Home » Our Suspension Engineer’s Thoughts On The Tech And Potential Engineering Compromises Behind This ‘Crab Walking’ Hyundai Ioniq 5

Our Suspension Engineer’s Thoughts On The Tech And Potential Engineering Compromises Behind This ‘Crab Walking’ Hyundai Ioniq 5

Crab Top

Are you tired of parallel parking your car every time you go to the store? Do you think your local driving instructor is wasting their time testing you on your parallel parking skills? Do you wish cars could do more than just drive forward and backward? Well, auto supplier Hyundai Mobis may have the answer for you as early as 2025 with its “e-Corner” technology that would allow their car to crab walk. The Bangles would certainly be proud!

How I Think It Works

First things first: Watch the video above. From what I can gather, the system looks like it uses electric hub motors and what appears to be a mechanism that can rotate the entire suspension a full 90 degrees. Put this at all four corners and the result is a car that can drive sideways or spin around on its own axis.

Crab1

What you are seeing is the rear wheel in an almost fully rotated position and you can clearly see an upper and a lower suspension link connected to some sort of aluminum casting and to a knuckle of some sort that is buried inside the wheel. The entire assembly looks like its connected to an actuator at the top which is likely the device that rotates the whole thing. The reason I think the whole assembly has been rotated is that the suspension links are clearly more or less perpendicular to the wheel in the image above.

The orange cables are the high voltage cables that power the hub motors.

(Sidebar: High voltage cables in all EV’s are colored orange to clearly differentiate them from the standard 12V wires so that emergency personnel know what’s what when they come across an accident involving an EV. So, if you see orange cables in a car, it’s best not to touch them).

[Editor’s Note: It’s worth pointing out that in 2021, Hyundai Mobis first showed off a revised version of its 2018 e-corner design, with the revision enabling 90-degree turning. From the company’s 2021 press release:

Hyundai Mobis announced its success in the development of new technology, the e-corner module, which integrates the steering, braking, suspension and driving systems into a wheel. 

[…]

The biggest advantage of the e-corner module is that it does not require any mechanical connection between parts, which thereby allows a better use of space within vehicle. Not only does it make it easier to change the wheel base, but it also ensures much more flexibility in designing the direction of doors and the size of the vehicle. It is essential for making PBVs that are designed to provide mobility services, for example for cafés and hospitals.

Here’s a clip from that press release:

And here are a few photos showing the company’s “e-corner” module:

Screen Shot 2023 01 13 At 9.08.24 Am

Screen Shot 2023 01 13 At 8.59.25 Am

As EV-focused website Electrek notes, an Israeli startup named REE Automotive has shown a similar technology:

Anyway, back to Huibert. -DT]

Potential Compromises Associated With This Technology

Now that we know how Hyundai is likely accomplishing this party trick, we need to talk about if this is actually a good idea. One of the primary functions of a car is to protect its occupants in the event of a crash with an object like another car or a tree. This is done by placing structural parts called rails in strategic places at the front and rear of the car. When the car hits something (or gets hit by something in the case of a rearend collision), these rails crumple in a very controlled way to absorb the energy of the impact. Since protecting the occupants in a crash is such a critical function of a car, there are many government regulations as well as industry standards that cover the ability of the car to perform this function. These regulations and standards differ slightly by country and region, but all require that the basic box that forms the passenger compartment remain undeformed within specific limits. The floor under the driver’s feet can only deform so much, otherwise the driver’s ankle could be damaged. The steering column can only move so much, otherwise the airbag would end up out of position and the driver could be hurt. Those are just two examples of the many requirements automakers must meet when they design a car.

Look at the image below. The passenger compartment is the box in red that surrounds the occupants. This is the box we are trying to protect to minimize injury to the occupants.

Passengerbox

The blue parts are the rails that stick out and support the front and rear bumpers. If we place these rails all the way outboard, they line up with the edges of the passenger box, like this:

Rails1

You can imagine what would happen in a crash. The rails would impact the object and crumple, pushing directly on the sides of the passenger box. The box itself would likely remain mostly intact.

Now let’s imagine the blue rails are located right in the center of the car, like this.

Rails2

If these rails hit something, they would push right in the middle of the passenger box and it’s easy to imagine how this would cause the front edge of the box to buckle rearward and into the passenger compartment. To prevent this, we would need to make the front edge of the compartment extremely strong and consequently extremely large and more expensive.

