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I think it is a dumb junction, yeah. But why wouldn't you use it, instead of creating a mess of soldered cables in the frame?
hippy-
My frame wouldn't fit it internally. At the BB its an aluminum BSA insert in a carbon frame, no clear access around BB inside of the frame as the original internal gear cables are running down outside the BB housing to the plastic guide, see pic below.
Issue no1: I cant route the Di2 cable through the original hole to the front derailleur as its way too small so it'll have to go around the BB housing. Not a clean look. Theres a lot of material there, and most of it seems to be the aluminum insert but Im not sure if I'd drill that hole up to 5.5mm to guide it through.
Issue no2: From here, I could use the external junction box, but theres no way to run the cable to the rear derailleur internally, the alternative is to use the adhesive cable guide on the bottom of the chainstay. Again, ugly.
This is a frame that I bought 7-8 years ago, and its been repaired after some damage so I'm willing to experiment on it.
So then I found this:
Its a long shot, but good thing is that at the cost of cutting a di2 cable and investing in the DIY needs (£20-ish?) I can make a proof of concept on basically any piece of plastic/carbon.
Heres the idea: The dummy connection would be laid out into/onto the paint of the BB shell with gold leaf. Think like a circuit board. A 3D printed connector (that also functions as the crimped end of a di2 cable with a standard di2 connector on the other end) would be glued on this with conductive adhesive and this would run up to the front.
These "painted" lines then would come up on the side of the BB and near the FD again it'd have the 3D printed crimp glued on it, ending in a cable to connect to FD. Same for RD, paint running on bottom of the chain stay. Note that the battery will be in the steerer, connected to one of the shifters, so it wont have to be taken into consideration at the B junction.
Once connectors are glued on and system is operating, time to nicely mask it around, and the whole thing of course would get the clear coat treatment. Extra layer on the one below the chain stay.
Ambitious? Very. Would the end result be super clean? Yes.
Seems like a nice winter DIY tinker project. Worst thing to happen is that I damage the paint on the bottom of a frame, which I dont care much about.
kiskubai
Anyone knows whats inside a Junction B box?
It is my understanding that with the e-tube system all the brains is in the derailleurs, shifters, junction box A (bar end in my case), and battery (assumption from the fact that syncro shifting isnt compatible with the older batteries).
What I'm getting at, is it possible in theory to splice the cables where they'd meet at the bottom bracket, and solder/crimp all red cables in a bunch, and all black cables in a bunch?
This is not the desired end result of course, but the easiest way to get the idea across.