Drone Pendulum Fallacy 

There are many questions about adding a hinge between the drone and the pendulum (with a short length of string), so I thought I should address my view here. I'm not 100% sure what would happen as it depends how far the string is mounted from the drones centre of mass, however I think it will be more of a issue than an assistance. With any change of speed/direction, the pendulum will swing and will drag the drone with it. Also, if the string is attached at the drones' centre of mass, it will be unable to induce a torque on the drone and rotate it to level. If the mounting point is away from the drones' centre of mass, I think it'll still crash as the pull from gravity is uniform, so the drone is pulled down as much as the pendulum. Thanks for getting me thinking about this, I should have tested it in the video! Maybe one for the future!

I keep watching this every year to remember the principal! Thank you!

This video and the one Scott Manley did do a perfect job of explaining the pendulum fallacy.

This is the most user-friendly explanation of this effect I've ever seen. Nice Work!

Hackaday journalists be like... Finally he made a new video,time to write another article!

Interesting that you do have pendulum stability when you build an airship rather than a drone - presumably because the lift vector is consistently vertical, unlike a tilting drone, so it is a pivot point, ^oo^

Great video!!! Always wondered about this when mounting my drone batteries. Falcon 9 example was a great example. Thanks for teaching this. The gas thruster drone is awesome

Tom, I'm the CTO of the Japanese drone manufacturer ACSL. I've had to attempt to explain this so many times, but I doubt I've ever been able to do it as clearly as you have here. I will be sure to point people to this video in the future. BTW, let me know if you have any interest in working in Japan :P

To the left, to the left This drone loves to go to the left. Pendulum Fallacy, At its best. Was a great video, I'll be waiting for the next!

When i saw the thumbnail, i was like "sure this wont work, the pendulum action doesnt have an effect on a flying machine." It was then that i realised that i knew this because it was exactly what i learned from tom's chinook build....🤣🤣🤣🤣

But what would happen if you replaced the rigid stick with string/rope/hanging by the cable?

Worth noting that if can control the pendulum's position (using servos) you can affect the location of the CG relative to the centre of thrust, which *can* be used to aid stability. ...which is basically what your Chinook is doing (in one axis at least).

Thank you Tom. I've been curious for years how a space rocket with rockets on the bottom managed to remain so stable during lift off. You explained it perfectly! Great video! Thanks again!

Your videos are always such high quality and rich with information. I'm a big fan! keep it up!

What if you use an unfixed pendulum attached to the drone, instead of using the drone as part of the pendulum? Basically, weight with a couple of strings attached so it can move independently of the drone and the extra strings on it avoid causing turbulence movement

this will help me when play KSP, I'll stop building unstable death machines instead of space ships :v

Brilliantly demonstrated!

The drone just loves that hedge what can you say? (Nothing because its true love)

Brilliant! Thank you Tom, every video you post is the promise of a good time watching it.

Really enjoying your channel these days. Thanks for making the effort you deserve to do well from it. :)

Great video and explanation 👌

I think you missed the point by not including a clip showing a weight the same distance above the props. *Dance the Skies*

Amazing video Tom! Sooo much work must have went into this video! Great production value, great explanations, great footage! Very good job explaining the concept :)

This is the BEST video explaining the pendulum fallacy. The example and reasoning behind different drones and how they work is extremely helpful to visualize. Thankyou.

Put fireworks on it like Colin furze

Talking about sticks, rctestflight made a fun flying stick video about 2 months ago. This complements it. Great video!

Great video mate. I've been getting into building drones lately and your channel has definitely enlightened me to a bunch of useful physics to keep in mind when I'm building. But nothing beats a good ole fashioned physical test like these to truly explore quadcopters and drones.

I see those editing skills have improved quite a lot. Love those graphics in motion all over the drones

The way I see it that a pendulum is a lever where the force is the direction of gravity and the fulcrum is a fixed point. Once the fulcrum is no longer fixed the lever doesn't work, neither does the pendulum.

If an offset center of mass produces torques that rotate the aircraft, could a drone be controlled only by shifting weights along tracks?

Looking sharp Mr Stanton. (I really like the increase in editing and detail, such as the gif-progress style bar towards the end.)

Thank you so much for this. I really loved your slo-mo footage of the Drone flying with a really low Center of mass. It is fascinating to watch the Drone (motors) attempt to do the impossible.

Nice!

Great work Tom! Could you do an electro-static thrust vectoring system? E.g. creating air currents via differing high voltage electric charges on different areas of the drone.

Brilliant. the physical demonstration with thrust vectors overlayed really hammered this home for me.

Thanks for this great video! I feel quite educated as your diagrams and models are truly simple and informative!

string vs wood as pendulum would've made any difference?

I find myself wondering if attaching a mass to the bottom via string (either one string at the CoM, or one string attached to each propeller arm) would make it more stable? I'd guess that a single string probably wouldn't make a difference (or maybe make it less stable), but I think it's worth an experiment. My idea behind attaching the strings to each arm is that when the drone tilts, some of the strings gain some slack, then the tension in the others would pull that side down. Then when it overcorrects, the tension on the new side would bring that side back down, and so on. I have no idea if it would work, but I'd love to see a video about it (partially because I don't have money to buy or make a drone to test it myself...).

Thanks for making this video, Tom. It is very through, clear, and excellently visual.

This man is so humble but still with the confidence to make these awesome videos and that's such a fun combination.

3:58 That’s really crisp video, have you upgraded your camera?

things leaving a static frame. Still funny in 2019 haha

I've been building Arduino projects for 4 years now, but your channel makes me feel like I have wasted those 4 years on boring projects. Your channel excites my creative side and that it awesome! Keep up the great work!

Been following your great videos for a while and this one in particular was very interesting. Thanks for sharing your knowledge with the world.

