[GreenKeys] M28 Stunt Box

[Jim Haynes]

On Sat, 2 Mar 2019, Roy Morgan wrote:
>
> I suspect mechanical wizards who designed the teletype equipment were 
> not real mad geniuses or from an alien race.  I suggest that:
>
> 1) All had an innate inclination toward mechanical stuff, and did NOT go

This became a weakness toward the end of the company's life.  One example
comes from Model 37.  Model 37 was intended to succeed Model 35 and to
operate at 150 wpm with upper/lower case ASCII.  Now one of the hardest
parts of the Teletype printer to design is the selector, the mechanical
serial to parallel converter.  Model 28 was designed to operate at 100
wpm with 5 level code, or 7.42 unit code including the start and stop
pulses.  This worked quite well.  Then Model 35 was Model 28 adapted to
use 8 level code so the bits were correspondingly shorter.  And in Model 
37 they were only 2/3 as long as in Model 35.  Recall that the selector
uses a narrow cam to sense the state of the selector magnet armature
in the middle of each bit.  You can't make the cam narrower and narrower
and still be durable.  So the Model 37 selector was up against the wall
in meeting the required tolerance for distorted signals.

But these mechanical guys were the best in the business, and they knew
it, and took on the challenge of designing a mechanical selector for
150 baud.  It was a hard job and took a long time and was one of the
reasons the machine was late in getting into production.  They could
have made the machine parallel input and used an electronic selector,
which would have other advantages.  It would have cost somewhat more
in those days before integrated circuits, and it wouldn't have
been manufacturable with punch presses and hardened steel, but it would
have been duck soup to design, and it wouldn't wear out or break.

A project which is challenging, which motivates the engineers to exert
their best efforts, in not necessarily a project which should be done.