Got the front triangle almost fully welded. Just need to finish the rocker pivot area and the gussets. My welding is getting better but still a lot of room for improvement 
. The frame pretty straight so far at least so that’s something.
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May I ask you, what WT that downtube is and how you attach the battery to it?
I’m building an electrified cargo bike at the moment, also with an external battery, and I’m slightly hesitant to attach the big chunk of juice only via four bottle bosses to a 40x0.9mm tube…
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Sure thing, this is the tube that I used: https://www.bikefabsupply.com/40-44mm-main-tubes/p/413-1-950-4130-downtube
And as for mounting, Bosch calls out some specific geometry for the external batteries so I 3D printed some hard mounts and welded them in. The picture isn’t great and neither are the welds but my hope in designing them was to spread out the force over more of the tube and I wish I made them a little bigger to spread it out even more because batteries are heavy. I don’t have any math to back that feeling up, just gut feel. Hopefully they hold
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thanks for the reply and that info!
Your tube is a bit beefier than mine but not by much…
I think I will do a quick FEA and compare a few designs to bottle bosses (I’m using a Bafang battery which uses four M5 threads spaced evenly across the length of the battery)
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Well I think it is ready for paint 
test fit up was successful. Just need to double check the battery fits and the speed sensor clears and it can go to powder coat. The built in fixturing for the rear triangle worked pretty well I think I will try it again if the opportunity presents itself. Pretty convenient and not too hard to remove.
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I’ve used batteries with a similar centerline water bottle boss mounting.
I found that the battery is much more solidly mounted with a bracket that fits the round tubing and makes a square flat surface. Here are pictures of two different ones that I’ve made. The one on the green bike has a hose clamp because it is a retrofit and I put the bottle bosses very low on the DT.
I CNC these out of aluminum but even a 3D printed one would help a lot. They just keep the battery from rocking on the DT.
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Looks amazing- nice work!
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Motor and batteries fit which is great. Weights of the whole frame together with battery are 27.4 lbs/12.5 kg with the big battery and 25.8 lbs/11.7 kg with the small battery. This thing is a chonk.
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I will get some more pictures later but it’s back from powder coat and the frame hardware is in. The color is MUCH louder than I thought but I love it. With a name like peacock sapphire I shouldn’t be surprised. I immediately had to go out of town after picking it up so I will get it all together and ride it soon. I didn’t give enough space for the powder coat in my tolerance stack so I had to shave it and file off in places. I will get it right one day. Just glad all the bearing and pivot bolts made it in and it cycles smoothly. There is a video of it that shows the color better on my insta.
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Alright it is all together. I need to clean up cable routing and source some decals but it is ready for a test ride. I have ridden it around the neighborhood and it feels pretty good. I am stoked! Fingers crossed it doesn’t break haha.
Weights are 51.9 lbs/23.6 kg with the small battery (400wh) and 52.6/lbs/23.9kg (545 wh) with big battery
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