So why not place the rails right out at the edges of the car? The problem is that we need a place for the tires to go. Not only that, but we need space for these tires to move up and down and in the front, rotate with the steering as well. This has the effect of pushing the rails inboard and away from the edges where we really want them to be. Of course, the more the tires steer, the more we need to move the rails inboard to make room for them.

Now let’s get back to the Hyundai. In a standard car, the front tires steer approximately 45 degrees at full lock and the rear tires don’t steer at all. This means the rails will look something like this:

Rails3

But now let’s suppose we are able to steer to tires a full 90 degrees, and not only that, but we will do this in the front AND the rear. Now the rails would need to look something like this:

Rails4

You can see how our fancy crab walking suspension has pushed the body rails way far away from where we would ideally like them to be. This makes the job of managing the energy of a crash considerably more difficult.

But there are also more practical reasons why turning the suspension a full 90 degrees may seem like good fun but may not really be all that practical. Look at the potential space we have for luggage. EV’s have a distinct advantage vs ICE cars in that they can often have storage space in the front of the car, i.e., a frunk. Looking at the difference between a normal car:

Frunk1

 

and a crab walking car:

Frunk2

We can see that the space available for a frunk is a bit smaller in the crab walking car. I could probably live with a smaller frunk, or no frunk at all, but when we look at the rear trunk space, it’s a different story. Here is the potential space in a normal car:

Trunk1

And here it is in the crab walking car:

Trunk2

The reduction in floor width in the crab walking car is huge and to me borders on unacceptable. There is a big loss of storage space caused by having to provide space for the rear tires to steer.

Is It Worth The Tradeoff?

In summary then, we have a car that can drive sideways and can turn on its own axis, but we’ve lost a bit of frunk space and a massive amount of trunk space. We’ve also given the engineers a much tougher job making the car safe in a crash. From my personal experience, if you make the engineer’s job tougher, they will probably end up making things heavier and more expensive. All of that because someone is bad at K-turns and parallel parking?! Doesn’t seem worth the trade-off to me.

Now let’s hear from you all. Do you think this is a good idea or is it a party trick best left in trash heap of innovation? Do we really need a car that can drive sideways?

All photos: Hyundai Mobis

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46 Responses

  1. Is this better than the Mecanum wheels? I see them as similar items in my eyes, and I see they both have major drawbacks, but for the consumer, I would think this would be better. Of course this is going to really affect the driving feel of the car, and I wonder what this does to the NVH.

    1. A set of mecanum wheels big enough to carry a car, with roadholding and ride characteristics comparable to conventional tires, would probably cost tens of thousands of dollars if it was possible at all.

  2. This also seems like it would seriously increase unsprung weight, while also introducing new potential failure points and driving up costs, in exchange for a neat party trick that nobody actually asked for.

    1. It’s an issue I have with hub motors in general. You still need brakes and bearings so all you’ve done is add the weight of a traction motor and removed nothing.
      The high voltage wires going out to the hub also have to articulate with the suspension which would seem to be a durability concern.

      1. I can’t imagine the shock (as in high G, not damping) forces at the wheels would be good for the motors themselves either.

        And imagine hitting a pothole and having to replace a motor!

        1. What all that mass will do is force the tire to deflect instead of the suspension. It will result in more pinch flats unless you compensate with a taller tire sidewall but that then limits what you can do with wheel diameter. Higher wheel mass (unsprung mass) gets back to some of the prime reasons we got away from solid axles in the first place: axle hop, wheel tramp and suspension shake over impacts.

  3. stop trying to make omnidirectional cars happen it’s not gonna happen

    I worked on a pretty similar system about 15 (yikes) years ago as part of the MIT CitiCar project, if anyone remembers the press releases about those little folding bean cars that were being studied in conjunction with the government of Spain. For those LSV/neighborhood car things, I could see it being a novelty. But as this article says, the tradeoffs are absolutely immense and I don’t see it being feasible in highway-going vehicles.

  4. From an engineering perspective, this is interesting for applicability to robotics and specialized autonomous vehicles and such, from a car buying customer perspective, this is like most new things and is something I wouldn’t want to touch with a 10 foot stick. Instead of adding all sorts of extra complexity to vehicles to do something that might be useful 1% of the time, it would be nice if someone would target simplicity, especially in EVs- give me a car that can be expected to go 200,000+ miles with only trips to the tire shop, and maybe 1 maintenance trip to the dealership to replace the coolant. Sometimes the best engineering solutions are the elegant ones that greatly simplify the design.

