Can Reaction Wheels control a Drone? 

Parent: Son, why is the lawn still unmowed? Son: Because I lost momentum...

As professional multicopter flight control engineer who did a lot of such angular rate loop experiments with DIY builds I would say the biggest catch with your quite nice setup is control bandwidth. The delay from the gyro measurement until your reaction wheel is finally counteracting the disturbance is too long to keep the drones attitude stable in the air. It took me a long time to figure out this problem with my own first flight control attempts (all from scratch). I'm guessing the bottleneck might be the motor controller of your brushed motors it's very likely not designed for low latency feedback loop reactions which all good multicopter ESCs are. The key is reducing the angular rate loop delay and then tuning mainly the angular rate proportional gain. You need to be able to feel a virtually instant and rather strong counter reaction from the actuator already in your one axis hanging test when pushing with the finger even only slightly. If you cannot get the gain high enough because it starts oscillating early you either have too much delay or too high vibrations in the gyroscope measurements. Be aware that the way (stiff, soft, vibrating part, ...) your gyroscope is mounted to the drone matters in this regard. The non-linearity of the torque response and the inperfect alignment of axis to the center of mass are certainly things you can improve as well but my educated guess is clearly that the delay in your feedback loop is currently the bottleneck holding you back from longer hover times.

Hey, a retired aerospace engineer here. All I can say is that your videos are a ton of fun to watch, and really inspirational; I should go build something. And I really liked your explanation of why you would try to use reaction wheels to control a drone.(something like "I have no idea") That is completely cool.

Great Experiment. But I feel that you missed a big opportunity here : You should have : *4 reactions wheels (2 counter-rotatings pairs) *Reaction wheel always spining at steady speed (e.g 5000rpm) This way -> you gain stabilization from the gyroscopic effect of the wheel constantly turing. -> you steer by applying torque and changing the reaction wheel speeds -> You can use brushless motor in their regular speed range and thus have much more reactive control and much less problems with saturation and linear torque/speed relation

Well colour me impressed.

You got very sidetracked, just because you didn't want to mow the grass.

I'll be honest this seems like the kind of thing someone in the 1800s would've thought up

Make sure your gimbals are center of mass and aligned with the other wheels rotational axis. Take into account gimbal procession induced from internal and external forces. Another useful tool would be utilizing the stabilizing effect of a three axis, high rpm, set of gimbals. This would help hold the craft in orientation and reduce wobble.

You just recapped 3 months of Physics class in 1 minute and 30 seconds... what have I been doing with my life?

Would love to see more reaction wheel stuff

Honestly, the fact that you got as far as you did with this project is amazing. I mean genuinely incredibly impressive that you were able to get it flying at all with even a modicum of stability. I would've expected this to never work in a million years just due to the difficulty that rotation stabilizers like that have of doing the fine controls that are needed to fly.

"Let me build a test rig" *Casually Approach 3D Printer

You madman! That's a great spin on drone control! Now I really, really, really have to make myself a CNC.

i know all about reaction wheels i play kerbal space program

I did my physics 'O' and 'A' levels over 35 years ago - was good then, would have been a hundred times more fun doing it now with drones and computers! Good video!

Keep it up Tom, I love these vids! Trying out stuff that is outside the box. Maybe the industry engineers know this stuff, but for you to show the different things you try with your 3D printed bits and pieces (which I love BTW) to show us the inadequacies of various effects, is just brilliant. keep it up.

I actually build and test the reaction wheels that go in to 6U cubesats XD So I'm pretty impressed with your attempt, but I think your control loop is too slow to keep the drone stable.

Fantastic original thinking -- your best project since the trebuchet. It wouldn't even have mattered if it hadn't flown at all; the concept itself is just great. Well done!

As always fascinating. Admire your persistence (as well of course as your knowledge and skill). Also love the sense of humour you bring to these videos.

I love this. Really want to see a follow up, V2, I find this infinitely fascinating and informative.

24:15 i knew it

I'm always amazed at your videos. It seems you've ignored the precession of a spinning wheel when it is moved is direction perpendicular to the wheels axis. Once a reaction wheels get a bit of spin up then the processional forces, which are 90° from the axial directions, can overwhelm latter. In other words, when the reaction wheels are spinning a bit you have to consider the perpendicular torque when the other wheel tries to rotate the drone. You can't treat the roll and pitch axis independently when you're controlling them with a pair of reaction wheels. The amount of torque on the drone depends both on the delta omega of one wheel on the precession the other rotating wheel. If one wheel is not rotating then the effects of precession disappear of course. But overall, net torque on the drone is a combination of precession and the change in omega of both wheels. Precession must be considered. I think rather simple algebra added to the flight controller program will take care of this. Great video. Science in action!

