@dth2m5 the answer: yes, it sounds appealing. but how is it possible?
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It’s not possible – this is all marketing nonsense and they have found the facts-based crowd and promptly evacuated.
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Hello all, we’re working diligently and will have another blog post and also contribute to the great conversation that has been happening so far. Will post tomorrow.
Do you think it’s at least worth it to do the math to prove that reducing moment of inertia is insignificant?
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Newton’s third law for a vehicle consisting of a turning wheel and a board+rider is governed by these two equations:
(1) Force_wheel = mass_total * acceleration_linear (2) Torque = Moment_of_Inertia * a_angular
To combine the equations together, start from the fact that the force applied by the wheel is given by the torque and radius of the wheel:
(3) (Torque/radius_wheel) = mass_total * acceleration_linear
This lets us substitue equation (2) into equation (3), so:
(4) Moment_of_Inertia * acceleration_angular / radius_wheel = mass_total * acceleration_linear
Isolating the term we care about, linear acceleration, yields:
(5) acceleration_linear = (Moment_of_Inertia / radius_wheel) * (acceleration_angular / mass_total)
Changing the wheels doesnt affect angular acceleration. It affects the mass of the vehicle, but only very negligibly (like maybe 0.5 lb, relative to the total weight of the vehicle which is close to 200 lb). So if changing the wheel increases wheel radius, but decreases the wheel’s moment of inertia so the value of (moment_of_inertia / radius_wheel) doesnt change, then linear acceleration won’t change.
This happens to be the exactly the same term that I calculated in my previous post, radius / moment of inertia, and where we found that the prototype wheel has a similar ratio of radius to moment of inertia as 90mm Flywheels. At the time I thought that the analysis was incomplete as it didnt consider the mass of the rider. But after exploring the more complete picture, it turns out acceleration is still governed by the same ratio.
Long story short, yes it is possible to have a larger wheel without impacting acceleration or range. How do we intuitively interpret this? Well, it takes a lot of effort to spin up a wheel. Imagine how much effort it takes to twirl a shotput, as opposed to something like a tennis ball. It takes a lot of extra torque to spin up the shotput. By reducing the moment of inertia of the wheel, we can divert all that extra energy that is being spent spinning up the wheel, and divert it to accelerating us forward instead.
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yes, but correct me if i’m wrong then it won’t give appreciably higher top speed as in the title of this thread…
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Compared to 90mm flywheels, roughly 11% higher top speed no? Assuming top speed is electrically limited, not aerodynamically limited anyway. That’s not a mind blowing, but actually it’s really not a trivial number. Its similar to going from 10s to 11s, essentially for free! And even if top speed is aerodynamically limited so that practically you dont actually get that top speed increase, it still means you can increase your gear ratio by 11% instead, to trade that theoretical top speed for torque.
I’m sure any of the car guys here could tell you how much they’d love to have a bolt-on mod that would instantly give some 25 more hp, while simultaneously reducing weight, and possibly improving ride quality!
Dunno man, I for one think this is a cool concept. Whether these guys will deliver a good product has yet to be seen. But the math shows there are significant gains to be had.
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No. They should just make 110mm spinner rims (compatible with kegel-core pulleys and normal-length axles, installed as an 8mm speed washer) so I can buy them for a dope-ass tricked-out shortboard and do what marketing does best – sell something “cool” – but not some kind of fantasy-land reinvention of a longboard wheel by folks who don’t seem to have any experience at all in longboarding but sound more like a venture-capitalist-funded dream-vision reality-production team who are about to sign up for some longboard-physics courses.
It’s almost certainly mostly limited aerodynamically and in almost every other way aside from wheel moment of inertia, which has virtually no effect on top-speed, only the most ridiculously-negligible effect on acceleration and range. And the ridiculously-negligible effect on range is only because the drivetrain is not 100% efficient.
But they probably aren’t going to listen… and I’m not even charging them for the advice…
If they want to apply this kind of expertise into electric skateboards, it needs to be put into high-drain, high-capacity, long-lasting, cold-temperature-tolerating, lightweight, fast-charging cells that don’t turn into an inferno at the slightest mishap. THAT’s where the improvement needs to take place. It’s the only reason electric longboarding didn’t happen 30 years before it did-- because batteries weren’t up to par yet.
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@Jmding you can have a larger wheel without affecting acceleration by also changing the gearing, but this doesn’t get you appreciably more top speed. if you increase the wheel diameter and proportionately increase the gear ratio, only then will decreasing the moment of inertia of the wheel begin to have real but subtle benefits, but again, not appreciably more top speed, acceleration or range, once you factor the 200lb rider mass. the extra top speed you mention with a bolt-on larger diameter wheel and no gearing change always comes at the propotionate expense/loss of vehicle thrust & acceleration, unless the original wheel you are comparing to has heinously high efficiency losses to begin with from rolling resistance.
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I thought that was racing flames It is well known that racing stripes have no effect on ride quality.
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@taz, the hell they don’t… I added flames and underglow… now I go 5mph faster and my board is more stable
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You are obviously confusing the effect the underglow has with the one from the flames. Make an experiment in a controlled environment such as this one and then we will talk.
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I wonder if the color of my RGB underglow has any effect 
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only if the colors changing according to the actual speed… you didn´t know that???
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Of course they do. Don’t be ridiculous, it’s called the doppler effect. I have to deal with it every time my battery is more than 50%. Fortunately, space/time bending only happens between 90-100% battery, so I have to be careful with the throttle, otherwise I may end up in the Jurassic period.
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See for me its the opposite… When i push the throttle, time begins to slow down, like some barry allen shit. Alas, never thought the lights could have something to do with it. Might have to lessen the strobe time to counteract the time phenomenon.
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just change the rgb scheme and all will be good… you run that shit backwards. first blue than into red…
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Ofcourse! Great Scott! This changes everything!!!
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@Jmding You are suggesting that if the 100mm wheels give 11% higher top speed than the 90mm wheels, then by reducing the 100mm wheel’s “moment of inertia value,” so that “the value of (moment_of_inertia / radius_wheel) doesnt change”, then the 2 vehicles can have equal acceleration. this is false.
consider a 200lb (90.7kg) rider with 100mm vs 90mm wheels, same gearing ratio, same value of (moment_of_inertia / radius_wheel) for both wheelsets.
60 / (2 * pi * 190kv) = 0.050259 newton meters per motor amp (KT) 0.050259 KT * 100a motor current = 5.0259Nm motor torque 38t motor / 16t wheel = 2.375:1 ratio 2.375 ratio * 5.0259Nm motor torque = 11.93651Nm wheel torque
90mm wheel (11.93651Nm wheel torque * 1000mm) / ((1/2) * 90mm wheel) = 265.25 newtons thrust 265.25 newtons thrust * 2 motors = 530.5 newtons thrust 530.5 newtons / 90.7 kg = 5.84m/s^2 acceleration
100mm wheel (11.93651Nm wheel torque * 1000mm) / ((1/2) * 100mm wheel) = 238.73 newtons thrust 238.73 newtons thrust * 2 motors = 477.4 newtons thrust 477.4 newtons / 90.7 kg = 5.26m/s^2 acceleration
conclusions: the 100mm wheel with 11% higher top speed & identical “(moment_of_inertia / radius_wheel)” has 90% as much thrust & acceleration compared to the 90mm wheel.
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