I’ve been riding around a lot lately, and thinking about balanced systems, and how complete systems are designed, as well as thinking a lot about the design challenges that teams like the Buckeye Racing guys faced putting a bike together for the Isle of Man race.
Here’s what got me going. Running RC lipo with a microscopic pack, I had a bike that weighed about 210lbs, a range of 10 miles, and astounding acceleration. Except it wasn’t as astounding as it could be because the pack was so small. Even if you can pull the amps, and the batteries can deliver the amps, when the whole pack is tiny you’re tapping it for all it’s worth, and at some point the voltage starts to sag. Once the voltage drops, you don’t go as fast. The answer would be to build a bigger RC lipo pack, or a bigger pack that can do what RC lipo does. A123 is a good example, or a nice array of god-awful expensive “lipo”. Kokam would be good and if anyone wants to buy me a Kokam pack, well, go right ahead, I won’t stop you. Hell, you can even have my last good kidney.
So then I put in a new pack with CALB LiFeP04 40ah cells. I get a good, 30 or so mile range, the bike weighs about 275 now and the packs are easy to maintain. Since the nominal voltage is lower the pack is now running at 80V at full charge. As a result, the overall acceleration is slower, but also, those cells sag a lot more than a lot of the current cells, so the voltage, on hard acceleration, will drop down to as low as 60V. No worries, it pops back up, but that’s now 60V driving the system. Remember, volts = RPM, so now at 60V I have much lower potential RPM. Since that means lower top speed, I geared the bike up a bit. Now at low end, it’s working harder, so guess what? The voltage drops… giving me another hit to my acceleration.
I changed my balance point.
Overall, my top speed is good, my acceleration is fine but I’m not pulling wheelies anymore, and the bike is still a blast to ride with a decent range and easy to maintain batteries. With the taller gearing it’s a pretty well balanced system. But it has one bottleneck – the current supplying ability 0f those batteries. Now, if I were to bust out that bottleneck by putting in some high amp batteries I’d be running at a whole higher level of performance. Higher top speed, faster acceleration, to a serious degree, not just a little tweak.
Then, it would be time to find the balance to that system. Suddenly I’m dumping huge amps, so my guess would be my motor is going to be getting hot and my controller is going to start to complain… but that’s only a guess.
It’s kind of like back when you took the air cleaner off your Dad’s car, and suddenly it ran well. There aren’t a lot of things you can do to most well-evolved systems to get that kind of quantum-leap in performance, but that’s what it’s all about. Finding the bottlenecks, eliminating them.
Lemmee see now. Balance. Bottlenecks. Kind of a yin-yang thing, huh? Zen and the Art of Electric Motorcycles? …hmmmm