Don’t forget abou the weight of the motor and the rest of the setup.
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on flat ground the weight doesn’t effect the drag at constant speed… only if you’re going up hill
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hah, that’s why you left off the end of the quote:
That’s under ideal conditions.
most of the losses other than copper losses (which are lower for the same performance with bigger motors) are wind drag losses which are proportional to the frontal area and drag coefficient (affected by shape) not the weight
for example a tesla going 70mph uses ~45kWh to go 135 miles… its kinetic energy at 70mph is only about 0.3kWh… assuming the motor is 90% efficient, only about 0.7% of the motor output goes to kinetic energy the other 99.3% goes to blowing the air around and deforming the tires.
you can double the weight of the car and the kinetic energy portion doubles to only 0.6kWh out of total 45kWh consumed.
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ups… Just realised that its the bs miles system.
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But you have to accelerate that additional mass if you don’t plan to push start every time.
see above
… same…
I mean thats just an invitation for skewing up results. My lowest so far was 7.8 Wh/km so 13 Wh/mi I guess.
Ok that is interesting. But. Air resistance is quadratic and no one here rides at 70mph, especially not if we are talking about efficiency. And the drag coefficient of a skater is probably a lot lower so that mass becomes more important?
a 200lb skater doing 30mph only has 2.2 watt hours of kinetic energy… where do you think the rest of the battery juice goes and how much do you think the 2.2 watt hours of KE portion will increase if you add a couple pounds of motor mass? not to mention you get ~70% of the 2.2 watt hours back from regen braking.
approximately every doubling of copper mass in the motor halves the copper losses and motor heating.
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I don’t actually think that a bigger motor mass makes a difference for power consumption. I was just a bit surprised about the dimension of the air drag (and other drags/forces).
see above
I don’t want to clutter this thread too much, but you would say that a 80100 is amongs the more efficient motors if you run it at low currents and go slow?
And why are two motors more efficient?
if one motor has half the resistance at the same kv (double the amount of copper), the bigger motor will generate half the heat/copper losses, all else being equal (same acceleration, performance, gearing etc)
Ok. But somehow the resistance of a 80xxx is often higher than that of a 63xx. That’s why in that case at least the smaller motor is more efficient, I guess.
it’s not only the size of the motor but the percentage of the innards that are filled with copper… it’s certainly possible a larger poorly wound motor could be less efficient (higher electrical resistance) than a smaller optimally wound motor. it’s just generally easier to get lower resistance when building a larger motor but also more expensive in materials. you want lowest possible electrical resistance at a given KV for efficiency. also considering iron losses from spinning the motor fast there’s some circumstantial evidence that it doesn’t make make much sense efficiency-wise to go above 180-200kv for our application.
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I see, that makes sense.
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It’d be a good idea to keep track of which motor manufacturers provide the lowest electrical resistance for each KV based on some kind of independent testing.
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wow, very very interesting! Did not know the weight has such a small effect (on flat highways)
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