Smallest, lightest hub motor?

Drunkskunk

Drunkskunk

100 GW
Joined
Apr 14, 2007
Messages
7,244
Location
Dallas, Texas. U.S.A.
So who makes the smallest, lightest rear hub?

And where can I get one as just the motor, or just the motor and wheel?

I have this idea thats been bugging me for a while, to build a sleek efficent roadbike, use an RC controller, and Lipo batteries, and see if I can get the total bike weight under 30 pounds. I want to go minimalist here, and see how far I can take the idea. I have 2 light weight race frames i'm not using, and it would be a shame to let them collect more dust.
 
been thinking the same thing but it's the 2nd or 3rd project down the road. I'm thinking along the lines of an electric brompton. It's been done before but I'd like to improve on the concept.

The motor is built in the UK. http://www.nano-motor.co.uk

2.2 kg is the motor weight. you can't get lighter than that.
 
The smaller 250 watt Bionx hub with their lithium battery is a 14 pound kit. I think realistically, you could put together an ebike in the mid 30 pound range if you started with a really light weight bike and weren't expecting a whole lot of power or range. 30 pounds is pushing it.
 
I wonder if we could get those nano motors from china? Everything from Europe is so overpriced with the bad exchange rate now.
 
I've been having some of these same thoughts. If the RC folks can build those powerful little motors that are smaller than a pop can (see Recumpence thread), why can't a really light hub motor, like the ones mentioned above in this thread, but with lots of power be made? It seems if a hub motor was real small, real light, real powerful, geared, and probably free-wheeling, it would have a huge market. You could even put two on a bike, one with high torque and one with high speed, and use one or two as needed.
 
Rassy said:
why can't a really light hub motor, like the ones mentioned above in this thread, but with lots of power be made?
Click to expand...

The RC motors are principally light and powerful because they run faster. So, to lose weight from a hub motor, you'd have to run it faster and gear it back down, even more than the Tongxin - the returns start to diminish....

You could always mount an RC motor, or two, in a hub with belt reduction, like the old Sanyo design.
 
Sorry to burst your bubble re:Tongxin motors, but they suck! My rear one lasted 4.5 miles and melted down! Check solarbbq2003 website. I think he still has the trials and tribulations of his battle with them!
otherDoc
 
Miles wrote:
Rassy wrote:
why can't a really light hub motor, like the ones mentioned above in this thread, but with lots of power be made?
Click to expand...
The RC motors are principally light and powerful because they run faster. So, to lose weight from a hub motor, you'd have to run it faster and gear it back down, even more than the Tongxin - the returns start to diminish....

You could always mount an RC motor, or two, in a hub with belt reduction, like the old Sanyo design.
Click to expand...

Miles, I think you missed my point, that it should be possible to design a hub motor from the ground up along the principles of the RC motors that recumpence is using, with the equivalent gearing and freewheel built into the hub (recumpence uses gearing that he designed and built himself). I don't know why this should be any less efficient within the hub then what Matt ended up with. Of course it would only be one speed.
 
Rassy,

I'm sure it would be possible. Whether it would be worth it is another matter, though.

Why only one speed? :wink:

I'm still trying to find the photos of the Sanyo hub that Rick posted.......

[edit] Ah, here they are: http://www.endless-sphere.com/forums/viewtopic.php?f=2&t=2744
 
One reason why hub motors are so heavy is because they have zero venting - thus require large surface area (=weight) in order to keep cool (short term - long term they fry) - with increasing surface area the hub construction has to be more beefy to cope with the loads the wheel presents. Just the shell of a 'Powabyke' motor weighs a kilo or more (not measured it though so maybe a touch high/low).

The reason RC motors are able to run the powers they do is purely down to really good or vented cooling - nothing special about it other than the fact the power ratings as given do not really mean much in our application. My 2.9KW motor for eg has airflow at 90 degrees to the motor axis thus zero 'through flow' and as a result is really only happy below 2KW on a continuous basis. Continuous here means 15min+ since being so light they reach peak temp very quickly. Small mass means they heat up fast - so peak power is just that - not something that can be sustained for very long at all. There are exceptions - unvented types exist but they don't fare well at all unless sat in a ducted fan pushing 200mph wind past their skin!
 
yeah, RC motors need cooling to be effective. I had a spare 400 watt when i first got the idea of building an ebike. but it needs at least 80mph wind being blown back through it to maintain for more than 10 or 20 seconds. If I took too long taxiing the plane, or tried to climb too steap after takeoff, the motor would heat up and blister the nose of the plane. I've melted the center of a prop out before doing just that. But once at cruising speed, It could handle full power for the full 15 minutes, crusing at 80 to 100mph.
 
I've been running a little Tongxin (marketed in the UK with an absolutely massive price hike as the "Nano") for a few months now. It's pretty good and so far has behaved flawlessly. It's very light and seems to have no drag at all when pedalling. The Aussie guy seemed to get hit with some reliability issues, but many others are, like me, finding the motor to be fine.

These motors are very cheap when purchased directly from Tongxin, around £35 or so each, plus shipping and tax. The controllers are similarly cheap, around £15, and are sensorless, like the RC ones.

The downsides are the low power output and limited top speed (about 16 - 18mph on 36V for my recumbent).

Jeremy
 
It would be fairly easy to design a hub motor based on an "outrunner" type design. The hard part is making it stout without adding a ton of weight. You guys have also touched on the venting issue, which is critical for having a lightweight setup. You just can't have a teeny high power motor with no airflow on the stator.
 
John, some of the Crystalite range follow the outrunner principle - magnets stacked around the largest diameter with the stator sitting in the middle. Can't do a freewheel using this method of course.....

Scott
 
Yep, thats exactly what a Gearless hub motor is, spokes laced to the outside of the motor. its roughly like gluing the foam of a RC wheel to the outside of an AXI outrunner. Crystalyte does it like that, and the Motor I'm running on my MTN bike works great, but weighs 16 pounds.

The problem with Outrunners is that to decrease the RPM by half at the same power outoput, you end up indirectly doubling the mass. so to get a 5000 RPM, 500 watt motor to run at 500 rpm, you go from a 1.5 pound motor to a 15 pound motor, roughly. I stress roughly. it doesn't always prove true, but it seems to be the norm. Call it Skunk's law.
 
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