Stepper motor

Stepper Motors

Stepper motors move a known interval for each pulse of power, making them handy devices for repeatable positioning. Generally they come in two flavours: bipolar and unipolar. The Darwin design uses bipolar motors,.

Bipolar Motors

These motors are the strongest type of stepper motor. You identify them by counting the leads - there should be four. They are also the type of motors we are using in the RepRap Project's Darwin design. They have two coils inside, and stepping the motor round is achived by energising the coils and changing the direction of the current within those coils. This requires more complex electronics than a unipolar motor, so we use a special driver chip to take care of all that for us.

US Suppliers

automationdirect.com

UK Suppliers

ST5709S1208-B 400-step/revolution motor from Nanotec Gmbh

Unipolar Motors

Unipolar motors have two coils, each one has a centre tap. They are readily recognisable because they have 5 or 6 leads. It is possible to drive some unipolar motors as bipolar motors if you ignore the centre tap wires. Their main beauty though is that you can step them without having to reverse the direction of current in any coil, which makes the electronics simpler. Some early RepRap prototypes used this trick. Because the centre tap is used to energise only half of each coil at a time, unipolar motors generally have less torque than bipolar motors.