Excellent proof of concept! Your channel is one of my new favorites thanks 😎👍🏼

Hi! I think you should try to pre-speed up the reaction wheels before the actual take off. Only the relative speed matters. If it has a certain speed at the start i think it was easier to just slow the reaction wheel down instead of driving it in the opposite way -> this means that you can use brushless motors too, but you will have to tweak the flight control for it too. Good luck!

"That's not flying! that's falling in style!" been a massive fan of your work for a very long time with very professionally explained videos, keep up the hard work!

Best explanation ever. I might even pass my mechanics class! Looking forward for part 2.

the reaction wheels cause an off center center of mass, saturating them. having them on both side will fix it.

Thank you for explaining physics in a way that my grade school kids can catch on. They finally know what dad does for a living. Showing your failures and explaining how you fix them has helped tremendously in their own experiments.

Tom, seems like a better test would have been to just have the cube balance itself atop a pivot at the bottom before trying to balance it in flight (read, less risk of damage)? i realize the pivot would be under the cube rather than somewhere within the cube, but it still seems like a quicker and safer way to test.

A part two of the project would be awesome !

Awesome effort for getting the drone airborne and one heck of an experiment to undertake. Rotating objects are a magnificent minefield, particularly when they number many and are counter rotating. You are entering the beautiful realm of field theory (fast becoming a profanity unfortunately these days) with all the joys of precession and inversion. I thoroughly enjoyed your video, especially all the construction editing. All the best and I look forward to more great vids. Cheers.

Thx für the video. Learned today for the 1st time about mass center orientation method in satellites. Found your video, learned a bit more saw this neat implementation. Thx for this from the social science department!

The issue here is insufficient feedback control, think of it this way, you have 3 PID loops for each axis of rotation , however the control for the motors requires their own individual nested inner loops, to deal with the non linear torque current relationship otherwise the resultant system is as good as being in an open loop configuration. So in each inner loop: we can assume a linear enough rationship between current and velocity , and between the input pwm signal (a double for votage ) and resultant current. then we know the the relationship between velocity and the output torque . so the inner loop must take pwm as the input and then using an encoder for velocity feedback take that as the output. this then feeds into the outer loop which for the time being is being provided by your flight controller

"Gyroscopic precession is a phenomenon occurring in rotating bodies in which an applied force is manifested 90 degrees later in the direction of rotation from where the force was applied." Any RC-heli pilot know this so... Counter rotating propellers should remove this, but couple precession with IMU and Yaw control: Who knows?

I'm binge watching your videos. It's amazing the amount of time you put into them. Thank you! I hope you're doing well!

I have been going through your video catalogue after recently discovering your channel. Your presentation style, broad subject matter, fountain of ideas, end-to-end integration, demonstrations of incremental design, creation of novel and cost effective instruments to see your design to completion, time investment, and reasonable monetary investment are inspirational. You straddle the line between pace, detail, and build process nicely. Thank you for sharing your failed tests, it helps learners understand the reality of integration and the hill climb it can be. I hope your reach can inspire others and look forward to see growth in your channel.

Haters: "Why are you trying to control a drone with reaction wheels?" Nerds: "F*ck off, it's cool."

The was one of the coolest videos I've watched lately. Really like the engineering background before the build.

Very neat. You definitely need the two reaction wheels to become 4, with a solid axle and counter-rotation gearbox in the middle, otherwise you have got two gyroscopes, off centre, pushing hard in not quite the right directions at all times, rotating the bird. Pick up a spinning bench grinder (carefully!) and rotate it and you'll see the issue. Have it counter-rotate to cancel the forces into the bending moment of the axles, and it'll be dead smooth.

Thanks for the pretty clear explanation of reaction wheels, I was never quite able to grasp them

You do such an amazing job with your videos an explanations!! The way you explained the physics of this project was very easy to understand and follow! Thank you :)

wouldn't it be more stable with both props on the top like a heli instead of one on the bottom? then the reaction wheels would only be used for pitching when you want to move it, rather than relying on them for stable flight

Fantastic post , that's knowing how reaction wheels work well and truly sorted .

Wow. What a wonderful and fun experiment. I was trying to learn about reaction wheels and this really helped me visualize how they work.

Your channel is Just getting better and better! Impressive video's!

my huge respects for completing such a complex and interresting project!

Very clever application of the use of angular momentum to set a position. Your diagnosis about the problem you had is probably good and the idea of using a motor and encoders is a good idea to have it right. Just another detail, maybe adding guards to protect the propeller against contact with the ground/objects would spare you a lot of time in repairs, between attempts in tuning.

Dude, new favorite channel. Everything's awesome!

In an alternate universe, this is what helicopters look like.

