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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