Fast/Slow winding - How to calc?

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gobi   10 W

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Fast/Slow winding - How to calc?

Post by gobi » Jun 09 2021 12:05pm

Though I understand the slow vs fast winding in a hub motor concept, how do I go about calculating/determining that in a motor?

For example my yescomusa 24inch 750w front hub

has a max speed of 25km/h
which translates to 220 RPM @36

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ZeroEm   100 kW

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Re: Fast/Slow winding - How to calc?

Post by ZeroEm » Jun 09 2021 1:09pm

you need unloaded RPM, wheel off the ground. Then get the rpm and the voltage that is driving that rpm. "rpm/V=Kv"

The formula to calculate Kv for brushless motors is:

K_v = \frac{Speed}{Volts*1.414*0.95}
http://learningrc.com/motor-kv/
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MadRhino   100 GW

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Re: Fast/Slow winding - How to calc?

Post by MadRhino » Jun 10 2021 6:47am

You need to make sure the motor rpm is not limited by the controller software before calculating the rpm per volt. The real RPM must be measured unloaded and unrestricted.
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E-HP   100 MW

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Re: Fast/Slow winding - How to calc?

Post by E-HP » Jun 10 2021 10:52am

Given variability of motors between brands or models, calculating the winding would likely be very complex. You could use the inversely proportional relationship between motor winding and motor Kv to calculate one or the other for motor, if you have a known motor of the same type, with a known winding and Kv. So if you know the Kv and winding of motor X, and you have the Kv of motor Y, you can figure out the winding for motor Y.

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Re: Fast/Slow winding - How to calc?

Post by gobi » Jun 11 2021 11:28pm

E-HP wrote:
Jun 10 2021 10:52am
Given variability of motors between brands or models, calculating the winding would likely be very complex. You could use the inversely proportional relationship between motor winding and motor Kv to calculate one or the other for motor, if you have a known motor of the same type, with a known winding and Kv. So if you know the Kv and winding of motor X, and you have the Kv of motor Y, you can figure out the winding for motor Y.
I bought a yescomusa's 750w 24 inch kit for my D.
it is not a geared hub and I was trying to figure out if it has a fast or slow winding.

in the specs, the only thing yescom mentions is max speed 25 km/h @ 36v

How do I go about measuring the RPM of the hub? does it output it?
The Yescom does not come with a lcd display just a throttle with led indicator for batt and on/off switch.

fatty   10 kW

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Re: Fast/Slow winding - How to calc?

Post by fatty » Jun 12 2021 12:19am

gobi wrote:
Jun 09 2021 12:05pm
Though I understand the slow vs fast winding in a hub motor concept, how do I go about calculating/determining that in a motor?
The slow vs fast winding concept is relative -- you have to have two motors to compare.
If they only sell one option, then.. well, you get what you get.

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Chalo   100 GW

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Re: Fast/Slow winding - How to calc?

Post by Chalo » Jun 12 2021 12:37am

fatty wrote:
Jun 12 2021 12:19am
gobi wrote:
Jun 09 2021 12:05pm
Though I understand the slow vs fast winding in a hub motor concept, how do I go about calculating/determining that in a motor?
The slow vs fast winding concept is relative -- you have to have two motors to compare.
If they only sell one option, then.. well, you get what you get.
Ultimately, it's a given RPM per volt you want, and winding is incidental to that.

RPM per volt is a pretty easy thing to measure. I use an optical tachometer, but before that, I used a metronome or beats per minute YouTube video to home in on the unloaded RPM.
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Re: Fast/Slow winding - How to calc?

Post by fatty » Jun 12 2021 2:24am

Chalo wrote:
Jun 12 2021 12:37am
Ultimately, it's a given RPM per volt you want, and winding is incidental to that.
But he already (almost) calculated (approximate) Kv:
25km/h * 1000000mm/1km * 1h/60min = 416667mm/min
24in = 610mm diameter = 1916mm circumference
416667mm/min / 1916mm = 217r/min
Kv = 217r/min / 36V = 6rpm/V
gobi wrote:
Jun 11 2021 11:28pm
How do I go about measuring the RPM of the hub? does it output it?
The Yescom does not come with a lcd display just a throttle with led indicator for batt and on/off switch.
I guess I should asked: to what end?
A good controller with display would output it. The Yescom -- obviously not.

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Re: Fast/Slow winding - How to calc?

