What innovation would you like to see next for hub motors?

Joined
May 19, 2012
Messages
813
For me it would be an geared hub motor using an IPM configuration rather than the usual SPM configuration.

In addition to being able to climb hills with heavier loads at slower speeds I imagine (on locked clutch models) regeneration would be very very good even at slow speed.




Perhaps the biggest advantage of IPM designs, one that gives them an edge in vehicle applications like traction motors, is the high-speed performance. The power versus speed curve for SPM motors is roughly hyperbolic, rising to a region of quasi-constant power over a narrow speed range, then falling off.



IPM motors, in contrast, provide a much broader region of more or less consistent torque. Using a technique called field weakening, designers can apply current to modify performance. As speed rises, the permanent magnets and motor generate highers voltage. At very high speeds, the back EMF of the motor times the speed can exceed the voltage of the battery, which limits drive current, and torque. Field weakening essentially involves tuning the magnetic field of the stator to partially oppose the effect of the permanent magnets. The process involves a control scheme known as direct (D) and quadrature (Q) axis current control. The D-axis runs through the center of the rotor pole while the Q-axis lies between two adjacent rotor poles in the center. “By breaking the stator vector into two vectors, and applying one current to the quadrature axis and one to the direct axis, they control the current phase angle between them, which allows much wider constant power control," explains motor designer and IEEE fellow Jim Hendershot, co-author of Permanent Magnet Brushless Motors and Generator Design.



For vehicle applications, the technique provides big benefits compared to SPM motors. “The IPM configuration allows more control over the magnetization of the magnetic circuit," says Hendershot.



That's not to say that field weakening isn't possible with SPM designs, as well, but because of the size of the air gap, the technique requires far higher currents. “Because of the current limit of the inverter on thermal limitations of the motor, you can't field weaken it enough to produce torque at high speeds," says Fulton.



At low speeds, SPM motor and an IPM motor of the same size can generally produce about the same amount torque, or the SPM design may even produce a bit more up until they reach the corner point RPM. At speeds higher than the corner-point RPM, torque from SPM designs drops rapidly. “If both of them have a base of 3000 RPM, the SPM motor will probably have zero torque at 5000 RPM whereas the IPM could continue on to 10,000 or 12,000 RPM," says Fulton. The behavior makes IPM motors a good fit for traction motor applications, which tend to demand high torque over a broad speed range. “With IPM designs you get the best of both worlds—you can get very good acceleration at low speeds and then run at very high speeds while at almost the same power level.”





A type of motor that has a rotor embedded with permanent magnets is called the IPM (interior permanent magnet) type. Compared with the SPM (surface permanent magnet), this type of motor can reduce the risk of a magnet being peeled off by centrifugal force, and take advantage of reluctance torque. The IPM type allows various structures for embedding permanent magnets.
 

Attachments

  • Screenshot_20230621-200548.png
    Screenshot_20230621-200548.png
    768 KB · Views: 7
Last edited:
Here is one of the type of bikes I would like to see such a hub used on:


So make a version compatible with a single rear cog and when configured this way make sure that there is no wheel dish.

Also make the gear hub easy to service so routine regreasing is easy to do.

Overall such a bike would be easy to own and use.
 
Last edited:
Interior Permanent Magnet implies magnets embedded inside steel laminates. And that rules out the outrunner topology usually used in hub motors. Going with inrunner-in-hub topologies is possible but that will require 2+ stages of planetary gears inside the hub housing to provide the same torque capacity of outrunner hub motors. With that much mechanical complexity you might as well go with Bafang's automatic transmission hub motors. There is no mature radial flux IPM/SynRM topology that can be applied in a hub configuration.

Some experimental axial flux IPM/SynRM topologies (e.g. this and this) might lend more naturally to hub configurations but their manufacturability is probably years away from maturity.

1690016586197.png
 
There was some interesting improvements recently in ferrite magnets that implied they could be used instead- cheaper, non rare-earths with modern cooling techniques could make eBikes way more common throughout the world with more factories building them.
 
I saw a car engine recently using 6 phases instead of 3:

Would be a nice way to reduce the problems with current big hub motors having to have such big phase wires and the connectors sometimes melting.
 
Interior Permanent Magnet implies magnets embedded inside steel laminates. And that rules out the outrunner topology usually used in hub motors. Going with inrunner-in-hub topologies is possible but that will require 2+ stages of planetary gears inside the hub housing to provide the same torque capacity of outrunner hub motors. With that much mechanical complexity you might as well go with Bafang's automatic transmission hub motors. There is no mature radial flux IPM/SynRM topology that can be applied in a hub configuration.

