continuous vs. standard servo: dangers?

Impulse

The "What's a Microcontroller" text cautions not to use continuous rotation servos in place of standard servos, saying the sample programs might damage the continuous sort. Why? Looking through the documentation, it looks like the only difference between them is a mechanical limiter on the standard servo. Is there more to it than that?
Thanks.

Andy Lindsay (Parallax)

Yeah, there shouldn't be any problem with using Parallax Continuous Rotation Servos instead of Parallax Standard Servos. The behavior will be different, but they won't be damaged by any of the circuits. At the time that warning was written, we weren't sure if changing servo manufacturers was going to result in continuous rotation servos that couldn't take 9 V batteries as a power source. With some of the carrier boards in circulation at that time, 9 V was the only option for servo power. It turned out that the new servos worked fine with 9 V batteries, but we didn't know for sure before sending the book to print. So, it turned out to be a "better safe than sorry" caution box.

The warning we are talking about can be found on page 104 of What's a Microcontroller v2.2.

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Andy Lindsay

Education Department
Parallax, Inc.

Post Edited (Andy Lindsay (Parallax)) : 5/3/2007 11:25:36 PM GMT

Peter Rand

exactly my question too - many thanks

Now can the miniservo be converted to full rotation? Can it be programmed to variable position and speed? Where is the software to do this?

Thanks

Franklin

The software to move a servo is the same for all Parallax servos (and MOST others) As to modifying the mini servo I suppose you could but I don't know if you have the skills or the tools. Its probably is not as easy as a full size servo.

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- Stephen

Mike Green

Peter,
It's not just a matter of getting 360 degrees of rotation. All standard servos have a mechanical stop inside that protects the mechanism that provides feedback internally as to the servo's position. This is usually a potentiometer which is not designed for more than maybe 270 degrees of rotation. The modification removes the potentiometer and the mechanical stop. The resulting servo has no way of telling its position. The control pulses that normally specify the desired position of the servo instead specify the speed and direction of rotation of the servo. There's enough effort in successfully opening up the servo, removing the needed parts and putting it all back together so it works that most people buy servos either already modified or built from the beginning as continuous rotation devices. I suggest you search the web for instructions, hopefully specifically for the servo you're interesting in modifying.