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EZ continuous rotation servo -- without solder! (CSRC-311)

Picture of EZ continuous rotation servo -- without solder! (CSRC-311)
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???)
 
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Step 1: What U need

Picture of 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

Picture of 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

Picture of 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

Picture of 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

Picture of Center the pot
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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

Picture of Put it back together
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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!

Picture of 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.
megaduty3 years ago
Thanks for the walk-thru, just bought a 4 pack on Amazon and will refer to your guide when the time for "continuous time" comes!
Well done! I just ordered some off Amazon(They are back in stock as groups of 4, 8 and 12!!).

I will look forward to ripping a few apart and following your guide ;D
AndyGadget4 years ago


That is the easiest-to-modify servo I've ever seen. With some types it's quite a fiddle isolating the pot from the output gear.

You mention setting the controller to zero - Normally you'd set it to mid-range (1.5uS) and adjust for no movement so you have forward and reverse control of the motor. Does zero correspond to the mid-point on the controller you're using?

The other thing about servos is that some types are better than others for fine speed control. I've had one which gives 20 steps each side of zero ramping up to full speed. Others have reached full speed at 5 steps. Digital servos are better than analogue ones for this.
PS118 (author)  AndyGadget4 years ago
Yeah, these things are great. They can be modded in like 30 seconds!

That's correct. When I say "zero", I'm referring to the center of the range.