Replaced the seat stays to make room for electric bike battery box

August 31, 2010 · 0 comments

I decided how I’m going to solve the problem described in the post ‘How to make an electric bike battery box that will fit all battery packs’. In this post I describe the first step: widen the seat stays to make more room to accommodate the batteries.

I’m using my new ½” tube bender to make rear seat stays for ShortHopper such that I can build a battery box within them. This required widening them by putting a 90 degree bend at the seat tube and running them parallel to each other down to the dropouts.
I chopped the existing rear stays to make room for the battery box for this, soon to be, electric bike. The stays will become part of the battery box. They had to be widened considerably to make room for the widest battery that I want to fit.
The new rear seat stays have a 90 degree bend where they would normally attach to the seat tube. This made for more space between them to build a battery box but also made a high stress point at the bend. I used ½” .035 4130 tubing and fillet brazed them in place so I think they will be strong enough. I might have to brace them in order to provide the strength needed. I’m going to build a battery box substructure around them so that might add some extra bracing. I’ll have to test this to make sure it’s strong enough.

Even though widening the seat stays will make it possible to build a battery box, it also introduced a new problem. Can you see what it is? It’s going to make mounting the brake bosses a challenge. I could put them on the chain stays but that might introduce other problems. I could go with disk brakes. More about this later.

My plan for the battery box is to make it as flexible as possible so I can use any number of different size and shapes of battery packs available. This is going to be difficult because of the many shapes and sizes. Not only that, they have different connections including charge ports and key switches that have to be taken into consideration. Stay tuned for more blogs about this design problem.

If you like watching fillet brazing in action, I shot some video and will be posting that as soon as I can get it edited.

P.S. I just finished my Motor Selection Guide and am giving it away. If you’re interested to see how I choose motors for my electric bike projects, click here.

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