Lightest possible hub motor for road bike?

[paul-home]

I'm trying to find a really light, slim hub motor for a very light road bike.
I'd like it to be a rear wheel version, ideally direct drive brushless, and it needs to be of good quality as it will be doing a lot of miles.
I like the 9 continent motors but I havent seen a light one.

Thank you for any pointers.

 

[TPA]

Smallest direct drive probably aotema maybe Clyte 4xx.

Smallest geared is bafang and cute motors. Also about half the weight of any direct drive motor.

 

[paul-home]

Smallest direct drive probably aotema maybe Clyte 4xx.

Smallest geared is bafang and cute motors. Also about half the weight of any direct drive motor.

Brilliant, I will investigate, thank you.

 

[vanilla ice]

There's the "cute" and the "209" but I'm not sure on dimensions or power specs. There should be some info in the forum. Ah the cute is geared huh, ok.

 

[Doctorbass]

The BionX hub motor are some of the lightest motors.

4.1kg and they very slim.

http://www.bionx.ca/en/products/technology/

Doc

 

[Russell]

The GM front Mini Motor I have is 5.75 lbs (2.6Kg) but the CUTE's are supposedly lighter with the smallest one on the ecitypower website listed as 1.6Kg (3.5 lbs). Of course the smaller the motor the lower the power handling capability so none of them will sustain high speeds for prolonged periods without getting hot therefore first and foremost you need to specify how fast you want to go and how much of the time you'll be using the motor. You also need to specify at what voltage you wish to run the motor. After you do that you'll have to find a motor which will achieve those speeds on that voltage with some measure of reliability.

Some examples;

I have a 36V Bafang (3.3Kg) which will propel me to approximately 17.5 mph with a 36V lithium battery (41.3V max) on a bike with a 700Cx35mm tire. On a bike with a 700Cx50mm tire and a "48V" LiFePO4 pack (actual 51.2V nominal) the speed is a bit over 23 mph. On longer trips maintaining speeds in the upper teens will heat up the motor. Holding full throttle with a 48V pack for several miles will get it HOT.

I also have the 2.6 Kg GM Mini I mentioned above (really a Bafang) which is spec'd as a 24V motor however what that means is it's wound faster so that it can provide the same speed as the 36V motor but do it with 24V, albeit while drawing more amps. When I run this motor on a 36V pack it can achieve 23 mph (700Cx35mm tires) however the same caveats regarding prolonged speeds over 20 mph and heat hold as the previous motor. I have also run this motor with the 48V pack where I attained 29 mph with no pedaling however the power drawn at that speed will get the motor very hot and can damage it. In fact I melted some hall wires on this motor on 48V running full power up a couple of steep grades near the end of a long ride.



The bottom line is that small geared motors like the ones I mentioned are neat and make great assist motors however their usual 200-250W rating means they are designed for continuous use in the 15-18 mph range. The small motors can be over-volted but care must be exercised to not overdue it or they can fail. The next step up from these lightest motors are the ~9 pound 350-400W eZee, BMC V1 or Puma geared motors followed by the slightly heavier 600W BMC V2. The lightest direct drive motor widely available is the Nine Continent front motor at 12.6 lbs (on my scale, rear is a bit heavier) though it is quite large in diameter. The Aotema/Wilderness Energy (front) direct drive motor is smaller but I haven’t seen a reliable weight given for it though I suspect it’s a bit heavier than the 9C.

-R

 

[spike]

When I tried a Bafang on my road bike I found that the weight of the batteries was the problem not the hub. It was unstable and I felt every bump in the road. I switched to an old MTB very quickly. Unless you are looking at LiPo then it might be something else to consider before you commit too much cash.

HTH

Spike

 

[spinningmagnets]

You may want to take a quick glance at an RC friction-drive. They're not for everyone, but useful to some. Here are pics of two:

http://endless-sphere.com/forums/viewtopic.php?f=28&t=14403

 

[jag]

A tradeoff in direct drive motors is that as they get small and lightweight, the torque also decreases. The 205 9C that is popular here in the US gets a very good torque/power to weight ratio just because it is a big diameter motor. 9C also makes smaller DD motors, but they would have to be privately imported. I don't know of any reviews of them.

As drbass pointed out, BionX has a light hub motor, and their whole system is pretty light if you choose the LiMn battery option. (Might be only one available now. Not sure if they still sell NiMH). Drawback is that it is not a very user configurable system. Say you wanted to buy cheap LiPo batteries from HobbyCity, it is likely difficult to figure out how to integrate these into the BionX.

If you are a tinkerer you could buy a BionX with dead batteries or broken controller, and just bring out halls and phase wires to run off standard controller and batteries.