Post by gobi » Jun 13 2021 8:51am

Ah, rpm, I watch a video on youtube where the camera frame speed matched the helicopter rotor rpm and the blades appeared to be stationary.

I need to check if I can vary the frame rate of the video function of my iphone or DSLR, thanks I will try that, I hate to spend more money and get a tool I will never use again. :roll:

6 rpm/V (thanks!)

so what does mean? slow? fast?


I just finished the bike few weeks back but did not get a chance to take it out for a spin, D had the flu (thank the Lord she came out negative for covid),
I tried the bike on the carpet in the living room, it is slow starting off the line compared to the bafang geared hub, according to my butt dyno.

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Chalo   100 GW

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Re: Fast/Slow winding - How to calc?

Post by Chalo » Jun 13 2021 9:31am

gobi wrote:
Jun 13 2021 8:51am
6 rpm/V (thanks!)
so what does mean? slow? fast?
That's a fairly slow hub motor compared to most. The flip side of that is you have a comparatively high torque per amp.

At 36 volts nominal, in a 24 inch wheel, the unloaded speed will be around 16 mph. The most efficient cruising speed will be about 12-13 mph. These are appropriate numbers for an upright trike, if that's your application. It would also be good for moving around a job site or a pedestrian area. Many bikes would feel frustratingly slow on the street at such speeds. For those, it would be better to use a higher voltage.

If you use a 48 volt battery with that motor, the free speed would be around 21 mph and the most efficient cruising speed around 17 mph. With a 52 volt battery, the free speed would be around 23 mph and the most efficient cruising speed about 18.5 mph.
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Re: Fast/Slow winding - How to calc?

Post by spinningmagnets » Jun 13 2021 10:09am

in the "non-hub" section, the thread stickie list has a link to a chart that spells out two formulas for calculating wheel-diameter to road-speed, and then simply lists a couple pages worth of RPM/ road-speeds for 20, 22, 24, 26, 29-inch wheels.

Once you know the tire-OD and the top-speed you want, that link tells you the wheel RPMs you need for designing a non-hub system

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Chalo   100 GW

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Re: Fast/Slow winding - How to calc?

Post by Chalo » Jun 13 2021 11:07am

spinningmagnets wrote:
Jun 13 2021 10:09am
in the "non-hub" section, the thread stickie list has a link to a chart that spells out two formulas for calculating wheel-diameter to road-speed,
I use this:

https://www.4qd.co.uk/road-speed-calculator/

The reduction ratio for a hub motor is 1.
This is to express my gratitude to Justin of Grin Technologies for his extraordinary measures to save this forum for the benefit of all.

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Re: Fast/Slow winding - How to calc?

Post by gobi » Jun 14 2021 8:57am

spinningmagnets wrote:
Jun 13 2021 10:09am
in the "non-hub" section, the thread stickie list has a link to a chart that spells out two formulas for calculating wheel-diameter to road-speed, and then simply lists a couple pages worth of RPM/ road-speeds for 20, 22, 24, 26, 29-inch wheels.

Once you know the tire-OD and the top-speed you want, that link tells you the wheel RPMs you need for designing a non-hub system
spinningmagnets, thanks, I have a read a few threads on custom wound hubs, nice, maybe someday! Right now, I gots to do with what I have and understand what I have :-)
At 36 volts nominal, in a 24 inch wheel, the unloaded speed will be around 16 mph. The most efficient cruising speed will be about 12-13 mph. These are appropriate numbers for an upright trike, if that's your application. It would also be good for moving around a job site or a pedestrian area. Many bikes would feel frustratingly slow on the street at such speeds. For those, it would be better to use a higher voltage.

If you use a 48 volt battery with that motor, the free speed would be around 21 mph and the most efficient cruising speed around 17 mph. With a 52 volt battery, the free speed would be around 23 mph and the most efficient cruising speed about 18.5 mph.
Chalo,
My girls and I are very happy cruising along at leisurely 5 to 10 mph, though my oldest likes to zoom zoom.

Yes, we are riding mostly on trails or inside roads around my little town, which is bit scary as drivers are very distracted. We have a 7 mile trail around the lake, I am going to take a stab at that today.

The most efficient speed - 17 mph supports using a 48v batt makes it a no brainer to migrate my bikes to 48v batts,

Pic of the yescomusa's controller with my first attempt at front carrier rack install, not as tidy as your but I like how everthing stays in one place
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