| Home |
|---|
| Categories |
| Coilguns |
| AVR Projects |
| Gumstix Projects |
| PIC Projects |
| Tutorials |
| The Forum |
| Contact Me |
If you like this site please |
  |
| |
Stepper MotorsA stepper motor is not much different then a normal brushed motor. In a brushed motor there are brushes that rub against the electromagnets and when the electromagnets spin they change polarity. In a stepper motor there are no brushes so it lasts much longer then brushed motors but, the switching must be done electronically, eg. with a micro controller.There are two kinds of stepper motors. The simpler kind is a uni-polar motor. In a uni-polar there are usually six wires coming out of them, two are center taps to the coils and the others are the ends of the coils. The center taps are connected to VDD and the other ends of the coil are connected to VSS in a sequence. In a bi-polar motor there are usually only four wires, the ends of the two coils. In the bi-polar motor the polarity must be flipped to change the magnetic field, making them need a more complex driving circuit. When using a uni-polar motor the only thing needed to drive it is 4 transistors, on the other hand a bi-polar motor needs something like a H-bridge that can amplify both low and high signals, Spark Fun sells a nice one. Why use a bi-polar motor if the uni-polar are so much easier? The answer is simple. A bi-polar motor has much more toque for its size and weight then a uni-polar. This is because the full coil is always on, and sometimes both are on. While in a uni-polar only half of the coil is on, and sometimes two halves. To drive a uni-polar or a bi-polar motor (with H-bridge) you need to sequence the coils. Both motors are sequenced the same, each has four wires to control. The sequence for full stepping is 0001 0010 0100 1000 or for more torque 0011 0110 1100 1001 There is also half stepping where the magnet goes between the two electromagnets doubling the resolution of the motor. The sequence for half stepping is 0001 0011 0010 0110 0100 1100 1000 1001 The best part of stepper motors is that a micro controller can keep track of its location if you know the starting point. For example if you have a 200 step motor that means for every 200 full steps (400 half steps) the motor will turn exactly one full revolution. Another good tutorial for uni-polar motors can be found here. A uni-polar stepper motor 
Two bi-polar stepper motors  |