I built a drone with only one motor [video]
youtube.com555 points by hakonjdjohnsen a day ago
555 points by hakonjdjohnsen a day ago
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.
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.
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.
Yeah but what if I want those RC plane to carry 100kg of metal (or more) ???
Underactuated robotics are so cool. In the hobby BattleBots community, there is a design where the whole robot only has a single motor, but it's able to move in any direction and damage the opponent, all just by controlling the single motor's speed.
Most robots have at least three motors, two drive sides and a weapon motor. The trick to getting away with one is integrating an impactor into the chassis of your bot, using the single wheel to spin up to ~3k RPM, then by tracking the rotation angle of the bot as it spins, you speed up a little while the wheel is pointing where you want to go, and slow it down a little when it's pointing the other direction.
Can highly recommend this course https://underactuated.csail.mit.edu/ Russ Tedrake is an amazing lecturer (and researcher)
This design is generally called Meltybrain, and it has been in professional robot fighting too. Nuts 2 was in Robot Wars, and got surprisingly far into the competition for being viewed as somewhat of a joke entry (all the roboteers were a bit mad and had silly clothes). It's success wasn't always its fault, but it was still very impressive
Well not just battlebots, real life 6th gen fighters now all lack the vertical stabilizer so they have to rely on very sensitive real-time software control of the elevator/spoilerons to do banks and yaws. Not sure if it counts as under-actuated but they are tremendously difficult to steer without computer control.
>Not sure if it counts as under-actuated
You're referencing the fact that it's dynamically unstable, and thus needs to be stabilized with a computer. That's a different thing.
You can also have aircraft which are under-actuated yet are dynamically stable. One example is a parafoil, which achieves controlled flight using only two actuators (pull lines).
I have wondered how far you can get without an engine and with computer stabilization. A plastic bag flies in the wind, and sailships can sail upwind to some degree, so surely someone is experimenting with solely wind powered drones?
I'm not super familiar with heavy equipment like dozers and such, but some of them may also have a single motor to pressurize hydraulic fluid and valves to articulate the various pistons. So may be able to make the argument there too
In that case, the valves/pistons pairs are all independent actuators. The hydraulic motor is more a constant power source for all of them.
Yeah, the analogy for drones is hydraulic piston -> electric motor and hydraulic pump -> battery
That is common and you can't run two different cylinders at the same time. Depends on how the pump and valves are plumbed of course. Sometimes you can run more than one but you split power.
That sounds like it could be solved with more valves.
it's not that easy.
You can run your cylinders in parallel, however that means whichever cylinder has its easiest time moving is going to capture a proportion more share of the power. If things are not perfectly balanced, which in reality they're never going to be, that means the cylinder that needs to work the hardest is going to work the least. And so it's going to take a huge amount of effort to control.
Alternatively, you can run your cylinders in series, however that means that if you're trying to feather one to move slow, all the others are going to have to move slower too.
You end up needing multiple pumps in order to make this work well, but pumps are rather expensive and so that's going to bring your costs up. Plus, multiple pumps mean that you're going to potentially want more power than your motor can deliver.
All the above can be solved with careful engineering. However, engineering is expensive too in order to get this right and it's going to take a lot of work.
I was thinking in terms of pressure regulating valves on each output. That would solve the problem of different actuators needing different pressures, at the cost of efficiency as the pressure drop across each valve is converted to heat. Or flow control rather than pressure control maybe?
I presume aircraft hydraulics must do something like that, as they have multiple moving parts under servo control (which must involve some clever valves).
Is there a way to track what's going on in the battle bots community? It was pretty cliche, but battle bots was fun to watch in the 90s/2000s.
Oh yeah, you can even get involved! There's probably a group near you and it's a great community. The highest production value events are on the east coast, https://www.nhrl.io/, but there are events all over, check out https://www.robotcombatevents.com/event_map
It was brought back by Discovery and videos are also published on YouTube: https://www.youtube.com/channel/UCxNDM5ZhvDa_Z1qTUap7IRw
> but they are tremendously difficult to steer without computer control.
they are not humanly pilotable without computers. they are inherently unstable.
