Can Reaction Wheels control a Drone?
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- čas přidán 17. 01. 2019
- Reaction wheels are used to control the rotation of small satellites by altering their angular momentum (sometimes referred to as momentum wheels). By rotating the wheel in one direction, the satellite must rotate in the other direction with the same angular momentum in order to have a net momentum of zero (Law of conservation of momentum). But is this reaction wheel effect able to control a drone?
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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.
increasing kp was also my first guess, going from the high-speed videos.
Another thing is, that the ardiuno code could be written in a way, that it is too slow in steady reaction time. Arduino's standart functions may not always be the best choice.
Also maybe as an idea, he could apply a lookup table into the arduino, resulting in a non-linear input to output (in Volt) function. Basicly it says, ok, at this input value i have to apply that output value.
My approach would be measuring the force of 0.1V steps from given voltages (0V->Vmax) and calculating the inverse function. Having these values could lead to the system having a linear reaction, so the same increment of input should apply the same amount of output, regardless of pre existing state.
What? man I should have stayed in school.....
Given that satellite reaction wheels operate in a "frictionless environment" I have to wonder if it would be easier to control a drones attitude, etc with gyroscopic precession than reaction wheels. I feel like having spinning gyros before taking off would stabilize the whole thing.
Do you mind me asking what the salary ranges from for that job? Curious in that career choice :D
@@WilliamDye-willdye Thanks, that's the first time I had it reliably in the air after "debugging" my setup for a long time, that's how I learned. I also shared some of my failure videos like czcams.com/video/J-U7txB47Ug/video.html and czcams.com/video/UMTZ6K-T_kc/video.html. The code of this experiment is available here: github.com/MaEtUgR/FlyBed although I can only recommend it for conceptual learning purposes. Today I use and improve the PX4 open source autopilot together with an awesome community.
Well colour me impressed.
hey cody, great to see you here! do you think one could make a reaction wheel out of a ring filled with electromagnatically propelled mercury ?
Shiny sylveon M.L.G. hasn’t he already been admitted to a mental hospital?
@@Chris-Workshop oh man that sounds awesome
You said colour instead of color. Nice.
@@gnostaoticanarchangautalch4225 what does that have to do with codyslab and why should he alert his subscribers? what would they do?
Parent: Son, why is the lawn still unmowed?
Son: Because I lost momentum...
The angular velocity of the mower is too slow to initiate destructive contact between the rotor and the target object given the current geometry of its leading edge. We can either improve the geometry or increase the momentum of the rotor. The rotors speed is fixed, however, so we will have to improve the geometry. Wheres the grinder?
www.myinstants.com/instant/the-simpsons-nelsons-ha-ha/
@@lev7509 thanks
0:13
Son, never let a lawnmower push you around...
nice
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.
I know right! It’s so cool.
You got very sidetracked,
just because you didn't want to mow the grass.
Well wasn't the grass already mowed?
Pay attention: he was mowing the grass...with the drone. Not to mention his mum's shrubbery.
Yea, mowing the grass with a word, was he? WTF is a drone, a noise?
@@mickcarson8504 a drone is the noise in your head that fills the void where the thoughts should be.
@@thePronto
Ah, LOL. Now 'drone' is that too, is it? In that case, whoever says 'drone' is definitely droned in their heads, right? Poor souls, how do they sleep at night with all that droning going on in their heads?
Would love to see more reaction wheel stuff
indeed, from the ty community too, so manyy toy applications, and big ones too ;-)
Tom would get thrown around by s stuff breeze
czcams.com/video/n_6p-1J551Y/video.html
Seen cubli? This is awsome project with reaction wheels
It would be really cool (and impractical) to try stabilising a camera with reaction wheels so it fights the operator.
I saw this vid about a self-balancing cube that used reaction wheels too. very cool 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.
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
That's an idea I would turn into reality instantly if I had the time and discipline to do so...
And one step further, you could even put blades on the reaction wheels so they supply lift too, and then they would impart momentum into the air, preventing them from saturating.
Of course then you've designed a standard quadcopter.
I think it's odd that the video didn't acknowledge that drones already use their rotors as reactions wheels for yaw control. The air resistance is the bigger part, but the momentum of the blades also plays a huge role.
