how come it takes so many watts and 8s escs

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Hummina Shadeeba   1 MW

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how come it takes so many watts and 8s escs

Post by Hummina Shadeeba » Feb 27 2015 3:42am

takes about 350 watts at the cranks to pedal a bicycle 25mph but a skateboard supposedly takes about 1000. Wheres all that energy going?

http://hobbyking.com/hobbyking/store/__ ... r_ESC.html
Last edited by Hummina Shadeeba on Feb 27 2015 4:06am, edited 3 times in total.

torqueboards   100 MW

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Re: anyone use this 8s esc?

Post by torqueboards » Feb 27 2015 3:47am

The ESC is quite huge and it's still only for a single motor.

Opto is a better bet though.
DIYElectricSkateboard.com Electric Skateboard Kits

Hummina Shadeeba   1 MW

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Re: how come it takes so many watts compared to..

Post by Hummina Shadeeba » Feb 27 2015 4:00am

http://diyelectricskateboard.com/produc ... c-opto-hv/
very nice
wonder how efficient more efficient is

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Chalo   100 GW

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Re: how come it takes so many watts and 8s escs

Post by Chalo » Feb 27 2015 4:42am

Hummina Shadeeba wrote:takes about 350 watts at the cranks to pedal a bicycle 25mph but a skateboard supposedly takes about 1000. Wheres all that energy going?
My calculator says that assuming a city bike and a 200 pound rider, 350W at the wheel yields 19 mph.

Bigger wheels are more efficient than smaller ones. Pneumatic tires are more efficient than solid ones. And standing up straight in the airstream is less efficient than crouching down even a little bit.
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brent   1 W

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Re: how come it takes so many watts and 8s escs

Post by brent » Feb 27 2015 5:11am

Chalo wrote:My calculator says that assuming a city bike and a 200 pound rider, 350W at the wheel yields 19 mph.

Bigger wheels are more efficient than smaller ones. Pneumatic tires are more efficient than solid ones. And standing up straight in the airstream is less efficient than crouching down even a little bit.
Care to share how you got 19mph? Maybe I'm missing something, but I don't see how it's possible to calculate speed from just power and weight.
I'd also tend to disagree with the pneumatic vs solid tire argument, but I guess that's really dependent on terrain.


Hummina, where'd you get the 1000W number?

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Chalo   100 GW

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Re: how come it takes so many watts and 8s escs

Post by Chalo » Feb 27 2015 5:47am

brent wrote:
Chalo wrote:My calculator says that assuming a city bike and a 200 pound rider, 350W at the wheel yields 19 mph.

Bigger wheels are more efficient than smaller ones. Pneumatic tires are more efficient than solid ones. And standing up straight in the airstream is less efficient than crouching down even a little bit.
Care to share how you got 19mph? Maybe I'm missing something, but I don't see how it's possible to calculate speed from just power and weight.
http://kreuzotter.de/english/espeed.htm

It works, given correct data.
I'd also tend to disagree with the pneumatic vs solid tire argument, but I guess that's really dependent on terrain.
In the real world, energy lost to jarring far exceeds energy lost to tire hysteresis. That's why Dr. Dunlop's invention became such an instant sensation, and why we never looked back (except those of us who ride skateboards).

If you live in a world covered with float glass or polished steel plates, your results may be different.
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brent   1 W

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Re: how come it takes so many watts and 8s escs

Post by brent » Feb 27 2015 6:56am

http://kreuzotter.de/english/espeed.htm

It works, given correct data.
Misread the original post, oops. Thought he was referring to a hub motor rated for 350W.

If you live in a world covered with float glass or polished steel plates, your results may be different.
Or somewhere covered with decently paved roads. :wink:

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made_in_the_alps_legacy   10 kW

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Re: how come it takes so many watts and 8s escs

Post by made_in_the_alps_legacy » Feb 27 2015 8:50am

Hummina Shadeeba wrote:takes about 350 watts at the cranks to pedal a bicycle 25mph but a skateboard supposedly takes about 1000. Wheres all that energy going?

http://hobbyking.com/hobbyking/store/__ ... r_ESC.html
Hummina Hummina Hummina... I think you mix up "specs" and "reality" and the "built factor" (to compensiate for efficiency losses) we choose inbetween
it's all here :
http://endless-sphere.com/forums/viewto ... ge#p875706
Image

and the same chart with beto's record (black curve is unchanged, I just tried different cubic laws)
Image

Hummina Shadeeba   1 MW

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Re: how come it takes so many watts and 8s escs

Post by Hummina Shadeeba » Feb 27 2015 1:01pm

ok so maybe a bike with a typical pedaler will hit 40kph at 300 watts and a board will hit the same speed at as little as 500...although some people are up to 900. Seems pretty inconsistent but makes me feel better that a board isn't quite so inefficient. but those graphs are average speed as well so not really showing what is required to keep at a steady 40kph

Sure a slick bike wheel with its pneumatics is better on even a well paved road for rolling resistance but even at only 40kph a skate wheel with its low frontal area and lack of spokes spinning back over the top will have such less wind resistance it could trump. That coupled with the crouch a skater can get into I'm thinking a board could win. Wind resistance past 20mph seems to be the real energy sucker.
https://www.youtube.com/watch?v=iCmGj9VbYE4

How much wattage on an electric bike to hit 40kph compared to non-electric? I'm still really trying to find out how efficient the brushless and trapazodial wave electrical system is.

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