# Newbie question about RPMs



## ww321q (Mar 28, 2008)

how about going 60 mph . A mile a minute . Divide 5280ft (mile) by the circumference of the tire in feet. That will give you the wheel rpm . J.W.


----------



## Da_Fish (Apr 28, 2008)

Wow, that is an undertaking!! First you have to figure out how to make sure each wheel is turning at the same speed so you dont pull in one direction or the other, then you have to figure how to adjust the speed of the motors in a turn to make sure you dont drag a tire. The inside wheel turns less than the outside wheel and if you dont figure this in, you will break components.


----------



## Ioku (Sep 27, 2007)

In wheel motor EV have been made befor the first was made over 100 years ago by Porsche. and here is some links to some newer ones http://www.worldcarfans.com/2050824.001/mitsubishi-lancer-evolution-miev http://www.motorauthority.com/news/coupes/700hp-lightning-gt-electric-car-available-for-pre-order/ http://www.treehugger.com/files/2006/08/the_hybrid_mini.php. The many problem with these cars is the motors are hard to find and expensive as well as the 4 controllers you need as well, but still a very cool system and something I would love to build.


----------



## Mastiff (Jan 11, 2008)

The term used for this would be "Direct Drive".

The weight loss of the transmission/drive shaft in a wheel motor system isn't the main performance improvement.

The improvement in performance comes from the mechanical resistance you remove by removing those parts and the well optimized wheel motors.

I don't want to be negative here, but if your going to do a vehicle _conversion_, a wheel-motor system isn't as simple as retaining your drive system and attaching a single motor to it.

Wheel motors are usually used in purpose built pure EV's.


----------



## shadarack (Apr 24, 2008)

ww321q - Thanks for the info, I feel really dumb now. The reason I couldn't find the information is because it was something I should have logically been able to work out for myself...

Da_Fish - Wow. Sounds like I may have bitten off more then I can chew, but I might give it a try anyways, just 'cuz. One question - how do IC cars handle wheel spin differential when turning?

Ioku - I am probably showing my ignorance here, but is there some reason you cannot use the same controller for all four motors as long as you want them to spin at the same speed at the same time? Maybe I'm misunderstanding what a controller does...

Mastiff - love the icon! I know it's going to be more difficult to build the way I want then simply dropping an electric motor into place, but I'm looking for efficiency over simplicity. I probably should not start off with something so complicated for my first project, but I've always been a bit silly when planning these things out - aim high - then when you fail, you at least achieve something mediocre. *GRIN* Thanks for the info on mechanical resistance and performance optimization. That hadn't occurred to me...


----------



## joseph3354 (Apr 2, 2008)

if you want to see what can be possible with wheel motors check out the eliica here: http://youtube.com/watch?v=g2X7TgpYIaY

enjoy !


----------



## Coley (Jul 26, 2007)

Quote:
"One question - how do IC cars handle wheel spin differential when turning?"

By using a "differential gear set".

I applaud your desire to lighten weight, but the multi-motor setup may not save you as much weight as you think.

Also, it has been my experience, that if you tackle too much of a complicated project, for a first one, the success rate is low.

This sometimes can be depressing enough to cause hesitation on trying again.

A small front wheel drive car, can be very rewarding and get you to a point of driving, as you plan your next EV.

I am at that point now.....I look at every sleek car I see, as a potential EV.

BUT, I am driving mine, all the while I think about it.....


----------



## judebert (Apr 16, 2008)

Of course, if the motors aren't accelerating through the turn, then they'll all spin at whatever rate they want.

If they are accelerating, they won't resist with any more force than the acceleration. It's possible -- even likely, in my opinion -- that the force exerted by the road through the tires will be sufficient to overcome the electric force. The wheels on the inside will go slower, because they aren't being pushed strongly enough to overcome the road resistance; the wheels on the outside will go faster, because they're not loaded as heavily as the inside wheels. 

It's not like the motors are locked together or anything. 

In fact, this kind of "road coupling" would probably make it so you don't have to get all four motors running at exactly the same rate. As long as the difference is less than the traction provided by the wheel, they'll all equalize. You'd probably pull to one side, though, or have some oversteer or understeer (depending on which wheels are providing the extra power).


----------



## ngrimm (Oct 19, 2007)

At first when I read this I was thinking that there would be a fair amount of power loss due to one motor trying to turn faster and another slower when turning. But now I'm thinking that it would only be during sharp turns that there would be much difference in speed between the wheels and in those cases you would be traveling slower like decelerating for a turn where the momentum carries you through. That is the way a posi works to some extent. They lock the wheels together when you apply power but allow slippage when power is removed. If you give full power to the electric motor on each wheel when making a sharp turn both wheels wheels would probably break traction which would probably be what you were trying to do anyway.  Norm


----------



## ace holmes (May 11, 2008)

a 20in wheel dia will move 5ft 8in per rotation
and a car going 60 mph is 90ft per second 
1000 rpm is 60 mph roughly 
f= cir x rps= ft per scond

rotations per second rps


----------



## Coley (Jul 26, 2007)

Quote:
"a 20in wheel dia will move 5ft 8in per rotation
and a car going 60 mph is 90ft per second 
1000 rpm is 60 mph roughly 
f= cir x rps= ft per scond

rotations per second rps"


My EV 
13" tire, 21.5" tall, covers 67" (5.58), @ 946 revs per mile.

3000 rpm motor, 3.25 final gear ratio (5th gear), = 58.57 mph

Note not many EVs will run in 5th gear and do it economically....


----------



## ace holmes (May 11, 2008)

on direct drive in wheel motor not your tranny driven car


----------



## DVR (Apr 10, 2008)

ace holmes said:


> a 20in wheel dia will move 5ft 8in per rotation
> and a car going 60 mph is 90ft per second
> 1000 rpm is 60 mph roughly
> f= cir x rps= ft per scond
> ...


I dont know of any off the shelf EV motors that would be happy at 1000rpm at 60 mph.


----------



## ace holmes (May 11, 2008)

actually most in wheel motors r max @ 1400rpm about 100mph on 20in wheels
if u want a higher top speed get bigger wheels


----------

