Direct drive non-hub vs hub efficiency

[Hyena]

Hey guys,
I've been a long time big powered hub motor user for simplicity but I'm now looking at making the step now into a chain/mid drive.
It's often stated that a mid drive is more efficient than a hub motor but in a higher powered setting where you're not driving through the gears and go with a straight direct drive from the motor to rear sprocket, is mid drive still more efficient ? If I have a hub motor that tops out at 100km/hr and I have a mid drive geared for the same, is there going to be any significant difference efficiency and acceleration ?

I'm planning a light weight e-moto build that will only be street ridden so the extra weight in the rear wheel isn't really a drama and it would be preferable to cut down on the moving parts. Plus not having anything motor-looking mounted to the frame will add to the head scratching at the lights
I'd be looking at either a HPM5000 or e-moto/e-scooter/cromotor style hub motor in a 16" wheel.

 

[Bike Xing]

A hub motor sounds fine for the application you describe; and yes, likely more efficient. I'm a huge fan of mid-drives. That's all I've ridden since around 2005 or 2006, but I like super light weight and therefore lower power. If you don't mind the weight, and you know you're going high power (for hills, etc.) then the hub is best.

 

[jk1]

It's often stated that a mid drive is more efficient than a hub motor but in a higher powered setting where you're not driving through the gears and go with a straight direct drive from the motor to rear sprocket, is mid drive still more efficient ?

The only reason mid drive can be more efficient then hub motor's is when it uses variable gearing. But if you bypass that and go direct to the wheel it kind of defeats the purpose ! as you lose that. Also you have extra drive train losses compared to hub motors, so why would you not go hub ?

This is one reason i think the GNG big block will be waste of time, as it will most likely have to run direct to the rear wheel. Already with the normal GNG overvoalted the bike derailuer gear systems cannot cope with the power, so why would go big block ?. So its a catch 2-2 if you want to go faster and then u lose the use of the gears, all of a sudden you need a lot more power and hence battery to accelarate. And then it becomes like a hub motor- but worse ! as you have the drivetrain losses that hubds don't have.

The sweet spot for light weight , poweful and fast will be mid drives that use the maximum of the rear variable gearing or power around 2000w .

 

[Hyena]

Yeah I figured in the absence of any gearing benefits or reduction there should be no real difference.
I'm looking at 10-15kw so not exactly small change

 

[NoneToBe]

Hi,

For the GNG 'big block', I'd imagine you would run it on the left side on a single chain to the rear wheel. Thus, it would perform as a hub but with the motor on the frame its sprung weight rather than unsprung weight.

 

[cal3thousand]

Yeah I figured in the absence of any gearing benefits or reduction there should be no real difference.
I'm looking at 10-15kw so not exactly small change

You can't put that much into these mid drive motors.

 

[Hyena]

When I say mid drives I'm talking about chain/belt/non hub drives in general.

 

[rp3]

There is already a thread about this. :wink:

http://endless-sphere.com/forums/viewtopic.php?f=28&t=52705

...

 

[Hillhater]

I would agree that the mid drive can only be (potentially ?) more efficient than a hub, if it uses the multi gear ratios of a cassette or IGH.
BUT... if your hub is wound for 100kph then its low speed acceleration is likely going to be compromised, especially compared to a gear train mid drive with similar power...but then again at your proposed power levels, a geared mid drive is not realistic unless you can find a small 2 speed transmission ( Thud ?) which would be the ideal solution.

 

[Toorbough ULL-Zeveigh]

There is already a thread about this. :wink:

http://endless-sphere.com/forums/viewtopic.php?f=28&t=52705

...

if you look closely & compare the thread title you'll discover it's the complete opposite.

When I say mid drives I'm talking about chain/belt/non hub drives in general.

but in reality what you're talking about is called rear drive if you bypass the gears.

 

[Hyena]

if your hub is wound for 100kph then its low speed acceleration is likely going to be compromised, especially compared to a gear train mid drive with similar power...but then again at your proposed power levels, a geared mid drive is not realistic unless you can find a small 2 speed transmission ( Thud ?) which would be the ideal solution.

Yeah speed winds can still get up and go if you feed them current, you just have to keep the heat in check. If you look at my last vid horsing around drag racing and hill climb comparing a 5404 stealth bomber with my faster wind scooter motor that tops out around 100km/hr i beat it from a standard start, rolling start and hill climb. That's with only slightly more power too (~10V less voltage but ~30A more current)
And yes I've been giving thought to making a simple and strong 2 speed transmission along the lines of thuds design. Maybe run 3 RC outrunners together for giggles
I do like simplicity though, both initially and for minimising ongoing maintenance.

but in reality what you're talking about is called rear drive if you bypass the gears.

Exactly right. My bad, mid drive was the wrong term - it's mid mount, rear, direct drive!
Sorry I'm new here

 

[LSBW]

You can't put that much into these mid drive motors.

15 KW, $3000 motor: http://www.astroflight.com/new-products/4535.html

 

[Ypedal]

going for a Deathbike Jr eh..

Chain driven high powered light weight bicycle looking objects are peaky off the line buggers to ride, if you get the gearing right.

so it's either geared for reasonable top speed and lots of pull of the line with fair efficiency, or geared tall for high speed that sucks off the line and makes a pile of heat if you push it hard.

Ask Deecanio how much fun his 3220 was lol.. if i can find that video of him and knoxie having the first go.

 

[Hyena]

going for a Deathbike Jr eh..

Yeah a more sensible version - perhaps I shall call it the 'sick of living' bike rather than death bike

it's either geared for reasonable top speed and lots of pull of the line with fair efficiency, or geared tall for high speed that sucks off the line and makes a pile of heat if you push it hard.

