This week, I got a
chance to drive a Tesla electric roadster on the twisty mountain roads above Silicon Valley. All electric,
lithium-ion, zero-to-sixty in less than four seconds – not that I stopped at
60. (Whee!)
The electric motor
feels very different from an internal combustion engine. Much smoother. In my
regular car, if I’m driving at 50 mph and then floor it, I get a jerk of
acceleration right away, and then a second jerk an instant later, when it
downshifts, and then a surge. In the Tesla, it was just continuous, smooth acceleration.
This makes the car track wonderfully through curves. The jerks in a normal car
sometimes threaten to shake loose the wheels if you hit the accelerator too
much at the wrong time, but in the Tesla, the power is a smooth surge no matter
how quickly you jam the accelerator.
In my regular car,
if I suddenly let off the gas after accelerating hard, I get a reverse jerk as engine
compression braking suddenly slows the vehicle. In the Telsa, no jerk at all.
The acceleration stops, and then a gentle deceleration kicks in. An induction
motor has no natural braking (no cylinders to compress), but it’s nice for the
car to slow down when you lift off the accelerator, so they programmed in some
regenerative braking. In a regular car, the amount of deceleration is a side
effect of cylinder size, compression, gearing, and so on, but in the Tesla,
they get to program in exactly what feels right. Turns out that people prefer
just a bit of deceleration at high speeds, but at slower speeds, for street
driving, people like more deceleration.
In a sense, driving
a Tesla is like a strange form of virtual reality. The sensations I’m feeling
are designed by a programmer who has full control of the mapping between accelerator pedal and torque. (In fact, one goal of the drive was to get feedback to the
Tesla engineers on their firmware choices.)
Another example is creep, which is the way that cars with
automatic transmissions creep forward slightly when you lift the brake. In a
regular car, that’s a natural side effect of how the transmission works, but in
a Tesla, they decided to maintain that same behavior for safety, so that you
won’t get out of the car with it turned on. Lift the brake and it “reminds”
you, by creeping, that it is still running.
I shouldn’t say virtual reality, because I was in a real car feeling real acceleration, but it has that same designed-by-a-programmer feeling that virtual reality does. At first I thought that designed reality might be a better description, but an internal combustion engine is certainly designed, and the acceleration and engine braking profile is something that designers take into account. I think the real difference is the level of direct control that you have with programming, as compared to the indirect influence you have when you design with physical materials.
What enables that feeling of programmed reality in the Tesla is the flat torque curve of their electric induction motor. Its torque is almost perfectly flat from 0 to 6000 rpm and then drops linearly to 50% torque at 11,000 rpm. An induction motor can generate full torque even at 0 rpm, and can go from no power to full power in milliseconds. By contrast, an internal combustion engine can’t generate any torque at 0 rpm (it stalls), and it delivers full torque only in a narrow range.
In order to generate programmed
reality, you need a physical medium that is sufficiently malleable, like an
induction motor or an LCD display, to give you full programmable control. Perhaps the real lesson here is that – given
the flexibility of programmed systems – we should have a higher expectation of
usability and design elegance for programmed
reality. With great power comes great responsibility.
