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This 25T rotary drive system (RDS) coupler is designed to fit our servos whose spline, at ø6 (6mm nominal), is found on most servos in our lineup to include 9-gram class, micro, mini, and standard-class.
While we offer a smaller ø5 size (part number PDRS12RDS-5M), at 5mm nominal diameter they are made for our DS115CLHV wing servos . . . our 8mm thick wonder.
Heads up!
Screw up ordering and postage alone will eat you alive. Don't say nobody told you!
Anyway, as regards the bore for the tube (on the drive-side), while the ID is 6mm, in practice, the nominal 6mm x 1mm wall carbon fiber tubing you order off eBay, or the like, is going to be slightly smaller. This is a good thing. Why?
Because it means lightly rubbing the end with 400-grit sandpaper knocks off the gloss and roughens the surface for those of you who rely on epoxy for the bond. Thus, resulting in a perfect fit!
For those who don't want to permanently epoxy the tube to the coupler, then the two small witness holes on the sides (whose purpose is to allow epoxy oozing out to serve as proof you have enough adhesive at the joint), serve another purpose. They are at the antipodes of the circumference, meaning diametrically opposed to each other, and are small enough you can drill them out larger. E.g. to be useful for passing mechanical fasteners. Good since it would suck it they started out too large, agreed?
Anyway, just size to whatever diameter suits your hardware (whether it's an M2 nut and bolt, or a spring pin like this PDRS3066, which we offer).
Finally, machining adapters to accept music wire, instead, is another drive alternative to the carbon fiber tube.
However, this involves custom machining and because we're a production shop (instead of a job shop), we don't offer these adapters because it would be foolish of us to get involved in all the unique possibilities people can invent. Point being, because it's not economically viable for us to guess what folks need, you're on your own for making these.
All is not lost as both aluminum bar stock and tubing are readily available on eBay, and locally at metal suppliers. Examples include solid 6063 bar stock like this . . .
. . . as well as tubing instead of bar stock, once again made of 6063 aluminum. So because it is available with a 3mm bore (and others), then you can drill and tap it to suit your needs.
Install either of these and presto! This is how you get a removable alternative to the carbon fiber tube, but if and only if, a threaded rod is adequate for your purposes.
Anyway, the 25T RDS coupler itself, however, allows you to customize for your specific application.
Finally, you may find it handy to use our sidemount adapters for mounting your servos within the structure. We make these of 7075-T6 aircraft aluminum (an alloy rivaling 1018 steel in strength). We offer them in sizes ranging from as small as our 9-gram class servos, through micro, mini, and standard-class like in this photo.
These are drilled and taped M2 in eight places and supplied with Allen head mounting hardware and washers.
