The website seems to end with a 2015 electric unicycle but not continue on with covering that form factor. Maybe because most people don't refer to those as monowheels anymore.
Also airwheel is kind of a random brand to showcase - Trevor Blackwell made an earlier one https://www.trevorblackwell.com/eunicycle and Solowheel got the majority of the earlier patents (and royalties to this day).
That form factor has come a long way since 2015 though.
Unicycle seems to be the winner. The "wrap around the body" form factor seems doomed from a physics point of view. That big of a diameter has way too much leverage, and the person sitting inside has too little. So you end up doing a flip instead of stopping. As such, their required stopping distances are very long compared to unicycles which can stop as well as a bicycle, if the rider is skilled.
In theory, the braking performance could be the same as the bicycle. In practice, the rider needs to guess the traction very precisely and to move their weight backwards to an angle just a smidge higher than arctan(static friction coefficient). Do you start to see a problem here?
While the bicycle rider only needs to move their weight so that the combined center of mass is projected between the contact patches of the wheels during the deceleration, the EUC rider absolutely needs this to be as close to the contact patch as possible. Shifting the weight too far back means an almost guaranteed wipeout, and you don’t know if the road is squeaky clean or has some trace amounts of sand that would reduce traction, so any sane rider would err on the side of caution and under-brake to avoid falling on their back.
>arctan(static friction coefficient)
>needs this to be as close to the contact patch as possible
That's not true, or perhaps you mean something other than how those words are directly interpreted? Static friction force isn't an arctan, it's just the normal force (which is you+wheel weight) x the friction coefficient. That's the force that's slowing your motion. And being close or far from the contact patch doesn't affect that at all. Elaborate what you're thinking?
Arctan(friction coefficient) gets you the "friction angle", which is a meaningful angle to know in a lot of physical systems. For example, it tells you how steep of an angled surface your object can rest on before it starts sliding downhill.
In this case, it sounds like the friction angle is important because it's the angle at which the reaction force is being applied to the unicycle by the road. (The normal force and friction force components make a right triangle with the resultant force, and their ratio - the friction coefficient - is by definition the tangent of that angle). I know nothing specific about unicycles, but it sounds like they're saying the rider needs to lean back so that the "shaft" between the seat and the axle is oriented along that line of force or else the system will become unstable.
Did you ever ride on one? They brake using the motor so it doesn't wipe you out. At worst you stand on the ground, but mostly you just start riding backwards.
I own one and I can assure you it’s very easy to fall on your back if you overestimate the friction when braking aggressively. Not even close to real life bike braking with disc brakes if you know how to transfer your weight properly (granted, a newbie would totally fly over the handlebars if they tried to brake to the limit without shifting their weight behind the seat..)
Odd - I ride EUC and bike mainly, and bike is easier to skid on accident. Opposite experience as you. It makes sense too, since on an EUC 100% of the normal force is utilized for friction force. On a bicycle you can only utilize 100% if you're extremely good at applying the front and back brake at the perfect ratio to each other.
I don't think (electric included) unicycles will ever have the same stopping performance of conventional vehicles - the center of gravity is just much further forward than in any two-wheeled vehicle. The requirements imposed by the balancing mechanism limits the possible braking force to how far behind the wheel a person can get.
They can still stop plenty fast enough for most purposes, though, and it's a very natural action compared to almost any other vehicle.
On wheel size - yeah, its the case that the smaller the wheel, the more responsive a unicycle becomes to torques applied by a person's body. It becomes a tradeoff between the resilience of a large wheel to bumps and terrain, and the responsiveness afforded by a tiny wheel (which takes less torque to apply a given forward/backwards force)
Emergency braking feels more like shoving the wheel forward than shifting oneself behind the wheel. You ignore balance for a while, get yourself into a sitting position fast, the system can right itself (or not) after you've bled enough speed.
