Re: (ET) Fine Control

["Bob Murcek" <rmurcek geisinger edu>]

Interesting.  If the upper positions are just for field-weakening, there's 
probably a good chance that a clever person could add the weakening 
controls from a 20 to a 12.

>>> "Christopher Zach" <czach computer org> 7/29/2002 2:07:00 PM >>>
Well, they used the same physical tractor parts, but the speed control is a
truncated version of the one used on the E20. Unlike the E20, there is no 
FW
circuit, the field is basically wired into the main power (full field all
the time) and all of the extra relays just aren't in there. Result is a
simple system with no high-end speed avail, and thus the 30 cent welded
plate as opposed to building a whole new part.

Chris

----- Original Message -----
From: "Bob Murcek" <RMURCEK geisinger edu>
To: <elec-trak cosmos phy tufts edu>; <wilbett earthlink net>
Sent: Monday, July 29, 2002 1:56 PM
Subject: Re: (ET) Fine Control


I'm fairly certain the plate had been welded on at the factory to reduce 
the
number of speed positions to the three that an E12 has.  Like perhaps GE
used the same control assembly for all the tractors and just blocked out 
the
upper positions when the assembly was used on an E12.  Or perhaps you're
right and someone replaced a bad E12 assembly with one from some other
tractor.  That may well be the case since the plate is very obvious when
looking down at the slots the lever moves in, and I would think that 
someone
would have jumped into this thread and volunteered that their E12 had a
plate.

I was too lazy to use a real pot.  I would have had to find an appropriate
gear to connect the pot to the big gear on the assembly.  Worse, since the
big gear continues to turn in the same direction as you go from full 
forward
to zero to full reverse, you'd actually have to use two pots and switch
between them or do some really tricky op-amp work.  And then you'd need a
mounting bracket for the pot(s).  It just sounded daunting.

>>> Bill Alburty <wilbett earthlink net> 7/29/2002 12:35:42 PM >>>
Bob,
I assume your E12 came that way, modified by someone else, since you
chiseled off
the plate.  Apparently you have a neat solid state controller fed by
discrete
speed commands. Why couldn't you put in a real potentiometer ( disconnect
the
micro switches) on the speed lever and get smooth speed changes out of your
SS
Controller. I'd like to have one. The pot apparently only has to handle 1/2
watt.

    I haven't opened up my speed lever yet to count my micro switches.

Bill A.