Hey folks, Tom and everybody... I've got a problem: I've seen the "pendulum effect" on a simple hand launched propeller (yes, the propeller on a stick). I launch it at an angle but it always pivots around the nose of the propeller during flight, and so during my younger years, I never got the clue of this fallacy. But then again why does this simple toy defy your explanation? air drag? gyroscopic precesion?

5:40 is that green screen?

Thanks for your videos Tom. They're very well explained, very well recorded and arranged, and I love airplane since 10 and i'm learning a lot with you. Thank you!

I absolutely LOVE your demonstrations!

Add a pivot point, have the stick on a hinge

Hi Tom what would happen if you had a pivot at the power source connection point.

Thank you for sharing your knowledge with us Tom!

Outstanding video Tom, really high production values and easy to understand graphics, Well done sir!

So, if you want to make your model/drone easier to control, don't stick a giant pendulum to it- that's the moral of the story here, right?

As always, nice video Tom;) and perhaps like one of the coments below, like colin furse...put some fireworks of one of your flying machines🥰

Fascinating as usual. I love how this model of smart TV that you and others like Applied Science are creating seems to be really sustainable. So much so that I might have to jump in!

When she says she's home alone 1:53

Why didn't you hand launch the drone straight up and see how it would work? Later brofesser! 😎💨

Absolutely amazing video. Started off with me unsure of what the solution to the problem would be and then concisely and clearly explained the solution. Thank you!

I think there's a semantics issue here. A fixed pendulumn won't be SELF stabilising. However it will add stability in pitch and roll (in your experiements). Stability is the state of being stable and more stability means you're less inclined to "give way" or "overturn", adding rotational inertia makes that take longer to happen and so makes the system more stable. However you are right in that it won't be self stabilising. Target archers regularly use long rod stabilisers (their literal name) which is a stick with a (usually dampend) weight on the end, attached to the front of the bow. It provides yaw and pitch stability through inertia (they can also use a V bar to give some roll stability, some balance to the bow and even more pitch and yaw stability). Even car designs use mass placement to affect the stability of the platform (i.e. front vs rear vs mid engined vehicles, whether brake calipers are on the inside (lower angular moment) or outside (higher angular moment) of the wheels, etc).

This has been eye-opening. Thank you, Tom. Much appreciated.

I always learn so much watching your videos, thank you so much.

Thanks for clearing that up.

Great video ! Very interesting subject ! Your production quality has really improved, I love the new visuals !

Glad you included the bit about it being good with thrust vectoring. You started to make me doubt my own design decisions.

Excellent Tom ...thanks for sharing your understanding.

Thanks for the intuitive explanation. I have heard you always want a rockets center of mass to be away from the center of thrust but it next clicked before now

Next level production value dude! Hat's off!

Love your videos! Thanks for sharing.

Nice lighting and motion tracking! well done tom.

Tom. Thanks for this video. It explains this issue so well.

Excellent explanation, thanks Tom.

i think one good parallel is trying to balance a large hammer on your hand, it a lot easier with the head of he hammer at the top.

Always love your videos

I really like the way you explain things. I have some understanding of what's actually going on, now! Thank You.

Love your projects, they actually got me into mechanics :)

Brilliant clarification of something you’ve mentioned a lot thanks👍

Very nice explanation of various scenarios, well done!

Love the explanation! I'd sum it up in one line: "the more perpendicular and farther from the center of mass, the easier it is for a thrust vector to rotate a body"

Outstanding explanation. As always, Thank you.

Fantastic videos clear and concise with excellent examples. Thanks 👍

Well done, clear and down to the point!

This is such a good video! Well done Tom!

I expected to see footage of the actual drone you mounted on the pendulum, which IS able to maintain level by thrust vectoring (different rotor speeds). I imagined this to be very useful for stable camera drone shots, because the pendulum adds a lot of pitch / roll inertia.

This needed to be done. Well done.

The best explanation I've ever seen for the pendulum fallacy! It was never quite clear how it worked before, since it's very counterintuitive normally.

Brilliant explanation. I love how your videos scratch my engineer-itch.

Great video, love your work.

Thank you! As an aero engineer, former mass properties engineer, pilot and participant in an unhealthy amount of enthusiast and pilot fora this, in the form of high wing vs low wing stability (and the associated dihedral fallacy), are high up on my list of regularly appearing pet peeves. Your video will probably make a few people catch on. Well done.

Magnificent video! Well done Tom 👍 I thinks it’s worth mentioning the DJI inspire series of drones, they raise the props up for clean air and in the main the get out of the way of the camera! And FPV race drones, lots of people have the battery underneath for racing, it’s not for stability, but in a crash you’re more likely to land props up and therefore maybe able to take off again. Both cases not related to the pendulum and stability topic. Thanks and keep up the good work 👍

Tom - you are a one of a kind wizard. I hope many millions of students watch and learn from your effort. Thank You!

It is a great video, and as part of your subscribers I want to point out that you might be able to stabilize the drone by increasing the aerodynamic drag at the top. The COG in front of the COA is what makes an airplane stable in any direction. But essentially this "any direction" is what you don't want. So if you put two sheets of plastic forming a cross (when looking down on the drone) on top of it, this should counteract the vertical velocity, which would probably make it asymptotically stable w.r.t the vertical velocity. Depending on the battery's weight, you might also be able to move this cross down the shaft, such that it sits right below the drone's frame.

Yet another great video. Thanks very much

An excellent video. Well explained.

What great information, love your work!

Excellent explanation... Thanks!

Love these videos

Dude your channel is awesome.

Finally I get it, thanks for the graphics and explanation, cheers from NZ

5:47 looks like someone got some new lights lol. Great video, explained well.

Love your vidsand your explanations