A Micro RC Plane Builder Shares His Tricks

There are individuals who push tools, materials, and craftsmanship to the limit in the world of micro RC aircraft, and [Martin Newell] gives some insight into the kind of work that goes into making something like a 1:96 scale P-51 Mustang from scratch. The tiny plane is 100% flyable. It even includes working navigation lights and flashing cannons (both done with 0402 LEDs) and functional, retractable landing gear. It weighs an incredible 2.9 grams. Apart from the battery, everything in the plane was built or assembled from scratch. A video is embedded below.

[Martin] shares some of the techniques that went into the many specialized parts of the plane. Two documents (Part 1 about techniques used for small aircraft and Part 2 about the P-51 Mustang pictured) are worth a read. In true craftsman fashion, he’s aware that while he rolled his own solutions and wasn’t aware of any similar prior work, he would be surprised if none of his innovations had ever been done by someone else before.

At such small scales many problems need re-solving, like electrical connectors. All the usual off-the-shelf connectors are far too big or heavy to go on such a small device where every fraction of a gram counts. Whenever possible, connectors are avoided entirely but sometimes — like to connect the custom-wound motor — it needs to be done. In these cases [Martin] made his own.

ultra-micro-connectors
Micro plug and socket [Source: Warbirds at 1:100 Scale by Martin Newell]
The pin on the left of the photo above is made from a 0.1″ length of 0.010″ diameter brass rod soldered to a wire lead, supported with 0.020″ ID heat shrink tubing. The socket on the right is a 0.1″ length of plastic insulation from 32 AWG wire, with the strands from the other wire drawn through and around, and covered with 0.020″ shrink tubing. Contact is made by the brass pin (left) being squeezed against the multiple strands inside the plastic insulation tube (right).

Another innovation was hinges for the control surfaces like the rudder, ailerons, and flaps. Unsatisfied with plastic hinges, [Martin] made his own nearly-frictionless and nearly-weightless ones complete with re-centering springs. Each weighs 1.6 milligrams.

hinges
Control surface hinge design [Source: Warbirds at 1:100 Scale by Martin Newell]
The hinges on the left are made from 0.008″ nickel wire and a 1 mm length of 0.4 mm plastic tube. The centering spring is a nylon bristle from a paintbrush, which [Martin] observed was pointed on one end and seemed quite springy. The tip of a single bristle is inserted into the model and by adjusting how far it is inserted, the amount of maximum deflection the control surface is allowed can be controlled. Once satisfactory, it is secured with a tiny bead of glue.

[Source: microflierradio.com]
A sample micro actuator. They get even smaller. [Source: microflierradio.com]
Servos are the usual means of actuating control surfaces like rudders and ailerons on model aircraft, but a plane like this one is far too small and lightweight to carry even the smallest servo. Instead of servos, these micro aircraft use tiny coils and magnets as actuators. They exert no force unless active, which means that whatever control surfaces they connect to need to provide their own means of re-centering and holding stable when idle. This type of actuator is common in micro aircraft, but understanding the design gives insight into why [Martin] designed the hinges and centering springs the way he did. Similar actuators are visible on the bottom of the wings in the video embedded below. They are responsible for moving the two ailerons, and the two flaps. More are present on the rudder and elevator at the rear of the plane.

[Martin] says that by far the most difficult part was the retractable landing gear. The solution uses 0.001” diameter Nitinol muscle wire. Muscle wire can be stretched about 5%, then when it is heated above a critical temperature by passing a current through it, it exerts a considerable force in attempting to contract back to its original length. By using two lengths of muscle wire, a pull-pull mechanism can be built in which the contraction of one wire has the effect of stretching the other while either raising or lowering the landing gear at the same time.

optimized-landing-gear
A push-pull system using nitinol “muscle” wire provides the raw power behind actuating the landing gear, but required a significant custom assembly to work.

