Another alternative of rigidbody.AddForce?

Hi! I was just about to release my game when I noticed something BAAAAD. While using rigidbody.AddForce on my player, I noticed that the higher the FPS is, the faster the player goes. So players with good computers can finish a level in like 10 seconds while it takes 1 minute for people with bad computers. So I need another alternative. I tried transform.Translate but that just messed up the whole thing. My player is a sphere that rolls around so the rotation gets messed up on the way. So do anyone know something like AddForce but doesn't rely on the FPS? Thanks in advance