Too Busy For Words - the PaulWay Blog

Mon 22nd Nov, 2010

Powered by cardboard

I spent a productive weekend of planning and preparation on the electric motorbike yesterday. This was different to the week before, where a combination of bad weather and apathy caused me to stay indoors and flop around for the time I had planned to be working on the bike. This time I was better prepared, and as an added incentive I made sure I got the friend of mine who's been helping me with it enthused so I knew he was coming around and couldn't prevaricate.

We got the fairings worked out. We discovered that the reason the front and left-hand side fairings weren't fitting correctly was that the headlight mount had been bent in the crash and the headlights were only fitting by virtue of the fact that one of the mounts had broken. We discovered that the measurements on the EV Works website say that the LFP60AHA cells are 203mm tall but that their specification sheet that's linked to on the same page says they're 212mm to the shoulder and 215mm to the top of the terminal post. Rob made plans for the cell mounting cages while I worked on trying unsuccessfully to straighten the headlight mount. We discovered that the controller will fit near perfectly under the seat - with a weatherproof housing for the electrics it will be perfect. We learned that buying a bike that's been in an accident might be cheap but it comes with downsides.

That afternoon I constructed the rest of the cardboard mock-ups of the batteries, and determined that they would indeed fit in the frame - just. Rob's preferred method of construction is to buy the metal, cut it to size, get a welder and start attaching bits of metal to the frame where they need to go. I need a bit more of an idea whether that's going to work, so that I don't find myself grinding it all off because I should have fitted the batteries some different way. We're going for four groups of seven cells in frames, set up so that the cells are fixed together with straps, joined in series, and then the whole group is slid into the frame together, with extra cables between the groups. Then we have two groups of five, or some other combination that's going to fit in the space available, joined together the same way.

The complicated thing is dealing with the tops of the batteries. They each have a BMS monitor module across the terminals, and a cell interconnect (basically a thick piece of braided copper mesh) between the batteries. By my calculations the sides of this interconnect sit just over 10mm away from the edge of the battery, so having a 10mm-wide right-angled piece of metal to clamp onto the top of the cells to hold them down gives too many opportunities to short something out. Yet how do we hold the batteries down, to make sure they don't vibrate in place and wear the interconnects and/or start moving more enthusiastically around the battery frame? Rob's idea was to have foam rubber on the sides of the battery cage and to design it so that tightening the bolts on the end caps clamps the cells in place, but I'm not sure that's going to really stop the cells lifting up if I hit a speed-bump too quickly. I need something non-conductive to clamp the cells down.

So I'm going to do up the plans in something (SketchUp possibly) to take to the engineer. I've taken the headlight mount off, removed the wiring loom, and readied it for a bit of blowtorching. I've taken some photos, but my Gallery setup at home has eaten some really rather toxic mushrooms and I'm currently trying to triage it. If Gallery2 would actually work, rather than sitting sullenly and ignore my uploads, that'd be great too.

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