I disagree. Having a single wheel has the benefit of maximizing traction. With multiple wheel vehicles, if you apply the brakes to some wheels and not others, the tires lose traction. This is because those tires don't have enough normal force (weight) pushing them into the ground. I know my car only applies brakes to the front wheels. Any all-wheel-braking vehicle like a unicycle can beat my car to a stop, for that reason alone. It takes a sporty rider to be good at hard braking on EUC but I've seen them stop extremely fast. Especially some of the riders who race around manhattan. They have a handle on their EUC, and throw their entire weight behind the wheel in a crouch, like a cowboy bucking a bull. Their center of gravity gets near the ground. The motors on their wheels are extremely powerful, 10kW or more in either direction. It takes a skilled rider though. The main danger of super hard braking in the EUC community is the notorious "death wobble" that amateur riders sometimes get, where it starts oscillating right and left the harder you brake. Good riders grip things stiff enough to not have that issue though.
Having fewer wheels does not mean you have more traction - contrary to popular belief, a racecar can trivially out-brake a MotoGP bike despite weighing an order of magnitude more. The contact patch size matters more than the number of contact patches. This is ignoring the issue of perfectly balancing a unicycle to stop effectively, where just the time it takes to transition from leaning forward to backwards is a significant cost in time and distance for braking compared to any vehicle that has inherent lateral stability (such as a car or a motorcycle).
> I know my car only applies brakes to the front wheels.
I doubt this. What kind of car do you have? Almost all modern cars apply brakes to all 4 wheels. In most cars which have most of the weight in the front the brake bias is approximately 80% front and 20% rear. For mid-engine cars this usually shifts to 60% front and 40% rear. Some cars might be somewhere in between depending on their weight distribution. The limiting factor in braking is tires, and the way to improve that is by increasing the contact patch size - which is done by increasing tire widths, diameters, and the number of tires.
Racecars are essentially wings due to the aerodynamic plate on their underbelly, sucking themselves hard downwards into the ground, that's why they can brake better than vehicles that don't do that. And contact patch has to be the most misunderstood and overanalyzed concept in racing. It's baked into the coefficient of friction already. The force it exerts is still directly proportional to the normal force on each wheel.
>What kind of car do you have? Almost all modern cars apply brakes to all 4 wheels.
That's good if it's true. Maybe they will make 18-wheeler trucks start having brakes on all 18 wheels so they can get similar stopping distances as those cars. Point is there are plenty of vehicles on the road where only 2 or the 4 tires go into a skid when they lose traction. Parent comment was absolutist about how unicycles will "never" match any other vehicle in braking. I figured I'd defend unicycles. Don't want to jump off the rails too much here.
I know my car has rear drum brakes actuated by the hand brake. It can lock up the rear tires for a drift. And front disc brakes actuated by the foot pedal. Perhaps it does use all 4 when I press the foot pedal - my mistake if so.
I think it's funny you're objectively wrong but continue to insist you're right. Anyway, I'm not gonna waste any more time correcting someone that's allergic to learning.
Ah, knocking all the chess pieces off the board and strutting away. It's funner to actually think about the interesting problem tho. I just got back from a weekend EUC race at Alameda naval tarmac, I love pushing what the things are capable of.
You joined the comment tree of "I don't think (electric included) unicycles will ever have the same stopping performance of conventional vehicles" and have taken the position of defending that absolutist statement.
I get it, not everyone is familiar with EUC racing. To help, here is a photo of the average hard brake from 40+mph on a modern EUC (probably a ET Max or Lynx or similar high kilowatt wheel), since you might not be familiar with what we are discussing -
Notice how far you lean to decelerate from speed. Note the handle you can yank as you buck your bodyweight back. That all forces the controller to compensate with more kilowatts of stopping power, instantly righting the gyro sensor. The more you try to tip it backwards, the harder it brakes to force itself back upright.
I don't have a mythbusters style video to make it crystal clear that you're wrong, but sounds like its a good idea, by how folks are reacting to the news. I'll suggest it to my youtuber friends.
For now, try to imagine a vehicle that invalidates your position. We only need one example after all, it being an absolutist statement. Think of edge cases. Something that skids around a lot. Fixie bike in NYC? The kind you see messengers whizzing around on all the time, that can only skid their rear wheel, and have no front brake, by design. Still defending the claim?
And to your point - an F1 car with thousands of pounds of aerodynamic downforce will stop shorter than an EUC, absolutely. We agree there.
