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Comment by mrandish | Hacker News Reader

Just want to mention that hobbyists into fixed wing RC aerobatics have been doing crazy stuff with variable pitch propellers (VPP) for several years. RC motors with integrated variable pitch propellers exist in small sizes, so no need to DIY the propeller for that application. Here's an example of the 4D aerobatics they enable: https://www.youtube.com/watch?v=j5EsvZNvVRs.

This is similar to but different than what the creator of the one motor drone is doing since he's spinning at higher RPM with the pitch varying under CPU control much faster than fixed wing aerobatic pilots who are controlling everything manually with insane skill. I assume the one motor drone guy already knows fixed wing RC VPP exist, just mentioning for others who might not.

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Bloody hell, I was expecting something interesting, but that level of control from a single propeller is a lot more than I had imagined.

Too many different things I want to play with and insufficient time in the day -.-

How is this working? I can't tell if they are using flaps as well??

the rudder seems to have a wire attached, barely visible in the opening shot. that seems to be it though.

I don't know the exact config on this plane as it's probably a custom design since Donatas is a well-known pilot in F3P indoor aerobatic competition. I fly small scale outdoor 3D aero and based on what I see it doing, I think it's traditional control surfaces, rudder, elevator and ailerons plus two additional elements: a variable pitch propeller and a thrust vectored motor.

VPP and thrust vectoring are two separate elements which do different things. A variable pitch propeller can reverse the propeller from pulling the plane forward to pushing it backward. That's what enables diving toward the ground and almost instantly reversing to start going back up. Thrust vectoring dynamically changes the angle of the motor allowing the plane to turn in an even tighter radius than a large rudder can alone. The turn can be so tight it's less than the length of the plane, technically becoming a spin.

In fixed wing RC aerobatics, thrust vectoring (TV) isn't a feature of the motor itself, it's actually a feature of the mount the motor is attached to, which can pivot left/right ~20 deg. A rudder changes the direction of travel by pushing the tail to the left from the rear indirectly causing the nose to turn toward the right. A thrust vectored motor mount increases the rate of turn by also angling the motor to directly 'pull' the nose toward the new direction. In RC the angle is usually changed mechanically by extending the rudder servo control rod forward to the pivoting motor mount and reversing the connection point so the motor pulls the nose toward the opposite direction the rudder is pushing the tail.

As a 3D pilot looking at the video, Donatas is doing things which are wildly impressive and, if you don't know about VPP and thrust vectoring, look impossible. Before we even get into VPP and TV, the first amazing thing about the video is simply the airspeed. I fly very lightweight 3D planes and the video looks slo-mo even to me. That size of plane shouldn't be able to stay in the air moving that slowly. F3P indoor-only competition planes are hand-crafted insanely light from esoteric materials using clever engineering tricks to sustain torsional rigidity. They sweat over every gram to maximize the cubic wing loading.

Second, is the insane piloting skill on display. Carving those perfectly straight lines and precisely uniform arcs so slowly in such a small volume takes years of practice. That perfection is what F3P competitions judge. Last is leveraging the VPP stopping the the plane in midair and moving back upward. Keeping the plane perfectly vertical on that down line is already like balancing an ice pick on your fingertip. Stopping and moving up is next level. The video is probably from an exhibition as I don't think they fly VPP props in F3P competition since they're heavier and these guys even test the strength vs weight of dried glues to save tenths of grams.

I watched the video. Should I be impressed, no emotions here? Is this a hard technical problem overcomed and demo-d?

Yes, you should be (besides the flying skills), and yes, it is a hard technical problem.

Normally the plane would use control surfaces, this one uses thrust vectoring with only one item providing thrust. I do think the rudder moves though, but technically that is still redirecting the thrust (because otherwise they'd have to move the motor around).

As near as i can tell this is very cool.

Most variable pitch propellers use a swashplate (helicopters) or just a collective yoke (also helicopters, and acrobatic planes).

If I understand what op has done is to print a propeller with NO FIXED LINKAGE to control the propeller pitch, but instead lead or follow the inertia of the propeller by rapidly-adjusted motor rpm to induce variation in the angle of attack of the propeller.

Yes, that is exactly what he's doing. I posted a link elsewhere in this thread where someone does the same thing but with a fixed pitch prop.

GP here. I'm an outdoor 3D RC aero pilot and explained what I think the config of the plane in the video is in this sister comment: https://news.ycombinator.com/item?id=50169548.

I now realize I should have explained more in my original post, since there's some confusion between the what's unique about the experimental "One Motor Drone" (OMD) and more 'normal' VPP and thrust vectoring (TV), which are fairly unusual in RC but still common enough there are existing components and designs on the market which all work essentially the same way.

The OMD technically fits the definition of VPP and TV in that the propeller pitch varies and the thrust vectors but it accomplishes this in different ways and with very different trade-offs than the existing RC components, which I mentioned because they're still new-ish in RC aerobatics, unusual enough many RC pilots aren't familiar with them and provide interesting capabilities.

