[Salty9]

Don't know the price but 4 of these might work: http://www.enertrac.net/

[ruckus]

Originally Posted by Salty9

Don't know the price but 4 of these might work: http://www.enertrac.net/

$1,295.00 -- for ONE.

sooo, about $5180 per 'moto' car. This doesn't include the 4 controllers...

[midget]

Good day,
I'm glad to see a somewhat recent exchange about hub motors. I have also been trying to research creating an EV using 72V 7kW hub motors from Kelly Controls. The donor I had in mind would be an MG Midget, and it would be just the rear wheels that would recieve the motors. Each hub motor weighs about 60 pounds, but some of the items that would be removed would be the transmission, differential, driveshaft, axle shafts, engine, gas tank, etc. I'm still trying to calculate how much total weight and sprung/unsprung weight that will eliminate. The donor vehicle would start at around 1620 lbs before stripping it down. For batteries, I've been looking at GBS Lithium 72V 60Ah pack (from electricmotorsport.com) with a weight addition of 122 lbs.

So my point is, am I setting myself up for disappointment if I go that route? Or will I have the potential to realize my modest goals of a 20 mile range with that set up?

[AussieRav4]

gday midget,
i know i'm not the best person to talk to on this one and i will be corrected later. If you see my earlier questions on the hub motors then you will even see me back away from their use. As a concept they seem really, really good and lots of potential.
In my line of work its as soon as someone says "but" you listen. they seem really good but they have other issues such as the points that were spoken about earlier.

i still want to build an electric car but im wanting to get a car i can work with first. i see car being something i will take a huge amount of pride in and potentially use as a rebuild, educational tool and general runabout. it means i want it to be safe and reliable and not bite me or students in the ass.

The issues that are part of a hub motor concern me enough to plan for a far smaller car to convert [eg an old mini or a 1960-1980 VW bug] and use it as an experiment.

[midget]

I think the MG qualifies as lightweight and small. Here's the part of the research that is giving me troubles:
I know my theoretical inputs, such as...
Two 72V 7kW hub motors, one on each rear wheel.
72V battery with 60Ahr (4.61 KW/hr capacity) 600 CCA and 61.8 max HP.
Donor vehicle of approximately 1500 pounds converted weight.
Access to machine shop to build custom hub axle supports.
The rewiring of the hub motor leads before assembly doesn't sound too intimidating.

But what I am having trouble figuring out is, will it be able to start from a dead stop. The "calculators" I have seen so far all make the assumption that the motor will be run through a transmission. I've tried looking for electric golf cart values to see how they rate in comparison by "scaling" up weight, voltage, power. But I can't find enough information to begin calculations.

I have the battery "HP", but I don't have the motor HP. Can that be calcuted by looking at given parameters or does it have to be tested in real world contitions?

So far nothing has been purchased. And I certainly don't want to be throwing money down the drain. The reason for not leaning toward the traditional configuration is budetary. The state of IL offers a $4000 tax rebate for conversions (80% of $5000 max) so the $6000-$7000 budget range plus donor vehicle cost is what I'm targeting.

Too bad LUNATIC FRINDGE won't fit on the license plate!

[PStechPaul]

As for starting from a standstill, that is all about torque. HP only is defined for a certain RPM. But you can estimate the torque, by using the formula:

T = HP * 5252 / RPM

For a hub motor, 1000 RPM is pretty much top speed, so if you have 14 kW or about 20 HP, your torque will be about 105 lb-ft.

If your wheel is 24" diameter, the thrust will be 105 lb. If your vehicle has a total weight of 2000 lb including driver, batteries, motor, chassis, etc, the vehicle will be able to just barely climb a 5% grade. Or on a flat surface, you will be able accelerate at 0.05G.

If the HP rating you give is nominal, you might be able to get more torque for short periods of time, but you won't be able to climb most hills. You need even more torque to overcome wind and Rolling Resistance if you want to achieve even minimal highway speeds.

There are many on-line calculators that can help with things like this. I made one you can use:
http://www.enginuitysystems.com/EVCalculator.htm

[midget]

Thanks for information.
I am coming from a position of ignorance, so please don't think of my questions as confrontational.

Now that I have some values, can I ask how to interpret them?
From my research I've read that the HP value of an Internal Combustion Engine is not the same as the HP value of an electric motor. An electric motor can have a value 10% that of an ICE and still be about the same power output. So is the 20 HP similar to a 200 HP value for an ICE?

And similarly, how does one interpret the torque value? If I look at the technical specs for a 1979 Midget, the maximum torque is listed at 77 lb-ft at 3000 rpm. How does that compare to 105 lb-ft from a hub motor. Is the transmission gearing the important link that changes everything? As I type that, I'm thinking thats the reason why 1st gear is easy to start in, and 4th gear not so much.

"Perhaps if we built a large wooden badger"
"Runawayyyyyyy"

[sunworksco]

Even IF the hub motors were efficient, it is like installing a heavy jackhammer on each wheel. Unsprung weight for an EV is very important to keep at a minimum.

[PStechPaul]

Well, this has been hashed out in several threads already since I joined, and I'm still pretty much a newbie. But I realize that the concepts of HP and torque can be confusing, and even though I attended a top notch engineering university (JHU), I did not really unerstand motor speed/torque/HP curves until many years later.

A general "rule of thumb" is that you can use an electric motor of about 1/3 the HP rating of an ICE in a car, and get just about the same "feel", if not an improvement. For one thing, the HP ratings you see advertised for cars and trucks are usually peak values for a "blueprinted" engine, and what you actually get may start at perhaps 20% below that. An ICE often has a narrow range of maximum power and maximum torque, and steep drop-off below and above those ideal RPMs. So to get maximum performance they are equipped with a 4-6 speed gearbox and it takes some skill (or a well-designed A/T) to shift at the right points.

What you actually "feel" when you drive is thrust, which is the forward force exerted by the tires on the road. This is derived from the torque of the engine through the transmission and differential. At low speeds, you need enough torque to propel the vehicle up any hill you may reasonably encounter, such as a driveway, which can easily be a 20% grade. And you also want to be able to accelerate, which is really the same thing as gravity and hill climbing. So you need to determine the minimum thrust as a starting point. On a 20% grade you push 20% of the car's weight so a 2000 lb car needs 400 lb of force. This is also 0.2G, or 1.96 m/s/s or about 4.4 MPH/sec. 13.6 sec 0-60.

Power comes into play at high speeds, whether to overcome wind resistance or to be able to climb hills and accelerate with heavy loads. It is possible to get a motor which has sufficient torque for take-off and also a high end capable of highway speeds, but it will be large, heavy, expensive, and inefficient. But sometimes the removal of he weight of the transmission and differential can compensate somewhat.

Please read the other threads on wheel motors and direct drive and general power/speed/torque discussions. Good luck.

[RIPPERTON]

These "hub motors" dont necessarily have to go in the wheel.
Im doing feasabilty on running 2x 7kW Kelly motors inboard in my Diahatsu
Mira 650kg.
basically where the diff used to be and bolted flange to the inner cv joint.
The longer of the 2 shafts would be cut shorter to make room for the 2 motors bolted together back to back.
The stub axle of the motor would be cut short and maybe bigger cabling fitted.
The inboard concept negates re-engineering your brakes steering and suspension, way too difficult and dangerous.
I asked Fany if there was a higher turn motor available to run on higher voltage but no options.
wait and see