- angle of CG to front wheel, tan(vert angle) == max stopping acceleration in g (assuming front/all wheel braking, rear wheel only is different)
- the coefficient of friction (generally in the rangeish of 1)
- shear strength of the rubber in the tires (wider/more is better if you're at other limits)
- other braking system issues -- heat dissipation, crap brake pads
The thing about single wheels is that the CG -> contact patch vector basically defines all of the instantaneous dynamics of the system. If you want to go from turning to braking, you have to change position, and there are limits about how fast that can happen that don't apply in a multiwheel system.
I think GP mistook a short summary for FWD that it “drives” on front wheels, as in it delivers engine output to front wheels.
fyi to all, brake hydraulic lines are still distributed to all four wheels in low-end cars, but “drum” brakes are often used in the rear, which stretch out to slow inner wall of a cylinder rather than squeezing together to hug on surfaces of a disc.
Thank you - you're right I did assume that. Plus the fact that my handbrake only actuates my rear drum brakes (and sends me into a fishtail drift). I didn't realize my foot pedal was also actuating that, but if so sounds like a smart design.
Discs are also exposed to wind and sand, drums aren't. Front discs and rear drums is just fine for commuter cars, ID.4/Q4 E-tron uses that if an example is needed.
Other guy lost interest, but a wheel being able to regen brake just means theres an ungeared electric motor on it. It's basically free for the manufacturer to add the feature, so they all do it. Mechanical brakes are seperate and still required for harder braking.
My 2009 has rear drum brakes, actuated by the handbrake. The front are disc.
It sound like folks are adamant that the brake pedal actuates all 4 of my brakes. I didn't know that. Sounds plausible, I never really thought too much about it. I'll take their word for it.
I don't know how many nights I've lost track of time reading through this site, mostly in the 'unusual locomotives' section.[1] (I'm in a rail modeling group where some of us are really into the oddballs, so it comes up pretty often there!)
"Left: The Brennan model, carrying Brennan's daughter on an aerial wire.
From a certain lugubrious quality in her facial expression, one has to conclude that the young lady was not entirely happy with her situation"
I find it interesting that there is such a convergence towards hubless wheels, which I think are challenging regardless of number. There are a handful that have hubs but if the passenger is on top they drift into unicycle territory, which feels like a different category -- and if the passenger is inside, then the whole vehicle is perhaps large enough that it's further out of reach for an independent hobbyist project?
"if my grandmother had wheels, she would have been a bicycle."
Vehicles with Insufficient Wheels do not go anywhere. A car with 4 flat tires, requires a vehicle with 4 good tires to tow it away. A Monowheel has the necessary and sufficient number of wheels to move. Monowheels are just way way cool.
But make no mistake, this website is a comprehensive catalog of ever mono/diwheel I have ever seen, known of, or heard of. The title is a terrible misnomer, and the web site, is absolutely comprehensive.
What happens when you brake hard? I imagine some bicycle caliper brakes grabbing the wheel's rim, which if the coefficient of friction between tire and road is high enough, causes the driver to just go round with the still rolling wheel.
If you brake too hard on a bicycle, you flip over too, especially downhill. You can brake up until the point that you've popped a front wheelie. Bicyclists usually forgo most of the available braking force, by solely using the rear brake, for this reason. Same for monocycles. If you go past 90 degrees, there's no point in further braking force. If the brakes are electric, they would throttle themselves to that limit, so you have max braking force. Just like anti-lock brakes on a car.
All that said, the terrible wheel-to-rider leverage ratio dooms the design to always have poor stopping distance. Probably not any worse that a bicycle without a front brake, though.
It's my firm opinion, and that of many people who've looked at it, that flipping over the bars is caused by the rider not bracing themselves as they use the very powerful front brakes.
If most cyclists don't use the front brake, that is their loss. Most advanced cyclists, in my experience, rely heavily on the more powerful front brake.
I'm a hardcore cyclist too. If you're bombing down a San Francisco hill at top speed and lock the front tire, no amount of crouching behind your seat is going to leverage it from flipping. The point is physics is physics, monocycle and bicycle follow the same simple kinematic diagram of pivot point x torque vs pivot point x inertia. If you use 100% of your braking ability you'd better be tall and heavy enough to torque it the other way, else the free body diagram rotates.
