Superlight Hub Motors??? Warning, first post makes no sense

[mdd0127]

Please forgive me if this has been discussed. I searched quite a bit and haven't seen any mention of anything like this anywhere.

Between seeing the performance possibilities of John in CR's hubmonster super-v and advice from Liveforphysics regarding gearboxes and the ultimate electric drivetrain design, while sitting here unable to do anything else, I've been thinking about hub motors. Yes, for real, hub motors. :lol:

I understand the reasons that hub motors can be super efficient, quiet, and have very high performance possibilities but my main issue with them is unsprung weight. For some reason, I can't get that limitation out of my head, probably because I don't like roads or traffic.

Anyway, has there been any research put into developing a light weight, let's say sub 5 lb, hub motor that could handle 10kw or so?

In just thinking it about it for a few minutes, I know that what makes direct drive motors heavy is the copper in the windings and the silicon steel in the stator plates. I must admit that I have an extremely elementary understanding of motors. But, just out of curiosity, what about winding with aluminum instead and using stator plates made of something like superconductive ceramic plates separates by really thin, hollow, silicon steel plates filled with liquid nitrogen? If the inside of the motor was kept in a vacuum, how long would the nitrogen stay cold? Since the volume would be small, what about a tiny unit that would extract nitrogen from the air, compress it into liquid, and pump it through the motor? The same unit could be responsible for the insulating vacuum...

Am I stoopid or is this something that could work if the physical aspects of putting it together could be figured out?

This thread is already reminding me of the time that I thought I'd figured out an awesome new outrunner design and one of the forum members pointed out that I'd spent all night designing a basic hubmotor....

Just brainstorming......

 

[John in CR]

I'm looking to move some of my bikes to mid-drives to get that weight out of the wheel. For off road the weight of hubbies is just too big a compromise. 10lbs or more extra in the frame is nothing, but in the wheel it is. Until the motorcycle companies step in and build a moto power geared hub there isn't a good solution.

If you want a lighter motor, then it has to spin faster. A high power DD will always be heavier than you want because of the steel, copper and magnets required to make sufficient torque at wheel rpm for good power means a heavy motor. The magic material that's missing isn't room temp super conductors, though that would be nice. Instead we need a far lighter material than silicon steel that can create as much or more magnetic flux for the same amount of electricity. Ideally it would have far greater electrical resistance too.

Here's one to chew on. How about a strong permanent magnet like our neo's that with a small electric pulse could turn off/on and/or switch polarity instantly. Of course that would make above unity possible, so it's obviously impossible.

In the meantime, I'll take batteries that have just twice the energy density and twice the power density. Imagine the 100 mile batteries at 100V that are the size of a pack of cigarettes that our grandchildren will have for their DIY ebikes.

John

 

[mdd0127]

It looks like you'd have to use a synchronous ac motor design with superconducting coils for that idea to work. Talk about hard on a controller though! http://forum.allaboutcircuits.com/showthread.php?t=42262

I'm just thinking that the ceramic would be lighter than the copper. Is there a lightweight material with good magnetic flux properties?

Then I thought about putting the magnets along the rim and having a rail gun type accelerator structure to spin the wheel, which has been done, just not on an e-bike as far as I know. Just have to keep the crud out of the magnet gap. It seems like the hub, spokes, and suspension could also be eliminated with that type of system.

I've also been thinking about linear, solenoid type drives that could simulate legs. Yeah....I'm really bored.....but don't have enough gumption to do real research right now. Maths and new big words hurt da brains.....

 

[mdd0127]

Here's one to chew on. How about a strong permanent magnet like our neo's that with a small electric pulse could turn off/on and/or switch polarity instantly. Of course that would make above unity possible, so it's obviously impossible.

Aren't they doing something like this with suspended ferrofluid in shock absorbers nowadays?

 

[Samd]

Maybe a loopwheel style for development. Maybe a bit small in limitation.
http://www.endless-sphere.com/forums/viewtopic.php?f=3&t=50256

 

[mdd0127]

I saw that a few weeks ago and have been thinking of something very similar for maybe ten years. Someday, I want to put a motor on something that will weigh 50 lbs that has a foot of travel though and like you said, I don't think a loop wheel would work unless it was a 36 incher....which might be cool....

 

[neptronix]

What would be really badass would be an oil cooled RC style motor with dual planetary reductions.
The oil would not only lubricate the gears but cool the motor and transfer heat to the outside.

Never heard of such a thing tho.

