Not long ago on Azamom.com (sorry, now sold out) I came across a pretty good deal on Common Sense RC CSRC-311 standard-sized servos.
Naturally, I wanted to modify a few of these for continual rotation. The method I came up with is super easy and requires no soldering!
Interestingly, you don't even break the "warranty void if removed" sticker. (What the...? We're not even voiding the warranty!?? Well what fun is that???)
(FYI, this is also found on my projects blog, here.)
Step 1: What U Need
Yeah, so here's what we need:
1) The servo to be modified, of course.
2) Some way to control your servo. (I'm using a Pololu MicroMaetro and control software.)
3) Some wire cutters.
4) A straight pin.
5) Small phillips screwdriver.
6) and probably a paper towel (cuz things are a little greasy in there)
Step 2: Take It Apart
Unscrew the four screws on the bottom and remove the top cap.
Once you get to the gears, remove the output gear. This is the only thing we'll need to change.
Step 3: Poke Out the Insert
There is a black insert pressed into the output knob. This normally turns the pot below, but we're going to take it out.
The easiest way to do this is to poke it out with a pin. There are two holes in the white plastic piece that make this really easy.
Once the insert is removed, you can throw it away, but be careful not to get it confused with the black washer. We still need that!
Step 4: Snip the Stop
Now on the white piece there is a plastic stop. We need to cut this so the servo won't... well um... stop. Actually.
Anyway, grab your wire cutters and do your worst. Just watch your eyeballs, because that thing can really fly!
Step 5: Center the Pot
Hook the servo up to your controller as-is. Set your controller to zero and the servo' motor will (probably) start running.
Then turn the brass pot shaft (formerly below our friend, the output gear) until the motor stops. You'll have to go really slow to find the perfect spot where the motor quits chattering.
Step 6: Put It Back Together
Now, being careful not to bump the pot shaft out of whack, jut put things back together.
I've included a pic of the gear train in case they all fell out and you didn't see what went where. Also, note: Of the two gears in the center, the fine-toothed one goes below the other one.
If you have parts left over, don't worry. Remember: If it works without it, you never needed it! :)
The only tricky part is getting the rubber band back in. I eventually found it was easiest to start the screws, press the package lightly together, then put the band on. Press it into the gap with your fingernail. Also, tighten the screws up evenly so it doesn't squish out.
Step 7: Have Fun!
One last tip before I go.
Since I have some regular servos, and some continuous rotation ones now, I scratched a great big letter "C" on the continuous ones so I'd be able to visually tell the two kinds apart.