Yeah this is why I want a middle ground of gearing around 100km/hr. The local streets I will take it on have speed limits of 70km/hr which means most cars do 80 so having it rapid up to those speeds with a bit more for winding it out will be perfect.
I suspect acceleration will be such that it will fairly rapidly take off but without being so twitchy that it flicks you off the back. It'll also be heavier than any bicycle shaped object (starting life as a light moto rather than a heavy duty bicycle) so it should be pretty balaced overall.
That said when you ride it daily you quickly adapt to any demonic undertones it has anyway.

And yeah, I think everyone that's been around for more than a few years remembers that classic video of Deecanio, err, "battling adversity" :lol:

 

[crossbreak]

I thought about such a drive as well for a while. You dont need 15kW for going 100kph, 5kW at the wheel is enough. Most RC motors run up to 8000rpm, loaded maybe 5500rpm. For example Rotomax 150cc, TGY 80-100, the CA120 or the astros. 100kph means 800rpm wheel speed for 26"..which means a single reduction of 7:1 which is still possible with a #219 chain, like 92T/13T. Just hard to find a controller that drives these beasts Saw some youtube vid of a guy that drove the rotomax 100cc with a Lyen 18fet controller. Always thought that would kill the lyen instantly due low inductance

Such a setup would be more efficient than a Hub, since the motors them selves are more efficient. Even with 5% chain loss there should be a gain in efficiency, at least during acceleration.

 

[Hyena]

You dont need 15kW for going 100kph, 5kW at the wheel is enough

It's not about the destination, it's about how you get there :wink:

100kph means 800rpm wheel speed for 26"..which means a single reduction of 7:1 which is still possible with a #219 chain, like 92T/13T.

I'd be looking at a 16" moto wheel which will be a fair bit smaller but that just means fiddling with the reduction.
As you say they're hard on controllers and everyone seems to like to push them to the max. I get it in the RC world but for ebike use I'd be happier to run parallel units at modest power and have reliability. Eg 2 motors at 150a ea instead of one at 250a

 

[Ypedal]

Prove me wrong.. but my findings are that a constant high speed load is where hub motors are the most efficient.

Chain driven setups benefit from rpm reduction for low speed, to take advantage of smaller, lighter, lower power motors... allowing you to climb hills, with a small motor, going slow..

I love my RC bike, it's loud, obnoxious, has chains, belts, tention pulleys and springs, after doing the walk of shame dozens of times for repairs it's finally reliable enough to venture further than i am willing to walk, but it's not efficient.

http://www.youtube.com/watch?v=onAbOtP_S-s

[youtube]onAbOtP_S-s[/youtube]

 

[liveforphysics]

Something like hubmonster may be the highest efficiency >10kW capable drive solution you can put together for a reasonable price.

 

[John in CR]

Something like hubmonster may be the highest efficiency >10kW capable drive solution you can put together for a reasonable price.

For what he wants I was thinking MidMonster instead....a bit smaller and 5kg less weight. Run at high voltage in a mid-drive it would be easy to keep cool while protecting it from sucking in debris, and with motor rpm not much higher than wheel rpm you get to keep noise down closer to hubmotor levels.

 

[waynebergman]

My input for mid drive verses the motor in the wheel is based on a 50 volt 1800 watt system so some of the benefits of what I experience from my mid drive will not really apply to what you are wanting to do with the high out put you plan to run. However for what it is worth my main benefit on the mid drive is effeciency for climbing hills and riding over bumpy trails where my little gear reduction motor really takes a beating unless its used as a mid drive. The problems & short comings however with my mid drive I think would also be short comings for your planed system even though its high powered, and that is..........

1. All that chain noise really adds to overall noise levels.

2. Its hard to explain but if you are coasting and hit the throttle there is kind of a lag time for the free wheel to catch up to the speed of the wheel (at least on my mid drive there is) and it just does not seem as smooth to me as having the motor in the wheel. If you have the power and it sounds like the bike will have lots of it, I would go for the motor in the wheel for sure.

 

[John in CR]

You dont need 15kW for going 100kph, 5kW at the wheel is enough

It's not about the destination, it's about how you get there :wink:

Absolutely. My cargo bike with 6-8kw peak input does 100kph, but things didn't really get fun for me until I got above 12kw and 100kph. Until I went to high voltage on my SuperV, all of my high power bikes topped out at around 100kph. Sure 6kw and 100kph max seemed fun as a noob, but it can't put cars and motos in their place. Pushing my big load that requires about 15kw geared for 100, and geared for 160kph it requires 26kw peak input like I have now. I also had 30kw geared for 100 and it was simply too much for me, even with my load.

Our electrics' relative silence and broad torque curves are our best advantages over gassers, and when you take it to the extreme the result is an amusement park ride without the lines that no gasser can duplicate. I don't know what my kids are going to do when I get really old, because I'm never giving up my high powered ebikes.

 

[speedmd]

Hi John

Your posts continue to renew my interest in building that DH bike road rocket. I have a few projects still in front of it unfortunately.

 

[Hyena]

Pushing my big load that requires about 15kw geared for 100, and geared for 160kph it requires 26kw peak input like I have now. I also had 30kw geared for 100 and it was simply too much for me, even with my load.

Too much ? Bah, you're getting old
The good news is you'll have the baddest ass electric wheel chair down at the old folks home

I think I've pretty much decided I'll go with a hub motor now, just because the bike is already so minimalist and it'll add to the head scratching if people can't see something resembling a motor driving a chain. I'll make a gokart or something for my kids with the HPM5000 instead.