However, that was much easier said than done. [Martin] explains:

“Unfortunately this appealingly simple mechanism is fraught with implementation issues when trying to meet the design requirements. One of them is that after stretching one wire by contracting the other, when the current is stopped the contraction recoils about 30%. Therefore a lock is needed to keep the wire fully stretched. Then a second lock is needed to secure the landing gear up or down, so that sharp sideways forces do not result in any forces back on the muscle wire, which could collapse the landing gear. These requirements were met with a unit that weighs about 400 milligrams. The muscle wires rotate a 0.030” diameter capstan 90 degrees. The muscle wire recoil is countered by an over-center spring acting on an idler at the end of an arm attached to the capstan.”

[Martin] goes into detail about the whole retract assembly for the landing gear in Part 2 of his documentation.

A familiar question has been whether these planes are available for sale. The answer is probably also familiar to people who make such labor-intensive things: [Martin] says they are not for sale, at least not from him. If he did offer them for sale, nobody would pay the price he would ask because of the amount of work involved.

It took [Martin] about a year to develop and build the 1:96 P-51D Mustang, and he just recently shared a video of the tiny plane flying on his YouTube channel. It is embedded below.

[Martin] demonstrates all 8 channels of control in the video below:

Speaking of scratch-built RC aircraft, we previously covered a project dedicated to 3D printing parts for a flying RC plane, complete with in-depth testing and analysis. RC hobby aircraft is an example of a field that, while filled to the brim with off-the-shelf systems, is nevertheless home to individual innovation and DIY spirit.

 

34 thoughts on “A Micro RC Plane Builder Shares His Tricks

    1. If it were made of something a bit stronger than foam I’d probably be willing to pay a pretty penny for one, it looks like an absolute joy to fly. I’m not sure what material you could use though that would meet the weight requirements. But I assume that because it weighs so little you might be hard pressed to actually damage it in a crash.

      I might make one of these little things my next project, Although I doubt it would come out as amazing as this guy’s planes.

      1. Foam is actually quite suitable – nothing else save balsa has the strength-to-weight, and foam is much less brittle.

        At 2.1 grams, it’s much more likely to bounce than crash.

        1. Agreed! F=MA. (Google it if not instantly obvious.) It will be near indestructible at this size.

          If you want to learn to fly R/C, get a SMALL plane. It breaks less often, is repaired less often, = is flown more often and many many more times = You learn to fly before moving to something that breaks easily cause it goes 150mph.

          R/C is an excellent hobby for Parent/Child.

      1. “Web 2.0” is practically wholly built on the premise the Einstein was an idiot, and everything your browser makes a request for magically materializes in full, regardless of how many terabytes in size, before said request is even sent. The real-world result is that you can have tho coolest-awesomestest-cuttingedgestestest dodecatillion-core beast of a computer and it will STILL become the equivalent of a dead brick as soon as the intertubes arbitrarily decide that you’re not that special of a snowflake and fail to respond to one of your requests faster than light. Many-mega full-HD full-motion animated GIFs are particularly likely to trigger the issue and considering it only recently dawned on the geniuses at Mozilla that a computer could actually do something else while the internet fails to give any fucks about its existence (see future feature “asynchronous scrolling”), most people affected either get white hair and chronic grump-itis or just use a GIF-nuking addon (or both).

  1. Wow – this thing has been shrunk down to the same scale range as model trains. But this one has way more independent moving parts than your typical model of a Diesel locomotive, and doesn’t have the luxury of being able to draw power through the rails. Very well done.

  2. My smallest quadcopter is a bit bigger than this amazing plane and it doesn’t take much distance before I can’t tell which way it is facing or flying. (Solved by using the FPV goggles.)

    Is a plane easier to manage because it is always flying forwards?

