How do you turn a unipolar stepper motor into a bipolar stepper motor?

Answer 1

It depends on how your motor is wired.5 wire , 6 wire or 8 wire (4 wire are nearly always bipolar already)

5 wire: For 5 wire motors you need to determine which wire is the common wire.

To do that use an ohm meter to find the wire that has the lowest reading to all 4 of the other wires that is the common. You will not connect anything to this wire in bipolar mode however to figure out which wires must be paired we need to hook it up to the positive terminal of a power supply or battery. Hook up one of the other 4 wires to ground. Note how hard it is to turn the motor shaft. Leave this wire connected and hook another wire to ground. Check how hard it is to turn the motor shaft. Disconnect that wire and connect to the next wire. When one of the three other wires is connected the shaft will turn with almost no effort. That wire and the first wire connected to ground are Motor phase A The other two wires should be paired and would be phase B. A pair of vise locks on the shaft will make it easier to turn the motor shaft. A vise helps to hold the motor. It does not matter that the center of the coils are connected. That point will always be the same voltage for all power connections to the motor at about 1/2 voltage supply. The common wire should be left unconnected.

6 wire: With the six wire version hook up the ohm meter to one wire probe the other five wires. three wires will be open they will be phase B. The other two will show a resistance one about twice that of the other or nearly the same value. If the values are the same the first wire you connected to was the center tap and is not used. The other two wires are phase A. If the values are different The low resistance is the center tap and is not used. The first wire you connected to and the high resistance wire is Phase A. Now connect the ohm meter to one of the wires that had an open circuit. Test the resistance to the other two wires and use the same logic to determine which wires are phase B.

8 wire: First you need to sort the wires out to coil pairs. Use your ohm meter. Hook up to one wire and check the other 7. Only one wire should show as connected. That is the other wire for coil 1 pair. Do the same for the remaining wires until you have identified all 4 coil pairs. Now use a power supply and hook one wire from coil 1 to positive. Hook the other wire from coil 1 to negative. Note how hard it is to turn the shaft. Leave coil 1 connected. Hook one wire from coil 2 to positive the other to negative. Turn the shaft. Reverse the wires to coil 2. Turn the shaft. Try the other two wire pairs. One connection for one of the wire pairs will allow the shaft to turn with almost no effort. When that pair is reversed the effort to turn the motor will be very hard. That pair of coils will be phase A. Hook them up so it is very hart to turn the motor shaft. Mark the polarity for phase A coil wires. Disconnect phase A wires and connect the other coil wires up to the power supply. Turn the shaft. Is it easy or hard. If it is easy reverse one of the coils. It should now be hard to turn the motor shaft. Mark the polarity for phase B coil wires. The phase coils can be connected in parallel or series. Just make sure you maintain the connection polarity that gives the highest torque to turn the shaft.