James Wilkinson Sword wrote:

On Sat, 10 Mar 2018 09:36:36 -0000, Chris J Dixon wrote:

The Natural Philosopher wrote:

I thought electric trains connect(ed) their motors in parallel mode to
start off, which is why they always (used to) start with a jerk.

Series, more like, to limit current.

That's right, start in series, then later switch to parallel.

Jerk is just the inability to reduce it ENOUGH.

Quite so. Until the advent of power electronics in rail traction,
then control was generally either by tapchanger, for ac supplies,
or series resistors for dc schemes. In both cases the steps (or
notches as they are known) are finite, not continuously variable,
and there will always be jerks. The art of the design engineer is
making them as smooth as practicable.

Somewhere in the loft I have the notching curves I drew for the
Class 313 rolling stock.

I wish someone would put soft start onto conveyor belts in supermarkets.
Actually it is kinda funny to put milk or bottles of vodka upright then
laugh when the supermarket has to replace them for free.


I expect they sometimes wish the mentally subnormal had minders to tell
them to put glass bottles on their sides.

--

Roger Hayter