This is well worth the entire watch. It feels like what would any hacker do in trying to figure out how to make something they want to exist. Also very well presented and good pace.
Inspires me to try and start doing some robotics.
Love the little side project of building a high resolution high speed camera to investigate the flutter.
Only to figure out that the vibration in his drone was due to vibration and it was easily fixed by swapping to rotors that he should've used in the first place. Oh well! Live and learn.
These things are not always as obvious as you make them out to be.
I was fighting a lot of similar instability when making my drone only to realize that a software regression many versions prior had introduced a bug that made flying the drone next to impossible. After fixing that bug a whole pile of issues went away. Debugging that on a drone that does not fly is super hard because you never get to the point where you can properly observe what is going on. So improving the observability by doing that camera trick was just what was needed here.
And not a mention of like and subscribe for my next videos. Pure passion video blog post.
A really neat concept. It uses a special hinge design, a magnetic encoder and torque modulation to control the lift of the rotor as it spins. Completely negates the need for a conventional helicopter's swash plate.
The single motor does have the pretty major downside that it spins the moment it's in the air. I suspect a 2 motor drone with a tail motor would be a lot more practical. But I really like how mechanically simple the rotor hinge design is - it pushes all the complexity into the control algorithm.
Note that the concept itself has been done before in RC helicopters. The only difference here is using a one-propeller drone.
https://hackaday.com/2020/06/25/building-and-flying-a-helico...
Yep, he mentions the video you linked as well. (Mentioning because I watched the video you linked first.)
Perhaps there are specific applications where the payload spinning could be an advantage, imaging/scanning perhaps (which in the video is going to be in the next iteration for the builder).
I don't think it would be all that useful, give the very way it works (modulating motor speed) - your rotation would not be consistent in speed during even a single turn, which makes exposure times different each frame, and possibly too low.
Couldn't you use one motor attached to two props spinning in opposite directions?
You absolutely could, and that's exactly how a lot of RC helicopters have been flying around for decades now.
Nice work! It's good to see things more from first principles also (although incremental improvements to mainstream things are also good). Also there's lots of historical things that could be revisited with modern technology. For example this is slightly similar: https://en.wikipedia.org/wiki/Dornier_Aerodyne
This is from the same guy (Joshua Bird) that built the 4 axis 3d printer (and special algo for it too) https://www.youtube.com/watch?v=VEgwnhLHy3g
The Picocolissimo also uses only one motor: https://www.youtube.com/watch?v=UE47bcCxT_I
Side note, I used those same moteus controllers for a decidedly less energetic use case (two axis gimbal for RF satellite tracking) and found them to be super high quality and the lead developer always super helpful. Been a few years but def worth a look if you want to get into motor control.
Very cool. I also built a drone with only one motor and only one rotor, it took about three months and I learned more about drone firmware than I ever wanted to. I can't fly it but one of my sons is an absolute genius with this kind of thing and he can make it do tricks.
This kind of project is extremely rewarding. What's interesting here is how many things we did different. I used four servos and vanes in the airstream so that the whole thing would be mechanically as simple as possible, which makes this solution even more impressive to me (though I think mine is a lot more stable in flight judging by the video).
I think I went through 10 prototypes before the first one actually flew and #13 flies very well.
He meant one motor all up, including actuators.
Yes, servos are motors too. But you'll notice that this drone here is not quite controllable. It is still unstable in flight. It can take off but it is seconds before it runs into something and it is yawing all the time.
What do you mean "I can't fly it"? You built a drone and only someone else can fly it?
It means my eyesight and control/reflexes are shot to the point where I can't fly a drone but my kid is super sharp with this stuff and can do it easily. Drones are fast.
