I recently purchased some new and used foot speed controls for universal
type motors, the AC/DC brush and commutator type motors commonly found in
many Foredom and other flex shaft motors, early Dremel Moto and other brands
of rotary tools.

The oldest one I bought was made in the '40s possibly, and uses a carbon
resistance type element.

A Foredom model SCR-1, made about '84, has a circuit board with about a
dozen fairly common components on an actual circuit board.
The clever characteristic of this unit, is a unique twisted section of flat
steel, making a helix (kinda like the antique toy tops used a twisted
"screw" to make the top spin as it was pushed down from the extended
position).
This helix is attached to the movable pedal (with a swinging mount to allow
it to travel in an arc), and fits into a slot in a low cost pot (the type of
PCB-mounted pot with a slot that allows the helix to pass thru it) . As the
pedal is pushed down, the pot wiper moves clockwise as the helix twist
contact area changes, and then CCW as the pedal is allowed to raise to the
stop position.
A hole in the ciruit board under the pot allows the helix to pass thru far
enough for the pot to make a full sweep of the resistor track.
The start switch is activated by a flat section on the rim of the plastic
pot disk/dial, it's open when the pot is at zero, then as the pot is
advanced, the switch is closed as the flat moves away from the switch (the
flat spot functions as a low spot on a cam lobe).
The switch is just stamped from plated steel to fabricate the stationary,
and the moving arm part of the switch.
This model needs a spring to return the pedal to the up/stop position.

A new Foredom model FCT-1 doesn't have a circuit board or a spring, they
simply utilize a switch from a variable speed 120VAC power tool (such as
drill, saber saw, sander etc).
The switch plunger is oriented pointing up at the moveable pedal, so there
is no need for clever levers, fulcrums, springs or anything other than the
switch. In the full upward position the outlet power is off, press the pedal
down and the tool starts and speeds up as the pedal is pressed further down.
The odd thing about this model is, the label states that the current
capacity is 2.5 A, although the switch itself is clearly marked with a
rating of 6 A.

Some fairly recent Linemaster motor speed control units, model/catalog
number 980-SC3 are made with variable speed power tool switches, the same as
the Foredom FCT-1, but they are labeled as a 6 A rating.

I remember opening an old Necchi foot speed control as a pup, and it had
resistance/heater wire on a big ceramic block and a wiper to make a crude
rheostat to change the motor speed. Alternate your feet to warm them both.

--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html