 

[mdd0127]

But planetary gears can't handle shock loads and if you've ever got the rear wheel off the ground during a jump and hit the ground on the throttle, you'll see how much force can build up. Some kind of slipper clutch would have to be implemented to save the gears which would drive weight and complexity back up. The "rail gun wheel" (there has to be a better term for it that I'm brain farting on) is making the most sense in my mind so far because it would just be a few big coils attached to the frame and a strong rim with magnets along the side.

Still wondering about how to make stator laminations out of lighter materials though.

 

[Samd]

More loops at the center of the planetary gear to take up shock loads?

 

[mdd0127]

After thinking about it a little more, the wheel design itself would probably take much of the shock loading out of the equation because it's able to flex backwards and rotationally in addition to perpendicular to the bumps. I hope they get the kickstarter off the ground and are able to manufacture those at least a few things. It will take a few years of just being a pedal bike wheel before they think to add a motor into the hub though. I suspect that the design only works on small bumps at low speeds, like a springer fork or spring seat would because I'm a little perplexed as to what provides the dampening effect if there is any. I find it difficult to believe that progressive dampening could be engineered into the loop material but we'll never know until we can try one. I have a feeling that hitting a large bump at speed would bounce the bike into the air instead of just soaking the bump up.

 

[iperov]

PatGear have world smallest hub motor used for commuting

 

[mdd0127]

If it'll take 10kw for a few minutes at a time I want one! It would be neat to have a quarter or beer can in the pic for a size reference though.

 

[neptronix]

Hey, if you have a wheel about the diameter of an RC motor, then you can get RC motor type power out of that size motor, as it'd be spinning at 1000's of RPMs, rather than just a few hundred

Our bicycle hub motors are much like giant V12 motors that spin up to just 1,000rpm.
Maybe you can get some lower weight materials in the hub, but you still have a lot of weight in copper and neo magnets. You are still using a tiny fraction of all that copper and magnet's potential by spinning it up to just a few hundred RPMs.

There is not much getting around it. A direct drive hub motor makes very poor use of the potential of materials inside it. A 3.5 pound astro motor can produce the same power as a 30+ pound hub motor.

 

[mdd0127]

You don't have to tell me about the potential of a 3220 :wink:

So basically, when it comes down to it, for offroad use where low unsprung weight is key and low overall weight is also very important, with the tech we have access to now, the complexities of gear reductions and power transmissions are the only way we have to get the power to the ground.

That's the conclusion I came to after a few years of serious research. Don't know why I'm going back and questioning it now??? Derp....

I guess the simplicity of the Super V just got into my head...

Still can't quit thinking about some kind of alternative, extremely light weight, non ferrous stator material because the magnets and some aluminum windings wouldn't be that heavy in comparison to the steel....

 

[neptronix]

I believe that aluminum isn't used just because it is not very conductive, so you would need a lot more of it. I believe that silver is more conductive than copper, maybe the only element more conductive than copper.

As for the stator steel, i believe you need a ferrous material. I'm not sure if there is a lighter weight material..

I forgot that you toyed with astros. The main downside of those setups is just the expense. But i think you had the ultimate setup already

 

[Punx0r]

You are still using a tiny fraction of all that copper and magnet's potential by spinning it up to just a few hundred RPMs.

There is not much getting around it. A direct drive hub motor makes very poor use of the potential of materials inside it. A 3.5 pound astro motor can produce the same power as a 30+ pound hub motor.

This sounds like an argument for geared hub motors, yet we don't seem to see powerful ones being made?

 

[salty9]

If it'll take 10kw for a few minutes at a time I want one! It would be neat to have a quarter or beer can in the pic for a size reference though.

The ad I saw for the scooter claimed 150W for a price of $1400. http://www.aliexpress.com/store/pro...ic-scooter-portable-car/508388_781829353.html

 

[MadRhino]

A DD hub motor wheel built with bicycle rim, spokes and tire, can weight about the same as a motocross wheel already. So that unsprung weight is not so much of an issue if you build and tune your suspension for it. Yet, hub motors that have true performance potential are heavy, and they could be built much lighter. Liquid cooling is the first step, for it does free the mass of the motor from heat shedding efficiency. A powerful, large diameter hub motor made with light weight materials like CF and Ti can be a viable reality if it is liquid cooled, so we don't have to rely on its mass to shed the heat.

Imagine an 16" diameter hub motor with 50mm magnets, that would weight short of 20 pounds because almost all of its weight would be the copper coil and the magnets. That would open the door to amazing hub motor performance.

 

[Njay]

The "rail gun wheel" (there has to be a better term for it that I'm brain farting on) is making the most sense in my mind so far because it would just be a few big coils attached to the frame and a strong rim with magnets along the side.

