I put up a new calculator at https://calc.esk8.news

It has a similar model to @saul’s that used to be at calc.esk8.today

Let me know if you think it could be better

I put up a new calculator at https://calc.esk8.news

It has a similar model to @saul’s that used to be at calc.esk8.today

Let me know if you think it could be better

23 Likes

This is great Brian, thank you.

Did you make that logo yourself?

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No; a computer made it.

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Hahaha, nice one !

And good job on the calculator by the way. But who did the code review for it ???

Is it possible to get a midichlorian count feature?

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Fucking George Lucas. Why explain the force through little creatures that choose whether to live in you or not. What a cock.

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You could implement some of your tests with it. If you do anything below 10s it reports back “You have MRSA”

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We have a beta unit with this as a hidden built in random number generator test haha shh don’t tell the FDA they have 0 humor stats.

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That is great and love that fact you can switch from volts to C rating because that is super helpful if you are using LIPO as they usually have the C rating for discharge.

You’re doing the code review

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I don’t ever recommend using C-rating and the only reason I put that there is because the old one had that there. You’re better off just typing your own current numbers in there.

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Damn broski. Thanks!!

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The root cause of the problem is that *the C-ratings are almost meaningless as they are mostly marketing jive*. It’s at that point where you move from “science” to “guessing”, as evidenced by one line in the source code:

```
miToKm:number = 1.609344;
lipoManufacturerExaggerationFactor:number = 5.25;
pi:number = Math.asin(1)*2;
```

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If you send me a spreadsheet in .ods format with inputs and output formulas, I will make a tab for that.

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@b264 how about a “peak loaded velocity & gear ratio calculator” for those uphill races?

suppose i’ll be climbing 1.8miles on a steady 5% grade…

i have 4x 190kv 0.05ohm motors & 83mm tires, 120a motor current and 60a battery current limit per motor, & 13S (48.1v)

what’s my maximum top speed up slope and what gear ratio gives this top speed assuming 0.6m^2 frontal area, 0.75 drag coefficient & 200lbs?

assuming battery current limit is 95% or less than the motor current limit, and a vesc with max 95% duty cycle is used in BLDC mode:

60a battery limit / 95% duty = **63.1578a motor current at peak mechanical power**

63.1578a^2 * 0.05ohm = **199.445385042w copper loss per motor at peak mechanical power**

60a battery limit * 48.1v battery = **2886w electrical power at peak mechanical power per motor**

2886w peak electrical - 199.445385042w copper loss = **2686.554614958w peak mechanical power per motor**

2686.554614958w peak mechanical power per motor * 4 motors = **10746.218459832w peak mechanical**

60 / (190kv * 2 * pi) = **0.05025945571323010603228Nm per motor amp**

63.1578a * 0.05025945571323010603228Nm per motor amp = **3.174276652045044390766 Nm torque at peak mechanical power**

2686.554614958w peak mechanical / 3.174276652045044390766 Nm = **846.3517548878964569933rad/sec @ peak mechanical**

(60 / (2 * pi)) * 846.3517548878964569933rad/sec = **8082.063923094534641801 motor rpm @ peak mechanical power**

^peak mechanical power is 10746.218459832w @ 8082.063923094534641801 motor rpm

A = meters per second = XX.XXX

B = drag coefficient = 0.75

C = frontal area = 0.6m^2

D = fluid density of air = 1.225kg/m^3

E = wind drag force in watts

F = sine of 5% slope = sin(atan(5/100)) = 0.04993761694389223373491

G = acceleration of gravity = 9.80655m/s^2

H = vehicle mass in kg = 90.7184kg = 200lb / 2.20462lb/kg

I = mechanical watts required for constant speed up slope with no wind drag

J = mechanical watts required for constant speed up slope including wind drag

K = H * G * F

L = (1/2) * D * C * B

E = ((1/2) * D * C * (A^2) * B) * A

I = H * G * A * F

J = E + I

J = (((1/2) * D * C *(A^2) * B) * A) + (H * G * A * F)

