Flywheel/Encoder patterns

[Kalle Pihlajasaari]

Hi Todd,

> > A neat and very reliable solution to taking up the backlash is to mount
> > an eddy current brake on the shaft.  Much easier than providing viscous
> > drag.  All you need is a plain aluminium or copper disk rotating in the
> > gap of a horse-shoe magnet.  Like a old electricity meter. (If you had
> > the rotating disk meters in the US)  The principle was also used as the
> > speed control a#on the old but revered Garrard 401 record turntable.
> 
> 	Pardon my ignorance, but what effect does a magnet have on a non
> metallic element like aluminum or copper.
> 	How's it work?
> 	And what kind of drag can you expect from such a device?

Basically it is a generator with just one turn of copper in the 
magnetic field and this is shrotcircuited.  This generates drag
simply because the energy gets dissapated as heat and it has
to come from somewhere.  Eddy current merely describes the
fact that the single turn of copper is actually just within
the bulk material and not specifically defined.

The Thelma prop-shaft retarder that was mooted as an electrical
dyno break on this list a while ago works on the same principle
so it is scalable to large sizes.

The effect is  proportional to the velocity of the disk which is
why it can be used to speed regulation as in the turn-table.

In the backlash take up it seems ideal but I have some reservations
of it working suitably over a wide enough RPM range.  If you set
it for drag at low RPM it may cause to much at high RPM and 
cause wear or lots of disk heating.  It has a marvelous damping
effect on vibration as they have high speeds and are braked the
the most.

Cheers     *<<<-|
-- 
Kalle Pihlajasaari   kalle at ip.co.za   http://www.ip.co.za/ip
Interface Products   P O Box 15775, DOORNFONTEIN, 2028, South Africa
+ 27 (11) 402-7750   Fax: 402-7751    http://www.ip.co.za/people/kalle