Lithium Battery Pack Design for Boosted's Electric Skateboard
boostedboards.posthaven.com
boostedboards.posthaven.com
I'm not exactly sure how much it costs them to produce the battery, but it looks like single cells of similar LiFePO4 batteries are about $20/ea. With 12 of them, that's $240. Add maybe $50 for the BMS and $10 for the enclosure, and the whole battery pack is maybe $300?
It'd be a shame to have to replace an entire $1,300 skateboard after a few years when your battery capacity is reduced, when all you needed was a $300 battery pack. Hopefully "non-swappable" means something besides "non-replaceable".
The whole reason I'm asking is this 20 year old skateboard I have down the hallway, which is working flawlessly with every single component easily swappable :-/
User serviceable is a part of the culture. It would be nice if that could survive.
BMS PCB has high current input rings and a blade connector for balancing (like removable laptop batteries).
Bottom of case has screw lugs going up through high current input rings in PCB. Battery has ring terminals that are crimped & soldered to high current wires. The battery is in a protective casing that holds mating balance connector and injection molded features keep the high current ring lugs in place.
Battery drops into board, high current rings go over lugs and balance connector engages.
Rigid plastic goes over the top of all this (bottom when in riding position) with silicone seal around the perimeter. High current lugs go through the cover. Special ratcheting thumb screws tighten down the cover using the battery lugs as a mechanical connection while also pressing the ring connectors into the BMS PCB. Conductive grease on the PCB helps keep out water.
Battery would be 100% rigid, no dangling wires. Installation is two lugs, drops in, can be done by hand. Battery should come with a protective pouch or have integrated flip-over cover so it can be dropped in a messenger bag etc.
Solves I think all the issues, including avoiding costly or underperforming connectors, environmental sealing, ease of use, and the expensive BMS does not need to be attached.
I emailed them something to this effect, since they asked for input, though it sounds like they've purchased battery packs already.
Plus they may have considered this, it sounds good but I know production high current battery stuff is really tricky, I've looked at the area quite a bit.
For the days I don't feel like riding a motorbike, I guess I'll keep using my regular $100 skateboard + train combo.
My initial intent was actually for carrying stuff for me. The idea came one of the many days that I was carrying a huge laundry bag to the laundry store a couple of blocks away. If only I had something I could just place the bag on top of with wheels. Then I thought it could also carry my backpack to school everyday, groceries, etc. Maybe I could tie a surfboard-like leash to it, and it would have a sensor attached that upon pulling it would know which direction to follow me on. The possibilities for my laziness are endless! Anyways, we ended up going with another idea, probably for the best, since the kinda board I was thinking off was probably out of the scope and time we had for the course.
Looking forward to how this goes. Best of luck to all involved.
If there was one thing about it that had a learning curve then it was pushing. Knowing where to put the food and how to evenly push off takes some getting used to but that's not even something you have to do with the boosted board.
It's weird that skateboards became popular and longboards took much longer to go mainstream. Skateboards are roughly like BMX trick bikes, cool but limited use and hard to learn, longboards are the road bike equivalents.
http://batteryuniversity.com/learn/article/types_of_battery_...
One thing I am missing is the ability to disengage the electric motor from the wheels - as it is, you can't just free roll on the board if you want to save power or the battery is depleted; the motor is engaged to the wheels at all times. I guess it is a difficult problem since no boards seem to be able to do this.
(By the way, I used to ride five-six kilometers through downtown Copenhagen to work, charge at the office and do the same trip back at the end of the day.)
Instead of a remote control with buttons to control the speed/braking of the board...
What if it had a pressure pad on top so that it would accelerate when you put more weight on the front [1], and brake when you put weight on the rear. How would that control scheme compare (after getting used to it)?
[1] - The opposite arrangement wouldn't work, because it would create a feedback loop that'd drop you out of control. As you put more weight back, it accelerates, shifting your weight more back, accelerating even harder.
B456 now.
"...the battery needs to deliver thousands of watts of electrical power"
should read "hundreds of watts" -- the watt has a unit of J(oules)/s. Thousands of watts then refers to thousands of Joules per second. They later clarify actual power output as being a sustained 230W (or 384W for a 10sec burst).
