Thursday, May 22, 2008

Identifying stepper motors

While buying a stepper motor you must note the following aspects

First, check for the number of wires coming out. If 5 or 6 or 8, that's good because you have a unipolar stepper. If 4, that's bad beacuse you have a bipolar stepper which requires two phase to drive. Confirm you have a stepper motor by turning the shaft. You should feel the little detents indicating each step. Most probably in ritchie street you will get unipolar motors with 5 or 6 wires.

Second, check the label on the side. The label will have the voltage and step size printed. Look for 12V steppers. If you have a 5V stepper, and it is large, the currents required will be large. Small 5V steppers are no problem to drive. If your stepper motor is new then it will have their voltage rating marked by its side, the problem arises when you are buying stepper motor in second sales. New stepper motor will cost about Rs.1500(for 1.8deg) whereas the second sales stepper motor with the same step angle would be just Rs.250.

Third, get out your digital ohmmeter (probably your multimeter) and start measuring the resistances between the leads. you will get different values depending on which pair of leads you measure. The lowest resistance you find is the coil resistance. Use I=V/R to compute the coil current. If 250mA or less, you are in good shape. Most stepper motors in Ritche street will have very low coil resistance and requires current above 1A.

Fourth, look at the output shaft and determine if it is something you can handle. Check whether the shaft has suitable height so you can use it. Common steppers have plain shafts with 0.125, 0.196 or 0.250 diameter. Gears press fit onto the shaft may be useful to you or can be removed. Don't try to remove the gears by yourself, you will damage the shaft if you try to remove it by yourself. Lathe with chuck must be used to remove the gears to avoid damage to the shaft.

very large or very heavy steppers will mostly require more current than you can control.


crawler said...

thanks for providing useful information

crawler said...

great work , was very helpful to me

Louis Aquilina said...

Excellent info. Many thanks for the help!