OK I guess I should describe what this circuit does. The potentiometer (R1) sets a break point with the zener diode to switch the chain of transistors, when the input voltage of the circuit falls below the set value the motor shuts off. So your battery does not drain too much. I am making this because my solar pond pump controller died on me. It is a piece of junk!
All I want is my pond pump to come on when the battery is charged up enough, then shut down when the voltage falls off. I still have to make a charging circuit for it. This is the motor control half. When I'm all done I'll probably write up a whole step by step of the entire project. Until then this is fun to play around with.
The zener diode I am using is a 6.2 Volt one, but with the adjustment potentiometer it is adjustable so I don't think it's value is too critical either. Anything from 5 to 9 volts or so should work. 5 volt zeners are really common. I just happen to have a bag of 6.2 volt ones so I grabbed one of those. This is a total junk box project.
P.S. connect your motor to the connections named MOT-1 and MOT-2
P.P.S. The circuit is supposed to operate off a 12 volt battery, or somewhere around 12 volts.