controlling stepper motor with aruino

[theRoBobuilder]

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

https://youtu.be/i6eGwuEiK0k

thanks in advance...

[groundFungus]

What stepper driver are you using?  

Stepper basics may be of interest.

[spycatcher2k]

And what power supply? A stalled stepper of this  size can easily draw 2Amps

[Railroader]

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.