this post was submitted on 02 Dec 2023
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From a mechanical standpoint, the new bearing saves a nearly negligible amount of space. Splitting the motor up and moving it to the notoriously wasted wheel well space is what clears up the center of the frame. Still very cool. It's basically a single output differential, which is already quite compact. No need to split the rotation for turning since the wheels rotation will no longer be mechanically linked.
But eliminating the long half shaft that accompanies the CV joint is what allows that space to be used.
I mean you're not wrong, but without separating the single motor to one at each wheel, you'd still have to translate the power from one point to each wheel. The uni bearing doesn't provide that benefit. Separate motors DOES. And tuned and articulating short shafts are not a new thing. So even without this new bearing as long as you had separate motors for each wheel all you would have is a short CV shaft between the motor and the wheel. Hell why not save all of the space and just incorporate the motor into the hub??? Since BDC motors are more efficient when wider and smaller, it would be very easy to fit them within current day hubs.
I mean, don't get me wrong, I honk for planetary gear designs every time. So I'm not knocking this design. It's simple, machinable, and direct. It's brilliant for what it is. It's just not the space saver that they are touting it to be. The video literally showed two seats side by side with a bed in the back. Unless kia started making a suburban, I'm just not that naive.
Having these gears in the hub instead of a motor would decrease unsprung weight.
I didn't think about that. Thanks for pointing it out.
~~The gears are necessary to allow the wheel to move without having to move the input shaft.~~
Edit: sorry, I misunderstood your comment. I agree.
Somehow I thought you're saying the gears should be attached to the motor.
It directly replaces the CV, so it's the thing saving the space. Sure, if there was still only one motor, and a shaft connecting the two sides, less room would be available. But the space saving, and the reason why splitting the motor in two makes sense in the first place, is the uni wheel.
Also, yes, there are shorter CV joints, but they lose efficiency the shorter they are, because they need to translate through larger angles.
As to why putting the entire motor into the wheel isn't a great idea for cars is because you want to keep as much weight of the vehicle on top of the suspension. If the motor is in the wheel, ride quality will suffer due to the increase of unsprung weight.
Ah, really good points. Thanks for the perspective. My expertise (if I may so generously call it that) ends at the manufacture and assembly processes. Thanks for the perspective.
Honestly, I get most of my knowledge from watching a bunch of youtube videos, so it's not like you're talking to an engineer or anything haha
But I do usually like to pick out the more technical videos, explaining the theory behind all this, so I guess I picked up on some things ^^