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Fine if you want to experiment. I'm not that excited by bodges these days. I want stuff 100% reliable. Since you're not too bothered re: the frame I'd be more likely to drill the BB shell to get the Junc B through it but then it wouldn't be as interesting as what you're doing. :)
hippy-
I had external cabling but wanted to put the battery in the seat tube. Allbeit mine is a Ti frame, I didn't have to drill the BB shell, I removed the screw you can see in the image but the hole was not big enough to get the cable connector through. Simply got a cable long enough to get to the top of the seat tube, cut it near to one end of the cable (3 or 4 inches from the connector) then threaded the cable through the screw hole, out of the bb shell and up the seat tube. Then soldered the cable back together and covered in heat shrink. As a BB30 BB I had to ensure I used a pressfit BB to prevent the cable rubbing on the spinning crank. The only external signs are the di2 cable sheaf running down the centre of the downtube and under the ds chainstay.
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Thats an option. I'll have a look how much space I'd have because it will probably end up with my Praxis crankset (30mm spindle with BSA bb) so might be a tight fit. But I still need to figure out a way to route to the FD.
@PhilDAS has the right idea, thats my most realistic option. I think I'll experiment with the paint stuff and see how it works. This wont be a complete build before next spring so ive got time :)
At the same time if anyone's got any cables, BT-DN110 battery, or internal battery charger to sell, let me know :) Thing about the cables, I cant really find them being sold second hand so I assume they are really reliable and people do keep them through groupset upgrades.
Alan_tbt
kiskubai
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:
Article on it
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.