Hello, Recently,I got 2 stepper motors,one which was dismantled from a blood analyzer machine and the other one was bought from a local store. The stepper motor spec from the machine is: 12V dc 1.8 degree resolution 1A The stepper motor spec bought from the store is: 12V dc 1.8 degree resolution 500 mA I wish I could provide more information but the datasheet is not available. The one which I got from the local store is very cheap approx 1/10 of the price from major electronic retailers.So I assume it is of inferior quality. And there is no spec available from the store too. The other one was dismantled from an expensive analyzer machine.So i guess it is of good quality. Now I tested both stepper motors using the same circuit (unipolar manual switch tester).I notice the cheap stepper motor steps are not uniform.Some steps are bigger and some are smaller. I tested them using clockwise and counterclockwise. For the good stepper motor, the stepping are all uniform. I didnt measure the stepping degree but i can see very clearly the stepping degree of the cheap stepper motor are not the uniform.For example,the second step is smaller than the first step. Can anyone explain why the cheaper stepper motor steps are not uniform?I am sure the sequence is correct and the same sequence is tested for the good stepper motor. Thank you.