X-File - The "Is My Math Right?!" Thread
#41
@Ackmaniac

If @ 1440W Electrical:

0rpm -> 13.33%
6718.93rpm -> 100%

We could say:

100% - 13.33% = %86.67 range of 1440W electrical duty cycles

So could we say ?:

6718.93 rpm / %86.67 = 77.52313 rpm per additional 1% duty cycle @ 1440W electrical?!

95% duty - 13.33% duty = %81.67

In simple terms 95% is 81.67 more percent than 13.33%

Could we say ?:

6331.31 rpm = 81.67 "More Percent" x 77.52313 rpm per additional 1% duty cycle @ 1440W electrical

So if I had to hazard a guess, I'd say:

1440w electrical @ 100% duty = 6718.93 rpm

&

1440w electrical @ 95% duty = 6331.31 rpm

^take this with a huge grain of salt :thinking:


Pack V = 36V
Ohm Resistance = 0.016ohm
Batt Max = 40A
Motor Max = 300A
Absolute Max = 1000A
KV = 190kv

In simple terms:
devin, post:30, topic:17037 Wrote:Which RPM does 1440W electrical = 95% duty cycle?

Ackmaniac, post:10, topic:17037, full:true Wrote:Correct. But lets imagine that the motor spins at no load with 94 % duty cycle. And now we want full power and feed the motor with 95% duty cycle. So my question is at which no load can i still achieve 1440 watts when i fed the motor with 95% duty cycle.

~0w electrical @ 100% duty = 6840.00 rpm
1440w electrical @ 100% duty = 6718.93 rpm
1440w electrical @ 95% duty = 6331.31 rpm <<- Is this the correct answer?
1440w electrical @ 13.33% duty = 0 rpm

@Ackmaniac ?! :thinking:

",0,0,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/70,2017-02-04 04:16:17 UTC
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#42
@Ackmaniac no H needed after all lol. :joy:

you just need very accurate pack v, ohm & kv measurements, a desired electrical wattage full throttle, and the correctly chosen xx/xx/xx batt/motor/absolute A MAX settings and you can predict everything in advance!

:joy::joy::joy:

",0,0,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/71,2017-02-04 05:44:47 UTC
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#43
@Ackmaniac

instead of user choosing batt/motor/absolute

user should choose:

W electrical full throttle

since:

motor max A is determined by ohm and desired W electrical full throttle

motor max A is proportional to desired W, but NOT pack V

since:

Pack V changes constantly

to maintain a constant desired W full throttle, and since battery amps x pack volts = W electrical, the battery amp limit should be updated continuously as the pack voltage changes and sags.

",0,0,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/72,2017-02-04 06:11:42 UTC
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#44
@Ackmaniac in simple terms xx/xx batt/motor max settings are the same as donkey/carrot cm.

<img src="http://udaypai.in/siteon/wp-content/uploads/2014/02/carrot.png">

the question becomes:

so how many centimeters in front of your donkey do you put your carrot lol. :joy:

[Image: fancy-switch.jpg]


",0,0,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/73,2017-02-04 06:38:58 UTC
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#45
@Ackmaniac here is a riddle for you:

Desired Full Throttle Electrical W: 2000W
Pack V = 50V fixed constant
Ohm Resistance = 0.0415ohm
No Load RPM = 4500rpm
Batt Max Setting = xx.xxA
Motor Max Setting = xx.xxA



~0w** electrical @ 100% duty = xxxx.xx rpm
1000w electrical @ 100% duty = xxxx.xx rpm
2000w electrical @ 100% duty = xxxx.xx rpm
2000w electrical @ 95% duty = xxxx.xx rpm
2000w electrical @ 50% duty = xxxx.xx rpm
2000w electrical @ 43.12% duty = xxxx.xx rpm
2000w electrical @ xx.xx% duty = 0 rpm

let's see how long it takes someone to answer...

<img src="http://www.uncommongoods.com/images/items/27200/2723411200px.jpg">

",0,1,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/74,2017-02-04 07:28:07 UTC
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#46
devin, post:74, topic:17037 Wrote:let's see how long it takes someone to answer...

Desired Full Throttle Electrical W: 2000W
Pack V = 50V fixed constant
Ohm Resistance = 0.0415ohm
No Load RPM = 4500rpm
Batt Max Setting = 40.00A
Motor Max Setting = 219.52A

~0w electrical @ 100% duty = 4500.00 rpm
1000w electrical @ 100% duty = 4425.29 rpm
2000w electrical @ 100% duty = 4350.60 rpm
2000w electrical @ 95% duty = 4083.92 rpm
2000w electrical @ 50% duty = 1690.37 rpm
2000w electrical @ 43.12% duty = 1324.43 rpm
2000w electrical @ 18.22% duty = 0 rpm

60240.96 W
1204.81A

40/1204.81 =3.32%

100-3.32=96.68%

4500 x .9668

100-18.22 = 81.78 range of 2000w duty cycles

4350.6 / 81.78 = 53.19 rpm per additional %

43.12-18.22 = 24.9

24.9 x 53.19 = 1324.42

50-18.22 = 31.78

31.78 x 53.19 = 1690.37

95-18.22 = 76.78

76.78 x 53.19 = 4083.92

20/1204.81 = 0.01660013

0.01660013 x 100 = 1.660013%

100-1.660013=98.339987

0.98339987 x 4500 = 4425.29

",0,1,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/75,2017-02-04 08:56:36 UTC
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#47
devin, post:75, topic:17037 Wrote:Desired Full Throttle Electrical W: 2000W
Pack V = 50V fixed constant
Ohm Resistance = 0.0415ohm
No Load RPM = 4500rpm
Batt Max Setting = 40.00A
Motor Max Setting = 219.52A

~0w electrical @ 100% duty = 4500.00 rpm
1000w electrical @ 100% duty = 4425.29 rpm
2000w electrical @ 100% duty = 4350.60 rpm
2000w electrical @ 95% duty = 4083.92 rpm
2000w electrical @ 50% duty = 1690.37 rpm
2000w electrical @ 43.12% duty = 1324.43 rpm
2000w electrical @ 18.22% duty = 0 rpm

Ackmaniac, post:76, topic:17037, full:true Wrote:So my math is more or less the same. But it's not what happens in reality.

@Ackmaniac :confused: ...so what happens in reality?

what is the proof this isn't what happens in reality?

all it takes is a screenshot of your No Load Rpm & Pack V, a screenshot of your ohm resistance, a screenshot of you batt/motor/absolute settings, and a log video to prove one way or another.

Is anyone who is capable of video logging willing to perform a measurement for science? @evoheyax @DeathCookies

Desired Full Throttle Electrical W: xxxx.xxW

& we need screenshots of:

Pack V @ No Load Rpm = xx.xxV
Ohm Resistance = x.xxxxohm
No Load RPM = xxxx.xxrpm
Batt Max Setting = xx.xxA
Motor Max Setting = xx.xxA
Motor Brand = anonymous

<img src="http://www.uncommongoods.com/images/items/27200/2723411200px.jpg">

",0,0,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/77,2017-02-04 14:53:00 UTC
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#48
@Rollbrett based on our lengthy private conversations it is my belief & understanding you are a material specialist.

in your opinion:

- if an 80mm diameter non-motorized skateboard wheel has twice the length of a standard skateboard wheel

- when subjected to non-impact related typical riding forces

would "leverage" forces alone have sufficient magnitude to cause total failure of an 8mm steel skate truck axle?

",0,0,http://www.electric-skateboard.builders/t/the-is-my-math-right-thread/17037/78,2017-02-05 02:58:54 UTC
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