You just recapped 3 months of Physics class in 1 minute and 30 seconds... what have I been doing with my life?
and also way more fun and easier to remember,
That's what was going through my head.
You understood him in 1 minute and 30 seconds because you already have prior knowledge and intuition to it from the classes you had taken
@@orkhanalikhanov bingo
Orkhan Alikhanov I get what your saying but I’m in 9th grande with no prior physics experience besides for what I know about roller coasters and I understood him perfectly.
You madman! That's a great spin on drone control! Now I really, really, really have to make myself a CNC.
Take apart a few of your printers and make one!!
Could be fun seeing a cnc with brushless motors and encoders.
@@TomStantonEngineering Yes that would be a great start and an interesting video too! :)
Hello Ivan ^^/
You don't need a cnc or a 3d printer or any of the similar hyped up crap. 20 years ago people(me included) were building heaps more complex(sans the flight control electronics) projects with a coping saw, a file and assortment of glues and epoxies.
I'll be honest this seems like the kind of thing someone in the 1800s would've thought up
yup. without a doubt correct man
It was a time of science!
They had the math and theory figured by then but no flying machines at all never mind a remote controlled drone. They had no 3D printers, router/cutting table or tools to make the machine in the vid but I think if they had all that someone would have built something similar.
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.
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!
Great stuff Tom your skills as a presenter are really coming to the fore.
*Well drone 😂
We typically learn more from our failures than our successes. I also applaud his original thinking and determination to work through the entire experiment. A very bright guy and a fun experiment.
Slap on 3 carbon fiber stand-off rods on top as well. Notice how it's never the bottom propeller that gets the worst.
Do you consider lack of knowledge in physics "original thinking"? :-D LOL ROTFL
i know all about reaction wheels i play kerbal space program
BNL ayy, same
thats why im here
But in KSP, everything is easier to fix... If 1 reaction wheel isnt enough, *duplicate, duplicate, duplicate, duplicate...*
Dead Meme then you have 16 reaction wheels and rocket tips still over
@@MarkStillPlays and thats why the offset tool exists lmao
just push them all together
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 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!
That's the BS equivalent right?
I do A level physics currently. What is O levels
@@zakr1187 wot we did 35 yers ago (GCSE, IGCSE etc)
agreed. totally correct man
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.
Saulius Noreika just a thought would it not be more stable if it had 1 larger propeller on the top and 1 more wheel where the bottom propeller is?
The wheel would saturate. Props don't because of drag.
There is latency because he used servo pwm signals about 4ms from send to receive. And then an arduino reading that and sending it to the 'esc'
@@Bean-Time The electronic’s latency is the least of his concerns it’s the mechanical latency causing the bug problem. Takes to long to spin up the motors and for them to change direction.
@@jacobleeson4763 there is latency getting the wheels up to speed, but there should be no mechanical latency to acceleration, just drag. (Assuming the motor has enough poles to precisely control at any angle)
Edit: actually that's a pretty shitty assumption
"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!
"Let me build a test rig"
*Casually Approach 3D Printer
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!
What I am so stoked about....is his CAD ability. To design and make his own parts from scratch is impressive, but today....not all that unusual. Guess I am too much from the old school.
Best explanation ever. I might even pass my mechanics class! Looking forward for part 2.
24:15 i knew it
Well it is a really good game
Thats what i was thinking of wonen i saw this video.
It explains everything
No Kerbals were harmed in the making of this video.
Excellent proof of concept! Your channel is one of my new favorites thanks 😎👍🏼
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.
A part two of the project would be awesome !
He could fly it near some form of beach to avoid hard impacts and increase the longevity of the prototype.
i agree
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!
Very well analyzed!
German mechatronics engineer passing through, I should continue to study form my mechanical dynamics exam, but:
To me it looks like the gyroscopic precession is causing the PIDs to oscillate. The result is the "jerking around the core" motion see in 18:40 and following.
So if you manage to calculate the precession within the flight controller or the Arduino, it should fly much more stable.
I will leave for now, but very very awesome project. I would love to see a 2.0 of this ;)
I came to the comments section for this reason exactly. Glad someone else has written it out already though!
