WEEK 3: Rotor End Cap CNC, Rotor Key Coupling, Battery Module Prototyping and Testing/Sorting all Cells

This week, I managed to get the rotor end cap routed out, which using the 2mm carbide end mill to do the tracks at 0.05mm cutting depth, took many hours to complete. I then used the 6mm carbide endmill to cut out the remainder of the steel to achieve a nice round looking plate design.

 After cleaning these parts up a bit, I moved on to getting the key coupling ready for welding into the inner bore of the rotor end cap.

I slowly turned down the coupling until it fit very snug into the rotor end plate, I then prepped the surfaces for welding when I get the chance. I am hoping that they will not warp when welding.

I also kept on working to perfect the battery module design for the best assembly I can make. I have decided on using 9mm ply to make 54 of these holders below.
In this prototyping I have also decreased the size as much as possible so as the modules stay strong and compact, and have added 2 slots down the sides to house the large copper shunts. I also have added 5 temperature sensor holes so it can be moved around to get a better idea of the cells temperatures in the battery modules.

Using my DIY battery spot welder, I began trialing out the resistor leg fuses and I am really happy with how they are looking so far. Each end is spot welded to the battery and middle part will be soldered to the copper shunt wire (6mm2 house wire doubled over).

I also began the long and tedious process of sorting each individual cell by their strength tests. I am classing all the higher quality cells as those that can deliver at least 14A short circuit and have not discharged below 4 - 4.1V over the year or so that I have stored these batteries as I collected and tested them.

I am happy with the cells I am left with and found about 20 to 30 bad cells in my lot of 650. This will decrease the number of cells but with safety in mind, it is the wisest idea to leave some out. Also because I am designing the battery packs to be largely expandable by twice the current size they will be.