[ExI] not that rare earth (part 2 of at least 2)

[spike at rainier66.com]

-----Original Message-----
From: Keith Henson <hkeithhenson at gmail.com> 
Subject: Re: [ExI] not that rare earth (part 2 of at least 2)

The worst course I had was a controls course.  At the time, I was working part-time for a geophysics company and lashing up a 400 Hz 20 kW aircraft generator to a VW engine to power field equipment.  So I asked the instructor how I should go about controlling the speed of the engine.  His response was, "That's a real-world problem; we don't work on those".  Needless to say, my enthusiasm for the class vanished.

A friend of mine suggested a phase shift circuit, 4 1/2 henry inductors, 4 1/2 mfd capacitors, which gave a 180-degree phase shift at 400 Hz.  I wired one phase of a two-phase motor to the 400 Hz power and the other to the phase-shifted 400 Hz.  The geared-down motor ran a link to the carburetor.  Zero to 15 kW, the generator dropped about
5 Hz.  Impressive sound for a VW engine running at 4000 rpm.

They used it for years.

Keith




All that cool interesting control theory they taught us was perfectly useless for the dirty real-world application of rigging up a generator.

We math hot-asses felt we were omnipotent, could solve any system of differential equations, and oh we were good.  I worked on motorcycles and cars.  So I had it covered.

But given a real-world engineering problem, such as using control theory to rig up a motor to a generator?  Forget it.  Those two disciplines were unrelated.

Keith the way I would have gone about that is with some caveman vacuum-operated flow restrictor on fuel line (which would allow the engine to rev up under sudden no-load condition) or some primitive embarrassing cutout switch made from the centrifugal clutch of a scooter.  I woulda felt my tuition fees were wasted.  Had it been toward the end of college, I would have gone completely digital with that task: taken a signal off of the distributor, controlled the engine speed using software.

Fun question: suppose you have a VW engine, very common in those days, and no computer.  What is the best way to run a generator with it?

Aside for the younger set: the VW bug had the simplest engine in the history of mankind: air cooled, bolted aft of the transmission.  If it failed, you could unbolt it, replace it with a spare engine, go to any local shop which every small town had, get them to rebuild or repair your spare engine at a very modest cost.  VW engines could be used for any number of alternative tasks besides running your buggy.  There has never been anything quite like it.

spike