5 ms·

I'm curious about this statement. Is there any electronic workaround for that? "BRAKING DOWNHILL ON A FULL BATTERY WILL CAUSE BOARD SHUTDOWN since the regen w

I'm curious about this statement. Is there any electronic workaround for that? "BRAKING DOWNHILL ON A FULL BATTERY WILL CAUSE BOARD SHUTDOWN since the regen will overcharge the battery. To prevent this from happening, the remote will warn you by beeping, and you’ll lose your braking power. Safely come to a stop before this happens, and ride on flats or uphill to drain the battery."

tlrobinson 12y ago
The energy would need to be dissipated through a large heat sink.
jff 12y ago
Switch the regen output into a big-ass heatsink so as to burn off the energy? Put actual brakes in there for this sort of situation? Nightmare situation for a SF resident who lives on top of one of the crazy steep hills, charges his board at night and is just about to head to work...
- vkjv 12y ago
  A simpler solution might be the ability to tweak the maximum charge percentage like you can do with a laptop.
skdoo 12y ago
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.
- mik3y 12y ago
  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!)
  - skdoo 12y ago
    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.
    - tomsaffell 12y ago
      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..
      - skdoo 12y ago
        Interesting idea. I think you won't be able to dissipate enough heat this way, but I'm not sure.
    - mikeyouse 12y ago
      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.
      - skdoo 12y ago
        There are some excellent cells out there developed for KERS. One example: http://www.ebaracus.com/product/a123-ahr18700-f1-kers-cells http://www.ebaracus.com/product/a123-ahr18700-f1-kers-cells
krasin 12y ago
In my non-educated opinion, one should never regenerate energy to a Lithium battery of any flavour. All of them are too unstable. A supercapacitor is what should be the destination for the regenerated energy: it's empty by default; stable; could be discharged at high rate
- jgable 12y ago
  This is indeed a non-educated opinion. Please don't spread FUD. Lithium-ion batteries are perfectly safe to regen. You need to monitor the cell and pack voltages and limit regen under certain conditions, but it's well understood how to do this. Any electric vehicle with a lithium-ion battery (and there are millions of them, from skateboards and scooters to cars and trucks) does regen braking. Without regen, you lose one of the most compelling advantages of having an electric vehicle in the first place. In general, supercapacitors do have much better power density than batteries, but much worse energy density, making them impractical for vehicles at this point in time. There's a reason the vast majority of electric vehicles today use lithium-ion batteries. Disclaimer: I was formerly a controls and systems engineer for a hybrid-electric vehicle company.
  - krasin 12y ago
    What you are saying (please, correct me, if I am wrong again), is that the Li-Ion batteries are unstable, but you can keep them safe (no over-current, no over-charge, no over-heat). That's fine. After all, multirotors are also unstable, but they fly pretty good. What I don't know (and where I might be totally wrong), is how bad are current supercapacitors in energy density aspect. The wiki page about Supercapacitors [1] mention it's 10% of Li-Ion, but I have heard about the supercapacitors which are 25% of Li-Ion (not sure, if they are available on the marker, [2]). With 25% of Li-Ion, the supercapacitors for regen would be a better choice than the batteries (see the reasons in my first message). At 10%, you're correct. 1. http://en.wikipedia.org/wiki/Supercapacitor http://en.wikipedia.org/wiki/Supercapacitor 2. http://www.technologyreview.com/view/521651/graphene-supercapacitors-ready-for-electric-vehicle-energy-storage-say-korean-engineers/ http://www.technologyreview.com/view/521651/graphene-superca...
at-fates-hands 12y ago
Or you could learn how to powerslide. https://www.youtube.com/watch?v=2QJVDGtzvEE https://www.youtube.com/watch?v=2QJVDGtzvEE Not sure if this is feasible on this board, but you never know. If the wheels are soft enough, I think you could pull it off.
philsnow 12y ago
I face a similar issue with my honda civic hybrid: they have worked to let you pretend it's a regular internal combustion engine (it looks nearly identical to the other honda civic trims, down to the instrument panels), but you _must_ actively pay attention to the battery level if you don't want to be surprised when trying to pull into traffic (if the battery is under half, it's _much_ more reluctant to boost your acceleration) or trying to brake (if the battery is topped out, it does not assist your braking _nearly_ as much). In general, if you're trying to evade (either with braking or acceleration), you have to know the state of your battery or else the car will not perform the way you think. I don't know if all hybrid/electric cars are this way or if it's specific to my particular year of the HCH or what.