If you take hobby remote control cars as an example, I just bought an average lithium powered one that can do 45A at 11.7v, or roughly 500w to drive a <5lb toy car (very quickly). A 12lb skateboard and a 180lb rider will need several thousand watts peak I would imagine, at least.
If you're sprinting or accelerating hard you could easily be putting down 800-1000 watts or more.
Electric motors have a far greater range of RPM at which they can deliver a sufficient power.
A motor that delivers 700W attached to any gearbox will deliver 700W after the gearbox (minus losses). The difference is that shaft will rotate at different speeds and with a different number of Newton / Metres. A slow shaft attached to a 700W motor (at full power) will have more torque than a fast one.
If that's what you're saying, you're making several false assumptions and your statement is incorrect (because electric motors DO have a medium high RPM range where they are much more efficient than when near stall). Although it is true that (for some but not all types) of motors the stall torque is very high, that uptick in torque does not and cannot rise high/fast enough to balance the loss of work output caused by choosing a gearing that results in a slow motor shaft RPM. Recall that work is force over distance. A completely stalled motor is doing no work yet consuming prodigious amounts of power (which all goes to waste heat). In order to produce "700W of mechanical power into the gear train", a motor in a stall or very near stall would have to produce infinite torque, which is clearly impossible. Furthermore even if you consider, not a stalled motor shaft, but one turning below optimal RPM, you don't always get twice the torque when you halve the speed, you get maybe a fraction of that. So there's still a power/efficiency curve. Finally, a motor that is turning at an RPM significantly slower than its optimal rate is usually drawing much more power than it will for the same input voltage if running at higher RPM, so looking just at motor RPM vs torque at the shaft as a measure of output power ignores the important fact that you're putting a lot more electrical energy into the motor to get that output.
The only way in which your comment makes any sense would be to talk only about torque and say that for most types of motors, if the motor has enough torque to turn the drivetrain at operating RPM then it will almost certain have enough torque to start the drivetrain from a dead stop. So the motor doesn't necessarily need changeable gear ratios in order to get going if you ignore or amortize the energy wasted getting up to most efficient operating speed.
Not only is it fascinating, it's great branding and marketing collateral. I wasn't sure I wanted a boosted board when they ran their KickStarter but I sure am ready to buy now.
>Cells
After realizing the inherent risks in some lithium chemistries and finding it difficult to source low volumes of high-power cells, we decided to use a different lithium-ion chemistry known as lithium iron phosphate (LFP or LiFePO4).
Not hating on the zboard, they're just different markets.
Would be amazing to control with the Myo. :D
Since I was young I have dreamed of a "boosted" snowboard, with a snowmobile-like tread that came down the middle and would accelerate me in slow areas. The weight and noise of an internal combustion engine would have been prohibitive, but clearly we're getting to the point where electric isn't so bad.
If I'm doing snowboard runs all day though, I want to show up with a handful of battery packs and run through a few in a day.
The same would be fun with Boosted. Not being able to replace it means I can't buy a handful of batteries and take them somewhere for a day of uninterrupted riding up and down my favorite hills.
Charge dead packs in the car while you ride and with a few packs you can manage a continuous day of fun. That's not possible with non-removable batteries, and customers willing to pay for all that are good customers to have and indulge.
If I have a fully charged board and 5 friends, I feel like "OMG look at how cool my $1300 board is" is going to turn into "oh it died, sorry guys, more fun tomorrow".
I think that even if people don't buy the spare battery, knowing it's an option will help them feel more comfortable with the $1300 purchase. If the current range falls just short of what you need, an inability to simply buy a second battery to keep in your pack is going to be pretty upsetting. And always being able to keep one topped off at home means that after your commute you can still go out and enjoy your board.
An electric kicker on a snowboard would be great, since it would be easy to keep up with skiers on long traverses. On the other hand, the extra weight is terrible - expensive snowboards use exotic composites to be lighter, and ounces matter when they're out on the ends of your feet.
Also they don't need to maintain ground clearance.
I think a lot of people think voltage means power, so the 9 volt battery probably sounds much more powerful than a 1.5v AA, but they don't realize the 9v has a bunch of smaller cells and the internal resistance is a lot higher, reducing the current output capabilities. I had a guy tell me one time I should hop up the strength of my walking robot by replacing my 6 AA cells with a 9v. :)
My pack is nearly 5 years old.