Help calculating max speed of my electric car

2886 Views 13 Replies 8 Participants Last post by sadcar, Feb 26, 2021

juliangliniecki

Discussion Starter · Feb 16, 2021

What would be the max speed of my electric vehicle? I need a systemic way to calculate this given BLDC ratings: Voltage, Rated Power, Rated Speed, Rated Torque, Rated Current, No load Current, No Load Speed. Also using these constants: Weight and coefficient of friction. There are two motors. We are ignoring any resistance from the shape of the vehicle. The car is in a vacuum.

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remy_martian

· #5 · Feb 17, 2021

Systematic, not systemic

Work your problem in pieces....nice easy steps.

Calculate the rolling resistance based on weight and Cf

Torque at the radius of the tire is the force has to equal that resistance

Power determines your speed as a function of torque and rpm. Once you get the rpm of the tire, compute its speed by using its circumference

The rest you need to do yourself. Remember that two motors doubles everything.

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remy_martian

· #6 · Feb 17, 2021 (Edited)

MattsAwesomeStuff said:
Mhm. Good good.

does some math

Looks like your top speed will be just slightly under 670,616,629 mph.

This is what happens when you don't do it systematically and by failing to recognize your constraints and degrees of freedom.

Matt gets an F

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remy_martian

· #12 · Feb 19, 2021

juliangliniecki said:
Thank you all for your insight. It's not for homework. I am on a team designing a scale model hyperloop pod and my partner and I are stuck on finding the best way to calculate the speed of our pod based on the BLDCs we are choosing. That is why we are ignoring air drag and I said vacuum.

Your pod doesn't need a propulsion motor. The little "pod" you put your deposit slip and money into at the bank drive-thru doesn't have one...

FWIW, pumping the tube down to partial vacuum will take more power than it's worth, not to mention the crush loads on the "pipe" you're traveling in putting materials costs/km(mile) through the roof.

I can see it now...after Musk got done reading his 1950's comic books, someone pulled him aside, showed him the math, and all of a sudden he abandoned the HL and had cars running in tunnels without the vacuum nonsense....which arguably is still nonsense.

I'm hoping this is a university project/competition and none of you quit your day jobs for Elon's hype-loop.

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