Bigfoot

Bigfoot is a sewing machine motor speed control made to truly control the speed rather than merely regulating the power.

Bigfoot and an Adler class 8 sewing machine

It uses feedback through a tachometer and a PID controller to maintain the speed set by the foot pedal. A sewing machine with a Bigfoot controller can steadily work its way through thick stacked leather - provided you are using a solid old vintage sewing machine.

More details of the background and development of Bigfoot can be found in this series of posts on my blog.

Here's Bigfoot and the Adler working through eight, then two, then four layers of fake leather while maintaining a steady speed:

bigfoot_-_sewing_machine_motor_speed_control.540p.mp4