There are two kinds of servos, and they look remarkably alike. The other kind is called a continuous servo. They work very similar to regular servos in Johnny-Five, as you can see in the documentation for servo.continuous, which is on the same page as the servo documentation. The main difference is that while a regular servo can only go 180 degrees, a continuous one can go full 360 and continue spinning in the same direction indefinitely. Some favor using these to move wheels in their vehicle projects, and that's just fine!