How It Balances on ONE Omni-Wheel
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- čas přidán 6. 03. 2022
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Last time I tried to make a robot which balanced on one actively-driven two-axis omni-wheel. This wheel is driven by two motors in a differential drive configuration so it can drive sideways as well as forwards and backwards like a normal wheel.
The design was mostly taken from a Honda Patent and Honda had showcased a proof-of-concept machine called the U3-X. The original design showed all the wheels around the circumference being driven together by a flexible shaft, but this is very hard to reproduce, so in my version I just attached all of the wheels to a central hub.
Those wheels are driven by two hubs with rollers mounted on them at 45 degrees. This causes the wheels to rotate as the hubs are turned in opposite directions on either side. It worked well during low-speed testing, but I couldn’t get enough traction while accelerating fast to make the device balance. This was largely down to slippage between the rollers on the hubs and the wheels around the circumference. There’s also quite a lot of friction between all of the rollers and wheels, so it’s probably not very efficient.
I’d also looked at another wheel design called OmBURo. This robot uses helical gears to translate the motion to drive the wheels around the circumference with a motor mounted in line with the main wheel axis. This design uses shorter flexible shafts so that each helical gear drives three wheels, although I guess more helical gears could be added, so there’s one for each small wheel.
This time I decided to make something totally different, using a twisted belt to translate the motion from a central hub to the small wheels around the circumference.
CAD and Code: github.com/XRobots/ActiveOmni...
Links:
• OmBURo: A Novel Unicyc...
arxiv.org/pdf/2001.07856.pdf
patents.google.com/patent/US8...
patents.google.com/patent/US8...
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Former toy designer, current CZcams maker and general robotics, electrical and mechanical engineer, I’m a fan of doing it yourself and innovation by trial and error. My channel is where I share some of my useful and not-so-useful inventions, designs and maker advice. Iron Man is my go-to cosplay, and 3D printing can solve most issues - broken bolts, missing parts, world hunger, you name it.
XRobots is the community around my content where you can get in touch, share tips and advice, and more build FAQs, schematics and designs are also available. - Věda a technologie
I love that the side of the final construction at the end of the video looks like the face of a person who can’t stay balanced. Love this project.
Ok, now I can't unsee that jester
I can't unsee that now
@@doxielain2231 i’m so glad i wasn’t the only one to specifically see a jester
Yes! I saw it immediately and I’m happy to not be alone.
Bf
Can we all take a second to appreciate the depth of incredible projects James as made, explained and published for free? These are not simple projects, but exceedingly hard electromechanical designs that would typically take a team of 3 to create. James pumps them out weekly 8]
thanks!
@@jamesbruton No. Thank you!
Given the encoder could you use that to determine the position of the large wheel on the bottom and use a velocity multiplier based on the known geometry for the tapered wheels? May not be perfect but better than unknown.
Seems pretty doable! If he's using a relative encoder then it will be difficult because he won't actually know the rotational position of the wheel, just the displacement from the initial position at power-on. Using an absolute encoder or being careful to power the machine on with the wheel in the same position each time (or rather, one of several equivalent positions because the wheel has some rotational symmetry) would fix this though. Maybe we'll see this in v3?
That's a cool idea and sounds like it should theoretically work on a level surface. But the moment you encounter any sort of incline you'll be in trouble because the part of the wheel that's in contact with the ground isn't at the direct bottom of the wheel.
yeah, this was the first thing that came to mind once he mentioned having problems with the taper on the small wheels. It's pretty doable and I bet James already thought of a similar solution.
I was literally thinking the same. The encoder would need to be quite high resolution though as even a single degree of precision would throw it all off. This could be get quite expensive so the trade off between this solution or just a bumpier ride via constant diameter "wheels" would be interesting. Mind, he's probably got enough encoders lying about that one will work.
I'm not a control theorist but..how about, instead of using a positional encoder you could see how much acceleration (from IMU) a certain movement of the wheels made, calculate the implied gearing (which side of the wheel is on the ground) and adjust the movement accordingly. I guess this would be akin to a double pendulum closed-loop? Success would depend on the sampling rate of the IMU, motor drivers, control loop, etc.
It moves a lot like my neighbour walking home from the pub, which is probably why he ends up crawling half the way. Very cool as usual James.
I have no idea how you manage to design, print, film and edit all these projects and get a video out every week, it's amazing!
12:47 The design is good because that's exactly what my face would look like if I were a one-omniwheel balancing robot.
Next iteration:
- using more and shorter wheels with constant diameter
- miniaturizing the belt system to fit more belt systems
- using one gear to drive 2 belts (effectively doubling the amount of usable belts)
Would the idlers perform better if they were a bar with a concave curve to them? Maybe less slop?