For the life of me I can't find the actuators, they must be absolutely tiny or camouflaged really well but there definitely is some kind of wire attached to the rudder. I can't find anything to the other control surfaces nor do I see any deflection there in the video, but it could of course be very subtle.

The flying is absolutely off the scale, that is unbelievable skill. The OMD is also impressive but it is very much a work in progress and I think it will be a while before we see fully control of the drone. But at least he has it stabilized.

> For the life of me I can't find the actuators

F3P indoor planes typically use de-cased linear servos which are flat and tiny. Their control rods are made out of piano wire so thin, there's no way it would show up on video. F3P plane designers go to extremes of miniaturization and weight reduction. F3P isn't the corner of RC 3D aerobatics I play in but it's fun to look at photos of crazy F3P planes and the videos just look... wrong :-). https://www.youtube.com/watch?v=lXD6vbGVROw

Unlike the larger, more powerful rotary servos I typically use which need to be mounted near the plane's center of gravity to maintain balance, F3P esoteric, custom linears are so light they can mount them right next to surface they move. F3P seems largely Euro-centric, but there's a growing scene in NA (https://nsrca.us/index.php/flying/f3pindoorsequencesseparato...) and a sub on RCGroups https://www.rcgroups.com/indoor-pattern-f3p-373/.

These days, quads get all the attention (and blowback) but fixed wing is the OG RC. In recent years, meta-materials + SDR + open source have changed fixed wing dramatically, unlocking breakthroughs leading to some crazy extreme flight envelopes and many sub-specialties. There's dynamic soaring gliders which reach sustained speeds over 400mph from hand launch with no motor, cross country motorless gliders can go a hundred miles from launch, and long-range powered FPV (long range = >25 miles), though lately the first rule of LR-FPV Club is 'Don't talk about LR FPV Club' :-)

Personally, I find outdoor 3D aerobatics and slope soaring to both be extremely fun. Although my 3D aerobats are a bit larger than F3P (~ .8 - 1.2M), they are still very light and quite unlike most RC planes in unexpected ways. My planes can fly low, slow and so close I can just launch and catch them by hand. They are quiet, don't need much space and bother no one. Yet, unlike F3P planes, mine can fly outdoors whether in a large backyard, local park or even the beach. Heading into a hint of breeze, they can slow down until they're just stopped, hanging in the air (which looks odd), then zoom off in a blink at over 30 mph, and they keep flying in high winds that ground most RC planes (in fact, it gets even more fun if you have sufficient skill). Because they all have a thrust-to-weight ratio far above 1:1 they also have pretty insane flight envelopes enabling high-torque and high-G aerobatics far beyond the reach of any full-sized planes at airshows. Yet they only cost ~$50 to $200, take maybe 90 mins of my time to build, and can survive high-speed crashes that would turn most RC planes into confetti (the old joke in RC is they tell newbies who insist on starting with too fast and fragile of a plane, "bring a trash bag for all the pieces").

That all combines to make my corner of RC: fun, cheap, low stress and easy to start yet with endless depth to learn ever-cooler aerobatics. I love doing crazy aerobatics only 3 ft off the ground and 20 ft away yet if I 'dumb-thumb' the plane into the ground, it just bounces - or worst case it's a 5 min repair I can do on the spot while changing batteries. All thanks to cutting-edge materials, new motors, HV Lipos, and tiny servos with crazy high torque. It's also engineering-centric and nerd-friendly - so very unlike the vibe of "Your Dad's RC Plane Club." No balsa wood, gas engines or special flying field needed. My radio transmitter looks like an XBox controller yet is modular, runs open source firmware, BT connects to my phone, has SDR features and can be scripted with Lua. I learn new aerobatics with an open source 3D simulator on my laptop or in VR so I can slow down real-time as I learn.

Here's a 1M wingspan outdoor foamy mixing high-energy and low/slow 3D aerobatics: https://www.youtube.com/watch?v=vgkrVimII1E

Fascinating comment, thank you very much. I'm in an entirely different branch of the field, a lot more practical and far less fun but I totally appreciate what you are doing. is there a good close-up picture of those linear servos? Is that like a solenoid or something more sophisticated?

Here's a 1.1g linear actuator https://www.aliexpress.us/item/3256801316383625.html. Third photo is it sitting on a fingertip. But 1.1g is heavier than ultra-micro flying guys want. They mod or assemble actuators under 1g that are smaller, stronger and faster than that one. F3P guys like Donatas are balancing weight and size against speed, torque and throw because they need high-precision and high-speed to carve those competition lines.

The motors, ESCs, servos and materials get ridiculously small and light. You can get a sense of it on this forum: https://www.rcgroups.com/scratchbuilt-indoor-and-micro-model..., though it covers a wide range of small models, some of which the hardcore would consider obese. Here's a 4.9 gram, 8.5 inch wingspan RC airplane with color LEDs :-) https://www.youtube.com/watch?v=4OKrL8o22uE

Yeah but what if I want those RC plane to carry 100kg of metal (or more) ???

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