I've had thoughts on that area. But the fact that magnets may attract every piece of iron along the way, made me think of the other way around: a pair of magnets on the frame and low inductance coils on the rim, near the tire for higher torque. The coils I'm thinking are just 2 or 3 loops of wire (small bent bars, actually), which will take power from the frame, through brushes. This would make up a DC brushed motor. All the iron will be with the magnets, in the frame. Since usually the frame has 2 bars to the wheel axis (back wheel), 2 such systems can be in place for double torque.

 

[mdd0127]

I hadn't thought of the debris being picked up! That's why brainstorming with others is so worthwhile. In my head, for the coil accelerated rim design, the coils would not only accelerate the wheel but hold up the weight of the vehicle and provide suspension travel and dampening. The rim/tire would not touch the bike in any way. No brushes, linkages, wires, nothing. Either way, this would require a lot more energy to magnetically support the weight and due to the debris pickup factor, would rely upon technology that doesn't exist yet, like materials that can be given a strong magnetism and specific polar alignment just before entering the accelerator/suspension coil array and that would lose that magnetism after leaving the array. Maybe good old iron would work though with the proper superconducting coil array arrangement? I can almost see the arrangement in my head. You'd have little blocks of iron stuck to the sides of the rim, a magnetizing/suspension coil, acceleration coils, and a demagnetizing/suspension coil.... I think that it should be possible but it's unlikely that it's something that a backyard/diy guy would be able to produce.

As far as using a heavy hub motor and tuning the suspension to handle it goes, that doesn't do anything about the overall weight of the machine, which is super important in my book. Having ridden 250+ lb dirt bikes on tight trails and ridden a 75 lb bike with similar acceleration capabilities, it's going to be really difficult for me to feel near as capable on a heavy machine again.

I guess that for now, and probably for a while in the future, nothing's going to beat the power to weight ratio of the 3220/HV160/CA current throttle/lipo setup so instead of developing new magic materials, our real challenge is making the components listed more affordable, more available, and able to be produced in a more reliable and sustainable fashion.....another conclusion that I'd already come to before giving up on my ultimate e-bike project.

Sure like the simplicity of an ultra light high power direct drive hub motor though if one could be made.

 

[neptronix]

You are still using a tiny fraction of all that copper and magnet's potential by spinning it up to just a few hundred RPMs.

There is not much getting around it. A direct drive hub motor makes very poor use of the potential of materials inside it. A 3.5 pound astro motor can produce the same power as a 30+ pound hub motor.

This sounds like an argument for geared hub motors, yet we don't seem to see powerful ones being made?

Ah, the real problem is packaging and all the extra parts needed.
I don't know if you have ever opened up a MAC or BMC motor, but the assembly inside is pretty tight, the innards are maybe 50% stator/magnet ring, 50% gears, clutch, bearings, circlips etc.

Making these geared hub motors more powerful is a challenge. If you make them wider, then you lose the ability to use a multi gear cluster, which limits the motor's appeal. You can make them taller, but then you need a custom clutch and gear holder that must be manufactured specially for your motor, and you need to re-engineer a lot of stuff. Or you end up doing some really weird and wacky designs. The question is - will people buy them if you go through all the work? The problem is that the market for a 2000W+ geared bicycle motor is very small, since such a thing is illegal almost everywhere.

It's much easier to put together a big DD motor. No need to sell 10,000's of units to make up for the R&D cost on that.
Damn you, economics and laws

So for lighter setups, it'll always be about chain / belt drives.

 

[dirkdiggler]

After watching some rail gun videos with my kids, I thought why can't we have a linear motor on a bike. Interesting old thread. Does four years seem old? Ebikes have progressed rapidly.
My idea would be to accelerate the chain instead of the wheel. Is this a viable option for us? Still might have debris issues, but why not turn our bike chains into the motor itself? Like the op, my motor knowledge isn't great, but the power of the rail motors combined with a bike sounds ideal.

 

[MadRhino]

Efficiency gets lower, as gears and drive means are added, and maintenance gets higher. A hub will be the best solution for a powerful ebike for a long time. Driving a chain is only a good choice for low power, or very high power with a motorcycle drive train.

 

[dirkdiggler]

Maybe I'm thinking too far ahead, but having the chain be what the electricity spins seems ideal for bikes. Cut to the chase by having the motor do the final job instead of the motor turning something that then turns another thing. Having two long electromagnets that run alongside the chain or even have the front sprocket rotate by the electomagnets would be ideal for weight and space issues on ebikes. A low power or high power option is really what people want anyhow. Either a low power city bike that is light weight, easy to carry and unobtrusive or the high powered quasi motorbike that endless sphere loves.
I'm not really a hub fan due to the issues involved with weight and where the weight is, but we all have different needs.