Recommended · for beginners
How to build the simplest DC Motor Speed Controller(Using Potentiometer and MOSFET)Updated
Why people recommend it
Offered as a simple way to vary a brushed DC motor's speed with a potentiometer and a MOSFET rather than dropping the supply voltage.
Watch for: Check component ratings before moving to higher current batteries
In their words
My reccomendation for this would be using 'Current control' not voltage control using a MOSFET, and POTENTIOMETER: See: How to build the simplest DC Motor Speed Controller(Using Potentiometer and MOSFET)Updated
Sebastian Scholle on electronics.stackexchange.com, Aug 2017. CC BY-SA.
So I moved on to a different guide which said all I was missing is a MOSFET.
totem on electronics.stackexchange.com, Sept 2016. CC BY-SA.