Monowheels: Vehicles with Insufficient Wheels
douglas-self.com
douglas-self.com
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.
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.
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?
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.
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)
> 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.
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 -
https://i.imgur.com/pDzPtvB.png
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.
Ah, now I see the problem. You get your information from clickbait YouTube videos instead of actually trying to learn things.
I'd point out more ways you're wrong, but you don't listen to what everybody else has already said so it's pointless.
- 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.
If that's true, your car needs urgent brake maintenance. Most cars' brakes are forward biased, and all cars apply brakes to all wheels.
Which vehicles don't brake on all wheels? I can only think of cruiser bicycles.
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.
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.
With the style of the website, I'm shocked it has anything after 2000
It probably took me about a week to get a full idea of how it works, and I'm hoping to create a model to help myself really understand.
http://www.douglas-self.com/MUSEUM/LOCOLOCO/brennan/brennan....
and
http://www.douglas-self.com/MUSEUM/LOCOLOCO/scherlgyro/scher...
"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"
Until seeing this, I didn’t realize they were parodying anything or that this design was a real thing. And with so many variants!
Personally, I'm offended they omitted the Cobra Buzz Boar. That's all I see when I look at these monowheel photos/designs.
Also love "I did a quick Alta Vista"
Nothing insufficient about monowheels. Should not the title be "When one is sufficient"?
(Oddly second site this week that doesn't work when you force https)
Seems unsafe.
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.
https://www.renehersecycles.com/how-to-brake-on-a-bicycle/ https://www.sheldonbrown.com/brakturn.html
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.
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.)
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)
(comment thread directly above is discussing the segway)
Love riding mine!
A somewhat unfortunate name, I guess: https://en.wikipedia.org/wiki/Gerbilling
Love this kind of site.