
Drivetrain Design for Boosted's Electric Skateboard - skdoo
http://boostedboards.posthaven.com/technical-progress-part-ii-dual-motor-drivetrain
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staunch
Any chance these will ever get down to ~$300? I guess what I'm asking is if
this is the Tesla Roadster and there's an economy model a few generations down
the line? Or will this always be for people more serious about using them for
commuting, etc?

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skdoo
It's possible to get something like an electric Razor scooter for ~$300, but
the parts they use to hit that price, like lead-acid batteries, make it a lot
less appealing.

Just like a car or motorcycle, right now there's a floor to how cheap it can
be and still be great. If that gets lower over time, all the better.

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dmd
It looks amazing, but I'm having trouble understanding where the power comes
from.

The Kickstarter says 20 mph, 6 mile range, 2000 watts, which gives an energy
of 600 watt hours.

A Macbook battery is around 60 watt hours, and weighs about 1.5 pounds; 10 of
those would weigh 15 pounds - and take up a ton of space. I don't see the
volume of even ONE in any of the photos I've seen.

Where's 600 watt hours of battery hiding?

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skdoo
The battery is just under 100 watt hours. The motor power lets you accelerate
uphill, but the range is calculated from riding at a constant speed on flat
ground.

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jlgreco
I wonder what sort of grade it can climb, and how far. As a "last mile"
vehicle this looks quite promising but for me the "last mile" of my commute is
my entire commute (well, two miles), and it is straight up a hill.

Eh, walking is probably good for me...

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clavalle
I rode one of these at SXSW. It has a lot of torque. I am 230 lbs and it had
no trouble getting to top speed in a hurry. I didn't try it on a hill but I
bet it'd do fine.

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zwieback
I love this post because it shows some real engineering. The fact they put so
much effort into the test equipment shows that there's some serious
characterization going on vs. just throwing together parts.

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pocketstar
I really wouldn't call this "real" engineering. As a mechanical engineer it
really sounds like they literally threw it together and hoped it fit after
they tested the motors "...models were assembled together in the CAD software
to check for fit, clearance, and interference." I saw no mention of fatigue
analysis or FEA, both are now days required for "real" mechanical engineering.
Without that just cross your fingers the motors don't fall off after 1000
miles. Other than that it is pretty comprehensive.

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pravda
>I really wouldn't call this "real" engineering.

Throwing stuff together and seeing if it works is the essence of engineering.

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jacquesm
How so?

Properly engineered stuff will work as designed. Imagine an A380 falling out
of the sky on the test flight and engineers exchanging betting money based on
whether it flew or crashed. "Well, that didn't work.".

Engineering does everything to take the uncertainty out of design as much as
possible. It's the anti-thesis of throwing things together to see if they
work.

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pravda
Ok, there are some things that don't lend to the iterative approach. Airbuses,
bridges and skyscrapers would be three examples.

When you are designing the wing for the A380, probably a good idea to bust out
the FEA software. But it's still going to be tested with hydraulic rams.

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guiomie
As far as I am concerned, bridges have fallen, buildings have broken, and
airplanes have crashed. I guess its a different iterative process then
software, but neverthless, it is an iterative process.

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jacquesm
I really hope the link between the remote and the board is secured properly,
it would be a really nasty prank to overpower the transmitter from some
vehicle and to cause it to accelerate or come to a sudden stop. Griefers are
not limited to being active online.

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doorhammer
I think this is still, by far, one of my favorite "last mile" solutions. It's
got a pretty slick look, it'll do basically all of the work for me, and I
could carry it inside somewhere pretty easily.

Biggest downside I'm wondering about is only being able to use it when it's
dry out (not sure there much to be doe about that while staying reasonable).

I'm a fairly avid cyclist, though. I think than between a boosted board and my
trusty bike, I'd cover a pretty huge swath of my use cases.

Really interested in this.

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oneiric
I've ridden a long board in the rain. My legs have never been so wet. FAR
wetter than biking or walking in the rain.

With this at least you could wear boots because you wouldn't have to
kick/push/coast.

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robomartin
One of the reasons for which motors in scooters and other electric vehicles
are large and bulky is that they have to be designed to last a long time in
real world environments.

The motors being used for this project are hobby model aircraft motors. These
motors put out a lot of power per unit volume but are most definitely not
designed for continuous duty at anywhere near to full output. They are also
not sealed against the elements and have bearings selected for reasonably
balanced loads with relatively low radial loads.

I have piles of these on my workbench ranging from cheap Chinese units to top
of the line German designs. I use these on our planes, helicopters, multi-
rotors, boats and cars. At the top end you have amazing hand-crafted quality
with a prohibitive price (unless you want to pay $8,000 for a skateboard). At
the low end they are cheap and they are junk. I've seen everything from
magnets coming off, coils burning out, power leads coming off, bearings going
bad prematurely and shafts bending.

In short, while the design process is interesting, I think the most
fundamental flaw is being ignored: The motors are not designed, nor are they
suitable for, this kind of an application.

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kunai
Obligatory: [http://xkcd.com/139/](http://xkcd.com/139/)

What are the safety concerns of something like this? A top speed of 20mph will
definitely be unstable for general usage, and even 15 seems more like bicycle
territory, where you're seated and have an aerodynamic shape.

We might see many people falling off of these in the future...

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penrod
A longboard turns in the direction you're leaning and so is dynamically
stable. In fact (counter)steering is more intuitive than on a bike because you
don't have to coordinate lean and handlebar angle.

The main issue with skateboards is 'speed wobble' vibration in the trucks, but
a well set-up board generally isn't prone to this.

