Gyroscopic Motion - II
From this, we see that the required moment on the top must be in the x-direction, since other components are zero.
As special case,
put 
and 
. Also put Mx = M, then from the above equation,
.
The above equation is the equation of motion of a rotor which is precessing at a speed of 
and spinning at a speed of 
.
Now, for a top, Mx is 
.