Very clever concept! Curious if you can now scale it to carry some payload. Reminds me of a story where drones deliver medicines / food to remote locations. And a drone with single motor is cost effective that can be used in low income provinces with no connectivity.
Payload attachment is hard on these. The COG is crucial with respect to maintaining control, you want it to be roughly between the battery and the rotor plane and as high as possible on the drone. So if you add a payload then you are immediately shifting that COG outside of the range were you have good control.
This is smart design and huge amount of work. Thanks the creator! Would adding a gyroscope help stablize the drone direction?
I imagine an alternative design with single motor mounted horizontally controls 4-wings like the dragonfly in Dune. It would eliminate the spinning.
Any recommended "drone for dummies" for programmers to fly their first drone?
Yeah that's probably the coolest thing I've seen all month. How could you not like this?
Slap a MEMS gyroscope on that bad boy. https://www.vectornav.com/resources/inertial-navigation-prim...
gyroscopes drift over time, that's why typically you need a kalman filter to combine the strengths of various sensors, magnetometers, where available, are bad at resolution, but don't drift.
MMs have their own set of issues though and calibrating them and knowing how the environment can influence them is a requirement for being able to use them productively.
Amazing work this is really innovative and it could be applied to a larger drones provided that the margin of error is reduced.
I was wondering did he use the control mixer MCU (initially mentioned in the video) at all? The encoder should always feed into the MCU directly.
I am surprised he is not wearing more protection. that thing looks like a hornet in bedroom test mode. Play safe.
Serious question - how do you even learn all of the skills to do something like this? Where would you start?
You learn along the way by finding something you want done, never giving up.
I want to build a robot that does one simple thing - follow my voice and deliver something to it's original location. That means I need to learn batteries and power loads, electronics, audio processing, directional acoustics, more programming, soldering, and a half dozen other things.
AI + deep thinking about the problem.
The goal is not the objective but to learn everything along the way.
I wanted to learn more about photography, I started asking an LLM and it helped me immensively. Definitely not the same realm but if you wanna pick up new skills, LLMs have tons of beginner friendly ways to explain things!
The best part about using an LLM for learning new things like that is not having to deal with snarky and snobby comments from the community members involved in them. Thanks to an LLM, I learned how to install, maintain, and winterize an above-ground pool. It's not rocket science, but it was not easy either. I peeked into the forums surrounding the pool communities for help first and they were always so hostile towards newcomers. It's very demotivating when you're excited about something new and half the people that are supposed to be helping you are just rude elitists; completely ruins the whole experience.
Yes, I’ve spent a couple hours lately asking Gemini about various home improvement topics in fundamental detail. I’ve learned a lot about:
- How to correctly hang a pre-framed door (shim it, tack it in place with 16 gauge nails, and use one wood screw in the top 2 hinges to prevent the door from sagging)
- How to properly adhere MDF trim to the ceiling to hide a closet door track (screw a furring strip or a header board to the studs above the drywall, shim it so it’s level in case the ceiling is uneven, and then nail through the face of the trim into the strip)
- What the difference is between the 27 DAP putties and spackles in the paint aisle (turns out Painters Putty 53 is typically used to hide finish nail holes, because you tend to make a lot of them and can just smoosh it in and level it off with a palette knife!)
For optics through photography (not CCD operation or post processing which are vast subjects themselves) I highly recommend View Camera Technique 7th Edition and Scientific America Image, Object and Illusion as general audience applicable introductions.
Serious answer - find something that you are so interested in that the problem is you can't stop. Become obsessed.
I went down a similar rabbit hole soon after covid started to build a small, eh, 'hand sanitizer factory' (that's my story and I'm sticking to it). By the time it was done I had a fully automated distillation setup complete with load cells, six different temperature readouts, solid state current control, flow/temp control for liebig condenser recycle, hierarchy of pid loops largely managing output flow and an attempt at live specific gravity testing. That with a nifty little dashboard to show live progress and compare metrics from various runs. Spent a couple grand on it in total and learned a LOT in the process.