Some experimental axial flux IPM/SynRM topologies (e.g. this and this) might lend more naturally to hub configurations but their manufacturability is probably years away from maturity.

View attachment 336968
That Bafang two speed you are referring to only applies to the pedal part of the drivetrain. It is a 1 speed geared hub motor with a automatic two internal gear hub occupying space in the center of the hub. It is not a two speed motor like the Xiongda.

Bafang does make a inrunner ebike hub motor called the G310 and G311 which is also used for the core of the Bafang Wheelbarrow motor. The Bafang wheelbarrow adds additional reduction bring total reduction to 30:1. It unfortunately suffers from the magnets coming off if RPM gets too high.
 
Last edited:
I would like to see machine wound or hairpin type windings, and high temperature magnets. This would increase the durability and current handling to make motors either more powerful or much smaller and lighter, or bothe
 
This is easy:

1. No more solid axles to force into 135mm dropouts. Thru-axled ones that have a special oval axle that accepts the hub motor's torque and also can substitute for those faustian bargain torque arms. Not to mention no more caveman era bolt-on wheels.

2. No more torque arms (see above).

3. Wider modern tubeless-ready wheels for the hub motor. So you don't have to worry as much about flats. And can also put in a 2.5 or 2.6 (possibly a 2.8) tire into a 142 or 148mm frame without it having to be a fat bike. Also the manufacturers actually lacing the hub motors to these wheels, as in they give the option of a modern rear wheel instead of offering a few different kinds of cheap, older 19mm rim choices to lace.

4. No more freewheels; 100% cassettes with a 7-11 speed freehub, 12-speed optional depending on if the frame is 148mm or not.

5. Internal gearing and programming that can raise the torque level to 50 Nm per 500 Watts; similar to a mid-drive's output.

6. Option for internal controller inside the hub like a direct drive.



In other words, bringing hub drives into the 21st century. It can be done. There just needs to be a demand for it. If there is not anyone saying anything about the issues above, hub drive technology will continue to stagnate relative to mid-drive technology. Not absolute stagnation, but yes relative stagnation.

If those 6 issues were addressed, I've have no problem buying another hub drive wheel. For now, because I offroad a lot, a mid-drive is a no-brainer, since they avoid all of the above problems (although they certainly have their own issues, but they are still worth the hassle compared to the above). If someone is 100% on the street, the older hub drive stuff will work but it still could be a lot better for not much more cost.
 
Two things: I would like to see AWD a systems designed from the ground up. An AWD system could allow for much better weight distribution. Instead of 8 lbs on the rear wheel, you have 5 and 5 on the rear and front.

Second one is integrating igh hubs into hub motors. The larger direct drive motors have the room.
 
Two things: I would like to see AWD a systems designed from the ground up. An AWD system could allow for much better weight distribution. Instead of 8 lbs on the rear wheel, you have 5 and 5 on the rear and front.

Second one is integrating igh hubs into hub motors. The larger direct drive motors have the room.
Right now Bafang is actually integrating igh into at least one of their geared hub motors. This with their two speed automatic igh (I am assuming their 3 speed and 5 speed automatic igh found Here will follow as well). So it's not just direct drive hub motors that can benefit from igh integration.

With that noted, I wonder what would make a better igh hub motor:

1. A igh integrated into a geared hub drive? This when the planetary gears of the hub motor likely restricting magnet width.

2. A igh integrated into a direct drive hub motor but with a diameter much closer in dimensions to the geared hub motor with igh.

Magnets that are narrower but spinning faster because of the benefit of gear reduction or magnets that are wider but spinning slower because they don't have reduction (i.e. direct drive)? Which one makes a better hub motor at 135mm O.L.D, 170mm O.L.D., 190mm O.L.D., etc.assuming P.C.D. (or hub shell diameter) is kept the same for both the direct drive and geared hub motor?
 
Last edited:
Right now Bafang is actually integrating igh into at least one of their geared hub motors. This with their two speed automatic igh (I am assuming their 3 speed and 5 speed automatic igh found Here will follow as well). So it's not just direct drive hub motors that can benefit from igh integration.

With that noted, I wonder what would make a better igh hub motor:

1. A igh integrated into a geared hub drive? This when the planetary gears of the hub motor likely restricting magnet width.

2. A igh integrated into a direct drive hub motor but with a diameter much closer in dimensions to the geared hub motor with igh.

Magnets that are narrower but spinning faster because of the benefit of gear reduction or magnets that are wider but spinning slower because they don't have reduction (i.e. direct drive)? Which one makes a better hub motor at 135mm O.L.D, 170mm O.L.D., 190mm O.L.D., etc.assuming P.C.D. (or hub shell diameter) is kept the same for both the direct drive and geared hub motor?