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devenson
Most wipeouts I've had on my longboard are when the board stops suddenly from
debris and you continue moving forward, usually with your feet trailing
slightly behind. Its a recipe for injury, and its why this mode of transport
is only for those capable of taking a good tumble every now and then. The
solution is to not travel faster than you can run, and to always be vigilant
for small rocks, twigs, sand, and especially things that will jam under a
wheel but continue to slide forward like pinecones.

The length of the longboard mostly prevents speed wobble which is an
uncontrollable side to side swaying which tends to increase in amplitude once
it starts.

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Widdershin
A few addendums, from someone who spends too much time and money on longboards
built for going fast. You generally only encounter the issue of the board
stopping suddenly on small debris (referred to by street skaters as
'chalking') when you are traveling close to walking speed on small wheels. I
personally skate around 3x walking speed, and these boosted boards would make
that even higher.

Secondly, speed wobbles are caused by riders primarily, with gear only
impacting it slightly. Put a new rider on a fantastic downhill setup, and
they'll probably get speed wobbles, whereas experienced riders can have no
trouble riding short, turny board at highspeed. (Look up Maryhill for more
info, it's a race where slalom boards are commonly used).

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grecy
Can you elaborate more on what newbie riders are doing wrong to induce speed
wobbles?

(I'm a snowboarder, and am thinking a lot about getting a longboard for my
~4km commute that I'm currently riding)

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Widdershin
It's partially about weight distribution, and partially about confidence. For
the most part, biasing your weight distribution towards your front foot, and
making sure you lead your steering with your front foot, and you'll be fine.
The rest comes with experience. Does your commute contain any downhill
sections?

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penrod
Absolutely correct. On a longboard at speed, you have to keep your weight
forward. This is partly to keep the front truck under control, and partly
because flex in the board means that the end of the board with most of the
weight steers more.

If you panic and lean back, you're effectively only steering with the rear
truck, which is _not_ a dynamically-stable situation. Things go wrong very
quickly at that point.

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Widdershin
Ah, I tend to keep my weight fairly centered at speed so I'm stable if I have
to break tuck. Also, I don't ride a deck with any flex, and I ride split angle
trucks so I inherently have more turn in the front. But yeah, for beginners,
weight on the front.

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penrod
Good point. A centered stance might be ideal, and may just seem 'forward' in
comparison to the typical shortboard stance.

And now I think about it, it might not be board flex that limits front-truck
turning when leaning back - rather, the lack of weight on the front truck
might allow the outside wheel to lift. Either way, it's a bad situation.

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mike_esspe
Can you apply this to folding kick scooter?

Lightweight electric kick scooter could be useful to larger audience as a
"last mile" solution.

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8ig8
For more than a year, I commuted to and from work (3 miles each way) on a
lightweight electric scooter I bought on Craigslist for $100. It's been a
while, but I used to skateboard, surf and snowboard, but having the handlebars
of a scooter in an urban environment is huge for me in terms of control and
safety. I used to call it the poor-man's Segway.

Edit: Not mine, but these look nice:
[http://www.goped.com/products/Electric.asp](http://www.goped.com/products/Electric.asp)

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mike_esspe
They are extremely heavy.

My current kick scooter weights 12 lbs and i consider it heavy. I can't
imagine handling 35 lbs, my bike is lighter :)

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ballard
Awesome.

A go pro video of going from Filbert and Lyon to Filbert and Van Ness, now
that would be rock: [http://goo.gl/maps/OlHc7](http://goo.gl/maps/OlHc7)

For those that don't live in the city, it's one of the steepest streets in the
western hemisphere.

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nl
[http://www.strava.com/segments/948473](http://www.strava.com/segments/948473)

The 11% average over 1km isn't too bad, but the start looks pretty steep.
Strava shows it at up to 40%. That's not exactly 100% accurate, but I've
ridden 25-30% slopes on Strava and they are hard enough that on my road bike I
can't stay seated (the front wheel comes off the ground) and if it is the
slightest bit wet the rear wheel slips when you stand.

I'd be very impressed if this can make it up there with a person on it.

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nikatwork
I'd love to see a mountainboard/pneumatic tyre version of this for us poor
souls cursed with terrible road surfaces. I'd also love to see compatibility
with Original Skateboards spring trucks.

But anyways fantastic product, I'll definitely be picking one up at some
point.

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beambot
On the image showing the brushed vs. brushless... How much of that size
difference is due to gearing? A scooter shaft's output is much lower RPM than
a skateboard. Your gearing seems to be via belt drive.

Any chance you'll sell just the motors...? ;)

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skdoo
You're right, there's a gearbox on the brushed motor and not on the brushless
one. The gearbox is the part with the shaft sticking out, and the motor is the
part with the heatsink fins.

And you can buy the motors already! We are using a slightly modified version
of a RC airplane motor. Our first prototypes used motors we bought at a local
hobby shop.

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samstave
Can we buy a kit of the motors and drive train and put it together ourselves?

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ececconi
I really wish the city I live in has much better bike lanes or sidewalks so I
could use this thing to get from point a to point b further than just my
suburban neighborhood. I can't wait to see people riding these things in the
city.

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Yaggo
I wonder if they ever considered hub motors for better efficiency and quieter
operation (no belt), or would it be too big technical challenge to custom-
build (basically the wheel and motor would be single integrated unit).

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ballard
Great video about boosted

[http://youtu.be/U1scP9uZP9Y](http://youtu.be/U1scP9uZP9Y)

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pkorzeniewski
Interesting, but I'm still waiting for hoverboards.. 2 years to go :)

