby, a square piece of balsa. The ribs, though, are 3D printed. They’re basically a single-wall vase in the shape of a wing rib, and are attached to the covering (foam board) with Gorilla glue.

Did the 3D printed ribs work? Yes, of course, you can strap a motor to a toaster and get it to fly. What’s interesting here is how good the resulting wing looked. It’s not quite up to the quality of fancy fiberglass wings, but it’s on par with any other foam board construction.

The takeaway, though, is how much lighter this construction was when compared to the completely 3D printed plane. With similar electronics, the plane with the 3D printed ribs weighed in at 312 grams. The completely 3D printed plane was a hefty 468 grams. That’s a lot of weight saved, and that translates into more flying time.

You can check out the build video below.

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Building An Ultralight Out Of Foam In A Basement

August 14, 2017 by 50 Comments

[Peter Sripol] is something of a legend in the DIY RC aircraft crowd. He’s friends with Flite Test, and there he built an enormous RC cargo plane that could easily carry a small child aloft. Now, [Peter] is aiming a bit higher. He’s building an ultralight — a manned ultralight — in his basement. It’s made out of insulation foam.

Yes, this ultralight is constructed out of insulation foam, but you can think of that as just a skin. The real structure here comes from a wooden frame that will be fiberglassed. The design of this aircraft is an electric, twin-engine biplane. The relevant calculations have already been done, and [Peter] is already flying an RC scale model of this craft. So far, everything is not as sketchy as it could be.

As with any, ‘guy builds an airplane in his basement’ story, there must be a significant amount of time dedicated to the legality, practicality, and engineering of said plane. First off, the legality. [Peter] is actually building an ultralight under Part 103. The certifications for a Part 103 ultralight are much more lenient than the next step up in FAA-certified aircraft, a light sport or experimental aircraft. An ultralight is not required to have an airworthiness certification, and pilots of ultralights are not required to pass any tests of aeronautical knowledge or hold a medical certificate. Yes, legally, any moron can jump in an ultralight and fly. Think about that the next time someone brings up the Part 107 ‘drone’ certification.

Next, the practicality and engineering. [Peter]’s plane can weigh a maximum of 254 pounds, and should not be capable of more than 55 knots in full power level flight, while having a stall speed that does not exceed 24 knots. This is slow for a Cessna, but just about right for the gigantic remote-controlled planes [Peter] has already built.  A few years ago, [Peter] built a gigantic remote-controlled cargo plane out of what is basically foam board and a few aluminum tubes. The construction of [Peter]’s ultralight will be a highly refined version of this. He’s using foam insulation sheets for the body of the fuselage, reinforced with plywood and poplar struts. This foam and wood build will be wrapped with carbon fiber and fiberglass sheet, epoxied, and hopefully painted with flames on the side.

The use of poplar is a bit curious for an ultralight aircraft. For the last hundred years, the default wood for aircraft has been either spruce or douglas fir. The reason for this choice is the strength to weight ratio; spruce and douglas fir have the highest strength to weight ratio of any other wood. Poplar, however, is ultimately stronger and available at his local home improvement store, even though it does weigh a bit more. If [Peter] can keep the weight down in other areas, poplar is an excellent choice due to cost and availability. The video (below) is unclear, but we can only hope [Peter] has read up on the strength of aircraft frames and the orientation of the grain of each structural member.

This is the first video in what will be an amazing build series, and [Peter] hopes to get this thing up in the air by September. If you’re concerned about [Peter]’s safety, he’s also put up a GoFundMe page for a parachute. [Peter]’s going to fly this thing if you complain or concern troll or not, so donate a dollar for the parachute if you’re that concerned.

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The Ultimate FPV Cleans House

February 3, 2017 by 8 Comments

With much of the world in the doldrums of the winter, hackers are getting a bit stir crazy. [Notamed Closed] would much rather be outside flying his First Person View (FPV) quadcopters. Sure there are indoor drones, but [Notamed] wanted to keep grounded. He grabbed his R/C equipment, his Roomba, and of course an Arduino to build the ultimate FPV experience.

There aren’t many details on this build, but it’s not too hard to deduce what [Notamed] has done. He’s using a standard R/C transmitter and receiver. Instead of driving servos, the receiver plugs into an Arduino Uno. The Uno translates the PPM R/C signals to serial commands. Most Roomba’s include a serial port made especially for hackers. [Notamed] simply sends the proper iRobot Serial Command Interface (SCI) messages, and the robot is his to control.

The FPV side of things is a bog standard FPV camera and transmitter, sending standard definition video to his goggles. A GoPro is along for the ride to capture high-quality video.

Sure this is a quick hacked together build. All the parts are taped on to the Roomba. We’re sure this is on purpose. When the weather warms up, the R/C equipment goes back in the air, and the Roomba becomes just another vacuuming robot – once again a danger to pet messes everywhere.

Check out the video after the break.

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Remote Controlling A Dog

January 21, 2017 by 40 Comments

Until the industrial revolution, humans made use of animals to make our labor easier. This is still seen in some niche areas, like how no machine yet has been invented that’s as good at sniffing out truffles as pigs are. [William] has hearkened back to humanity’s earlier roots, but in a more modern twist has made something of a general purpose dog that could feasibly do any work imaginable. Now his dog is remote-controlled.

[William] accomplished the monumental task in a literally cartoonish fashion using the old trope of hanging a hot dog in front of something’s face to get them to chase it. The attachment point was fitted with a remote control receiver and an actuator to get the hanging hot dog to dangle a little bit more to the dog’s right or left, depending on where the “operator” wants the dog to go. [William]’s bulldog seems to be a pretty good sport about everything and isn’t any worse for wear either.

Believe it or not, there has been some actual research done into remote controlling animals, although so far it’s limited to remote-controlled cockroaches. We like the simplicity of the remote-controlled dog, though, but don’t expect to see these rigs replacing leashes anytime soon!

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