Tips for next time: Your reaction wheels have too much mass and drone has more mass in one corner. Otherwise great work 🤙

Cool idea! In my experience, reaction wheel speeds are usually biased to avoid zero crossing. This may also serve to put them into a more linear (though lower) torque region. Some analysis of the expected control torques would help to determine proper sizing (wheels and motors) and appropriate bias speeds.

Your videos are so good at being entertaining, educating, and showing your thinking for the engineering.

18:00 Why does this reminds me of the Iron Man test flights ? :D

One of the things that seemed off about this video was the lack of measurements - so building a simple rig to measure the torque-per-amp might be a good idea if you ever revisit this project! Also, aligning the rotational axis with the center of gravity, and having a wheel on each side - it seemed to favor diagonal reacting. Very, very interesting and well documented!

Thanks for doing that project Tom

Man you're brilliant. I could listen for you for hours. You're super smart and articulate

Just a mild machinist tip. If you are cutting aluminium with HSS cutters, please don't use lubricant. You are kind of just increasing the thermal capacity of your cutter, which is bad when trying to cut a gummy material like alu or copper. I suggest cutting with a low spindle rpm or using an air duster to cool it off. Machining aluminium dry is always the preferred option, unless you are using a higher grade like 70**. Rule of thumb. Short chipping materials don't need coolant. Gummy materials don't like coolant. And if you're using tungsten, screw the coolant.

Man when you cut those two wheels I thought I was losin a harddrive!

Amazing work..the small flight time demonstrated great balancing and the gyro

The spirit of reasoning is stunning for me. Especially this can be a passage of physic learning and metalization. Love it.

It flew! Very nice, even though it was a short flight! It seems like the PIC values of the reaction wheels were not tuned correctly, but this might have something to do with the nonlinear torque of the brushed motors and not really the fault of the PID? Just speculating here. Also, do you really have to get encoder motors for your future version ,or couldn't you just output a series of currents on the bench and measure the RPM with an LED and a timing mark or just using your slow-mo video. Once you have a number of current vs. RPM data points, you can come up with an appropriate lookup table for your software to use to scale the current appropriately. This was a fun video. Great stuff as usual!

You could use gimbal brushless motors, those have rather accurate rpm control at lower speed. Also it looks like the wheels stop rotating too hard and put turque back into the cube and make it oscillate. But you know what you are talking about and it is very nice, only way this could have been better would be to have Scott Manley in the video

Watching this thing try to sustain flight then crash was actually amusing, thank you for brightening my day and teaching me about the conservation of angular momentum. It makes me wonder how this law would apply to my sport.

Hey Man! Maybe a little bit late, but I came along your vids just recently. Really fun to watch dude! It would be very interesting if you could show some telemetry plots of the tests, like the input sensor values, and actor values like valves, and motor rpms. Thank you!

I don't understand how is it possible YOU out of all makers did not yet printed some vacuum hose holder for the CNC :)

a little oversimplified the inertia calculations :( the inertia of the spoked wheel has to be calculated with the radius being 1/2*(inner diameter+outer diameter) of the hoop plus inertia of the spokes + hub, the width of the hoop is NOT 0, therefore if using m*r² is wrong, the actual radius is smaller.... actually it is the same for the disc, with the inner diameter being zero! ... well, I guess you would calculate it correctly and just simplify it for an easier explanation

Brilliant as always! You have one of the best RU-vid channels

Great video! Was just wondering about gyroscopic precession. If one of the axis is rotating, the required torque on the other axis is larger and makes the drone rotate unexpectedly.

You need to maybe add a stabilizer gyro where the bottom something with a little more mass than your counter rotation prop design. Maybe do a double deal on top. I really enjoy your short videos.

I think it suffered from gyroscopic precession.

Need to cancel out the Y vertical force input for the gyro's, it's trying to balance in place but getting thrown off from vertical force reading. you'd be better with a tilt sensor flat set to attempt idle level on x & z, same drone can be used but apply acceleration or breaking, from a mid range RPM, so it has room to slow down or speed up the wheels, though for best in-flight balance the balancing wheels would need to reach their full mid range rpm Before going vertical. Really amazing shop and you've always got a nicely detailed build and mathematics behind it, Great content!

Ksp players.

Maybe you could use brushless motors with esc's. Non linearity in momentum and problems with changing direction of rotation goes away when you spin up those motors initially before lift off. Then pitch and roll will be controlled by altering the rpm of those motors but in different range (high from the beginning). But.. then the gyroscopical effect comes in to play and you would have to use counterspinninng pairs (doesnt solve that 100%, but should be not worse than right now with slow spinning brushed motors)? Just a bunch of ideas. Great and entertaining video :)

Here’s my take on the instability of the drone... The reaction wheels were not spinning true, they were wobbling. This imparted a vibration through the chassis to the accelerometers, which in essence, added noise to the sensitive accelerometers input data of the angle and acceleration of the drone. Clean up the reaction wheels trueness and see if stability improves.

