Weight Sensing Longboard with Inline Wheel Motors

[sk8norcal]

With respect, I disagree for longboarding. In the case of longboarding its pretty typical to shift your weight forward when accelerating downhill, especially when fighting a wind resistance.
.

i realize that, but its different, that lean forward when downhill is slight, you can go down a hill standing up, the acceleration is constant.
you get the most acceleration on a push board when kicking hard from stop,
you upper torso 'naturally' lean forward, its like sprinting.

leaning forward at 0mph is completely weird to a skater.
its almost like leaning forward for a drop in.

yes, the speed wobble thing i thought about before also,
will it be easier to get wobs under acceleration, from the rear weight bias? possibily...
this is a concern more for high powered setups, especially when doing straight line speed while tucking on the flats.
but i think we are talkin about speeds 40+, which i haven't seen anyone hit yet.

regarding using motors to dampen the wobs,
i dont know much electronics, but that sounds far fetched.
if someone can make it work, i would be amazed.
people have experimented with dampeners but it effects the way the board turns.
wobs is a very interesting phenomenon, depends on many factors, flex of the board, looseness, design, bushings, angle of the truck, etc., and of course on the rider.
today downhill skaters routinely go 40,50,60+ (record is 80+)
mostly due to the "RKP" geometry pioneered by Randal trucks.
IMO, the holy grail for truck design is to have a loose turny truck at low speed and somehow offers stabilty at high speed.
Few riders can ride super loose 50degs and bomb hills,
if someone makes a truck that allows your average rider to do it, that would be something...
(and yes, people have thought about on the fly truck/bushing adjustment based on speed sensors)

 

[sk8norcal]

I'm not a fan of software-controlled "soft-starts" of "soft-stops". I rode a popular board that boasts such features, and it was one of the scariest electric-skateboard I have ever ridden. I prefer a direct-drive "instantaneous" throttle-response. It seems like a "traction control" vs "no traction control" argument, and I guess I'm a "no traction control" guy.

i think when i test rode ur board,
wasn't it soft start?
u had it on beginner mode if i recall.
maybe i am mixing soft vs smooth

There is only so hard u can accelerate an eboard anyways, (nothing to grab on to, unless u nosegrab)

I have not yet hit the physical-limit of acceleration. With decent grip-tape and the willingness to lean forward, I imagine it would take a lot of force to shear a rubber-on-grip-tape connection.

i see ur point, meant to say " there is only hard u would want to acceleratate on eboard"

For me, hard acceleration from stop is just not that fun to me, doesn't feel safe, and tires my back leg out.
and yes I have seen the video of you racing corvette. :wink:

 

[EBJ]

i think when i test rode ur board,
wasn't it soft start?
u had it on beginner mode if i recall.
maybe i am mixing soft vs smooth

Yeah, you rode it. No soft-start and no beginner-mode.
Just clean and smooth (linear) acceleration.

 

[Chalo]

Go find me a video of someone taking a slam pushing a longboard on the flats.

Okay.

It took a few minutes to find the first two of them, because there were so many spectacular downhill longboard falls to dig through (including one I found with a fatality). It seems longboarders can easily crack their heads open in conditions where a cyclist would gently apply a brake instead. Q: So why don't longboards have brakes? (A: Because if they did, longboarders would crack their heads open.)

(Videos presented as links to keep the thread tidier.)
longboard crash on flat #1
longboard crash on flat #2

The appearance of powered boards has provided a new, but very predictable, kind of fail video. I'm looking forward to years of entertainment from this stuff, but hopefully not too many fatality videos. The best is yet to come!

electrically powered road rash
dirt path dump on e-board
electrical problem resulting in self-KO

 

[flathill]

Imagine a world filled with no risk takers
What is the purpose of pointing out the obvious over and over
Save yourself
Ruin vibe
I'm retiring on Mars

 

[justin_le]

yeah, that would be holy grail #2, kick-assist.

OK, that grail I'm pretty sure we can reach.

here's holy grail #3,
carving and pumping.
there is a lot of fore/aft weight shifting going on,
experienced riders would not like to be lock into a 50/50 weight distribution at all times.
pump-assist?
carving under acceleration? deceleration?

Now, you are way out my league! OK I don't even know how to pump assist. But I have a feeling that whatever modes are implemented to facilitate the kick-assist would probably help pretty well with the pumping and carving too. What I'm thinking to implement is an acceleration limit of sorts. So when the board detects pulsing changes in the weight distribution, be it from kicking or from pumping, then it attempts to maintain close to a constant speed on the wheels. That way motor wont accelerate or slow down inadvertently from your actions, but would instead strive to keep a fixed velocity as though the board had some large inertia. It would still slowly speed up or slow down depending on the forces, but to really get motor oomph to accellerate or brake you'd have to be steady on the feet.

