Hybrid home conversion with rear hub motors

[Clev]

Originally Posted by Christ

That statement is exactly the sole reason that MasterLock is still around.

People perceive weight to be strength.

Which has nothing to do with motors. An electric motor is about torque, and bigger IS better. Thicker shaft, more magnets, more insulation...

Think about it like this. If you wanted to make an MIW EV, you wouldn't have to use that 48V motor. You wouldn't have to use a single 30HP motor mounted to the transmission. The motor wouldn't weigh in at 60-100 lbs.

You would be using 2-4 motors.

Now, worst case scenario, the each motor is 24V, 15HP, and only weighs 30-50lbs... roughly the same weight as many cars' wheel and tire combo.

Or about 60-70 pounds with tire... EACH.

Divide the original motor between 4 wheels, and you've got 4 motors, each 7-8HP, each 15-20lbs, each 12V.

Even when you consider removing the engine and transmission, drive line (CV axles or drive shaft) etc, you still have removed more weight than you're adding on.

Lets say that you take a 1989 Honda CRX HF (lighest, smallest engine), remove the engine, transmission, both axles, and all eletronics associated with both.

The engine weighs in at least 230LBS,
Tranny is another ~100LBS,
Axles are close to 40LBS,
Remove engine wiring, fuel tank, pump, lines, filler nozzle, filter, charcoal can, associated equipment ~30LBS (rough estimate)
Remove complete exhaust ~30LBS (depending on cat/muffler, etc.)

In total, you've lost ~400LBS.. now you can add those 4 EV motors at 60LBS each, and still be ~150LBS lighter... add in the electronics to run them, and you're ~100LBS (I have no true idea, that was a guess.), Add the batteries, and now you're JUST starting to get overweight.

Replace those 60LB EV motors with 20LB EV motors, that run on 12V, and produce 10HP each, and you've got roughly the equivalent of a bone stock Geo Metro anyway, as far as HP.

You have the equivalent of a bone-stock Geo Metro perpetually in 4th gear. Without any kind of gear reduction, you're at basically a 1:1 fixed ratio between the motors and wheels. 10hp is about 7,460 watts, or 621 amps at 12V (not counting sag at the batteries.) That's to produce the same base horsepower at the wheels. Plus, add some weight (or exotic materials) to be able to hold together and absorb pothole impacts at 60 mph, and you're talking about a lot of weight, money or both.

And now you're looking for a wheel motor that can handle 621 amps at 12V for the amount of time required to climb a hill, and that motor can only weigh 20 lbs. Then add the 1/0 welding cable to each wheel to handle the amps, and you're dangerously close to being back at that 100 pounds you saved by dumping the transmission. Add four times the electronics for a controller that can drive four motors, and you're talking a lot of money for not a lot of advantage.

Acceleration will probably be faster, since you're not waiting for the engine to get into it's "torque range"... E-motors have a torque figure while idle (potential torque), and you're not experiencing ANY drivetrain losses.

Compared to the ICE, maybe, but compared to the simple forklift motor/transmission combo, I'd put my money on the forklift motor. The drivetrain losses will be traded for resistance losses because of the lack of gearing, as the motors struggle to translate 600+ amps into forward motion from a stop.

Now, you could still attach those motors to the chassis of the car, and attach from the chassis to the hubs using CV axles, but you'd experience at least some drivetrain losses, have another breakable component in the mix, be adding another 80LBS of weight (All 4 corners). And adding almost no benefit, other than "less unsprung weight" which isn't helping you at all anyway.

I wouldn't underestimate the impact of an extra 20-30 pounds of rotating mass at each corner than needs to be accelerated. Couple that with 1:1 gearing, and you're talking about a system that will cost at least 4 times as much, but actually do worse. At least with axles, you can go with a lighter weight motor, as it only has to deal with rotational stresses--something every cheap motor can do. A transmission provides even more protection, as the clutch and transmission/engine mounts provide some cushioning as well.

