Droning On: PID Controllers And Bullet Connectors

July 7, 2014 by Adam Fabio 30 Comments

Not all drones are multirotors – Posing in our title photo are Maynard Hill and Cyrus Abdollahi. Maynard’s plane, TAM5 aka The Spirit of Butts Farm, is the smallest aircraft to make a transatlantic flight (YouTube link). Retracing the path of Alcock and Brown from Newfoundland to Ireland, the 6 pound (dry weight) model made the trip in just under 39 hours. All this happened in 2003, and was the cap on a lifetime of achievements for Hill. These are the types of pursuits that will be banned in the USA if the FAA restrictions go into effect.

Flight Controllers

Quite a few of you thought the Naze32 was left out of last column’s flight controller roundup. I hear you loud and clear! I’ll add the Naze to the controllers which will be tested on The Hackaday Testbed. The hard part is finding the darn things! I currently have an Acro Naze32 on its way to Droning On HQ. If I can find a full version, I’ll add that.

PID Controllers Deep Dive

I’ve gotten a few questions on Proportional Integral Derivative (PID) controllers, so it is worth diving in a bit deeper to explain what a PID controller is. PID controllers are often found in process controls managing parameters like temperature, humidity, or product flow rate. The algorithm was initially designed in the late 1800’s as a method of controlling the helm of large naval ships. In fixed wing drones, PID keeps the plane’s wings level and on course. In multicopters, PID loops control heading, but they also provide the stable flight which allows the quadcopter to fly in the first place. A full explanation of PID loops would be beyond the scope of a single article, but let’s try a 10,000 foot explanation.

P: This is the “Present” parameter. P Has the most influence on the behavior of the aircraft. If the wind blows your quadcopter from level flight into a 30 degree right bank, P is the term which will immediately take action to level the quad out. If the P value is too high, The quadcopter will overshoot level flight and start banking the other way. In fact, way too high a P value can cause a quadcopter to shake as it oscillates or “hunts” for level. Too Low a P value? the quadcopter will be very slow to react, and may never quite reach level flight again.

I: This the “Past” parameter. The I term dampens the overshoot and oscillations of the P term, and avoids the tendency of P to settle above or below the set point. Just like with P, too high an I term can lead to oscillation.

D: This is the “Future” parameter, and has the smallest impact on the behavior of the aircraft. In fact, some flight controllers leave it out entirely. If P and I are approaching a set point too quickly, overshoot is likely to occur. D slows things down before the overshoot happens.

So why do multicopter pilots dread PID tuning? Quite simply, it’s a tedious process. Couple a new pilot and an unproven aircraft with un-tuned PID values, and you have a recipe for frustration – and broken propellers. Things get even more complex when you consider the fact that there are at least 3 sets of PID variables to be tuned – Pitch, Roll, and Yaw. Some flight controllers now support multiple PID values depending on the style of flight. Want your plane or multicopter to fly around like a hotrod? You need a totally different set of PID values than a docile trainer craft. Rolf Bakke (KapteinKUK himself) made a video illustrating how multicopters behave when tuning PID values. You can easily see how a quad can go from “drunk” to “angry bee” with just a few value tweaks. All this is coming together with The Hackaday Testbed, which will help me in posting a few PID tuning videos of my own.

Hackaday Testbed Update

As for the testbed itself, it’s nearly complete! You can follow the progress on my Hackaday Projects Page. Most of the assembly has been relatively straightforward. though of course there are always a few snags. It seems I always forget something when ordering up parts for a build. In this case it was 2.5mm banana plugs and motor mounting screws.

The Hobbyking motors attach to the frame with 3mm screws. The problem is that there really is no way to know how long the screws should be until you have the motors, mounting plates and drone frame on hand. I have a bunch of 3mm screws of various lengths, and thankfully there were enough screws of the correct length to mount the motors. Murphy is always at my side, as I accidentally grabbed a screw that was 1mm too long and, you guessed it, screwed right into the windings of the motor. Doh! Thankfully I had spares.

Bullet connectors can be a real pain to solder. There are some jigs out there which help, but I’ve always found myself going back to the old “helping hands” alligator clips. Bullets tend to use lower gauge wire than we’re used to with regular electronics. 14, 12, even 8 gauge wires are used on R/C aircraft. A low power soldering iron with a surface mount tip just won’t cut it. Those irons just doesn’t have the thermal mass to get the connectors up to soldering temperature. This is one of those places where a decent 40 watt or better Weller iron (yes, the kind that plugs right in the wall) can be a godsend. I’m using an Metcal iron here, with a wide flat tip.

Bare bullet connectors and alligator clips can also create a problem – the metal clips create even more thermal mass. Years back an old-timer showed me a trick to handle this. Slip a piece of silicone R/C plane fuel tubing on the bullet, and then clip the helping hands onto the tube. The tube will act as insulation between the bullet and the clip. Silicone can easily withstand the temperatures of soldering. I’ve also used the silicone tube on the jaws themselves – though eventually the jaws will cut the soft tubing.

That’s about it for this edition Droning on! Until next time, keep ’em flying!

Title photo credit Cyrus Abdollahi.

Retrotechtacular: Build Yourself An Airplane

July 1, 2014 by Mike Szczys 18 Comments

retrotechtacular-cub-j-3-piper

Planes these days are super complicated – think about the recent flaming-lithium battery issues in the B787 that may or may not have been solved – but it wasn’t always this way. Here’s a great example. The manufacture of a Piper J-3 Cub shows simple and efficient mechanical design brought to life in a multitude of steps all performed without automation.

