how come it takes so many watts and 8s escs

[Hummina Shadeeba]

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/__24754__Turnigy_Trackstar_1_5th_Scale_Sensorless_200amp_8s_Opto_Car_ESC.html

 

[torqueboards]

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

Opto is a better bet though.

 

[Hummina Shadeeba]

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

 

[Chalo]

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.

 

[brent]

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?

 

[Chalo]

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.

 

[brent]

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:

 

[made_in_the_alps_legacy]

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/__24754__Turnigy_Trackstar_1_5th_Scale_Sensorless_200amp_8s_Opto_Car_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/viewtopic.php?f=35&t=58661&p=875699&hilit=battery+range#p875706

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

 

[Hummina Shadeeba]

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.