Personally, I think that if you want to eliminate the transmission, go with a motor coupled via a differential and axles. You can gear it properly to match your speed range and RPM range, and you can use standard proven brakes, wheels and tires, motors, controllers and wiring. Plus, your motor can be out of the salt and dirt, and it'll be far cheaper to boot.

[MazdaMatt]

Just because two cars weigh the same doesn't mean they will operate the same if one is 400 pounds lighter in the body and 400 pounds heavier on the wheels. I like the idea of hub motors, just that argument isn't helping it.

oh and since i live in the heart of frozen tundra (i get a little dramatic about the weather at this time of year) keeping the motors out of the sand, salt and water sounds like a great idea.

[Christ]

Look, I'm not necessarily saying it's a better idea, at the moment, but what I AM saying is that it shouldn't be dismissed so easily.

If we dismissed every idea that came about because of it's potential downfalls, cars wouldn't exist to begin with... Hell, we'd still be pre-fire... making fire is dangerous... It burn Trogg.. Trogg MAD! LOL.

Fact is, while right now, it's not the best methodology or application, it will evolve.

Dismissing an idea for garbage without actually trying it out in the real world, citing a jumble of numbers and every excuse they can think of why it won't work, is not progress...

I personally believe it could be a very good method of implementation, regardless of current limitations. I also believe that if you had the choice between a 600HP Mini that got a minimum of 80MPG, and could potentially use no gasoline or combustible fuel directly, You'd take it, over the other option of a forklift powered EV that can't even get on the highway safely (in most instances.)

[MazdaMatt]

You are right.

The mini is hauling about 65 pounds per wheel, according to that article. My tire/rim combo is about 25. I think on a vehicle larger than a mini it would be more practical... but aren't we all trying to get away from larger vehicles? I suppose there will always be a need for pickup trucks and people haulers so that would be a good place for hub motors - beefier suspension and more %weight in the body.

[MetroMPG]

Christ: good point. People should be encouraged to try to solve problems.

Consider the OP as well, though. Someone basically floating ideas, who presumably hasn't tried anything like this before (just an assumption, apologies if it's not true).

Some of the people I most admire on the EV Discussion List regularly reply to "floaters" with a response that goes something like: (1) Neat idea! (2) Here are the reasons why nobody here has done it so far. (3) Harness your enthusiasm, solve some of the aforementioned problems, and maybe you'll be the first!

[metromizer]

Originally Posted by MazdaMatt

You are right.

The mini is hauling about 65 pounds per wheel, according to that article. My tire/rim combo is about 25. I think on a vehicle larger than a mini it would be more practical... but aren't we all trying to get away from larger vehicles? I suppose there will always be a need for pickup trucks and people haulers so that would be a good place for hub motors - beefier suspension and more %weight in the body.

A minor point to add;

higher unsprung weight <a heavier wheel, essentially> doesn't require anything more than a different valved <stiffer> shock absorber or strut cartridge, to control the wheel assembly during a bump. The spring, a-arms, etc can remain unchanged. Heavier springs or air bags might be needed to handle the additional batteries, but you have that issue with most EV conversion, don't you?

Personally, I love the flexibility afforded by the Pulson retro-fit idea. Any 'clean sheet of paper, from the ground up' new design can be fully optimized, but a retrofit is an awesome stepping stone toward mainstream.

[MazdaMatt]

I must dissagree with the statement that a wheel weighing 40 pounds more can be simply compensated for with a stiffer shock. The car will absolutely handle adversely in comparison. In racing circles the affects of lighter rims and wheels on handling is well known and that's why people pay big bucks to have a 20lb wheel/tire combo instead of a 25lb combo. Going to 65 pounds turns your sporty mini into a slug.

[Christ]

Due to the laws of inertia and centripetal forces, I'd venture to say that you're correct on that, MazdaMatt.