    1. A VERY Emphatic YES. Quads add a dimension of difficulty discerning which way is forward PLUS still have the left/right reversal confusion that planes and cars do, and altitude control is simply throttle instead of elevator/airspeed/throttle. You can learn them all, but each is a completely different beast. You lose out on things like an airplane’s speed is controlled by elevator setting, and altitude control is actually throttle, both of which are the reverse of intuitive and have a time-lag you have to anticipate. Piloting is MUCH different than flying anything with a processor between you and the control surfaces. Quads are almost exclusively computer controlled… you aren’t piloting… just steering.

      For planes it’s best to teach your brain to handle left/right reversal and do it automatic by spending time with tiny R/C cars and your cat first till your thumb knows left/right vs coming/going it on it’s own and you don’t have to stop and think (= crash). This would help all R/C, it’s needed. Avoid squirrels! They will take and eat your car.

      Gyros…. be it planes, helicopters, or quads, take away from the piloting skills needed, and YOU aren’t really flying anymore. A computer is, and it’s just trying to obey your sticks, and that depends on somebody else’s code. It is a totally different experience. Both need skill. One as a pilot, the other as something more approaching just a navigator. These are where you see the amazing videos of helicopter tricks and such… there’s a computer with gyros flying it, the sticks you push just say “go here”.

      If you really go for the computer assisted piloting check out Ardupilot. A full Arduino Autopilot.

  3. The same Martin Newell that developed the Newell algorithm and is known for the Utah teapot (used as a standard benchmark in CGI)?
    Why am I not surprised! His hobby is epic as well.
    This format of scale modeling is coming into its own with the recent FAA rules.
    I think it is a wonderful scale to use in exploring historic designs. I’d love to try this with the Demoiselle, featured in an earlier post.

    1. Based on the footage on his channel, I would say he is Dr. Martin Newell who developed the Newell algorithm and the teapot.
      His hobby is indeed as epic as what he has achieved in computer graphics!

  4. These micro machines are very impressive builds!

    I recall reading about a guy who scratch built live steam engines in Z scale and electric engines in 1/2 Z

    ill try and dig the article up – it was buy an Australian guy from memory.

  5. Amazing it will even fly at those low reynolds numbers! Yet it flies realistically! And seems reasonably close to scale speed! These alone are a lot more incredible than than you suspect. Amazing! Next the pilot skills being displayed are phenomenal despite the fact that gyros are in use, and cudos to his optometrist as well. Yet still there is more, the retracts, machine guns, landing lights too?

    I was heavily into AMA Model Aviation for a long time, AMA club President, etc… and never dared dream such a model could be built so tiny AND flown to be so scale realistic. Yet here it is! OMG! Schoolyard Scale has been superseded. The only detraction is that it uses gyros (meaning you aren’t flying, just guiding… a whole world of difference) but those are almost mandatory at this size. Makes sense that nitinol would function perfectly well at this scale.

    1. Haha this plane is going way faster than the scale speed. At 1/96 scale this plane should only be moving at 4.5mph top speed (Real P-51 top speed = 437mph / 96 = 4.5mph). In reality is doing somewhere in the neighborhood of 15-20mph which means this plane is going 3 to 4.5 times its scale speed. It is like a real P-51 mustang breaking the sound barrier and reaching a speed in Mach 2 to 2.5 territory leaving an F-22 to eat its contrail. This is just my initial calculations. Not knocking on you, just making funny observation.

      I am also an avid R/C flyer been apart of the AMA for many years and started flyer schoolyard R/C planes many years ago, but you are right this guy took schoolyard scale to a whole new level. Over the years I have seen many R/C planes in the past using all the same tech this guy is using it is nothing new. The real difference is this looks like a miniaturized P-51 mustang, which is quite impressive. The others planes I have seen were simple balsa construction that utilized a stick fuselage suspended below a parasol tip dihedral wind design and simple flat surface controls affixed to the tail end of the stick.

  6. I’m very impressed after reading the articles. Mr. Newell is an incredible engineer with expertise in many different areas that all came together in these projects. To be able to design, build, program, and fly these planes is quite an accomplishment.

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