"MIG" wrote in message
oups.com...
On Apr 26, 4:59 pm, "michael adams" wrote:
"peter" wrote in message

oups.com...

I could spend my spare time reading an improving book. Instead I find
myself wondering why do some escalators have the handrail running
slightly faster than the steps? I've noticed this on and off over the
years, and currently am most aware of it on the Jubilee line
escalators at Westminster. If you step onto the escalator at the
bottom and keep holding the rail, then by the time you reach the top
your arm has been pulled about 18 inches forwards relative to the rest
of your body!

Assuming the same motor drives both the handrail and the steps, I
would have thought it takes some quite complex engineering to achieve
this feat. Why???

Presumably because the handrail follows a larger radius than the steps,
and thus has a larger circumferance, and so travels a greater distance
for each rotation of the motor.

michael adams



I can't see how that explains it; it should still stay level with the
same step surely?

(If you you drew a line along the radius of a disc,
the line wouldn't split up as it rotated.)



Instead of an escalator just imagine a large cable drum, where you
were walking on the hollow hub in the middle. The circumferance of
the outside edge of the drum which would represent the handrail
would probably be at least twice as long as the circumferance
of the hub which represented the tread. So your hands would probably
need to cover twice the distance of your feet. i.e they'd be
twice as busy.

If the sides of the drume was large enough you for you to just roll
along on the hub and stay in one place while hanging on when it
rolled upside down then you woudn't need to move at all. And the
same on the escalator.

But you don't. Both distances are flattened out and the distance
around the handrail - as on the drum is that much longer than that
on the tread.


michael adams

....




with




It is a common phenomenon, although I thought it affected the older
escalators more.

There must just be different gearing between the motor and the
handrail, assuming it is the same motor.