Anyways, we've got the sensorless field oriented motor-controllers installed and dialed in today and have been having a blast riding around with a temporary throttle control and battery in the backpack. The assist is smooth as silk, and we've got the ramp rates for accelleration and especially for braking set for gradual motor engagement and it's pretty comfortable to ride. The controllers are programmed for 60A max phase current limit in each motor, and that had no problem with any of the hills around here. But admittedly they are just like 4% grade.


Have had a number of test riders Chalo and no fail vid material yet

-Justin

 

[adrian_sm]

Anyways, we've got the sensorless field oriented motor-controllers installed and dialed in today and have been having a blast riding around with a temporary throttle control and battery in the backpack. The assist is smooth as silk, and we've got the ramp rates for accelleration and especially for braking set for gradual motor engagement and it's pretty comfortable to ride. The controllers are programmed for 60A max phase current limit in each motor, and that had no problem with any of the hills around here. But admittedly they are just like 4% grade.

Looking great. Watching with interest.

BTW what controller are you using. Sorry if I missed it earlier in the thread.

- Adrian

 

[Chalo]

Have had a number of test riders Chalo and no fail vid material yet

That appears to be the idea you're getting at. I think the key is a board that responds to what you do kinetically, instead of taking commands you feed into a controller. The heart of all powered vehicle fails is a vehicle doing what it was told instead of what the operator had in mind.

 

[LEVer]

Have had a number of test riders Chalo and no fail vid material yet

That appears to be the idea you're getting at. I think the key is a board that responds to what you do kinetically, instead of taking commands you feed into a controller. The heart of all powered vehicle fails is a vehicle doing what it was told instead of what the operator had in mind.

You mean like this... http://www.youtube.com/watch?v=zqYJQGk5I4M

 

[justin_le]

You mean like this... http://www.youtube.com/watch?v=zqYJQGk5I4M

Ha ha, I'd never thought about taking it quite to _that_ level.

But, I can say definitively that the weight shift control works brilliantly and is a perfect extension of natural boarding motions. We had it running last night and from like 2am to 4am could not get off the thing, zooming up and down the quiet midnight streets, gracefully stopping and accelerating though subtle shifts in position.

I wrote a simple modification to the CA3 code that treats the Aux input and Torque inputs as front and rear weight sensors respectively, so you dial in the scaling factor for each strain gauge amplifier:



The difference in weight between the front and rear is then scaled into a throttle output voltage, that goes above and below a mean value for forwards and reverse torque on the controllers:


The sum of the front and rear weights must also be above some threshold weight in order for the board to work. That way if you just have one foot resting on the deck as you mount or dismount it won't power the wheels, and it shuts off immediately once you get off.


The underbelly with the controllers and battery bay are still somewhat crude, we'll be tidying this up in the shop this evening to make it all look neat and enclosed:

View attachment 1

But even in it's current form you can't really see any of the controllers or wiring because centered and low enough profile that at normal viewing angles it's just a regular deck, with a CA on the front.

 

[LEVer]

This by far, is the best powerboard build I've seen. It combines the stealth and sleekness of Boosted Boards with the intuitiveness and familiarity of use of Zboard. Well done sir.

 

[sk8norcal]

very nice,
I was gonna mention what happens if I foot brake but i think u got that covered.
skaters also unweight the front and rear truck to go over cracks in the sidewalk, hopefully the board will not interfere.

How about doing manuals? and not having the brake activate....
i think the CA should be inside the battery box with a cutout for the display and buttons. (or a display cutout on the top of deck)
now you would be able to nose manual, and also not trip over the display when running off the front....

btw, that girl test rider with the platform shoes and restrictive skirt scares me... :wink:
u should make your test rider wear a helmet.
it would make Chalo happier, or maybe not...

 

[justin_le]

very nice,
I was gonna mention what happens if I foot brake but i think u got that covered.
skaters also unweight the front and rear truck to go over cracks in the sidewalk, hopefully the board will not interfere.

It handles that kind of stuff fine. We rode it between work and home today along many rough patches and speed humps etc. and never had issues. There is a fair bit of software damping that goes on before anything really changes at the wheels, so brief impacts or unweighing don't have any consequence.

How about doing manuals? and not having the brake activate....

Kinda tough to do manuals on a longboard in the first place, but I could see doing a short-board firmware revision to accommodate that.

i think the CA should be inside the battery box with a cutout for the display and buttons. (or a display cutout on the top of deck)
now you would be able to nose manual, and also not trip over the display when running off the front....

