If you're familiar with some of the other tutorials out on the Interwebs to modify servos for continuous rotation... you might be wondering what this guide has to offer.
Many of the mods / hacks I've seen use low precision resistors which will require you to poke around until you find what the servo thinks is center-position. That approach will require you to capture that value and use it as an offset in your software... which makes re-using your servos much more difficult. Using high-precision resistors is the way to go.
Cracking off a piece of the potentiometer housing is a quick and easy way to remove the servos rotational limits. It's also a great way to make the servo wobbly and grind it's gears; there is a better way.
Matched resistors give you sweet and smooth variable speed coming or going.
Before we get started, I have a few words of advice.
First, you will be modifying tiny precision molded parts. One small slip-up can transform the servo you are working on into spare parts. I would recommend buying three or four servos just in case.
Second, this guide will require time, a steady hand, and some patience.
Last, buying continuous rotation servos is alwasy an option!