The build starts with the frame. Pipes are nibbled into specialized fish mouths for a tight fit before being strapped to a jig and tack welded. With the fuselage in one piece the frame is removed for each joint to be fully welded and subsequently inspected. Cables are run through the frame to connect control surfaces to the cockpit. Continuing through to wing assembly we were especially surprised to see hand hammering of nails to secure the wood ribs to metal spars. How many nails do you think that worker pounded in a career? The entire aircraft is covered in fabric, an engine is added, and it’s into the wild blue yonder.

The look back at manufacturing techniques is interesting — do you think the large model shown in the video would be built these days, or would they just use a CAD rendering?

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Hackers In Africa Are Building Their Own Aircraft

June 27, 2013 by Mike Szczys 78 Comments

hacked-heli

While you’re trying to come up with an idea for your next project this guy’s been building his own helicopter from whatever parts he can find. He’s just one of the aeronautical hackers featured in a story in the Daily Mail. The article’s narrative leaves us with many questions, but there’s enough info to make it worth a look.

In addition to the heli seen above there are also a couple of airplane builds to gawk at. Africa has already produced a couple of very ingenious hacks like [William Kamkwamba’s] projects which improved his village infrastructure. He gained enough notice from his work to land a scholarship to continue his education and that opportunity has also been afforded the creators of these aircraft.

At first we figured this helicopter project was possible because of lack of air traffic regulation in this part of the world. That’s not the case as [Onesmus Mwangi] — who makes his living as a farmhand — has been forbidden to fly the craft by local police. There may be another opportunity for him to fly later in life. He’s received funding to study aircraft maintenance abroad.+

Unfortunately we couldn’t find any video of this thing in action. If that’s unacceptable to you try getting your fix from this human-sized octocopter.

[Thanks Brandon]

Watermelon Air Boat

December 17, 2012 by Mike Szczys 35 Comments

We think you’ll turn a few heads in Central Park if you’re driving a water melon around when everyone else is piloting sailboats. This watermelon is both sea worthy and radio controlled thanks to the work which [Starting Electronics] put into it.

We used this image because it shows you what’s inside of the hull, but you don’t want to miss the thing motoring around an above-ground swimming pool in the clip after the break. The hollowed out shell is quite buoyant and has no problem staying afloat and upright with the addition of a propeller. The parts from a remote control airplane kit have been mounted on a wooden scaffold. This provides plenty of thrust with a servo motor moving turning the prop for directional control. There is no dagger board so the craft is a bit slow to respond to turns. But how responsive do you expect a floating melon to be?

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How To Watch Your Own Videos On A Plane: Barf Bag

October 2, 2012 by Mike Szczys 31 Comments

Air travellers take note, [Asthmaticatom] figured out how to comfortably watch your own videos on the plane. We know you always have your phone with you, now you just need to find a barf bag. A little bit of papercraft turns the waste disposal device into a neat little hanging dock.

The bag in the image above is actually upside down. A rectangle the same size as your phone’s screen is ripped out of the top. The metal clasp used to seal the top of the bag is rolled up to hold the phone securely in place. The bottom of the sack has a flap which acts as a one-way catch. When it is shoved into the crevice on top of the monitor it holds the whole thing in place.

Of course we don’t remember ever having been on a plane where there was a monitor in the seat in front of us, but perhaps we’re just buying tickets on the wrong airlines.

[via Reddit]

Autonomous Fixed-wing Drone Threads The Needled In A Parking Garage

August 16, 2012 by Mike Szczys 23 Comments

We’ve got something of a love affair going on with quadcopters, but there’s still room for a little something on the side. This fixed-wing drone can pull off some pretty amazing navigation. MIT’s Robust Robotics Group is showing off the work they’ve done with the plane, culminating in a death-defying flight through a parking garage (video after the break). This may not sound like a huge accomplishment, but consider that the wingspan is over two meters and repeated runs at the same circuit brought it within centimeters of clipping support columns.

Unlike the precision quadcopters which depend on stationary high-speed cameras for feedback, this drone is self-contained. It does depend on starting out with a map of its environment, using this in conjunction with a laser rangefinder and inertial sensors to plot its route and adjust as necessary. We think the thing must have to plan a lot further ahead than a quadcopter since it lacks the ability to put on the brakes and hover. This is, however, one of the strengths of the design. Since it uses a fixed-wing approach it can stay in air much longer than a quadcopter with the same battery capacity.

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Human-shaped Planes Troll NYC

February 28, 2012 by Mike Szczys 30 Comments

It looks like a genetic leap has unleashed the age of mutants, but this is really just a few guys trolling New York City with some custom RC aircrafts. The video after the break shows the fliers up close. They’re pretty much full size, we’d guess 5’10” from head to heel. The outstretched arms and body act as wings, while the legs act as ailerons and rudders. But from afar (or even a medium distance) it’s quite difficult to make out the flat surfaces… they look like office workers loosed from their cubicles. ~~Unfortunately we don’t have more than a flight demo to share with you. If you know where to find build info (or any extra details at all actually) don’t forget to send in a tip.~~ We wonder if these are the same guy who made the flying hero we posted back in July?

There’s another nugget of delight right at the beginning of the video. A sweet octocopter which looks much like this one was used to capture the aerial footage.

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