Larger motor pulley = more efficient?

How-Tos & Esk8 mechanics Esk8 Mechanics
#34

The more I learn about these motors, the more it seems they are all very efficient in the ranges we use them, and the kind of efficiency differences we may be chasing are relatively small.

Equal Load is a 2s or 3s Brushless Motor More Efficient on the Dyno? - YouTube

#35

If you want the most efficiency then set your gear ratio for lowest no load ground speed you are willing to accept.

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#36

My understanding is the bigger pulley won’t necessarily help increase range, its how you’re using the board with the new pulley.

With a smaller pulley(more torque) you’d be using more battery accelerating hard off the launch, but with the bigger pulley if you are exceeding the new top speeds then there won’t be any battery savings.

its only if you accelerate the same way as before with the bigger motor pulley, then it should be more efficient at the cost of torque.

#37

I think that’s backwards actually, the motor would be doing less work for the same acceleration thanks to the increased mechanical advantage.

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#38

It is entirely dependent on how you ride.

If you ride fast and hard, then bigger motor pulley is going to hurt you.

If you ride chill and cruise, then it is possible because outrunners have a whole lot of magnetic losses, and it is very possible those losses can dominate at lower speeds. Bigger motor pulley means motor spins slower which reduces magnetic losses.

This can only be the case if you a lightly tapping the throttle throughout the ride.

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#39

@rafaelinmissouri shared some interesting findings here The Carver... My final frontier - #210 by rafaelinmissouri

Very surprising that 200mm Kenda tires result in better wh/mile efficiency than 155mm metros. Seems like bigger tires with more rotational mass should be worse on efficiency. I don’t understand it.

I might swap kenda’s onto my TB AT wheels to see if I get the same result.

I’m also coming around to the idea of doing some real world testing / science.

  1. 12t vs 20t motor pulleys
  2. 10mm belts vs 15mm belts

Both tests would involve cruising at 20mph for a couple miles, starting from full battery pack to control for voltage. Anyone have predictions?

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#40

this surprised me as well.
mind you none of it was very scientific.

but metros may have been softer and more contact and yada yada yada!!!

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#41

There seems to be correlation with grip and effeciency. The less grippy tire getting better effeciency, even with the same same size tire a harder durometer seems to get better wh/mi.

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#42

I see this a lot on here, but rotational inertia is not related to rolling resistance at all. An object in motion stays in motion, and all that.

Rolling resistance, as a first approximation on smooth surfaces, is determined by three squishiness-based things:

  • Hardness: The further the wheel squishes into the ground, the more “out of round” it becomes, so it’s harder to roll. If you were to draw a force diagram, resistive forces from the contact patch would have more leverage with a softer wheel that squishes more. For pneumatics, this hardness is the tire pressure, and for urethane the hardness is the durometer. More weight squishes the wheel further, and so of course it increases rolling resistance .
  • Diameter: For a given amount of squish, a larger wheel is less “out of round” compared to the size of the squish itself. More rounder means more faster.
  • Rebound: The process of the contact patch becoming squished and unsquished as it rolls in and out of contact with the ground is analogous to the process of compressing and releasing a spring. The spring stores energy, but not all of it gets released because thermodynamics is a bitch. Some of the energy is lost to the material of the wheel as heat through internal friction. The rebound efficiency of the wheel can be measured by removing all the bearings and junk from it, dropping it on the ground, and seeing how high it rebounds. With urethane, rebound is just down to the chemistry of the compound. With pneumatics, the compound is important, but air is high rebound and rubber is not, so you should have more air and less rubber.

One possible reason people often say that larger pneumatic wheels have more rolling resistance is that they are often run at lower pressures, so they are softer and sink further into the ground.

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#43

No.

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#44

The choice of inputs and outputs is subjective. 1:1 gearing will produce a more efficient heater.

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#45

science_drink

Please do this :slight_smile:

Seriously though, do it once holding a constant speed and once doing starts and stops, the same number and location of starts and stops.

But on different days, so each time the battery starts off at the same SOC.

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#46

Everybody is wrong

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#47

correct. if you walk and leave your board fully charged your wh/mi is technically 0

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#48

Seriously tho, It depends. In this case it’s like overdrive, better cruising speed, but less punch. But it would be less efficient in conditions that need more torque to the wheels like steep hills and such

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#49

Better yet, you can get negative Wh/mi if your board isn’t fully charged at the time you leave it on a charger and walk away.

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#50

I feel like that’s a double edged sword, by going faster you’re inherently increasing air resistance at an exponential rate, which is less efficient, much more so than whatever losses the motor has internally. And if you stay the same speed, you get less efficiency from the lower torque.

#51

Ok, on my street bro, if I gear it high, like I do:
18s, 140kv, 165mm tire, 72t/20t = 48mph
But I’m not riding at 48, I’m cruising at 25-30mph, kinda in the middle where it’s efficient 35wh mile

If I did a smaller motor pulley, I would have more torque, but I would be riding near the higher limit of the motors, in a less efficient band (idk what else to call it) 45wh mile

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#52

Source please, the way you worded it sounds more like conjecture than hard data. I’ve personally found air resistance much worse, an increase of 3mph uses 3Wh/mi more on my setup, and this is <15mph average so air resistance isn’t even that high.

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#53
  • source: yeahthatperson - yeahthatperson’s 18s5p 3link street bro experiments 2021-2022:
    cruising at 25-30mph
    20t better WH than 16t
    King County, WA - Seattle, Redmond
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