We almost did a board cutout for a small screen CA that was flush with the top of the deck, but got a bit concerned that there wouldn't be enough wood left for structural reasons. This will be a later refinement for sure, but at the moment am happy to have a working platform to test and develop a bunch of ideas on. There's a thick plastic bumper in front of the CA as well so that if it goes nose first into something hard, all the electronics and CA enclosure will be spared.

 

[sk8norcal]

manual is a really popular trick in the longboarding world,
especially nose manuals (cant do them to save my life.)

once you board gets some attention,
first thing the longboard kids gonna say is can u do tricks on it :wink:
http://www.youtube.com/watch?v=nPX5AX6qnpI

 

[justin_le]

first thing the longboard kids gonna say is can u do tricks on it :wink:
http://www.youtube.com/watch?v=nPX5AX6qnpI

That is a kind of dancing I could get into, wow! I really didn't realize how much was possible on this platform, but I notice that their decks stick out further over the trucks on the front and back than most of the boards I see here so they have better leverage. To lift up the weight of the onboard batteries would require some leverage for sure.

Anyways, it's just a quick iPhone video but Frank got shot of the board in action yesterday:
[youtube]SzqqD-PYjC0[/youtube]

We've been playing with the gain settings that determine how much you need to shift weight forwards and backwards in order to activate full acceleration and full regen, and I've been steadily stiffening it up and finding it still feels pretty stable. But it might be nice to incorporate integral gain so that your equilibrium weight at steady state always winds up in the middle when you are at constant speed, and leaning only brings about acceleration or deceleration around that point.

 

[sk8norcal]

i don't really understand the last part (electronic noob here)
"integral gain"?
can u put in layman's term?

u have to be 50/50 to maintain constant speed correct ?

ha, I knew u gonna like the 'dancing' :wink:
forget the shuvits,
if you can walk the deck and do a little nose manual, that would be cool enough...
standup check slide without the board interfering would be awesome also.
180 slide to switch.... hmmm.....

 

[liveforphysics]

That is so awesome Justin!!! Woot!

 

[montyp]

i don't really understand the last part (electronic noob here)
"integral gain"?
can u put in layman's term?

It's the I in PID (Proportional, Integral, Derivative) http://en.wikipedia.org/wiki/PID_controller

Basically, it is the part of the control that will take care of the constant (or very slow changing) parts of the system. I'm guessing the integral gain is going to try to figure out where you feel like your aren't shifting your weight too much and still be able to go at a pretty constant speed.

 

[xenodius]

Despite the cool-factor of a weight-sensing throttle, I think I'd prefer a tiny little remote hand-throttle like these Kickstarter folks use:

The analogy is probably pretty similar to ebikes too. I used to believe I preferred throttle control over a torque sensing pedalec style ebike. But then, once I started riding more ebikes that had nicely integrated pedalec I realized that for the most part this was a nicer and more natural control interface between the human and the bike, since it's using the same input (your leg power) that you already use. Similarly, since leaning is such a core part of how you maneuver a skateboard (or surfboard, snowboard etc) I think that it would be a more natural control extention for motor power than moving one of your digits across a throttle. If you've ridden a throttle controlled board, you learn quickly that you need to lean forwards first before you engage it or the board will shoot out from under you. So the leaning already has to take place, and the brain has to learn to do that first in anticipation of you hitting the throttle.

In any case, our brains have a great way of figuring out control schemes and turning them into an extension of ourselves regardless of how they're implemented, so pretty much anything can work. Like gamers who achieve all kinds of delicate feats from pushing buttons on a keyboard or control pad, even though those button presses have nothing to do with the action going on the screen. We are used to pushing foot pedals to accelerate and brake a car, but why not instead have little throttles and buttons on the steering wheel for that? Or why have a steering wheel at all when you could use your feet to turn and then use your hands on a joystick to accelerate? I don't know if anyone's actually studying what is the 'best' way for a human to control a 2000lb vehicle, but given that we're no longer constrained by having to do everything with mechanical linkages like in the old days it's a question worth asking.

-Justin

I like your out of the box thinking When I was a kid I actually told my parents I wanted a joystick-controlled car. I'm not much of a longboarder, but I get what you're saying about leaning. I imagined a throttle that engaged as soon as you try to lean, which I imagine would be disastrous. Now, a 'Segway' CG type throttle would be awesome. If you could manage to control a board like that, well, that'd be perfect!

I've always thought the idea of a torque pedelec is awesome-- a'la eRockit. unfortunately, I expect I'll need a Schlumpf drive for my 20" single-speed KMX. so I can't do torque, but with a single-speed a simple pedelec RPM output might be useful. Especially with your awesome CA throttle ramping. I love you, man.

 

[Chalo]

I've always thought the idea of a torque pedelec is awesome-- a'la eRockit. unfortunately, I expect I'll need a Schlumpf drive for my 20" single-speed KMX.

