Hub vs non-hub motor drives.

[Matthijs]

Hello all,

Reading through the forum seeing all this wonderful developments on e-bike technology I cannot find a thread that discusses this matter. I was wondering if there already are any threads on the subject. Is it possible to have a general pros and cons list and maybe go from there? I am sorry if this is already beaten to death elsewhere.

 

[Ypedal]

Oh it certainly has been beaten to death and does so daily around here lol..

bottom line is that both setups can rule or drool.. depends what your goals are.

 

[Matthijs]

Well I would like to build an highly powered velomobile in the future. But what I am seeing now is that the non-hub (rc) motors are advancing with ridiculously high power to weight ratio's, good efficiency numbers, things like water cooling etc. While for example the Crystalite hub motors are pretty heavy, (compared) have to drill holes for cooling when pushed to the max. Are they on top of their game? Also in combination with gearing how does it compare? Or things like regen (mostly to spare the brakes) and the possibility to pedal without power for example? Allot of questions I know. I think I am just looking for some experiences from people having used both systems and see what they liked better or did not like at all.

 

[swbluto]

Well I would like to build an highly powered velomobile in the future. But what I am seeing now is that the non-hub (rc) motors are advancing with ridiculously high power to weight ratio's, good efficiency numbers, things like water cooling etc. While for example the Crystalite hub motors are pretty heavy, (compared) have to drill holes for cooling when pushed to the max. Are they on top of their game? Also in combination with gearing how does it compare? Or things like regen (mostly to spare the brakes) and the possibility to pedal without power for example? Allot of questions I know. I think I am just looking for some experiences from people having used both systems and see what they liked better or did not like at all.

For "ordinary bicycles", hubs can work well if you need under 2-3 kW output continuous. Above that and RC motors shine. RC motors and other geared motors also tend to excel with torque and hill-climbing efficiency, if appropriately geared.

For example, if you want 60+ mph, external motor. If you want ridiculous power, external motor. If you have a huge mountain to climb and your slopes are 15% and you can't tolerate under 10 mph, external motor. If you're hauling big loads up hills or want to go fast up really big hills, external motor. If you're a daily commuter that does fine with 20 mph up a 7% not-so-big hill, hub motors work well. If you're a flat-lander commuter, hub motors excel. If you want relative simplicity and non-fussiness/reliability, hub motor. If you hate ANY noise at all, hub motor.

I'd like an RC bike, but it wouldn't be much more than a play toy. For practical uses with my 250 pound load and 7% hllls and not exactly needing "insane performance" (30 mph up a 7% 400 foot hill will do fine for me), hub motors are fine.

 

[Sturdly]

I've run BB drive and hub motors. The hub motors, especially the geared ones are pretty hard to beat for all around performance and reliability. My BB set ups all needed fairly constant tinkering but when they worked were excellent. The direct drive to the rear wheel with broached freewheel, SRAM dual drive and chain are gaining favor as the best all around. It's kind of ironic really with the RC motors getting so advanced now that is such a good set up for the people that couldn't get the infamous Randy motors back then. Ironic because that's what Randy was preaching in a rather obnoxious way years ago as the best set up..... I'd just go with a geared hub motor myself. KISS works for me.

 

[swbluto]

Well I would like to build an highly powered velomobile in the future.

If you define that with a desired speed, hill-climbing percentage and vehicle weight, I can tell you what output power you're looking for. Based on your results, I'm guessing you'll want more than 35 mph up a 7% hill with a total weight of 400 pounds which will require about 3500 watts of output. If it's a really long hill, you'd probably need two C'lyte 530x motors, otherwise for shorter hills (Like less than 700 feet rise), one may work fine. You'd likely need a smaller wheel (20") and a high voltage.

If by "highly powered", you also want the fastest or nearly fastest acceleration possible (Like 0-60 mph in 4 seconds), then external motors excel. Otherwise, "pretty brisk acceleration" can be accomplished with hubs.

 

[Matthijs]

Well I would like to build an highly powered velomobile in the future.

If you define that with a desired speed, hill-climbing percentage and vehicle weight, I can tell you what output power you're looking for. Based on your results, I'm guessing you'll want more than 35 mph up a 7% hill with a total weight of 400 pounds which will require about 3500 watts of output. If it's a really long hill, you'd probably need two C'lyte 530x motors, otherwise for shorter hills (Like less than 700 feet rise), one may work fine. You'd likely need a smaller wheel (20") and a high voltage.

If by "highly powered", you also want the fastest or nearly fastest acceleration possible (Like 0-60 mph in 4 seconds), then external motors excel. Otherwise, "pretty brisk acceleration" can be accomplished with hubs.

Well it will replace my car. Because I realized I am blessed with the best cycling infrastructure in the world. (The Netherlands) (Also look here for examples: http://www.youtube.com/user/markenlei) So no hills, all flat. And it will be used for commuting and longer rides. I can walk the rest, my street consists out of a cycling lane and wide sidewalks. No cars allowed. And a Velomobile can use the inner-city roads as well as the many bikelanes. Well the weight would be around 40kg (optimistic) and a top speed would be around 100km per hour. Some good aerodynamics would be king. Fast acceleration would be nice. But I would have to watch out for EU regulations and ideal would be to have a feature where I could be road legal with the push of a button. (EU regulations) I would not even mind all time pedelec but also with full power capabilities. Yeah low noise levels would be very nice as well if I want to be stealth.

 

[swbluto]

For flatland and ~60 mph, assuming you can get the aerodynamics to half that of a standard cyclist (A "normal car" has a third the drag coefficient of a typical cyclist), it looks like you'd need about 3 to 3.5 kW output to sustain that speed. Assuming you set up things right, like the voltage, wheel size and winding choice, it looks like you could keep motor heat under 500 watts and the motor at ~85% efficiency. That looks like it'd be a cinch for a 530x. You could also get some pretty good acceleration. According to my simulations, it seems to predict a realistic 0-60mph of 10 seconds. It might actually be something like 15 seconds with magnetic saturation, but that's still pretty good. If you wanted better acceleration, you could always add another hub.