Rotation control

Hi.
I want to control the Speed of a rotating object like helicopter blades.
I know the right way is animate that but is there anyway to control the Speed of rotation with a parameter?.
I tried the multiplier curve and also the rotation expression like ( parameter*S or NT or F) both method lead to a problem. The rotation reverse when I set the parameter to zero .
Because both of them control the value of rotation not the timing of rotation.
How control the timing of animation?
Thanks
For more information please watch this video
https://youtu.be/u2I5gVwYSig?si=kUfl1YQd-GqMVpMY