New to your channel. This is the first "failure" I've seen and it was probably my favorite so far.

Sir, I think the only problem that the drone was facing at end was equal weight distribution. That is actually why it was getting dis balanced. And the torque issue can be fixed by using encoder motors or by having a wheel on each side. The video is really great. You were successful in sharing the project experience.

This is a stupid project that nobody asked for. I love it.

Nice video! I Just Subscribed. I like these kind of videos

Thank you so much for this!

It would be quite interesting if you replace the reaction wheels with weights on linear motors below the drone. So you don't use the momentum but the weight shift to control the orientation. Batteries could be a great weight, so just attach two battery packs on rails. Instead of using two motors, I would just use one with a small gearbox to drive two propellers at the top. Which intersect each other on 90°s (for extra coolness factor) like on a K-1200 K-Max. To add yaw to the controls you could add a smaller reaction control wheel (you don't need that large amount of momentum for yaw).

Use reaction wheels as a stabilization system on a RC drift car.

This was a fantastic build, definitely worth the wait and very informative. Ultimately I don't think a reaction wheel design can ever work long term because any slight imbalance in weight will end up saturating a wheel. If your propeller based drone is imbalanced, it will just constantly run the motor on the heavy side faster than the opposite ones for constant torque. If this has weight off-axis from the thrust, the wheels will constantly accelerate to fight the torque until one saturates. Note that you *can* have torque indefinitely using gyroscopic precession, so a flywheel in a cage being turned by servos wouldn't suffer from this problem. An idea for V2.0?

Well you gotta make this work, ya know, sometime.. such an awesome concept

Toujours aussi captivant !!! Un beau bravo du Quebec !!! 👍🏻

I wonder also whether, as the reaction wheel velocity increases, you'll need to take into account gyroscopic precession as well (though the videos I saw, I don't think the reaction wheels were spinning fast enough for this to be a concern)

You Should try continuing with this it's really cool

I really enjoyed to see how your mind works (including motor control solutions towards the end). Many years ago (back in the 90's in fact), I had the idea about using flywheels to dynamically modify the momentum of a moving vehicle (car, plane, drone, sub, etc.) to assist in better maneuvrability and directional changes (including acceleration bursts and deceleration absobrtions). Having seen your video, i do believe I shall do a prototype as soon as I can afford the time and expenses to properly do so. Thanks for the inspiration to move ahead with my own crazy ideas. I will check more of your work & subscribe. Cheers & keep on the good work! M :) PS Keep that mind sharp! You will probably go far (also "errors & mistakes" are a normal part of moving ahead and learning through experimentation). :)

I actually got tears in my eyes when it woke to life around 19:40. Love your videos and persistance. :-)

Next try to power a propeller plane using reaction wheels and RTGs

reaction wheel way to strong and needlessly fast for the fine-tune type corrections that were needed. regardless I loved your video straight from that start. there's definitely something there. if you're still up for it, try again but with smaller reaction wheels that don't react to every little change, think "precision controls" in KSP. also focus more heavily on what center of mass is and how well aligned the wheels are so that they aren't wobbling the slightest bit. very fun and educational video!

This was a cool video! I learned a lot. Thank you!

What a great experiment! I love seeing all the fails and attempts.

Hmmm, I wonder what would happen if you went from reaction mode to resistance mode. By this, I mean you could have those wheels working against the air, like steam boat paddle wheels, instead of manipulating momentum.

Nice Mate you tell the remote that tells the receiver that tells the flight controller that tells the arduno that tells the motor controller that tells the motor how to make it complicated and absolutely awesome!!!!!!!!!

If you do continue with this project, perhaps add a contact switch on one foot of the legs. Include in the code that while the switch is detecting contact, that motion to the reactions wheels is disabled. That way, they only enable after the drone lifts off of the pad.

suuuuper super interesting, that slowmo footage is absolutely awesome to watch.

2つのホイールをあらかじめ一定の速度で高速回転させている状態をニュートラルとすることでジャイロ効果で安定させ、そのニュートラルの回転速度から加減速することで姿勢制御として使用すれば安定して飛行できるのではないでしょうか。

Back in college, I made a reaction submarine. It was fun and we all laughed.

you need one smal fast rotating disk (gyro) for each axis you want to stabilize, because if you counter-rotate with flywheel, you have to keep it rotating or leave the environment to stop it (friction), because if it'll stop by axel friction/brake you'll be thrown in the compensated rotation again...

You’re a wizard! Thanks for the extremely entertaining physics refresher! 👍😁