I agree with John H and all the others below, and would like to suggest an idea:
Why don't you have one single fast spinning wheel oriented parallel to the two thrusters? If you mount it on something like a helicopter rotor head (with some adapted parts), the wheel will act like a self correcting gyroscope. By changing the angle that it spins at using the 3 servos from the rotor head, you will be able to change the direction. Just an idea mate, hope you like it !
@@DZARO that's adding another cook to the already busy recipe with the flight controller working to compensate.
These reaction wheels are too slow to have a real precession effect, don't you think? And even if the propellers are spinning fast, they have so low inertia that precession is negligible too. Based on my experience of working on an attitude control system with 3 reaction wheels, it seems like the PID controller have too high Proportional values, resulting in a periodic oscillation.
I love this. Really want to see a follow up, V2, I find this infinitely fascinating and informative.
YESsssss.....I would love a followup video as well. Intriguing concept to say the least. Love this guy....!!!
Dude, new favorite channel. Everything's awesome!
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
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.
This. And start with one axis of rotation, then two, then three. (i.e. build a hinge, then a gimbal, then a gimbal with yaw,
@@charleslambert3368 it also looks like the flight controller is trying to adjust too rapidly then it over adjusts. maybe very slightly increase the "level" field and have a curved current so that the motors move smoother. Just a small idea I don't code much it just looks like its rapidly adjusting on an aggressive scale and then has to counter it.
The www.tsiriggakis.gr/sm.html sets the pivot point higher when the motors are on, so it is able to lift.
Why stop at merely balancing? Make it maneuver all the way around the shop!
czcams.com/video/n_6p-1J551Y/video.html
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.
Exactly my thought ^^ i actually got to this video because i watched videos about precession.
Your videos are so good at being entertaining, educating, and showing your thinking for the engineering.
Your channel is Just getting better and better! Impressive video's!
The was one of the coolest videos I've watched lately. Really like the engineering background before the build.
Brilliant as always! You have one of the best CZcams channels
Wow. What a wonderful and fun experiment. I was trying to learn about reaction wheels and this really helped me visualize how they work.
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 :)
"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?
With such masses, precession can be a problem even on low rpm. And also trickiest math of this project.
Tom, you should at least check magnitude of this effect.
there a bit more math than you can chew on this one...would one gyroscope work better on the bottom?
i have a airhogs heli. i dont know this :(
@@honkhonk8009 air hog helie..lol, takes me back to 2009 when I had one...toy madness to git that rear rotor right.
Fantastic post , that's knowing how reaction wheels work well and truly sorted .
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!
Haters: "Why are you trying to control a drone with reaction wheels?"
Nerds: "F*ck off, it's cool."
Variety_Pack I think a real nerd would admit it is cool but a completely inefficient way of moving a drone
Because, whilst having fun, he might also discover something truly useful. People who bitch would still be living in trees is it wasn't for people like this guy.
handy in space.
I mean, I think the really cool part people are missing is that - in a finished product - the reaction wheels could be *inside* the body of the drone, out of view. :-D
my huge respects for completing such a complex and interresting project!
Thanks for doing that project Tom
Man you're brilliant. I could listen for you for hours. You're super smart and articulate
Man when you cut those two wheels I thought I was losin a harddrive!
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!
Exactly, when I hung it from the string and was adjusting PID values, the PID tune for when the motors were stationary/low RPM was different to if they were already spinning. The only problem with measuring the current vs RPM is that RPM isn't always relative to current. For example, if a large current was applied to the motor, rotating it to 1000RPM, then a small current was applied in the opposite direction for a short period of time, the motor wouldn't necessarily change direction, but maybe just decelerate (depending on how long the current was applied for). Then if current is switched again, the motor could still be spinning at 500RPM in the wanted direction and therefore the current applied won't be able to apply the torque that the flight controller expected. Thanks!
I get it. The lookup table fails if you're changing the speed constantly. Oh well. I guess you do need encoders. Go ahead and rip them out of an old "ball" mouse. That's how we used to do it. LOL!
Would a stepper motor help? Since you can count steps and control speed, acceleration, and jerk.
Yes a stepper motor would be another good option!
The problem you are having is the response time of the brushed motors being too slow to accurately control the drone.