Powertap power meters have strain gauges in the rear hub; Polar power meters read chain tension from its vibration frequency, like listening to a guitar string. Either of these regimes could be hacked for a torque-sensing pedelec.

 

[xenodius]

I've always thought the idea of a torque pedelec is awesome-- a'la eRockit. unfortunately, I expect I'll need a Schlumpf drive for my 20" single-speed KMX.

Powertap power meters have strain gauges in the rear hub; Polar power meters read chain tension from its vibration frequency, like listening to a guitar string. Either of these regimes could be hacked for a torque-sensing pedelec.

Thankyou for pointing those out-- Unfortunately they're both way too expensive for me. And I couldn't use a Powertap meter with hub-motor. I dunno-- I may end up deciding that a 60t chainring is the better bet, and use a THUN bb.

 

[Kin]

It's already been said, but I love that this is a combination of the best of Zboard and boosted board. And just as a side-project!!

!

 

[justin_le]

Thankyou for pointing those out-- Unfortunately they're both way too expensive for me. And I couldn't use a Powertap meter with hub-motor.

Much less expensive than either of those are the rear dropout chain tension sensors like the TMM device. These measure the deflection on the rear dropout caused from the pedal torque. If you run a a single chainring on the front then you can correlate this plus your cadence data to get actual human watts, but if you have a multiple speeds chainrings or a shifting front bottom bracket, then the torque/tension ratio changes depending on your front gear.

I dunno-- I may end up deciding that a 60t chainring is the better bet, and use a THUN bb.

That would be easiest bet if nothing else. Did you get a 13T BMX freewheel on the back? -Justin

 

[justin_le]

It's already been said, but I love that this is a combination of the best of Zboard and boosted board. And just as a side-project!!

A side project for now, but I do say that if ebikes.ca / Grin Tech stops dealing in ebike stuff some day this will be why :wink: Powerboards are such a thrill to ride, just like I remembered from 7 years ago, and everyone who tests this sports a grin bigger than I've seen from a first ebike ride. We showed our postman who took it for a spin and swears he'll be delivering mail on one in a heartbeat once it's available!

We did a few upgrades to the board in the last little while to better prep it for maker faire. Here's what the underbelly looks like with new panels to cover both the battery pack and the controllers and all wiring. Plus we've got a lumenator light on the front for night riding:
View attachment 5

The motors shells run fairly close to the ground, and have been getting a bit dinged up from occasional encounters with rocks and pebbles. For the most part they roll over objects find just like the rubber wheel, but I'm a bit worried that larger rock could dent the metal and possibly crack a magnet internally:

So we've since wrapped the motor body in several layers of self adhesive silicone rubber tape which should help soften and spread any impact forces.

The toothed interface between the wheels and the motor rotor is holding up great with no signs of wear, and the fit is still nice and snug:


Riding around with it, the stats are almost always coming in at between 10-11 whrs/km. An ebike doing the same speeds and stop-go riding without pedalling would be more like 13 wh/km, so its certainly a notch more efficient, and I'd say thats mostly due to reduced airdrag from being sideways compared to facing forwards where your shoulders and torso have a larger frontal area:


Speeds of 30 km/hr feel really comfortable, while you need to be a bit brave to take it over 40. I'm sure as confidence builds we'll start trying to max it out but so far no one has been able to hit the top-end (which I suspect will be between 45-50 kph)
View attachment 2

Right now we have two batteries, a 3.3Ah nanotech and a 4.0 Ah regular RC LiPo. It's easy to tell which battery is currently connected by checking out the battery internal resistance screen on the CA3. Nanotech is always between 0.36 to 0.38 mOhm, while the 15C turnigy pack is more like 0.1 mOhm.


And since all braking happens via regen, the numbers for this are pretty good, about 10-12% on the flats due to stop and go at intersections, and more like 20% if you ride in an area with more hills:

 

[bandaro]

Subbed. I have built a few boards and some trucks myself, have an idea floating around for electric conversion to try when I get back home (currently in dublin for 8 months studying).

It's interesting how you have the motor mounted to the wheels, I was avoiding having things mounted that low as I was worried about them hitting rocks or bottoming out, do you have to nurse it much/be very careful what you run over to keep the motors clear?

As for the weight activated power, have you taken the board on some downhill runs to see what it does when you slide/throw it around? I take it dancing with this type of throttle would be impossible?

On a side note, I completely agree skating is the best way to get to class, I'm buzzing about 5km in the cycle lane on the road to class every day, and there are times when I wish I had that 30km/h cruise, would be much safer than the 20-ish I sustain. And that breaking ability... the lane isn't nearly wide enough to carve/slide