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comment by b_b
b_b  ·  3531 days ago  ·  link  ·    ·  parent  ·  post: The Mercedes Robo-Car That Made Me Want to Stop Driving

Forget the interior; what about the exterior? Why should there even be a concept of front and back anymore? It's not like there's a transmission that dictates in which direction the car moves fastest. For single gear electric motors whose direction is dependent on the direction of the current, can't we imagine a perfectly symmetrical vehicle that doesn't have a concept of reverse? LED lamps means that either side can shine red or white. If no driver is required, then we needn't worry about sitting in the driver's seat. Therefore, with all these factors, front and rear are meaningless. Perhaps from an aerodynamics perspective it makes more sense to have a dedicated front end, but aerodynamics aren't a big consideration for commuter type vehicles anyway, as the fuel economy is mainly dictated by stopping and starting, and not drag at high speed.

Anyway, I think I'm the only person left on planet earth who isn't looking forward to the day when everyone can watch Keeping Up with the Kardashians on their morning commute. I have very few pet peeves I loath more than driving behind a minivan that contains children watching a video of some sort. At least driving forces us to focus on something. I find it hard to believe that we'll have a better attention span for anything once our main barrier to TV watching during non-work hours is removed.





kleinbl00  ·  3531 days ago  ·  link  ·  

For any four-wheeled vehicle there will be two wheels that turn (or turn more). Doing it any other way leads to radical instability.

For any vehicle with more than one axle, one of the axles will absorb 80% to 95% of the braking duties.

For any vehicle that travels through a fluid such as air, there will be a favored aerodynamic direction. Aerodynamics does not reward symmetry.

Brakes go in front. Wheels that steer go in front (this is why anyone driving a forklift any great distance does it in reverse). Streamlining goes in front, K-tail goes in back.

b_b  ·  3531 days ago  ·  link  ·  

Except for the aerodynamics, the other problems are easily solvable by a little extra hardware and a little extra software. You put four wheel disk brakes (which many performance cars already have), then let the computer decide which two get the most pressure. Then you put four wheel steering, with similar computations. Sure it would add expense, but these things are already going to be phenomenally expensive for a while.

The aerodynamics, as I already noted above, are problematic, but not as problematic as it might seem. You only really need a fast back when you're racing, and nobody is racing a self driving car for fun on the weekends. Drag is dependent on speed, and I can't see anyone building a performance car that is autonomous (beside Tesla, but that's an ego thing), because what's the point?

kleinbl00  ·  3531 days ago  ·  link  ·  

Here's where you're wrong.

    Except for the aerodynamics, the other problems are easily solvable by a little extra hardware and a little extra software.

but there's no reason to solve them. There are no vehicles that are ambidextrous. Not even Amazon's warehouse bots are ambidextrous. There's zero need here other than "it would be neat if."

    You put four wheel disk brakes (which many performance cars already have), then let the computer decide which two get the most pressure.

Right. Sure. And they're the exact same size, right? The rear discs aren't any smaller than the front? And the venting is symmetrical, right? And the geometry of pad and spindle are symmetrical, right?

This is just physics: You put the front brakes in the back and you've doubled or tripled the weight of your back brakes for no reason other than "I don't believe in 'back.'" Never mind the fact that you now have to gusset against two different directions of stress, rather than one or the fact that the design of brake pads is asymmetrical to improve cooling, reduce ablation and minimize weight.

It also isn't up to the computer as to which gets more pressure - when you decelerate the center of gravity shifts forward. It just does. This is why you turn tighter if you accelerate into a corner; the CoG moves backward. So you can either design for efficiency or you can refuse to choose.

    Then you put four wheel steering, with similar computations.

Except that the added complexity of steerable, driven wheels adds an easy 150% to the assembly weight of an unsteerable wheel. And you're never going to use it. It's possible to parallel park a 4-wheel-steered vehicle such that it can't be unparked - it was a going concern with Mules.

    Sure it would add expense, but these things are already going to be phenomenally expensive for a while.

Disc brakes and CV joints aren't cutting edge by any stretch of the imagination. The expense isn't in the management which is also old hat. The expense is in the physical components.

    You only really need a fast back when you're racing, and nobody is racing a self driving car for fun on the weekends

Also not true. Aerodynamics determine fuel efficiency and once you're in a turbulent regime (in air, anything over 7mph) you're there. The overwhelming majority of aerodynamic improvements instituted in the past 50 years are all about efficiency - that's why spoilers are generally articulated these days, so they don't cost you 10MPG when you don't need them to.

Gentle reminder: I have a degree in this shit and have built 4 electric cars. I don't do it anymore but I did the hell out of it for a while. Symmetrical cars buy you nothing and cost a whole lot from a physics standpoint, not an electronics standpoint.

mk  ·  3531 days ago  ·  link  ·  

You know what would be a real trip? Autonomous motorcycles.

My wife and I were positing a Zip Car like service with auto-mopeds that drive up to your house when you need them, but you must drive them yourself. Since they are so light and slow, they are far less likely to kill people when in autopilot.

kleinbl00  ·  3531 days ago  ·  link  ·  

Fuck everything about that.

Any mode of transport depending on you knowing when to lean will never be autonomous.

mk  ·  3531 days ago  ·  link  ·  

Yeah, it would be a death trap.

But there's no reason they can't drive themselves up to your house.

kleinbl00  ·  3531 days ago  ·  link  ·  

...other than the fact that the weight used to shift stuff around goes where the people go.

mk  ·  3531 days ago  ·  link  ·  

No, check out the video, no shifting weights. It simply leans in when the wheel turns, and acceleration keeps it from falling over.

kleinbl00  ·  3531 days ago  ·  link  ·  

Okay, more precisely put:

They're using weight where the people go in order to use the geometry the way it's intended. Yes, they're dinking with the steering column to accomplish their balance. That's why it's wobbly as fuck at low speeds - they don't have the balance one would get from riding it.

If you take that bike and try to put a person on it, that weight needs to move. It can't stay where it is.

There's an easier way... but it's about as dorktastic as a self-driving Vespa.

mk  ·  3531 days ago  ·  link  ·  

That's an interesting point. Forwards and backwards might be arbitrary when the human isn't the head of the motorized horse. Now I wonder about anterior/posterior symmetry in aerodynamics...

I'm not going to be watching the Kardashians. I'm going to be replying to your grumpy comments.