There's a world of difference between locking up your front wheel and not using the front brake at all. A reasonably skilled cyclist is able to use the front brake effectively without locking it up.
We are in total agreement. I was illustrating my point that a unicycle rider avoids flipping because they never use the full braking power (lock up the wheel). The gyroscope controller won't let you - you can only brake as hard as you can counterforce (throw your entire body weight hard backwards). As soon as the gyroscope senses a change in angle, the P.I.D. motor controller compensates.
The angle of a very steep hill makes it easier to do a front flip, but such steep hills are an exceptional circumstance. Most of the time, experienced cyclists can safety use a great deal of front braking.
Bicycles are not a physics 101 problem. In practice this just doesn't happen. See the links I provided. You can also read more about this in the "Bicycling Science" book.
A unicycle or bicycle flipping is a Physics 101 problem. First you must lock up the wheel if you want to flip, meaning the complications of kinetic friction are irrelevant. There's a center of mass, a contact point, a velocity, and a force. You can make a free body diagram to accurately calculate if you have the speed and CG to rotate forward (flip). Newtonian physics isn't magic. Telling someone to "read a bicycle science book" just sounds like a flippant dismissive insult. You're safe to assume I'm already well studied. This is a conversation, not an insult battle. If you have a point in mind, then bring it to the conversation in plain english to be inspected under the light of day. What juicy morsel is contained in this book of yours - perhaps it will sell people on moving it to the top of their reading list. Until then it's meaningless.
This is indeed true -- I try to get my wife to use front brake more, and I sure will teach my children to.
But it remains the fact that many cyclists don't use the front brake -- or are even aware of its advantages.
(If you want to find out yourself, step off your bicycle and move it gently either forward or back. Try applying first the brake in the direction of travel, and then the trailing brake. You may be shocked at the difference!)
Heck, most people I know have the kind of rear brake that applies when you pedal backward. They find it more important to have hands firmly gripping the bars than pulling levers in situations where they want to stop. (Not saying it's sensible, but it is what they report. It's hard to convince them to use the front brake when their lives have stacked them against it.)
In a physics sense it would happen when the torque applied by the forward momentum is higher than the force applied by gravity - the higher you are above the contact point with the ground, the more torque you apply and the more likely you are to rotate around the wheel.
The lower and further back you can get your weight, the more force you should theoretically be able to apply (being wary of deweighting the front wheel too much such that a hard front brake causes a skid instead)
I've been riding those daily for years. Today I am going to Alameda naval base where they've set up an EUC racetrack on the tarmac at noon. I don't know what part your'e taking issue with, but physics is best communicated with free body diagrams and equations, which are difficult to articulate in conversational english and interpret correctly as a reader. I'm sure there's countless ways to misinterpret and nitpick my comments, but I'm not going to squabble over those or spend too much time rewriting anything — I'll just say I stand by my arguments from years of experience, so try to read my comments in that light first. If you had an actual point to share, share that instead.
It defines the monowheel as 'one big wheel with rider and engine (if any) INSIDE its circumference' so unless you are riding inside yours, it's probably not a miss.
http://www.douglas-self.com/MUSEUM/TRANSPORT/motorwhl/motorw...
Also airwheel is kind of a random brand to showcase - Trevor Blackwell made an earlier one https://www.trevorblackwell.com/eunicycle and Solowheel got the majority of the earlier patents (and royalties to this day).
That form factor has come a long way since 2015 though.
Check out this MotoGP style race, they're hitting 50+mph: https://youtu.be/fbX6qaWINBk?si=l2G0JnBxxCMP8a7e
I see them every day whizzing across San Francisco, especially on Van Ness passing all the cars.
I know there's at least two shops in SF selling them, one in Potrero and one in Hayes Valley - https://alienrides.com/collections/electric-unicycles - https://lastmilepev.com/collections/electric-unicycle-euc
Unicycle seems to be the winner. The "wrap around the body" form factor seems doomed from a physics point of view. That big of a diameter has way too much leverage, and the person sitting inside has too little. So you end up doing a flip instead of stopping. As such, their required stopping distances are very long compared to unicycles which can stop as well as a bicycle, if the rider is skilled.
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