tlrobinson 12y ago

The energy would need to be dissipated through a large heat sink.

jff 12y ago

Switch the regen output into a big-ass heatsink so as to burn off the energy? Put actual brakes in there for this sort of situation? Nightmare situation for a SF resident who lives on top of one of the crazy steep hills, charges his board at night and is just about to head to work...

vkjv 12y ago
A simpler solution might be the ability to tweak the maximum charge percentage like you can do with a laptop.

skdoo 12y ago

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.

mik3y 12y ago
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!)
- skdoo 12y ago
  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.
  - tomsaffell 12y ago
    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..
    - skdoo 12y ago
      Interesting idea. I think you won't be able to dissipate enough heat this way, but I'm not sure.
  - mikeyouse 12y ago
    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.
    - skdoo 12y ago
      There are some excellent cells out there developed for KERS. One example: http://www.ebaracus.com/product/a123-ahr18700-f1-kers-cells http://www.ebaracus.com/product/a123-ahr18700-f1-kers-cells

krasin 12y ago

In my non-educated opinion, one should never regenerate energy to a Lithium battery of any flavour. All of them are too unstable. A supercapacitor is what should be the destination for the regenerated energy: it's empty by default; stable; could be discharged at high rate

jgable 12y ago
This is indeed a non-educated opinion. Please don't spread FUD. Lithium-ion batteries are perfectly safe to regen. You need to monitor the cell and pack voltages and limit regen under certain conditions, but it's well understood how to do this. Any electric vehicle with a lithium-ion battery (and there are millions of them, from skateboards and scooters to cars and trucks) does regen braking. Without regen, you lose one of the most compelling advantages of having an electric vehicle in the first place. In general, supercapacitors do have much better power density than batteries, but much worse energy density, making them impractical for vehicles at this point in time. There's a reason the vast majority of electric vehicles today use lithium-ion batteries. Disclaimer: I was formerly a controls and systems engineer for a hybrid-electric vehicle company.
- krasin 12y ago
  What you are saying (please, correct me, if I am wrong again), is that the Li-Ion batteries are unstable, but you can keep them safe (no over-current, no over-charge, no over-heat). That's fine. After all, multirotors are also unstable, but they fly pretty good. What I don't know (and where I might be totally wrong), is how bad are current supercapacitors in energy density aspect. The wiki page about Supercapacitors [1] mention it's 10% of Li-Ion, but I have heard about the supercapacitors which are 25% of Li-Ion (not sure, if they are available on the marker, [2]). With 25% of Li-Ion, the supercapacitors for regen would be a better choice than the batteries (see the reasons in my first message). At 10%, you're correct. 1. http://en.wikipedia.org/wiki/Supercapacitor http://en.wikipedia.org/wiki/Supercapacitor 2. http://www.technologyreview.com/view/521651/graphene-supercapacitors-ready-for-electric-vehicle-energy-storage-say-korean-engineers/ http://www.technologyreview.com/view/521651/graphene-superca...

at-fates-hands 12y ago

Or you could learn how to powerslide. https://www.youtube.com/watch?v=2QJVDGtzvEE https://www.youtube.com/watch?v=2QJVDGtzvEE Not sure if this is feasible on this board, but you never know. If the wheels are soft enough, I think you could pull it off.

philsnow 12y ago

I face a similar issue with my honda civic hybrid: they have worked to let you pretend it's a regular internal combustion engine (it looks nearly identical to the other honda civic trims, down to the instrument panels), but you _must_ actively pay attention to the battery level if you don't want to be surprised when trying to pull into traffic (if the battery is under half, it's _much_ more reluctant to boost your acceleration) or trying to brake (if the battery is topped out, it does not assist your braking _nearly_ as much). In general, if you're trying to evade (either with braking or acceleration), you have to know the state of your battery or else the car will not perform the way you think. I don't know if all hybrid/electric cars are this way or if it's specific to my particular year of the HCH or what.