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Thought I saw this like over 10 years ago on like a mechanics for kids episode.
They pitch it as a space-saving design for EVs but the space saving actually just comes from running a small motor on each wheel. The main advantage seems to be more efficient torque transfer at different angles which seems relatively unimportant tbh
How expensive is this going to be to maintain/fix?
I know it’s just a rendering but those planetary gears look really tiny to be transmitting that much torque. And the test vehicle has only gotten up to speeds of 120kph, or 75mph. That’s basically the minimum speed on my local highways
Sure they do. That’s cause they’re not transmitting much torque at all. They don’t have to. You don’t have a lot of torque anywhere except at the ring gear - and not on the gears driving it. You’re thinking based on traditional drivetrain heuristics, where you might easily be putting upwards of 8000lbft through the axles. But as this eliminates the need for most or all pre-reduction, even direct driving off an enormous electric motor, it’s a way, way less torque than you’d see even on the cv joints of a geo metro.
torque is the same across the system of gears, regardless of the lever, that’s why its Newton-meters. In engineering terms, you’re primarily concerned with the shear load on the axles or gears at their specific loading in the power transmission chain. Even with the CV joint or this uni-wheel, the force of engine braking and acceleration is going to put similar shear loads. In fact, I would think other similarly sized gears are subjected to similar loading in differential gearboxes and the actual transmission of most ICE engines. Making gears tough enough is easy. Even in the insane shock-loading they will see as a unsprung wheel assembly.
the whole point of this design is expressed in the video: efficiency.
It doesn’t matter what the longevity or durability of either design is, the problem is that a short axle produces high angles on a CV joint and lowers the power transmission efficiency of the CV joint dramatically. in order to pack the motors close to the wheel, and maintain a suspension system with enough travel, they have to use a different design to maintain the range and performance.
They didn’t test it to a particularly high torque. The video embedded in the article claims they tested it to 1200nm wheel torque. A Civic type R makes more at each of its front wheels in first, second and third gear assuming maximum engine torque. Not only that but they also claim a 6.241 ratio on the thing so it’s still going to need a fairly substantial input torque. With the specs they posted, it would make for a car that goes down the road just fine, but probably isn’t going to be in any of the fastest categories.
Oh boy I can’t wait for this to miserably fail!
Massive durability and other concerns aside, where are the brakes?
Just move them inboard. Might as well. You’d want to offset the additional unsprung weight, plus with the axle shaft being unreduced, you can now use much smaller and lighter brakes spinning at a higher rpm for the same effective brake torque.
Part of the motivation for this Uni Wheel is to free up the space between the wheels, so moving the brakes inboard kind of defeats the purpose. Also it would probably make changing the brakes more difficult.
On an EV you really don’t need to change any brake parts, there’s many people who’ve put on over half a million kilometers on their stock rotors and pads on EVs, they’re supposed to last the entire lifetime of the car without needing to replace them, so 20+ years. The only thing you really need to do is flush the brake fluid once over its lifetime.
On an EV, conceivably the life span of brake systems would increase.
Typically they last the lifetime of the car, so 20+ years.
Shit on my hybrid they’re supposed to be good for 250k miles. (and it’s a Kia)
depending on the design of the electric motor, its weird to consider but the brakes could be put in board between the two motors.
I do believe that motors in the wheelhubs are the future, but i think it either needs to be a direct drive or use a robust inbuilt planetary gear set, like the drivewheels in diggers
A company called Elaphe already has an electric hub motor design that was originally going to be in the lordstown trucks. Also the Aptera will be using a custom version designed for maximum efficiency and better suited to their application. So hopefully the future will be here sooner than later.
Years ago I thought we were moving to 4 individual motors on all 4 wheels. Guess it never took off.
Aptera is actually doing that now, they’re doing some really great stuff
How would you seal that to prevent the gearbox oil from leaking out and dirt getting in?
With a boot.
That doesn’t even work reliably for grease and much less relative movement so I’m skeptical about thin gear oil.
Well the reliability of a boot has really nothing to do with the fluid it contains. Either it has a hole in it or it doesn’t. And there’s actually no reason this couldn’t just use grease, in fact it might have to. But unlike a CV joint, this only needs to articulate in 1 axis. No rotation, no translation. Clearly this is not the complete assembly we’re seeing here however. There’s a wide range of much more fundamental mechanical problems that must be solved that this simple animation doesn’t show. There’s a number of other ways to seal an assembly like this as well. I’m very interested to get my hands on one to tear down. Maybe I’ll go patent diving and see what I find.
I mean, i don’t i had “innovating on the CV joint” on my bingo card for this decade.
Kinda neat, though i wonder about its limitations for output, i’d assume its strong enough to take the torque of Hyundai’s EVs, but they didn’t technically say what the overall design’s actual maximum is.
They didn’t innovate the CV joint, if you looks at the video this still has one, it’s just that it only handles the left/right movements.
So basically they delegated one of the functions of the CV joints with this new design, but it still has a CV that looks pretty much identical to what exists in current cars.
It’s only a concept. The Uni Wheel has to be a sealed unit for longevity.
Nah.
Going to suck being a first adopter of this lol
I understand how this allows the wheel to move up/down/side-to-side, but I don’t understand how the wheel turns (ie to turn the car left or right)? Unless the motor turns with the wheel?
Tank turns only
I was thinking the same thing.
I watched the video and at a certain point it shows that this is still connected to a CV joint. It’s just that the shaft connected to it is stationary now, and the up/down motion is passed over to the Uni Wheel assembly. The CV joint would only handle the left-right movements.
I saw that too, but it’s a single CV joint, and to be constant speed those need to be run in pairs…
Interesting. It still looks like it utilizes a CV joint for the wheels that steers but I guess it still allows for a much shorter axle?
Like everybody has been posting. I’m curious how robust it will be.