Sambal

Motorcycles have had shaft drive for years, nice to see it come to bikes too. I think it’s not quite as efficient as a chain, but more reliable and lower maintenance. If you’d like continously variable gears, that’s also possible, though not everyone thinks it’s necessary.

First day on the bike in awhile. Windy as heck this morning (flags straight out, ripping), so I tried to preserve the assist for playing with traffic. Just blasting through the wind is taxing on the battery, because the motor is geared high, so draws lots of current at low speed / high load. (Thus, the thoughts about transmissions.) Mostly I just pedalled, which though slow, worked fine. If I wanted a bit of assist, though, that’s not so easy. There are two problems with the throttle. One is ergonomic: it’s a thumb controlled pot, and bumps jitter it around. There’s no doubt a reason motorcycles have adopted the twist grip for throttle control. The other is electronic: I suspect the pot controls the effective battery voltage, using PWM. But until the effective voltage exceeds the back emf of the motor at the current speed, there’s no assist at all. So the entire range of available assist is wrapped into a short range between some partial throttle position, a position that shifts with increasing speed, and the top. It’s as if the accelerator pedal didn’t work until you’d pushed it down 3/4 of the way, then leaped forward. (Jerking you around, resulting in the pedal wiggling more, etc.) The interface is wrong: it should control current, which turns into torque, not voltage. This would make sense for a cruise control, where you wanted to set the speed, but for throttles we’re used to acceleration. The bottom line is, at speed, the Currie thumb throttle is only good for on/off, though it’s nice to have fine control for maneuvering at parking speeds.