Its that gearbox in the motors most likely.
It might fly with some tuning, but what software are you running on that fc?
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.
Thanks for the pretty clear explanation of reaction wheels, I was never quite able to grasp them
In an alternate universe, this is what helicopters look like.
Until they discovered how ineffective -or at least inefficient- it was
@@MsHojat Пока автомат перекоса не изобрели...
@@MsHojat And there's another alternate universe where they never figure it out, because they're all too stupid.
Come to think of it, I'm surprised that isn't this universe.
@@wugu42 true
18:00 Why does this reminds me of the Iron Man test flights ? :D
Pitching and yawing about an odd centre of gravity before understanding the controls?
brillant
Amazing work..the small flight time demonstrated great balancing and the gyro
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.
Tips for next time: Your reaction wheels have too much mass and drone has more mass in one corner. Otherwise great work 🤙
I thought the same thing he must add counterweight to the reaction wheel
Thought it was quite obvious, really thought he was going to add two more wheels , or tinkered with their size ... Hope he doesn't give up on this ,
Thought same thing, needs two more reactions wheels rotating in the opposite directions, may be he can use a reversed gear box on the bottom of the motor to use a single motor to control the two opposite reaction wheels and keep them in sync.
Actually 2 corners only, causes _"spin precession oscillations"_ especially with the feedback control loop delay. The gyro/momentum control must be centered not on lopsided 2 out of 4 edges; I mean it must be on 4 edges symmetrically. Putting weights on the legs does NOT counter osculation, but does reduce the _"spin precession oscillation frequency"_ just enough to allow the control feedback real-time loop to not fly out of control. Momentum does not work well compared to gyroscopic reaction idea where you put a blade onto the gyro (weighted prop) to cause a reaction at 90 degrees to the application of the point of force. You know the free spinning heavy bicycle wheel idea in physics where you tilt the wheel vertically and it produces a force/gyroscopic reaction horizontally. You also failed to remember with your helicopter that the reaction is 90 degrees off which caused another instability with your software control being not quite right. With the body of the drone hanging down in gravity, saturation of the gyro idea would not become a problem. In space it does become a problem.
Another way to stabilize the drone would be to move the second propeller upwards - this would require an in-laid counter-rotating powershaft to allow for two propellers moving in separate directions on the same axis, but would cause the center of thrust to move far enough above the center of mass to allow for more in-flight stability, partially countering the spin precession oscillation by forcing the drone into a sort-of stable equilibrium when thrust is applied. Torque-steering the drone's rotation could also be used via software to counteract the weight imbalance, together dampening the oscillation to allow for more stability without big modifications (except for the second shaft forcing the usage of some sort of a bevel box to allow for single-axis propellers).
Interesting engineering challenge, if you ask me, but would increase the complexity of the whole contraption to levels I'm not sure he wants to go to :)
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
Either way, it's like balancing a pencil on it's point, you need constant fine adjustments to keep it upright. Even traditional helicopters pivot their main blades to stop it pitching uncontrollably. Helicopter pilots have to fight all three axes constantly in order to hover, especially in wind. I think the reaction wheels in this design had too big of a moment of inertia that ended up being a drawback due to that non linear torque he mentioned. Also, I didn't expect to see you here!
They found that with rockets it doesn't matter whether the engine is on the top or the bottom (so putting it at the bottom means it's a lot easier to get the fuel to the engine). Not sure if that same theorem also applies to multicopters.
@@thewhitefalcon8539 It may not matter to the engineers if the rocket motor is on the top but I'd bet it matters to the pilots sitting at the bottom of that thing who are about to become roasted barbecue from the engine exhaust.
(I'm kidding, this is a joke. A poorly made one, but a joke nonetheless)
What is this a crossover episode
AYYY! Rocket pendulum fallacy!
This was a cool video! I learned a lot. Thank you!
Thank you so much for this!
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!
Torque per amp is not linear with rpm.
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
The point of this project is to not use gimballed motors.
@@linecraftman3907 i think he did not meant gimballED motors (aka tilting rotor assembly) but to use actual gimbal motors to power wheel, they usually have higher torque for their size... they have built in sensor that knows exact position of rotor... quite precise controll
You’re a wizard! Thanks for the extremely entertaining physics refresher! 👍😁
suuuuper super interesting, that slowmo footage is absolutely awesome to watch.