@@reubenj77 either straight or convex, since the belt will walk itself off a concave roller
@@WetDoggo, yeah, I saw a demonstration where a belt will center itself on a convex pully. He should be able to prevent the belts from walking, by making the mating surface convex.
@@notahotshot the idlers/tensioners can be convex, but the gears can't be convex for good meshing.
At least not strongly convex...
A little bit of "convexness" might actually aid a bit in keeping the belts in center.
It might be worth a Test 🤔
@@WetDoggo
Steve Mould did a video about this. It's actually called a 'crowned pulley'.
czcams.com/video/TNuzi-jMXoY/video.html
There's actually a clip in that video of a belt, twisted 90° between two pulleys, no idlers, staying on the pulleys because they are crowned.
pretty interesting design! 👏
First reply
BTW love your design marsgizmo and James
If you could predict the position of the shaft you could predict the cone of the smaller wheel and adjust your algorithm accordingly. Incredible video as always thank you for making these!
Differential equations. Little bit of math would solve this whole thing
The coding needs to be tweaked so it's horizontal axis isn't as glitchy and mechanical, using no gradual braking or acceleration, just full power, full stops making it compensate itself by incremental building up reverse inertia via momentum.
Always love watching your videos. There's something that almost borders on magical about how good you are with robots combined with how much you clearly enjoy working with them.
Just a quick tip: adding a bulge to the belt driven gears will keep the belt in the middle of the gear. Not sure if it will work with a twisted belt. Cheers
Crowned like on a band saw
Whenever I encounter this concept, I always have to convince myself that the belt would actually move towards the bulge.
@@milandavid7223 It keeps train's central to the rails too
3:12 or you could print your gears with angled teeth so they grip the belt at a proper angle.
Brilliant! I love this design. I still have no idea, how you able to make such high quality build and video EVERY week!!! Impressive.
So very cool! Really loved this design! You are almost there!
Great design! I really enjoy your problem solving process. Thank you for creating and sharing!!
Incredibly cool! The belt solution was really great!
so much work goes into these revisions!
Yessss this is such a cool project, glad to see an update so soon! You're so fast with this :D
12:34 the sheer terror of an always falling robot that just saw its robot graveyard.
Videos keep getting better, awesome work!
Great job with all the improvements!
12:37 an appropriate face for this robot.
Very nice how you back engineered this solution after a search, learning and own try and error.
A true engineer, design. works as intended but 20 different screws just to replace even one part should it go bad lmao. I love your content and I'm only picking on you because I like you.
cool video. i was super impressed with that mechanism in that toy!!! kudos to those designers.
wouldn't dust and debree be a major disadvantage of designs like this where the wheels that contact the ground act as part of the internal mechanism? I imagine it could jam up pretty quickly
That's mostly true of any omni wheel.
@@aviphysics not that motorcycle
@@ionbusman2086 It's also the case for the mini motorcycle. Drive it a little bit into the mud and even those nice molded plastic gear will eventually jam.
Sir James, always amazing projects & videos...your can-do attitude is addictive... & your efforts are undoubtedly inspiring so many ... Cheers ! from across the pond in Ottawa.. :)
i love when he says there's too many gears for his liking from the toy design and instead adds way more gears.
That was really cool! Well done!
Been waiting for this for a while awesome work mate !! 😛
You are a mad man James! The fascinating kind!
You are very smart on designing
The noise of this thing and the motion as it moves makes me think to "Red's Dream". It's a short by Pixar and it is adorable.
Impressed as always. Hall sensor the wheel position and add a oscillatory coefficient to compensate for the tapering rollers.
Great engineering mate!
Wow that got complicated. And I thought it was stuffed before. I love how you never give up on an idea until you've exhausted a whole bunch of variations. Can't tell you how many ideas you've given me (read: designs I've stolen).
Awesome. Your getting much better.
Can you add an encoder to get orientation of the big wheel? then you should be able to know the diameter of small wheels contacting ground. Then add it to calculation of required motor speed. A bit of an overkill, but I see the wheel will vibrate when moving forward.
i really enjoy how it's constant movement makes it look properly alive. It's like a little star wars droid.
What a remarkable person you are!
This is really cool!
I would love to see a version of this where the wheel is a bit wider (Or maybe there are two center/doubled up wheels?), and the machine is rideable like a One Wheel.
I'd just like to see a board like that cruise around somehow.
Ty for the link! Wonderful work!
Once you see the face in side view, you can't unsee it.
Amazing work, thanks for sharing.
Hey, Motorsport engineer here.
Really cool wheel mechanism on that robot. Although, I don't think the tapered wheels are hurting it as much as you think.
I have a hunch that controlling the lateral motion with only one motor is creating a yawing moment due to gyroscopic effects from the motor.
