Ask HN: Why do cars use turning wheels instead of independent motor control?

[gajus]

I was watching a YouTube video (https://youtu.be/6jzG-BMannc?si=GcuFJ0MvVKH-rDgL&t=189) showing an RC car with 4 electric motors, each individually controlled. The car turns left or right by speeding up or slowing down the motors on one side, instead of using traditional turning wheels.

This made me wonder: why don't we see real cars using this method?

[Festro]

So many reasons. All centred around the practicality of early engineering that remain relevant to some degree today.

1) 1 engine/motor is more efficient to manufacture 2) 1 engine means one point of failure 3) Early engines were not small or light enough to mount 4 of them on a vehicle and power to weight was an important aspect for those early vehicles, now it's still relevant for energy efficiency 4) Distributing energy to 2 or 4 wheels from a single point is very efficient mechanically, so there's not much lost in the process to heat, sound etc. So, why not? 5) Independent control often means more friction and wear because the wheels don't need to turn on their axis to make the vehicle turn, they just slow their rotation (causing friction). Regular cars still create friction when they turn but less.

[gajus → Festro]

All interesting and rational points. Thanks!

[theGeatZhopa]

If one thinks of a car at velocity turning to left, then the mass pushes forward and it needs to be pushed to the left. This is done with the wheels by friction and the changed line of contact with the floor effectively increasing the friction on the opposite side.

If the same is to be done with different rotation speed of wheels, then the friction force is the only force to push the mass to the left. And it needs to be much higher (with higher velocity even more higher).

So it's all about the mass and velocity and friction.

[brudgers]

Tracked vehicles such as bulldozers steer that way.