On 24/04/2017 10:44, Huge wrote:
On 2017-04-24, RobertL wrote:
On Thursday, April 20, 2017 at 8:11:00 AM UTC+1, Tim Watts wrote:

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I have no idea if this method is used by any car motors but I think some
trains do - you can hear the "whirrr... drop pitch whirrr" which I can
only explain as pole changing as the motor is otherwise directly
connected to the axel.

I have also noticed that sound and imagined it to be due to exactly what you have described. A neat way of 'changing gear' electrically instead of mechanically.

Having listened to Tube trains "changing up" as they accelerate out of the
station, and assuming that they can't possibly have mechanical gearboxes, I
found this quite interesting!

I think they used to run pairs of motors in parallel on starting and
switch over to series at higher speeds. That was some time ago and I
don't know if they still do.

--
Mike Clarke