I think when the robot leans to left, the motor spins up to lean it back to the right. But in doing so, also yaws it to the left due to gyroscopic torque. There's probably some unintentional feedback that is created from there.
The easiest fix would be to spin up the second motor as well to control lean angle and see if that does anything.
Well done James
They're getting better!
It's totally amazing to me watching you build these machines. I only wish I had the knowledge you have to do this.
I do have a question about the brushless motors you used in this build. I have a desire to build a couple cordless woodworking machines using brushless motors that could be run by established power tool batteries (Makita). Could you direct me to a supplier that may have appropriate motors and controllers? Looking to build drill press, tablesaw, etc...
Awesome! Looks like he'd make a decent little claptrap bot if you wanted to add some body panels and stuff! But I love the twisted belts and was thinking of trying a similar belt design myself so wanted to say thanks for giving me a better idea for it!
you made a design jump!! great for you
I even enjoyed the sponsor segment, cool stuff!
very awesome, huge step up from the last design. I'm wondering about something, is there no need to grease the cogs and other moving plastics? eitherway, looking forward to the next iteration! great work!!
Yeah I thought maybe this could help with acceleration and give the PID a bit of a helping hand.
If you added one more drive motor and made every other small wheel turned by the new motor, you could potentially gain another axis of control, i.e. yaw.
It looks like you have 2 small wheels contacting the ground at any given time, driving them in opposite directions will give you that ability to turn.
Though, you would almost certainly have to add an encoder and programming would be a right pain (every time the main drive wheel advances another small wheel, the rotation would have to flip between the small wheel motors to continue turning in the same yaw direction).
Actually, that sounds really complicated. Maybe just a huge flywheel and use it like a spacecraft reaction wheel, haha. The Honda 'single wheel thing' essentially did the same, except the reaction wheel was the user's arms.
I love this series. I'm hopeful you figure out any issues. I was thinking this would be very cool to have for a "fresh cut grass" robot/puppet.
well done on getting it to work. Also some bonus pareidolia at 12:38.
awesome man🔥🔥🔥🔥🔥, I am such a beginner that I feel bad as I cannot fully appreciate ur work
Amazing work James!! 👊 Genuinely innovative! Please make four wheels, bust out your welding gear, and make a go kart with these wheels!!! 😆
interesting video)) engineering is on top as always)) now we need to complicate the task, and make the whole structure spin around its axis 360 degrees) it's time to add the 3rd engine, and figure out how to make the pair of wheels that is responsible for lateral movement spin in different directions for a turn)
Cool project! Can't help thinking you'd need a physical inertia damper.. Like a damped pendulum, or whip antenna with a weight on top. Maybe you could do that in software, but possibly better to somehow engineer it in physically to the wheel? (a flywheel in the wheel?) On the Honda mono wheel, the active inertia damper is the person sitting on top. I used a passive method to damp out motion on a tall camera mast, rolling slowly on a DIY track and dolly. Worked really well!
I'm not sure if using belts is really better than using gears. The non-constant shape of the small wheels though is definitely something to re-visit... but it looks and works amazing already!!!
A few years ago Self balancing wheels were mindblowing and today we got People Building them at Home. We slowly get to the Future
This is fascinating!
Wow, amazing video
Good job.
I know it's a lot of work has been done behind the scene.
With a position encoder on the big wheel, you could "know" what the circumference was of the part of one of the little wheels that was touching the ground at the moment. Use this circumference information to tune-on-the-fly the side-to-side balance feedback.
Man james loves his belt drives
Amazing. Wondering if you could use a position sensor to know whether it’s riding on the larger or smaller diameter of the cones. Or perhaps set rotation to where it only stops on a single diameter of the cones.
u inspire me a lot 🔥🔥🔥
Thats so cool man. You should try the same thing but go back to un tapered wheels! You cant stop now your so close to making perfect!
saw the tapers on the toy bike wheels, interesting, great low backlash build. Balancing , APPLAUSE, APPLAUSE
Ever thought about using machine learning to balance these robots? seems like the perfect use case for ML. It could optimize for stability and least wobbility.
Gather lots of Input and sensor output data using this crude stabilizer (add some randomness to it) and train a sensor output predictor. This is a physical model of the bot. Use it to train a second model that optimizes input to predicted sensor output for stability and least wobbility.
The gathering and learning could be done more or less in realtime. Let it do its thing and collect more data for both models and train it at the same time.
Hey James, to prevent 3D printed parts to slip you can wrap around them some heat shrink sleeving. That's some quick and easy rubber coating. Regards.
Hi James. I was wondering if you had thought about adding balance weights on the -y and +y axes above at mid height so balance side to side and also add weights to balance the Mid height -x and +x forward and backwards to more center balance is the 4 quads . Hope this helps. Thanks for looking.
