Topband: Yikes! Heavy snow, freezing fog and 23 degrees F in Raleigh, NC

[Tom W8JI]

> Gee, that should work great, Tom! How is the shaft rotatoion speed
> controlled to maintain 60 Hz?
>

Tractors are like almost any other thing that has an engine and a manual 
throttle control, including lawn mowers. They have engine speed feedback 
that works like "mechanical ALC".  It isn't like car or something that has 
an open loop system with a human stuck there pushing a pedal to regulate 
power with varying loads. If it didn't have that feedback system, a person 
would have to constantly adjust the throttle when mowing or plowing. I guess 
you could think of it like a cruise control, except unlike cruise it is the 
primary throttle and has wide dynamic range. Lawnmowers regulate the 
carburetor throttle plate with a connection to a flapper plate. Air from a 
finned wheel hits that plate. The plate works against a spring, and the 
throttle just changes spring tension. The tractors around here are a little 
more sophisticated, but same basic concept. They stay put pretty good. 
Within a Hz or so at the most.