Now with LLMs? Super easy. Just ask for step by step instructions to build a standard drone. You will learn about micro controllers, physics, pcbs, 3d printing etc.
If you have some time available definitely worth it.
A good engineering course would cover most (if not all) of the skills necessary to do this. This is notable because the person is young and wielding a broad slice of the discipline with maturity.
> Where would you start?
Exploration and tinkering! But you have to have passion and deep interest in that topic/problem
It's a pretty cool concept, however, fails to mention coaxial rotor design that has a single motor and has much simpler control systems. I am also curious on how this affects frame vibration.
This is a newer trend in mechanical design that leverages more complex control software to overcome mechanical issues. A good example is https://turntide.com/
It’s an entertainmening YouTube video not a phd thesis. Bizzare standard to hold him to
He leads the video with claims of being the first, and it’s reasonable to expect him to have done sufficient research on that claim. It’s a different claim than what GP thought.
If I understand correctly, those are single rotor but NOT single motor. This is a single motor design, which is why it's neat. There are no additional control servos/motors.
I am humbled. Wow!
Open source ?
How will this new tech affect the current drone war between Russia and Ukraine?
Smaller, cheaper, more numerous offensive drones?
I strongly doubt adding a ton of extra weight in aerodynamic surfaces, and drag, and complex mechanical parts, to avoid a few motors/servos is worth it in that context.
Every gram of weight you remove is another gram of explosive you can add. Also consider the difference in supply lines for aerodynamic surfaces and mechanic parts and motors and servos. If you have four hundred servos, you can make one hundred quadcopters, or four hundred of these things. If you only have one hundred control boards powerful enough to control the single motor design though, you can still only make one hundred. (Tho the quadcopter can lift 4x the weight)
What's interesting is that the Ukrainians are building drones near their front lines because if they build them too far away and ship them in, the game has evolved and those drones are already yesterday's news.
A fixed wing drone only needs one motor, the control is easier, and the physics are more favorable for carrying high ordnance. I'm skeptical that this is going to change much.
It's cool in that it can hover and do quadcopter type flight with only a single motor, and it's that second part that is interesting, because a fixed wing can also do a prop hang, but it can't do quadrotor-like flight from there.
It's usefulness is likely to be in other areas -- mainly applications where that flight mode is important.
Larger fixed wing drone could deliver many smaller quadcopters that don't have the long range.
A fixed wing drone needs at least one extra motor for the control surfaces. More likely two or three.
This design still requires an additional servo for rotor actuation, so the minimum number of actuators is the same as for a fixed wing (roll and yaw are coupled, so the bare minimum is a single rudder servo).
No, the rotors are tilted by timing the acceleration from the single motor - there's no servo in the design in the video.
My bad. I skimmed the early part of the video with the sound down on the train this morning and thought I saw a servo in there. That's clever, but it doesn't really change much. There's not really any advantage in terms of payload or performance over existing designs.
maybe new breakthroughs for the darpa project. kamikazes drones do not need so advanced prop tbh it is against the idea of being cheap.
There's also been a few people building monocopters with a fixed, non tilting motor and prop, and four servo motor actuated fins at the bottom that can be used for thrust vectoring and to counter rotational forces.
That's pretty close to what I built only I'm using a far more efficient motor/prop setup so much longer flying times as well as the option to transition to level flight.
Neat. I wonder if you could use the air it generates by having directional ports louvers that open and allow the air to flow for more control. Would need 2 more servo, left/right port louvers.
I love this angle so much! Do you know if there's been more detailed analysis of performance?
Very good control, low flying time (those ducted fans use an insane amount of energy like this).
Generally those small diameter motor/prop combinations aren't very efficient, in grams/watt of thrust. They look really bad if you compare them to like a 15" size carbon fiber prop from t-motor and one of the tmotor "antigravity" series motors on a thrust stand.
