Hey there, total newbie here - and just looking for advice on a small (ideally less than 40mm) high torque stepper motor to grab likely on Aliexpress, plus a dead simple controller. Cheap. Basically I'm doing some prototyping and just need a stepper motor able to plug into a driver/controller and turn a knob to control the speed for testing. I don't want to have to program anything, if possible. I'd be grateful for any advice. Thanks, Peter

 

There are plenty of cheap stepper motor drivers available. I have just had a quick look on ebay. Lots there!
They all need pulse and direction inputs.
So, if you want to control the speed with a potentiometer you will need an oscillator where the output frequency can be controlled. A simple 555 circuit would do for this.