Speed/Watts test, more speed = MUCH more watts

[Debunker]

I make recently a 3000w motor E-bike, whit 3 electric power adjustments, according to reads, 1rst caps the motor to 900w, 2nd 1200w or so, and 3rd goes full, burst 3400w for one second or two and stabilizes around 2400w as time pass.

Well... lets test that babe, plain track, no pedestrians, all green.

-1rst test 900w cap, Max speed 50km/h (around 31 mph) wooo, not bad for a start.
-2nd test 1200w cap, Max speed.. more or less the same... hm... is this 3 shift piece of crap working?
-3rd test, full power 2500!! 65km/h (around 40mph) What the... its almost 3 times the power!!?? Why??? Whyyyy!!???


And there's why... the speed/power equation is a bitch.

I'ts not that I'm dissapointed, I highly doubt that anyone needs more than 30mph in a friking bike, but the power scalation is just insane.. according to simulator, to go 100km/h (62mph) you need +7200 watts, and so on, and of course, I can make more than 70 miles if I don't pass 20mph (around 32km/h) or so, but the battery only gonna last for 21 miles if I go full power.

The conclusion is... at actual development level, the most practical solution if you want the best is to go for a 1000w mottor and 48/52v battery whit a good amount of amps, at that point... every small increase is gonna cost you much more than it gives. At least is what I come of whit the test.

What do you think is the best performance/configuration?

 

[amberwolf]

-3rd test, full power 2500!! 65km/h (around 40mph) What the... its almost 3 times the power!!?? Why??? Whyyyy!!???

Wind resistance.

Make a velomobile with a very aerodynamic shell and you could cut that way down. Probably by half or more.

Just dress differently (smoother) and you could reduce it a little.

Ride in a different posture, and you'll change it up or down depending on whether it's more aero or not.

And of course, it also depends on the efficiency of your particular motor/controller/battery system at any particular speed.

It also makes a difference if you are contributing via pedals, which also means your gearing is important, as it changes the upper/lower limits at which you can provide significant assistance.

If you're interested, there's lots of discussions about how this stuff works, but not sure of any one search that would find them all. Search terms like
aero*
rolling resistance
wind resistance
watts speed
power speed
will find at least some of them, though there will also be a lot of irrelevant results. (and that's just here on ES, not counting the rest of the web).

What do you think is the best performance/configuration?

There isn't one.

Or rather, there isn't a single configuration that is best performance for everyone--each situation is different, as is each bike (or trike or other vehicle).

That's why this thread
https://endless-sphere.com/forums/viewtopic.php?f=3&t=66302
exists, because all of those things and more determine what would be best for any given rider.

 

[MadRhino]

... I highly doubt that anyone needs more than 30mph in a friking bike...

Some bikes are not friking, obviously. I like more than twice that speed. My street bike sees bursts of 20kw everyday, 25kw occasionnally, and set to feed max 32kw.

What do you think is the best performance/configuration?

The best power to weight ratio of course. I am at theorical 463:1 (w:lb). Real effective ratio is lower but still pretty high. The next will beat it.

 

[d8veh]

You can't ignore the motor's winding speed. It's probably the most important characteristic. It affects speed, torque and power. Without knowing the motor's kV, you can't make any sensible judgement of how much power to give it, what voltage to use or how fast it's going to go.

 

[dogman dan]

At some point, you do reach the motors max RPM at a given voltage, however many watts you feed it, its topped out. You can see this best by looking at no load rpm at different voltages, which sometimes is in the motor spec sheet. When you go too far past that motors capability, it just melts. which is kind of fun in a pervert way.

So if you want to haul ass, you need to do like Mad Rhino, and use a big motor that can do the high rpms and has the heavy copper to take the watts. This costs you, in motor weight, in watts, or watt hours, or put more simply, you can't use small cheap batteries anymore, and your motor will not weigh 15 pounds or less.

In terms of just wattage, I found about 400w gets you 20 mph, 1000w gets you 30 mph, but 40 mph takes a whopping 3000w. Because of shitty aerodynamics of a guy sitting upright on a bicycle, you really take a beating in power use above 30 mph.

this is why we will say over and over,, dude, just build your first bike to go 30 mph, 1000w is plenty, etc. 52v max, etc. Once you get so hooked you need an ebike 12 step program, you can then fork out the cash to go 40-50 mph.