Bioboards Thorium X4 AT Ferrari Edition - possibly the fastest eks8 ever made!

[mackann]

Thanks, I dont plan to ride that fast. But will try for 65-70mph

[professor_shartsis]

But will try for 65-70mph

for 70mph w/ 18s and 4 of the 220kv motors:

^now you only need 34a motor current limit per motor, 32a battery current limit per motor, 3.83:1 gear ratio, 1.46nm motor torque, 165mm tires, 69 wheel teeth and 18 motor teeth (the motor will be doing 232 revolutions every second)

[Halbj613]

34a motor current limit per motor, 32a battery current limit

That’s exactly what the 18s4p with 40t will give him 35a per motor

Excited to see where this goes

[kevingraehl]

I’m still calling bs

[whaddys]

the motor will be doing 232 revolutions every second

how man rev/sec per tire does that equal??

[professor_shartsis]

@whaddys 60.5 tire revs per sec since the gear ratio would be 3.83 (it’s the 3rd # from the bottom in the upper chart)… the motor would be putting out it’s peak mechanical power with that motor current limit at 13925rpm (14th # from the bottom in the upper chart)

to get those rpms, you

• look at the battery current limit per motor (32a)

• divide 32a by the max duty .95 to get the motor current at peak mechanical power

• I^2R = W to get the copper loss in watts at peak mechanical power (in this case 0.05ohm was chosen for R)

• multiply the battery current limit by the battery voltage to get the electrical watts at peak mechanical power

• subtract the copper loss watts from the electrical watts to get the peak mechanical power per motor

• calculate the torque per motor amp KT = 60/(2 * pi * 220kv)

• multiply the motor current at peak mechanical power by the KT to get the motor torque at peak mechanical power

• divide the peak mechanical power in watts by the motor torque at peak mechanical power to get the motor angular velocity in radians per second at peak mechanical power

• convert the radians per second at peak mechanical power to rpm

• divide the motor rpm at peak mechanical power by the gear ratio to get the wheel rotations per minute, then divide by 60 seconds to get the wheel rotations per second

the trickiest part of the entire equation is starting with a slope, vehicle mass, frontal area, drag coefficient, fluid density of air, peak mechanical power and then converting that to max possible meters per second which is done at the 8th number from the bottom in the upper chart… in this case that’s slightly simpler since 0 slope was chosen.

i previously described how that’s done here:

Esk8 calculator

^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

[esk8jpn]

Use this to protect your head.

[malJohann]

60.5 tire revs per sec

@Trampa what’s the speed rating on Urban Treads?

[Trampa]

We do not want our gear to be used at such speeds. We also do not want to advertise going that fast.
30mp/h is already plenty fast on a skateboard and well enough to hurt yourself badly. We enjoy riding with friends, riding on trails, pull off a jump, cruise up a nice hill, carve into the sunset etc.

[Kellag]

30mp/h is already plenty fast on a skateboard

[BillGordon]

It’s true. I read it in The Verge.

[Mainflow]

That point is true.

[BluPenguin]

I was like, maybe I should build a Trampa. Trampa be like, nah, you should reconsider.

[Fosterqc]

I’d (very first diy went 30mph) venture to say the safe limit is below 50mph but I don’t see anything wrong with runs up to 70mph on good tracks.

Not that 30mph felt safe on that peice of junk

[Andy87]

well enough to hurt you badly.

Don’t pick out just the half of that sentence.
He is not wrong with the full statement.

[Mainflow]

I meant, that the full statement point is true.

[Kellag]

it’s totally true, it’s just also boring

[BluPenguin]

I’m setting my VESC erpm limit to 29.9mph. I’m never getting hurt again

[Kellag]

I’ve found the slow falls are actually the worst too, I fall at 15 and sprain an ankle but fall at 39 and I just slide🤷‍♂️

[wandagoner]

To be faiiiirrrr he’s speaking for the brand and likely needs to be clear Trampa does not endorse certain activities. If Trampa were to provide a speed rating it may be construed as endorsement and expose the company to potential liabilities.

But yes its not exciting