Roland Perry wrote:
In message e.net, at
10:29:44 on Sat, 14 Nov 2015, Mark Goodge
remarked:
I'm a little surprised that they claim it uses less power than a
conventional lift. If you have to raise a given mass through a
given vertical distance, shouldn't the answer be the same?

That assumes 100% efficiency in the mechanism. Not a safe assumption.

Yes, I agree about the *energy* consumption. But perhaps it gets away with
a less powerful motor, as it's slower than a normal lift.

In addition, the fact it's sliding down rails rather than hanging in
free space may alter the efficiency of the mechanism.

Yes. A simple thought experiment works here. It clearly requires less
energy to push a wheeled object horizontally than it does to lift it
vertically. So there's clearly also a continuum between 0 degrees = least
energy and 90 degrees (from the horizontal) = most energy, and therefore
something like 45 degrees = somewhere in between the two.

If it's the same weight, and with the same frictional losses as a
conventional lift, it would take the same energy to make the journey
[gaining potential energy in the process].

If the journey takes longer, the *power* (energy/time) would be less.

But it's complicated by the presence (or absence) of a counterweight,
which transfers its energy to the lift (and vice versa).

What the chap in the video is probably saying is that (without having
really thought about the physics himself) that the wattage plate on the
motor is less than you'd expect to find on a lift motor.

Yes, I agree. It probably has a less powerful motor than a vertical lift,
but because of the extra friction, uses more energy. But the extra energy
cost is probably trivial compared to the capital saving from not needing a
new vertical lift shaft.

Incidentally, for those who don't know the station, the
stairs/escalator/inclinator are right at the western end of the island
platforms, so the station building is beyond the end. If they'd fitted a
vertical lift, it would have popped up well beyond the western platform
ends, with the horizontal route to the platforms blocked by the stairs,
shaft etc. The inclinometer is a nifty and cost-effective way of dealing
with this problem.

I do hope I'll be able to spot whether or not there's a counter-weight when
I take a look at it.