Yes, I am aware of the bafang automatic shifting hub.

I have a SRAM automatix auto hub and I really like it. I have considered turning it into an ebike with a mid drive.

I can’t see anywhere to buy this bafang automatic hub, and I remember reading about it a few years ago.

There already exists a direct drive motor with an IGH built in. Some Taiwanese company makes it.
 
I really wish that there were a way to make hub motors lighter. The weight is a genuine problem both for ride quality and also because the shock that is transmitted to the motors can damage them IMO. Mid drives are more insulated in contrast, and generally, wheel weight is worse than frame weight.
 
I think it would be cool to put an Envilo hub in a motor. I assume it would be a DD hub motor, and also that it would be one heavy wheel.
 
There already exists a direct drive motor with an IGH built in. Some Taiwanese company makes it.
Yep, here it is:


Notice (in picture below) it does appear to have quite a bit of space between igh and copper windings/permanent magnets.

This is why I am wondering how much the diameter of the hub could be reduced. Obviously with reduced diameter comes reduced magnet speed (which hurts power output) but then again since it is igh and doesn't need to fit a gear cluster the magnets could be made wider to compensate.
 

Attachments

  • IMG_20230731_200306.jpg
    IMG_20230731_200306.jpg
    38.2 KB · Views: 4
Last edited:
Here is the product listing for the sturmey archer 5 speed used in the TDCM direct drive:


And here is a diagram of another direct drive hub motor (made by Accel) which also uses the same igh:

 

Attachments

  • IMG_20230731_202223.jpg
    IMG_20230731_202223.jpg
    25.8 KB · Views: 5
  • IMG_20230731_203008.jpg
    IMG_20230731_203008.jpg
    48.8 KB · Views: 5
Last edited:
Yep, here it is:


Notice (in picture below) it does appear to have quite a bit of space between igh and copper windings/permanent magnets.

This is why I am wondering how much the diameter of the hub could be reduced. Obviously with reduced diameter comes reduced magnet speed (which hurts power output) but then again since it is igh and doesn't need to fit a gear cluster the magnets could be made wider to compensate.
It must not have worked out because all the links are dead and it appears that they haven’t pursued the idea any further.
 
It must not have worked out because all the links are dead and it appears that they haven’t pursued the idea any further.
I'll bet Ebikes.ca is planning to use the Sturmey Archer 5 speed with the 45mm magnet version of the Grin direct drive. This would be a big jump over the 30mm magnets used by the TDCM motor.

Grin rear hubs would then be:

28mm magnets with cassette gear for 135mm OLD.

45mm magnets with SA 5 speed igh for 135mm OLD.

45mm magnets with cassette gear for 190mm OLD.

P.S. The 45mm magnet version of the Grin direct drive can be found here in marine format:

 
Last edited:
The issue to me is that no major automaker makes an electric car with a hub motor. They likely have considered it but have decided against it.

For bicycles, honestly the best application for hub motors are for recumbents. But overall mid is better for bicycles. It’s just that regen is only possible with hubs. A mid setup that could regen would solve all problems.
 
The issue to me is that no major automaker makes an electric car with a hub motor. They likely have considered it but have decided against it.

For bicycles, honestly the best application for hub motors are for recumbents. But overall mid is better for bicycles. It’s just that regen is only possible with hubs. A mid setup that could regen would solve all problems.
A left hand side direct drive mid drive can be set up for regen. It is only single speed though.

The only right hand side mid drive that I know of that claims regen is Bikee bike's upcoming lightest drive.


However, this is only possible when using a multi-speed fixed gear igh like the old Sturmey Archer 3 speed fixed gear (which still can be found for sale new).
 
.... I have a SRAM automatix auto hub and I really like it. I have considered turning it into an ebike with a mid drive....
Please don't...

I have one of those two-speed hubs (and an i-3) both new and unlaced. Would I feed either electrons?... hell NO. It was discontinued almost 7 years ago.... implying replacement parts would likely be about as difficult to find as parts for a vintage Sachs Orbit.
 
A better much bigger reengineered version of the Xiongda 2 speed (2 internal gears) would be perfect.
 
I liked the concept of the now-discontinued Bionx D500 hubmotor. Large diameter that inherently provides strong torque (through mechanical advantage) yet the spokes attach near the axle flange so it uses full size "normal" spokes as with a "normal" wheel. Wish it was made without proprietary circuitry inside.
 
Bionx a manufacturer that use good quality batteries I believe they were internal inside the hub and had a lot of territory things that you couldn't use unless you got the factory product yes they did work very well 15 years ago but we have moved on from that. Overpriced only can buy parts through them that match. Now outdated do not buy a used one for a headache.
 
Back
Top