      1. You’ve kind of summed up what I was going to say; there is a market for four-wheel-steer vehicles, and it’s in industrial settings. Where they already exist.

  5. Not liking this system. For starters, since it is presumably controlled by a computer, there’s a large potential for mechanical mischief built in from the start. Granted, automotive computers seem to be very reliable, but a software glitch or some hardware screwup could leave the driver, well, inconvenienced. Combine it with “self-driving,” and the likelihood of problems only increases. And that doesn’t even address all the drive mechanisms and the chances of them messing up….

    How much weight does all this add? Not just the means for making the wheels/suspension pivot, but also the chassis reinforcement the author (rightly) suggests would be needed.

    To me, this looks like a solution in search of a problem.

    You could really wig out the techs at the alignment shop, though!

    1. You could argue the chassis structure would probably be there anyway in one form or another, but those motors rotating the whole shebang will be heavy and there are 4 of them. You can kind of see in the photo how big they are.

      1. I don’t think I’ve parallel parked since my driver’s test.

        Illinois replaced parallel parking with backing into a parking spot on their test, which I thought was interesting.

  6. What you guys talking about, it is the future in the world of semi-passive low skilled drivers.
    It may actually make sense for a small low speed urban vehicle in tight confines, maybe better than a Morris Minor.
    What’s wrong with a powered central mounted steerable wheel and and shopping cart casters with brakes? (-;

  7. This kind of “innovation” is driving EV costs higher than they need to be. Greater adoption rates would occur if there were a greater focus on getting safely and efficiently from A to B. Scrap the half dozen screens per car, disco dancing, self crashing, and gaming systems. This would reduce vehicle weight, lower costs, and increase range. Let’s begin with the car I have, just electric, and build out from there.

  8. Seems like maybe it could be useful for large box delivery trucks because they can be difficult to park in some situations but I’d imagine the parts would have to be incredibly tough to stand up to pivoting while supporting a heavy load. The weight would be terrible for efficiency and reduce the payload so maybe there’d be some niche applications where maneuverability is important on something that can also drive on the road but that’s about it. Maybe some type of crazy off-road vehicle could use it?

  9. Yeah, I don’t see me ever buying a car I intended to take on the highway with this.
    BUT, you gotta admit that the donut potential is absolutely insane. Would love to see James Garner updating his signature move in one of these, too!

  10. Wouldn’t the use of hub motors also be a significant compromise? Don’t they add a lot of unsprung weight? Does the current production Ioniq use hub motors? I don’t recall seeing that mentioned.

  11. I’m no engineer (I tried, but wasn’t meant to be), but if you absolutely haveto add crab walk or whatever, why compromise the main systems to do it? Those big wheels are for moving at full speed. Add some auxiliary wheels that pop in place and be done with it. One under each jack point, job done. You can even use them to lift a corner to change a tyre! Gimnicky, for sure, but won’t eat as much cargo space, no structural compromises, and no unsprung weight!
    Please note that I’m not saying this is a good idea by any means, it is just less problematic than the one demonstrated here.

      1. Actually even earlier; this system using the spare tire as a parking aid dates back to the 1930s (although it wasn’t patented until the 50s).

    1. No,that IS a good idea! So much cheaper.So easy to integrate
      The only problem i foresee is the smaller wheels needed to make it work.They will have greater ground pressure so may be unusable on soft surfaces.
      I cant yet see any other issues…?

      1. I thought about that carts that ferry the bodywork during restorations, or even the way they move clay models – fits the intended purpose, at least 🙂

  12. Inspector Gadget and people who can’t park are the only one who need this. (And by the way, my 3 ICE cars with frunks dispute your “EVs have an advantage” claim on frunks.)

  13. I could see this as a really beneficial tool for low speed commercial purposes, not for something being driven by the average joe as a daily driver. Actually, this could be really handy on something like a fork lift. It’d be nice to be able to shift more than a couple inches left and right with forks

    1. Such a thing already exists. It’s called the Mecanum wheel, and it allows exactly what you describe. It’s not really suited to street use though.

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