What is exactly is a geared hub motor and how does it work?

[MikeFairbanks]

What is exactly is a geared hub motor and how does it work?

What are the advantages and disadvantages of geared vs. direct drive?

 

[TylerDurden]

Geared has a planetary built in, so it has more torque.

[youtube]REsMbCNwbEY[/youtube]

http://endless-sphere.com/forums/viewtopic.php?f=31&t=18732&p=314528&#p314528

 

[John in CR]

Nice clip TD, I hadn't seen one in operation without the cover on.

Mike,
What you can't see is that the actual motor is inside behind those gears. The motor itself turns 4-5 times faster than the outside shell via that planetary gear reduction. Higher rpms means the motor can be much smaller for the same amount of power.

 

[Anonymous]

for overvolting purposes can you get one with metal gears? plastic ones always break if overvolting from 36v to 48v. what do you suggest John?

Nice clip TD, I hadn't seen one in operation without the cover on.

Mike,
What you can't see is that the actual motor is inside behind those gears. The motor itself turns 4-5 times faster than the outside shell via that planetary gear reduction. Higher rpms means the motor can be much smaller for the same amount of power.

 

[John in CR]

The gears can be limiting. Also, the power is driven through the freewheel mechanism (that round part in front of the gears in the vid), which is also a point of limit and failure. In addition, since the motor is completely housed in and separate from the outer shell, and the exterior housing has less surface area, as a result geared hubs have less ability to shed waste heat.

What all that means is that they don't survive if you try to push high power through them. eg I've run my 1200W rated direct drive hubmotors at 10kw+ with zero issues. That's just not possible with a geared hubmotor.

Geared hubs are smaller and lighter, and many have had pretty good results using geared hubs within their designed limit. For the specific question of going from 36V to 48V, that shouldn't be an issue, and steel gears should help with durability. I'd worry more about current limits than going from 36 to 48. Also,there's a fairly wide range of geared hubs, with some designed for significantly more power and torque than others, so their true performance limits will vary accordingly.

John

 

[spinningmagnets]

Lots of geared hub pics here, and a list of available types, with specs also....

http://endless-sphere.com/forums/viewtopic.php?f=3&t=4892

 

[Anonymous]

Thanks John,
I very much appreciate the help.
Just wondering..Where did you get those moped hub motors? were they expensive?

What all that means is that they don't survive if you try to push high power through them. eg I've run my 1200W rated direct drive hubmotors at 10kw+ with zero issues. That's just not possible with a geared hubmotor.
John

 

[MikeFairbanks]

More moving parts means more to break.

Got it.

 

[neptronix]

Think about it this way.. in a manual transmission car, 1st gear is usually a 1:1 or so ratio. Electric motors basically make TONS of torque at first, and then gradually poop out.

A geared hub motor has a little 1 speed planetary transmission in it, essentially.. which basically puts you in 3rd or 4th gear; with a much longer gear ratio you can go *much* faster.. but you accelerate much slower at the same time.

One bad part is that the gears are a weak spot. Metal will grind away and deposit shavings all over the place over it's lifetime, it is also loud! plastic/nylon is very quiet and can wear out or melt when given more power ( more volts/amps ) than the gears were designed for; but theoretically if it is not abused, the gears should last a long time.

If you want a pedal assist type of bike, a geared motor is great because you can make up for the lost torque by pedaling. If you want essentially an e-motorcycle, a direct drive is the way to do it.

What would be best? a stinkin' huge 1000w nominal/2000w peak geared hub... you wouldn't have to overvolt/overamp it because it would already be a barn burner

 

[MitchJi]

Hi,

A geared hub motor has a little 1 speed planetary transmission in it, essentially.. which basically puts you in 3rd or 4th gear; with a much longer gear ratio you can go *much* faster.. but you accelerate much slower at the same time.

Its exactly the opposite (acceleration is faster).

What would be best? a stinkin' huge 1000w nominal/2000w peak geared hub...

A major advantage of a geared hub motor is smaller and lighter for the same performance. So what's the point of a "huge" geared hub?

Excellent explanation here:
http://www.ebikes.ca/hubmotors.shtml

 

[neptronix]

Hi,

A geared hub motor has a little 1 speed planetary transmission in it, essentially.. which basically puts you in 3rd or 4th gear; with a much longer gear ratio you can go *much* faster.. but you accelerate much slower at the same time.

Its exactly the opposite (acceleration is faster).

What would be best? a stinkin' huge 1000w nominal/2000w peak geared hub...

A major advantage of a geared hub motor is smaller and lighter for the same performance. So what's the point of a "huge" geared hub?

Excellent explanation here:
http://www.ebikes.ca/hubmotors.shtml

Okay, i wasn't clear.
I mean higher top speed, not faster acceleration.

The point of a huge geared hub would be to have a very high speed without thirsting for more power; you'd have enough from the get go!
Huge is relative here, since geared hub motors are pretty dang small. Look at the BMC Puma, it's small by direct drive motor standards, but huge by geared motor standards. And it packs a big punch.

 

[MitchJi]

Hi,

A geared hub motor has a little 1 speed planetary transmission in it, essentially.. which basically puts you in 3rd or 4th gear; with a much longer gear ratio you can go *much* faster.. but you accelerate much slower at the same time.

Its exactly the opposite (acceleration is faster).

Okay, i wasn't clear.
I mean higher top speed, not faster acceleration.

Which is incorrect. With geared hubs the gearing is such that the motor is spinning faster at a given bicycle speed.

Geared has a planetary built in, so it has more torque.

More torque equals better acceleration.

http://www.ebikes.ca/hubmotors.shtml

The geared hub concept takes the weight advantages of a transmission drive and packages it into the simple looking and easy to install hub motor. These typically weigh about 50% less than an equivalently powerful direct drive machine, and they often have superior torque outputs. The german-made Heinzmann for instance can produce up to 80 Newton-meters (N-m) of torque, compared to about 35 N-m for typical direct drive machines. There are also geared hub motors made by Sanyo, eZee, Ethinkar, and several other Taiwainese companies.