It's basically impossible with our current electronics to only charge the battery to 95% and leave headroom for regen braking. We could let the battery charge to 100% and then bleed off energy slowly, but most users keep it charging and then start riding immediately after unplugging it.
The other option is to divert braking energy to heat instead of recharging the battery. But on steep hills, braking energy can reach hundreds of watts, which would quickly overheat the electronics or motors without regen.
This is an issue that affects a very small subset of users, almost all of whom live at the top of a hill - definitely a unique corner case to design for. We tell them to discharge the battery by running it uphill or on flats briefly to discharge the battery enough to allow some regen headroom.
Yes, but the added weight of something as large as a 1kW resistor compromises the portability of the board. We're looking into how to do this without adding weight.
A bit of a higher price point, but some Formula 1 teams went through similar issues with their KERS system in regards to performance and weight. I think everyone converged on extremely high speed flywheels, but there was a fair amount of work into ultracapacitors. I'd imagine a 1,000F ultracap could handle the ~20-30 seconds of 100W braking power at well under a pound? I know nothing of their reliability or availability and I'm sure you guys have done your own research but just thinking out loud.
Would it be possible to arc it over an air gap? I.e. allow the energy be dissipated over the resistance of the air? I have no idea whether the power numbers work out, and maybe you'd need to step up the voltage, which adds complexity. Just a thought..
Random thought: Would it be possible to incorporate a resistor directly into the board stackup -- eg. the "board" part itself becomes a large carbon resistor?
Comments
It's basically impossible with our current electronics to only charge the battery to 95% and leave headroom for regen braking. We could let the battery charge to 100% and then bleed off energy slowly, but most users keep it charging and then start riding immediately after unplugging it.
The other option is to divert braking energy to heat instead of recharging the battery. But on steep hills, braking energy can reach hundreds of watts, which would quickly overheat the electronics or motors without regen.
This is an issue that affects a very small subset of users, almost all of whom live at the top of a hill - definitely a unique corner case to design for. We tell them to discharge the battery by running it uphill or on flats briefly to discharge the battery enough to allow some regen headroom.
Naively I would have guessed you include something like a 1kW resistor + heat sink package, and divert to that.
Assuming such parts exist, are they just cost prohibitive, or is there more to it?
(Thanks for taking questions!)
Yes, but the added weight of something as large as a 1kW resistor compromises the portability of the board. We're looking into how to do this without adding weight.
A bit of a higher price point, but some Formula 1 teams went through similar issues with their KERS system in regards to performance and weight. I think everyone converged on extremely high speed flywheels, but there was a fair amount of work into ultracapacitors. I'd imagine a 1,000F ultracap could handle the ~20-30 seconds of 100W braking power at well under a pound? I know nothing of their reliability or availability and I'm sure you guys have done your own research but just thinking out loud.
There are some excellent cells out there developed for KERS. One example:
http://www.ebaracus.com/product/a123-ahr18700-f1-kers-cells
Would it be possible to arc it over an air gap? I.e. allow the energy be dissipated over the resistance of the air? I have no idea whether the power numbers work out, and maybe you'd need to step up the voltage, which adds complexity. Just a thought..
Interesting idea. I think you won't be able to dissipate enough heat this way, but I'm not sure.
Random thought: Would it be possible to incorporate a resistor directly into the board stackup -- eg. the "board" part itself becomes a large carbon resistor?
Cool idea! I'm not sure about the conductivity or thermal properties of structural carbon fiber, but it may end up being a good option.
what about charging the onboard laser?
One of my cofounders worked on this before we started Boosted.
http://en.wikipedia.org/wiki/Boeing_YAL-1