Continous vs. "Unmodified" Servos

Bipedguy

What is the difference between a Continous rotation and an "Unmodified" servo. Everyone tells me that a continous rotation servo is basically just a regular motor. What is this all about?

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"Robots are just lights...and clockwork."

Detective Spooner
iRobot

Mike Green

You really need to download some of the tutorials from the Stamps in Class web page on the main Parallax website. The "Robotics" tutorial discusses this.

An unmodified servo is a standard RC (radio control) servo that turns anywhere from 180 to 225 degrees under control of a logic level pulse repeated about every 20ms. The width of the pulse determines the position of the servo and ranges roughly from 1ms to 2ms in width. Some servos will accept a pulse as wide as 0.5ms to 2.5ms.

A continuous rotation servo effectively has part of the servo mechanism disabled so that it will rotate in either direction continuously. The pulse width determines the direction and, to some extent, the speed of rotation. The pulse width is still roughly 1ms to 2ms. A pulse width of 1.5ms will stop the rotation. A shorter pulse will cause rotation in one direction and a longer pulse will cause rotation in the other direction. The 1.5ms stop point is set approximately with a trim-pot inside the servo.

allanlane5

The benefit of a "Modified" servo for a BOE-Bot is that in a single inexpensive ($12 or so) package , it gives you a motor, ALONG WITH drive electronics, ALONG WITH a circuit to read a "PULSOUT" from the BS2 and convert it into forward, stop, or reverse.

Compared to all that H-Bridge, PWM, or Stepper stuff you have to do to get other motors to work, this is quite nice, inexpensive, and simple.

Philip Gamblin

In addition to the abve mentioned points, it reqires virtually no interface and has a readily usable torque and appropriate speed for small robots.