Connect the GND of the battery to the GND of arduino – common GND. If you are using a 5V relay instead of 12V relay, you only have to connect the arduino GND. I am using a 12V relay. So the coil ...

So long as the 0V rail is connected to the Arduino 0V rail, the positive rail can be any dc voltage – more or less that the Arduino, so great for 12V motors. And it is compatible with both 5V and 3V ...

It is a Clarke DCM10, a variant of Sieg’s X1, sometimes knows as a ‘micro mill’. Mine has a ~230V 150W brushed dc motor that needs driving from 240Vac mains power. Almost randomly, I settled on a ...