Fwd: eddy current brake

[Kalle Pihlajasaari]

Hi Pete,

Long and dubious treatment of electromagnetic stuff.

> think the Eddy.effect is exlained enough, so lets go back where the idea came 
> from (can't remember who it was, but what it was):
> reducing/removing backlash of the ignition rotor!
>
> IMO, the ign rotor is a very good place to get the signals from, its (most of 
> the times)good accessable and you don't have to bore holes into the engine 
> block or clutch housing to gain acces for the sensor.
> 
> Back to Eddy. :-)
> Someone mentioned, the higher the RPM the higher the drag. In fact, thats 
> right, but only for a constant magnetic field.
> What would you guys think about using an AC driven E-magnet (no experience 
> yet, only thinking about) with frequency varying over RPM, in order to 
> establish a (nearly) constant drag over the RPM range?

I keep suggesting the distributor housing as I have no love of cutting
into engines, also as an electronics guy I try to make things nice
for me.

Some other bright spark suggested the eddy current brake which might
be the way to go with some more thought.

The dizzy is in older cars attached through just one helical gear to
the crank shaft so ther are no chains and belts to go wrong but in the
newer cars the coupling is not as positive.  I would not suggest putting
it behind a resilient link that has other laarge drag forces on it as
even if it is backlash free to the last link it is not positively
referenced to the crank any longer.

The Eddy current brake is a great idea as it has not real brain and
if one does not care about the extra drag at high RPM it will probably be
the answer.  There might be a way around that minor problem as well
using the skin effect.  Induction motors have an armature that
has a number of shorted turns of winding and the inducted voltage
created the armature field against which the starot works, that said
the shorted turns typically form a squirrel cage, (like a hamster
training wheel) BUT the bars have a specially calculated shape that
makes them thinner on the outside so that on starting the high frequency
relative magnetic field between the rotor and stator does not penetrate
deeply into the cage and only works against the outer thin portion of
the bars, this has an increased resistance so the starting current
does not become very large.  Now back to the dizzy drager, I was wondering
if slotting the disk would make it less efficient at high speeds as the
magnetic field would have to move from one finger to the next.  This would
be less efficient at low speeds to start with but might not increase
with RPM.  The slots must not cut all the way to the perrifery in any event.

Nuff said.

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