controlling stepper motor with aruino

please help me i am controlling a old 6 wire nema 17 stepper motor by converting into 4 wire motor using arduino mega but motor keeps vibrating and rotating randomly and "also it stops rotating when i touch the shaft" a for more detail watch the video...and provide me possible solution

thanks in advance...

What stepper driver are you using?

Stepper basics may be of interest.

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Maybe there is a loss of one of the coils. I received a stepper motor that had one broken cable.... It behaved strangely. Check Your convertion from 6 wire to 4 wire.