Infinite Stepper Mechanism
A mechanism that transforms a PF Servo motor into a stepper motor that can rotate infinite number of times left or right. Free building instructions available.
Stepper motors are essential in operating many LEGO mechanisms, for example remotely controlled transmissions, and the only ready-to-use LEGO stepper motor is the Power Functions Servo motor. The problem is, this motor rotates 90 degrees left and right and then needs to rotate back. It can’t rotate one time after another in the same direction. This mechanism solves this issue.
The mechanism aims to solve two separate issues. One is that regular LEGO motors can be transformed into stepper motors by adding mechanisms that limit their rotation, usually to 90 degrees at a time, but such solutions are inherently imprecise and unreliable. In essence, it’s difficult to control such a mechanically limited motor precisely without watching its output or at least listening to it. The other issue is that the LEGO PF Servo motor is a perfectly precise stepper motor, it doesn’t need to be watched and it always rotates exactly 90 degrees, but its limitation is that it has to return to the starting position before rotating another 90 degrees in the same direction as before. This is obviously a problem when e.g. controlling transmissions, because you usually want to shift gears in sequence, one after another.
The infinite stepper allows the PF Servo motor to rotate an output axle infinite number of times, one after another. It does it by employing two moving one-way ratchets that rotate the output when the PF Servo motor rotates, but not when the motor returns to the starting position. This allows to control the output in a precise manner without any limitations – you can rotate it as many steps as needed, in either direction. The main drawbacks of the mechanisms are the size, the number of rubber bands required, and a somewhat noisy operation.
Free building instructions are available on the Downloads page.