J = (1/2) * D * C * B * A^3 + H * G * F * A

J = (L * A^3) + (K * A)

^this can be rearranged to:

A=(sqrt(3) * sqrt(27 * J^2 * L^4 + 4 * K^3 * L^3) + 9 * J * L^2)^(1 / 3) / (2^(1 / 3) * 3^(2 / 3) * L) - ((2 / 3)^(1 / 3) * K) / (sqrt(3) * sqrt(27 * J^2 * L^4 + 4 * K^3 * L^3) + 9 * J * L^2)^(1 / 3)

we know:

J = 10746.218459832w peak mechanical

L = 0.275625 = (1/2) * D * C * B

K = 44.42622815547907982077 = H * G * F

therefore:

A=(sqrt(3) * sqrt(27 * 10746.218459832^2 * 0.275625^4 + 4 * 44.42622815547907982077^3 * 0.275625^3) + 9 * 10746.218459832 * 0.275625^2)^(1 / 3) / (2^(1 / 3) * 3^(2 / 3) * 0.275625) - ((2 / 3)^(1 / 3) * 44.42622815547907982077) / (sqrt(3) * sqrt(27 * 10746.218459832^2 * 0.275625^4 + 4 * 44.42622815547907982077^3 * 0.275625^3) + 9 * 10746.218459832 * 0.275625^2)^(1 / 3)

**A=32.32551993764664323864 meters per second**

**^therefore the peak velocity up slope is 32.32551993764664323864 meters per second**

**72.31024856931928212624mph** = 32.32551993764664323864 meters per second * 2.23694 mph per m/s

**^72.31mph is the maximum possible top speed up 5% slope w/ 200lbs, 0.75 drag coefficient, 0.6m^2 frontal area, 4x 190kv 0.05ohm motors & 120a motor current limit & 60a battery current limit per motor w/ 48.1v battery**

therefore we need:

**8082.063923094534641801 motor rpm @ peak mechanical power @ 72.31024856931928212624mph w/ 83mm tires**

83mm * pi = **260.7521902479528387924mm per rotation**

1mph = 0.44704 meters per second

72.31024856931928212624mph * 0.44704 meters per second per mph = **32.32551993764664323864 meters per second**

32.32551993764664323864 meters per second * 1000mm per meter = **32325.51993764664323864mm per second**

32325.51993764664323864mm per second / 260.7521902479528387924mm per rotation = **123.9702719540260136714 tire rotations per second**

123.9702719540260136714 tire rotations per second * 60 seconds per minute = **7438.216317241560820284 wheel rpm required for 72.31024856931928212624mph @ 83mm tire diameter**

8082.063923094534641801 motor rpm / 7438.216317241560820284 wheel rpm = **1.086559408652925905457 gear ratio**

**^1.08:1 gear ratio is needed to obtain maximum possible 72.31mph top speed up 5% slope w/ 200lbs, 0.6m^2 frontal area, 0.75 drag coefficient, 4x 190kv 0.05ohm motors, 83mm tires, 120a motor current limit, 60a battery current limit per motor & 48.1v (13S) battery**

answer:

**72.31mph & 1.08:1 gear ratio**

^graphed out it looks about like this 25T wheel & 23T motor = 1.088:1 ratio for ~72mph up 5% slope w/ 4x 190kv 0.05ohm, 83mm tires, 120a motor current and 60a battery current limit per motor, 13S (48.1v) w/ 200lbs, 0.6m^2 frontal area and 0.75drag coefficient.

8 Likes

Good god I am so hard right now.

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I think my brain fell out of my head

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It will probably help if you use the markdown to break the entire analysis into heading, sub headings, sub sub heading, bullet points etc. People are not generally inclined to read a wall of text unless there is an outline of what they are about to read.

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I can directly turn a spreadsheet into an online calculator. A wall of text would take me 8 hours to turn into a calculator

3 Likes