Nice video! I Just Subscribed. I like these kind of videos
I don't understand how is it possible YOU out of all makers did not yet printed some vacuum hose holder for the CNC :)
maybe to have better footage for the timelapse, as it would take some space.
I was literally thinking the same thing then I saw your comment - omg this guy's gets it
Toujours aussi captivant !!! Un beau bravo du Quebec !!! 👍🏻
New to your channel. This is the first "failure" I've seen and it was probably my favorite so far.
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
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!
I don't think this would work well. As it spins faster, friction does more to help you slow the wheel down, but it also does more to keep it from speeding up. Furthermore, at higher RPMs, the motors can provide lower torques than at lower RPMs.
As a result, you may get somewhat better torque/response in one direction, but the other direction would be significantly worse.
Not only is this a problem because the worse direction ultimately defines the performance of the reaction wheel, the asymmetrical nature of this is also something flight controllers aren't made for and the process of getting that to work properly would be incredibly tedious.
If you did decide to go through that effort, though, a way to overcome the asymmetry and low performance issues would be to have two wheels for each axis, spinning in opposite directions. One would speed up as the other one slows down, and you'd have to program it so that when little to no output is required, both accelerate, as otherwise, RPMs would go down with flight time. Unfortunately, you'd probably still end up losing RPM somewhat quickly, meaning while this may actually lead to a more stable flight, it wouldn't last long.
thats hat i meant with other words
Be careful with fast spinning reaction weels. The spinning rings can cause the drone to move differently than if there was not a gyroscope on the drone. As the weels spin faster it is more difficult to move the wheel out of the orientation where it wants to be. The force could be stronger than the drones ability to react, crashing the drone. See youtube videos of people moving fast spinning gyroscopes and the behavior of the gyroscope..
My grandfather always told me that at his work (building test aircraft) they would spin up an airplane gyroscope and put it in someone's lunch box. When the guy picked up his lunch box and moved it in a direction that countered the movement of the gyroscope the gyroscope would keep the lunchbox moving in the original direction to the surprise of the person holding the lunchbox. The lunchbox would often be ripped right out of his hand by the force of the gyro.
That would reduce the dynamic range of the wheel. It has a maximum RPM and the performance degrades at high speeds. By having the "neutral" at 0 RPM then it has more range in both directions before it maxes out. Of course, you can end up in this state regardless, as any asymmetry in the drone, environment or flight path will just add up over time. But by starting at 0 you maximise the mean-time-to-failure.
What a great experiment! I love seeing all the fails and attempts.
I have new respect for test pilots.
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.
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.
@Obelisk Tungsten behaves very similar to grey cast iron when being machined, although it depends on the alloy composition. Pure tungsten is extremely rigid and tough, higher alloy concentrations become more like stainless steels to "cut". But you can "cut" it with pretty much any machining tools like 98% tungsten carbide tips or even HSS if you just control your feed and vibration enough. I say "cut" because tungsten chips rather than being cut or sheared. To answer your question. It is very very hard/rigid, and very abrasive, but its not impossible to cut, just not very pleasant.
Great video! Thank you for making the otherwise boring parts interesting. Would you mind telling us what CNC your using? Thanks.
I started out as a machinist and when cutting aluminium we use to use paraffin which worked great most standard water-soluble coolant has very little lubricating properties unlike paraffin or most other thin oils with grey cast iron all we did was use air to help keep the cutter clean of any build up of cuttings and help with temp control the main thing was to take as deep a cut as you could as the casting has a sort of skin on the outside due to it cooling faster than the inside once you are past the skin it is easy to cut and produces just dust and not normal curly cuttings like most other metals.
@@meusana3681 What a load of bullshit if I've ever seen it. Aluminum galls like a mofo without coolant. I wouldn't use high sulfer like he did, probably WD40 or kerosene or something. But defiently not dry.
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.
Well you gotta make this work, ya know, sometime.. such an awesome concept
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). :)
You Should try continuing with this it's really cool
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.
The spirit of reasoning is stunning for me. Especially this can be a passage of physic learning and metalization. Love it.
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.
