need some help with sinusoidal movement of axis

[magicniner]

A Scotch Yoke with the drive pin mounting point adjustable for radius, a variable speed drive for the motor, tachometer on the shaft of the Scotch Yoke.

That gives you variable amplitude from zero to the size limitation of the Scotch Yoke you build, with variable speeds from zero to things you could only dream of with steppers ;-)

[donkeyot]

A Scotch Yoke with the drive pin mounting point adjustable for radius, a variable speed drive for the motor, tachometer on the shaft of the Scotch Yoke.

That gives you variable amplitude from zero to the size limitation of the Scotch Yoke you build, with variable speeds from zero to things you could only dream of with steppers ;-)