For a start, this Dahon MuSP frame was never designed for Di2 wiring, let alone internal wiring. However, since I already have the frame in hand, I can experiment to see how to wire up the whole Di2 system.
My first thought was to use the internal Di2 battery and try to fit it somewhere within the frame, since there are openings in the frame and also sufficient space within the frame.
Shimano Di2 internal battery, BT-DN110. It is long and slim, unlike the external type battery that I used on the Dahon MuEX.
As I did not have an extra internal Di2 battery on hand, I could not check if the battery can fit into the frame or not. What I did have was the battery dimensions which I found online. I tried to find an item of similar dimensions, and use it to test fit it into the frame. Coincidentally, I found that one of my screwdrivers has almost the exact same dimension as the internal Di2 battery!
Internal Di2 battery size is about 16mm in diameter, and about 160mm in length.
The diameter of this screwdriver is almost the exact diameter of the internal Di2 battery!
The length is almost the same too, although this is less important for testing the fitting.
The idea is to slot the battery inside the frame, through the holes at the joint area. Let's take a look at the joint area first.
The holes that are found at the frame joint. Although the joint is big, the holes are quite small...
The metal sleeve is first removed from the frame. This metal sleeve guides and protects the outer casing when it crosses the joint area.
Using the screwdriver to test, it is just unable to go into the hole, by a small margin.
Unfortunately, based on the testing, the internal Di2 battery is unable to fit into the frame through the holes at the joint area. Even if it just manages to fit inside, it is also not recommended as it will be almost impossible to get it out the next time, unless there is sufficient space to pull it out.
Therefore, I have to drop the idea of using the internal Di2 battery on the Dahon MuSP. It would be a really clean setup if the battery can be stored internally, but it is not possible for this frame design.
The only way is to mount the Di2 battery externally, same as on the Dahon MuEX. The best location will be behind the seat tube, where it is relatively well hidden and does not interfere with the folding of the bike.
I removed the external Di2 battery and battery mount from the Dahon MuEX to test the fitting on the Dahon MuSP frame, as shown below.
Ideal location of the external Di2 battery. However, the two curved parts of the frame seems to get in the way.
It will protrude from the top of the seat stays slightly.
At this position, still able to open the lever to remove the battery from the battery mount.
Just for record, the battery plus battery mount weighs 102 grams.
With the battery location decided, the next step is to think how to attach the battery mount to the frame. Last time, I made a custom adapter so that I can velcro the battery mount to the seat tube. This time, it will be the same concept.
With a scrap piece of aluminium, I cut the shape to the required design, and tapped 2 x M4 thread holes for mounting the battery mount. This aluminium piece weighs about 50 grams.
Spray painted black colour to blend in with the frame. Two short M4 bolts are needed as I did not drill and tap the holes fully.
On hindsight, I should have designed the adapter in 3D software, and 3D printed the part. It would save me a lot of hands on effort, be lighter in weight, and probably fit better to the frame. That is what I would do if I had to design an adapter the next time.
Mounting the battery mount onto the aluminium adapter.
With the battery secured in place. The cutout under the battery mount is for the velcro strap to go through.
Due to the limited space around the seat tube, this is the only location available for the velcro straps. Cannot be higher up or lower down, this is already the optimized position.
View of the battery location from the back. Well hidden by the tall seat stays on either side.
Sufficient clearance to open the lever to release the battery from the mount. I also added a piece of rubber in between the seat tube and the aluminium adapter for additional grip.
Although this method may not seem very secure, it is actually good enough. Apart from being extensively tested on the Dahon MuEX, which uses essentially the same design, I also tested this Dahon MuSP on a long ride of 60+ km and there was no issue at all.
The battery may sometimes shift slightly to the left or right side, but it will not slide downwards as the two velcro straps plus the rubber provides sufficient grip to hold the battery.
With the battery location finalized and confirmed, the complete Di2 wiring layout can be made. This is a new arrangement which is not conventional, and which I am trying out for the first time. The good thing about the Di2 E-Tube system is that the components do not need to be wired up in any specific order. As long as you have the components located somewhere within the layout, it will work fine.
Di2 wiring layout on the Dahon MuSP
Referring to the Di2 wiring layout above, let's take a look at the conventional and also non-conventional areas. For the rear of the bike, between the rear derailleur, battery mount and Junction B, it is a standard layout. The Junction B will link up the battery, rear derailleur and the front of the bike. This is quite standard and similar to on the Dahon MuEX, except that this time the Junction B will be placed internally instead of behind the seat tube.
As for the front of the bike, the usual layout is to link the two shifters to Junction A, with one wire linking up Junction A to Junction B. In my case, a different layout was used.
From the diagram above, the left shifter will be linked to Junction A, by running the Di2 wire internally inside the handlebar. The wireless unit will be installed in series, also inside the handlebar. Also note that this Junction A is an internal bar end type, which I will show more in another post.
The wire then runs from Junction A, out of the handlebar and into the right side shifter, before another wire runs from the right side shifter to Junction B. This simplifies the wiring layout and avoids duplicate wires running up and down the same area.
Weight of the six Di2 wires used in the wiring layout above.
New challenges in this Di2 wiring layout:
1) New type of Junction A, which goes into the end of the drop bar instead of being exposed outside.
2) Running Di2 wire internally through the drop bar.
3) Hiding the wireless unit inside the drop bar.
4) Internal wire routing through the frame.
Some of these points have not been elaborated on, but it will be shown in the next post.
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