Quadcopters that are designed for 45 min to 1 hr loiter time carrying a useful payload, while not being too big for a person to move around seem to be converting on 15 to 18 inch size prop and motor and esc combinations carefully chosen for optimal grams/watt thrust.
Yes, that's in line with everything I've seen.
I've built a whole slew of drones over the last couple of years, quadcopters are hard to beat on many axis. But I have some proof that it may be possible to do substantially better with a monocopter in terms of efficiency. The hard problems you will then have to solve are payload attachment because unbalance is very tricky to deal with (whereas that is trivial in a quadcopter) as well as transitioning to level flight so that you can make good forward speed.
I think the recent winner of the DARPA life challenge was a 'traditional' single rotor helicopter with tailrotor. The very large disc area of the traditional heli design made it more efficient than quad/hex/octo designs.
https://www.google.com/search?client=firefox-b-d&q=darpa+lif...
Yes, but their forward speed is limited because they can't translate into level flight and that also means the range is limited. I was trying to get the best of both worlds (but that's a hard problem to solve).
I know very little of the field, but aren't there applications where the ability to carry ad hoc payloads doesn't matter? Integrating a fixed sensor suite into the ring and balancing it ahead of time is possible then, right?
And what can be learned from full-scale classical helicopters that frequently carry underhanging payloads?
(I don't at all wanna be the typical HN person who thinks their questions about a field they know nothing about are in any way insightful. I'm just trying to learn.)
That's all true. But (1) that's not the application that I have in mind and (2) forward speed of helicopters is not fantastic (3) neither is their fuel efficiency.
For a fixed payload it is indeed possible to set up the balance beforehand, even then you will probably end up with a drone that will translate slower or faster depending on the inbalance instead of hovering in place.
It's incredible that changes in velocity still work to adjust the angle of the blades even at the insane speeds they're moving at. I would never have thought that was possible.
I have to wonder why this guy didn't give his drone a leash while testing so it couldn't go flying off. It's the first thing that popped into my head, so I'm sure it's something he thought of as well and didn't use for a good reason. Maybe a string would get caught in the blades?
This one is very impressive too:
https://www.youtube.com/watch?v=K0POjjIC5xs
It does use a bunch of external sensors but the control is all with just the prop and rapid speed changes, they don't even use a variable pitch prop.
Maybe the pull from a string/leash would affect how the thing flies, kind of like kites.
I like how he built a test stand near 7:22, which solves the motor flying off problem and is probably easier to iterate on. It reminds me of how rockets are tested.
Possibly the fact that the TPU fin body doesn't stop all counterrotation so the leash would get twisted into a cord and interfere with flight?
I’m sure glad we are making immense progress towards the dystopian hell where massive swarms of mini drones are hunting down obsolete and marked for termination flesh bots, aka humans.
I am torn about drone tech now.
I used to be super stoked about it.
But watching drones kill civilians kind of ruined it. [0]
Then again ... they do put a dent in superpowers powers apparently so ... like I said ... I am torn.
Likewise. Even companies like Saildrone where ~100% of the marketing before 2025 was about mapping the oceans and autonomous storm monitoring with their bright orange craft are now releasing videos with missile launching pods attached to navy gray versions: https://www.saildrone.com/news/us-navy-rimpac-lockheed-marti...
To be fair, a lot of it is moving to drones killing drones.
My prediction is that future wars will actually involve increasingly fewer humans and will be more about tech+manufacturing vs. tech+manufacturing. And of course insurgents + lowcost tech vs. increasingly nonlethal hightech.
This would allow wars to continue without as much of the growing political backlash.
The next iteration is the drones removing those pesky humans from the command chain too :/
Do you want superpowers to be able to wage wars, foreign or domestically, with hordes of non-human combatants that can't refuse orders or defect on moral grounds?
You could say the same about smelting iron. Now we can wage war without tin.
oh yeah? leonardo davinci built one with zero motors
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