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 :)
This is a stupid project that nobody asked for. I love it.
FYI they used gyroscopic stabilizers to stop ships from rolling, same principle... and wow nice move calling people stupid, who actually do their own thinking... I think it is the other way round
@@gshaindrich **facepalm**
@@gshaindrich please stop
@gshaindrich r/woooosh
@@gshaindrich you tell them trooper!
Wow! some brilliant stuff in here! how come I didn't find this channel earlier
your videos are amazing Tom.
the reaction wheels cause an off center center of mass, saturating them.
having them on both side will fix it.
I think it suffered from gyroscopic precession.
Counter rotating propellers should cancel each other precession...
I think so too, the two propellers will dampen and translate the reaction wheels force, and induce the wobble of the body. Try spinning the propellers and moving the body in a jig.
@@HVM_fi And the precession of the reaction wheels themselves?
The problem is probably not so much the lift motors, it's the un-countered gyro effect of the wheel motors spinning 100's of rpm -if the motors spin same direction as wheels. This will induce a 90deg shift in force applied (gyro prec) -then the other motor tries to counter it -then the regulation loop time goes bananas and oscillate.
my guess is some non linearity somewhere in the system. even the DC motors alone are not translating voltage to rpm/torgue in a linear fashion, where I guess the controller tried to calculate speeds based on a linear response. If you noticed the craft can keep itself stable as long as it stays between a certain angle. So to control the system properly, I would try to capture the impulse response of it. There are simulation programms like BORIS where u can simulate this kinda stuff
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.
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 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)
Use reaction wheels as a stabilization system on a RC drift car.
Or in a full size recumbent motorcycle, a la Akira....
I actually got tears in my eyes when it woke to life around 19:40. Love your videos and persistance. :-)
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.
Next try to power a propeller plane using reaction wheels and RTGs
Should be far easier
It wouldn't really be possible. Almost all airplanes are designed to be self stabilizing. Thus directional control would require constantly increasing inputs to maintain a constant control. In short, the reaction wheels would reach their limit far too quickly and you'd lose control of a relatively fast flying aircraft. On top of that, to maintain flight the aircraft would need no inputs whatsoever which somewhat defeats the point of the demonstration.
The alternative would be an unstable aircraft, like the F-16. This requires a small force to start the control followed by a constant force against the control prevent the control from increasing. Again this would quickly reach the control limits. Additionally it would require controls too fast for the current setup to manage.
Finally you have a poor interaction between the reaction wheels and the flight imparting not only turbulence from the shape of the wheels but unwanted controls from one side rotating into the wind and the other with wind (creating a differential force). On top of that the filming of such a setup would be harder than a camera/phone on a tripod because its constantly moving. Whilst it might sound cool, the idea is entirely impractical even (moreso than a reaction controlled drone).
And it wouldn't really be a plane in the sense that control would not be through aerodynamic deflection
If by RTG you mean Radioisotope Thermoelectric Generator, then I'm down for this
And it must hit 300 m/s or more :>
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.
The Problem is much simpler:
1. The asymetrical layout have also an issue withe the PID regulator of the flight controller. Thats why it flys in one direction on start. The P-amount in the positive direction is not the same as in the negative. This is very complicated to compensate with software.
2. The current regulator do not effect the reaction time directly. Only the momentum from zero of mass. (And maybe the coils of the motor.) The speed increasses logarythmic and needs a lot of power on zero rotation. An efficient way were to spin one other wheel on each other side the opposit way and change only the rpm of it.
Awesome vid, thank you!
Top notch educational content. Thank you!
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?
PKMartin That's called a control moment gyro. Satellites use that control method sometimes.
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.
What about the turbulence caused by the blades doing the actual lifting
@@callmezucc9318
That may not be a problem, as the attitude control system should automatically compensate for it.
Impressed :)
Well done
Really cool videos man. Just found your channel.
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!!!!!!!!!
Haven't watched the video yet, but I remember making my first drone in Besiege, it worked with reaction wheels.
Soo, I guess your drone will work ?
I'm glad I was able to find someone else who has played Besiege here.
Please continue with this project!
Damn it... Why didnt I see this video a week ago, when i was studying about momentums... Great channel i love it :D