There are a variety of engine types, and everyone wants to be otherwise controlled. Asyncron, stepper motor or series motor, servo or linear motor, a dozen technologies in the market and each has its particular application.
The Leisungsspektrum it can range from a few 100mW to several kilowatts.
Here is a small selection of drive circuits common engine types.

Here you will find Schematic Circuit Diagram for DIY and further information on Engine control unit wiring diagram
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3 axis stepper motor control	www.electronics-lab.com/projects/pc/008/index.html
Ansterung for Universal Motor with Triac (with Layout)	www.spelektroniikka.fi/kuvat/triacd.pdf
Fundamentals of induction motors	www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1824&appnote=en012135