But, you have to remember that they're removing the entire brake assembly from each wheel. Federally illegal in this country, as yet, but still a big step... have you weighed rotors? They're not light.

You're substantially reducing both rotating mass and unsprung weight, before adding a stationary (not rotating) mass which adds back unsprung weight.

Homework for someone: Is there a law that requires that vehicle braking systems be hydraulic/air actuated?

I don't think there is for a modified vehicle... or for a period correct vehicle. This means there is a loophole in the "you can't use it without brakes" arguement.

[Clev]

Originally Posted by Christ

Due to the laws of inertia and centripetal forces, I'd venture to say that you're correct on that, MazdaMatt.

But, you have to remember that they're removing the entire brake assembly from each wheel. Federally illegal in this country, as yet, but still a big step... have you weighed rotors? They're not light.

You're substantially reducing both rotating mass and unsprung weight, before adding a stationary (not rotating) mass which adds back unsprung weight.

Homework for someone: Is there a law that requires that vehicle braking systems be hydraulic/air actuated?

I don't think there is for a modified vehicle... or for a period correct vehicle. This means there is a loophole in the "you can't use it without brakes" arguement.

Now you're asking even more from your 20 pound motors, as they'll need to deal with the resistance heating from converting that 621 amps of braking back into electricity and sending it back to the controller/batteries, or roughly twice the duty cycle if you're in stop-and-go. Then add resistive radiator elements to the car, since you can't overcharge the batteries, so if somebody starts at the top of a hill on a full charge, that electricity has to go somewhere. Finally, your motors have to be able to regenerate a LOT more than they output, because 40 horsepower worth of braking isn't going to be very good in a panic stop, or on a long downhill, or pulling a trailer...

And hope you don't blow a fuse, because then you're relying on your handbrake. Whoops, that's gone too, because you've eliminated the discs or drums it operates.

This is an interesting academic discussion, but any practical technology is unobtainium right now, so to go back to the OP's topic of "how about hub motors for my truck?", the best current answer is "fine for scooters, but not ready for prime time in automobiles, and won't be for a while."

[metromizer]

Originally Posted by MazdaMatt

I must dissagree with the statement that a wheel weighing 40 pounds more can be simply compensated for with a stiffer shock. The car will absolutely handle adversely in comparison...

you know me better than that... every vehicle will respond to lighter unsprung weight, particularly a sporty car

It looked to me as though you were saying you'd need to step up the carrying capacity and beefiness of the overall vehicle if you added weighty hub motors, if you added a bunch of unsprung weight.

I was trying to point out this fact; as unsprung weight goes up, <other than the shock> the car's suspension isn't working any harder. Said another way, fill your tires with concrete. The overall weight of the vehicle gows up, but the required spring is the same, the ride height stays the same. But yes, the car with concrete filled tires now handles like a pig, on that we certainly agree <although I've never tried riding a pig.. not on on ice anyway >

The job of the shock is to control the velocity of the wheel tire assy when a bump excites it. Not stop, but slow down at a controlled rate. Increase the unsprung weight, and the mass set into motion by that bump will still need to be controlled, thus, a heavier valved shock (to have similar control). Acceleration of the <now heavier> rotating mass is slowed somewhat, but you know, at eccomodder/hypermiler acceleration rates, I doubt you'd notice. The Pulson hub motor's mass looks close to axle centerline, making it much better than my 'concrete in the tires' example.

Going the other direction for a moment, one way to give the effect of a stiffer shock on a performance car is to just reduce unsprung weight. That is one reason there is such a performance and 'feel' difference on a sporty or race car when you put on a set of race-weight wheels. Acceleration feels quicker, as well. Lighter wheels don't change the rate or degree of body roll, or change the ride height, or have much effect on overall weight of the vehicle, however, the 'feel' difference is a result of an effectively stiffer shock and slightly quicker acceleration from the lighter wheels (a couple things you'd not notice or care about in most EV's) It's a tough concept to wrap you mind around, but it's real.