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jonjon

S3003 Variable Speed Rotation Hack

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Hi-

I hope this is a very simple question, a sort of surface-mounted "Where's Wally" Puzzle; I'm trying to find out which of the components in the jpg is the "right capacitor" to replace. But first, since I'm new and far more ambitious in my projects than my limited electronics knowledge should allow I need to write a huge long introduction establishing what I want to do, where I got the idea, ... and a whole lot more padding for what I hope is an almost trivial question...

I am about to sacrifice a couple of these S3003 futaba servos, that I have lying around, to the gods of Continuous Rotation. In particular I was tickled by the Seattle Robotics "Encoder" article, available here (Variable Speed Control Modification to the Futaba S3003 RC Servo), that suggests a very neat looking hack to improve the functionality of a continuous rotation-hacked servo. (Can I just shorten "Continuous Rotation" to CR?). By replacing (or bypassing) a resistor value and replacing a capacitor the speed-feedback element of the servo positioning apparently can be coaxed into behaving like a little speed controller. The article even includes pictures and a short looking BOM – this was perfect because I can just take the print-out down to Jaycar and buy the right parts this time.

Unfortunately for my limited electronics knowledge the jpg with the article

fig2.jpg

of the PCB inside the servo doesn't look 100% like the ones in my servos, seen here

s3003newPCB.jpg

... it's a bit blurred and lower resolution too, but my main concern is that the 47µF capacitor I am instructed to replace appears not to be there (if you were to look at the other side of the board you'd 'see' it wasn't there(?!)) you can see the pins in the original jpg where the capacitor should have poked through along the lower edge. Instead I have one extra of the surface-mounted strangeities – which are scarey and small, very very small.

My questions are : Is the black rectangular part labeled "CS" in the lower left part of the board a capacitor and so the right thing to replace ? What is the best way to remove this (I guess it will just fall off if I wick the solder away) ? I have a dremmel and some small drills that I thought I could drill through and mount the capacitor like the original plan. Is that feasible or would I mess something up just driving a drill bit through the board ? (Space is tight already when the new resistor is mounted across the back like that, adding a capacitor too would be a squeeze, if I can mount it on the other side it would be cool).

Thanks and I hope these questions weren't too dumb ! :blink: The servo is the pan mechanism for my KAP rig. "Rig waiting to be (re)built" at least. Assuming this bit goes okay, the next challenge is my new Tx-only Video-asssist, replacing the 'sighting camera' with the video-out from the digi-cam. I'll be building my own aerial from Mr. RC-Cam's project site too!

When I searched the archives (sorry I couldn't search the old forum) I saw a post by someone else from NZ asking a KAP servo question too. Excellent coincidence! :) I hope that image doesn't make this post too wide ...

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Is the black rectangular part labeled "CS" in the lower left part of the board a capacitor and so the right thing to replace ?

Yes, that is the part to hack.

What is the best way to remove this (I guess it will just fall off if I wick the solder away) ?

You can use solder wick and patience, or two low wattage irons and care.

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Thank-you thank-you thank-you !

I removed the little black thing, drilled a few holes, maybe should have soldered the capacitor first, added the resistor and replaced the trimpot (with the suggested 22-turn version, much easier to tune). The result below (I'm not yet knowledgeable enough to be ashamed of my soldering ! :lol: )

s3003soldered.jpg

...best of all, and against the laws of reasonable likelihood, it works !! Thanks to your advice I still have a spare servo left for more experiments too ! Excellent. Next up (after installing the servo) is the co-ax aerial and this rig looks like it might get made ! woohoo !

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