Would be very curious to know the total print time you've put on your printers. Assuming you use octoprint or some other management software, may be possible to calculate. Love the content, always amazed by your weekly progress.
You could reprint the soft wheel section with the opposite tapper to cancel the taper out as easy way to check the stability
This guy is amazing and extremely smart. Wish he lived around my area.
Another solution to the belt walking might be to just make the gear teeth concave, like an hourglass, so that the belt wants to just stay in the middle of the gear, rather than adding more parts to complicate things and increase the total print time. EDIT: Perhaps sticking with the belt strategy and "pinching" the gears to keep the belt centered you could double up on the smaller wheels to improve big wheel's roundness, without tapering/rounding the smaller wheels? Otherwise I was thinking somehow track the position of the big wheel to know where along the smaller wheels is contacting the ground and modulate the speed of the smaller wheels from there - which would be a bit of overengineering IMO. I'd try just increasing the total number of wheels at least by double first and if that didn't pan out then I'd resort to tracking the big wheel's rotation and compensating for the radius of the tapered smaller wheels.
Flat belts tend to walk themselves out of dish pulleys, a crowned pulley makes them center but the twist complicates this, also the fact they're toothed. You can't keep a constant tooth profile on a crowned or dished pulley.
Ooh i'm early! can't wait to see the crazy awesome stuff you make next!
James did it again
Would the idlers perform better if they were a bar with a concave curve to them? Maybe less slop?
Good job 👏
some sort of rotary encoder and mix of a depth map of the wheel/circumference of the second axis would help the balancing probs.
Well done
you also could make a kind of coloured / white spot based circle and work with as Photo cell that tells the pcb in wich place the wheel is right now and how fast it should rotate to stay stable
For better side to side movement. Could you use a sensor (maybe an encoder?) to determine the angle of the wheel and adapt the speed depending on the circumference of the small cones that are currently straight down.
12:40 It has a face! Looks like a drunk dude stumbling around 🤣
I wonder if you offset the central gear down and have an idler to keep it "tensioned" if you could make the the outer wheel gears engage as they move towards the ground, that way the mechanism only drives the outer wheels when they contact the ground further reducing friction
Another great design! Could you accommodate for the variable diameter by putting an absolute position encoder on the wheel to vary the speed based on wheel position and device angle?
Yes, but it's quite a lot of workaround ;-)
I was looking at the final product. The space at the sides of the robot is notably open. Maybe place some kind of balancing mechanism at the sides of the tall skinny bot. Reason is that a person on a unicycle find their arms instrumental for balance. Some kind of gyros there maybe? With small rubber tube bumpers wrapped around the whole of the sides to protect bot if it falls.
At around 3:00
Would it be possible to angle the teeth of the gear diagonally to match the angle of the drive belt to prevent it from walking or am i overlooking something. Perhaps even create a valley in the gear using the teeth to persuade the belt to stay in the middle, something akin to two bevel gears kissing but with a smoother gradient.
Might be able to condense the design if feasible though i haven't considered much in the way of the gear's integrity.
Really impressive
That's a really great build, you nailed it this time, tricky software to write! I'd be tempted to cheat by evolving neural networks.
If you mark positions of the wheel you and have a reader for those positions you could program in the varying wheel height.
Your parts are becoming more and more stylish. I enjoy the way you're utilizing existing patents, while deftly dancing around their violation. When you're ready, I would sure like to converse with you about the generation of unidirectional force.
Could you use the position feedback of the main wheel to adjust the algorithm to accommodate for the different diameters of the small wheels? Might have to couple that with the IMU data to determine which part of the small wheels are in contact with the ground.
Thought : the coefficient of correction for the small wheels taper is a modulus of the big wheel absolute angle.
Is the backlash too great for this to be put in practice ?
I think you can compensate the tapered wheels problem in the software. You need sensor like an accelerometer to tell the position of the bug wheel or which part of the tapered wheels is touching the ground.
Do you think it might need any compensation for the gyroscopic moment when the motors spin up throwing it 'forward' when you're trying to get it go sideways?
Excellent 👏👏👏
Very cool!! You are missing control authority on yaw. Ideally, you are now balancing only on a contact point. If you add your vertical fly wheel, you might have a very nice balancing system!
I'm investigating reaction wheels in a couple of weeks.
Curious why you chose straight gears instead of helical ring and pinion type gears like the bike had? The bands and stabilizers seem like a weak point. Idk anything tho, love your vids
Amazing!
0:23 that main middle wheel, with those tiny side wheels needed to be rotated 45° and in the shape of a foot ball clipt at the edges for the accels. When the main wheel rotates, it will not have uneven wheel bumps, and the bottom main and rim wheels, will sync combo to all required ground direction.