Tuesday, August 16, 2011

Thinking About Cars: Stick Shift

I mentioned David S. Platt a couple of weeks ago, and his video that discusses the mindsets of people who use software: they don't want to use software, they want to have used software.  But before he said that, he used the example of driving, that the vast majority of drivers are much less interested in the act of driving than they are in the fact of having arrived.  They aren't interested in the mechanism by which arrival happens, so long as it happens.

Specifically, his example pointed up stick shifts, manual transmissions in cars.  Software engineers, at least the sample of them in Platt's audience, like them.  They are simpler in their function, more reliable, more efficient and offer more control to the user.  But they are more difficult to use.

There's a subtle but very real change in the function of the accelerator pedal when it's in a manual transmission car vs. a car with an automatic transmission.  Not the function of the pedal itself, but the function it serves to the driver.  To fully understand it, let's first look at the transmission itself.
Here's one stripped naked.  This appears to be a five speed (plus reverse).

The interesting thing is that it looks like all the gears are already meshing with each other, right?  Except that last pair at the right.  That last pair is reverse.  Looking at everything else, you just see four pairs, so you'd think four-speed transmission, right?  Nope: in a typical five-speed tranny, fourth is actually a straight-through drive.  Fifth is the first pair of gears on the left, the input gear is a tiny bit bigger than the output gear.  It means you have the output shaft turning faster than the input shaft: overdrive.  Slows the engine down for economical turnpike cruising.

But they're all meshing.  Except they aren't.  The greeblies between the gears are what make the actual engagement happen.  Without those being engaged, the gears just spin freely on the shaft.  And to make that engagement easier to do, there's a sort of mini-clutch inside the transmission that make the two different parts of the shaft match speeds, so there's no grinding when you shift.  You can, if you have the time, eventually get your car up from a dead stop and fully engaged in first, just by gently leaning on that synchronizer clutch inside the transmission.  Make no mistake, it's a terrible thing to do to a synchro, but it can be done.

If you drive a stick, you probably know about all this already, or at least some of it.  And that picture of shafts and gears and whatnot up there, you can probably correctly identify at least half of the various parts.

Now let's take a look at an automatic transmission.  There are a few different varieties and the newest, most modern automatics are radically different in design from the ones that started the automatic transmission industry fifty years ago.  And yet, there's one thing most of them have in common and so we'll take a look at that:
An automatic transmission.  Image from Topspeed.com

Now of course that image isn't of the transmission itself.  And if you drive an automatic, you probably don't really care.  Just so long as it works.  Reverse to get out of parking spaces, Drive to go forward.  Neutral between them to avoid unpleasant mishaps, and Park so you can get the key out.  What does the actual transmission look like?  I sincerely doubt the majority of automatic drivers know, and couldn't describe one if asked to do so.

In the manual transmission-equipped car, you use the clutch and accelerator pedals to decouple the transmission from the engine, match engine speed to transmission speed (if already moving), modulate the takeup of load onto the engine and increase then engine's torque output (if at rest) to get the car going and increase its speed.

You have to choose which gear.  You have to decide when to select it.  You disengage the clutch, let up on the gas, reengage the clutch and get back on the gas, all in a sophisticated, rapid and carefully timed dance.  Don't forget you're also steering and thinking about the brake while all this goes on.  The gas pedal is how you make the engine do what you want it to do, because you want it to do different things at different times.

In the automatic, you put the gear selector in Drive and go.  You use the accelerator pedal to control only the car's speed.  Not the engine's speed, the car's.  What the engine and transmission are doing is not a consideration you worry about.  Having selected Drive, your further involvement with the function of the transmission and engine is not required.  You want the car to go, and it's going.

Do you see the difference there?  The difference in wants.  The manual transmission car requires that you want different things to happen even as the car is going down the road and take the necessary action to make them happen; you already want to arrive at your destination, but operation of the manual transmission predicates a bunch of other wants in order to make that happen.  The automatic, however, doesn't.  It leaves you only with your original goal-oriented want.  It takes care of everything else.  There are other wants associated with the operation of the car, of course, but I'm not talking about them.

I prefer not to abdicate the responsibility for my car's proper operation.  In fact my favorite vehicle doesn't even tune itself on the go the way a modern fuel injected car does; if the fuel-air mixture is off it's up to me to figure that out and to fix it.  Fuel injection is constantly self correcting things like that and it's great - but I like to know what's going on.  If the engine tunes itself, then me knowing what's going on is completely unnecessary.

How long before the driver is completely unnecessary?  Not long, it appears.  You can have an automatic and abdicate the operation of the transmission.  You can have satellite navigation systems and blame an electronic device when you get lost.  You can have adaptive cruise control that brings your car to a complete stop with no intervention from the driver if it detects an obstruction.

You can have a car that drives itself.

Remember when it was up to the driver to operate the car safely?  How much more of that are we going to trust to automated systems?  It started with the automatic transmission, ostensibly to make driving easier, safer.  But I think it's accelerated the surrender of personal responsibility worldwide.  That's a larger question about human culture in general, a much bigger question that I'm not ready to tackle.  And with hackers, EMP attacks and the occasional solar flare, I don't think it's a great plan to give over so much responsibility to devices that are fallible.  If we learn to rely on the machines, we don't have to learn to rely on ourselves, do we? 

Shift for yourself.  I said it before, but it's worth repeating.

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