Hub or gear/chain

[Desertprep]

Hi! This seems like a really FRIENDLY forum so I thought I would post this question. I am doing some research on this in prep for my own venture and want to get a broad variety of opinions.

The question is whether a hub motor or non hub motor will be more efficient? The most balanced answer I have received is that for common use the hub motor is usually more efficient because you don't have freewheels, etc to loose efficiency but that if you need to climb hills/mountains or routinely go fast (more than 40 km/hr) than a non hub motor with transmission will be a better choice. Any comments?

And remember...please be FRIENDLY

 

[lazarus2405]

I've found that folks here are pretty darn friendly. No worries, mate.

When you're talking about efficiency, do you mean power per unit weight or do you mean in terms of power lost between the batteries and the road?

The biggest disadvantage of a direct-drive hub motor in terms of efficiency is that its speed is locked to that of the wheel, keeping the RPMs relatively low. You can get a lot more power out of a motor whose windings spin faster relative to the stator magnets, so a direct-drive hub will actually have a low power output relative to its weight. With a geared hub motor, like the Puma, you can often get much more toque out of less motor weight, but it is not without its drawbacks. Because of its gears, it is audibly louder. Others can tell you exactly how much louder. Furthermore, since it has gears, the gears are prone to wear.

With non-hub motors, like chain drive systems, you can get the same power in a much lighter motor. However, any way you downgear your motor will cause energy loss and noise. I would not consider the energy loss significant, but I would consider the noise a factor. Not that it will sound like a motorcycle, but it won't be stealthy.

The hub motor is really popular here primarily because of its ease of installation. Those of us who cannot weld, or who do not have access to welding equipment, pretty much have to go with a hub motor. A chain drive system can be better, but it's a lot more work and a lot of things can go wrong compared to a hub.

In my opinion, a hub motor really is the best choice, because it is nearly silent, is very easy to install, has fewer points of failure, and looks cleaner. The big disadvantage is that for a hub to do everything a geared motor can, you have to throw more power at it, so that the same motor can both power you up hills and speed you along the flat.

 

[Jozzer]

Welcome to the forum. Laz's advise is correct. Hubmotors are the easiest way by far. Puma's do indeed offer much better torque off the mark, they are only slightly louder than nongeared hubmotors. Best of all, http://www.teamhybrid.co.uk/ will have a decent stock of these in, hopefully by the end of november. Still no idea how long the gears will last, but after much abuse from several users here theres still no sign of actual wear really, and replacement gears will be stocked by teamhybrid, also metal gears should you wish more power/longerlife at the expense of slightly more noise.
Good luck with whatever route you try, theres lots of people here to help the brave :lol:

 

[xyster]

...Best of all, http://www.teamhybrid.co.uk/ will have a decent stock of these in, hopefully by the end of november. Still no idea how long the gears will last, but after much abuse from several users here theres still no sign of actual wear really, ...

Not true.

http://endless-sphere.com/forums/viewtopic.php?t=2470&postdays=0&postorder=asc&start=15

At just 48V 35A it is possible to quickly wear the planetary gears with hard acceleration, this of course inst unacceptable as the motors are not rated for this power use, that said they can be made to take the increase in power.

Another thing that can happen is the free-wheel body slips on the main inner drive gear, this can be fixed simply by dropping 4 blobs of weld on to the rotor and drive gear, I did this on mine only to have the gears wear about a month later.

On my old school Puma (BMC Really) the gears have worn some and are slipping, from a dead stop if you open the throttle you go nowhere, if you go easy its fine and doesn't slip, I haven't had this motor apart nor am I too worried as I just peddle from the start and go gentle on the throttle (none of my other Pumas have done this).

 

[Desertprep]

Thanks!...no alligators out there

I live in the northern part of china and am working with disabled and orphaned Chinese children. Lately my job has changed so that I have to cover a lot of distance. When I asked about efficient I am looking for a motor that will help me squeeze more miles per charge out of the battery. My dream bike will take me at least 100 miles on a charge with a speed of 25-30 mph, combining the speed of the motor and my pedaling, have a built in charger, have both front and rear suspension, be about 10" longer than normal (comfortable touring bike) 2X7 speeds and weigh less than 80 pounds. I bought an ebike here in China as my first to help me get around and to have the experience of using an ebike. It has a 240 watt motor with a 48 volt system. Controller is nondescript but gets the job done. I have made two observations:

1. SLA batteries suck! Not only do you not get much range out of them there are so many variables that it is hard to know exactly how much range I will get from day to day. I usually get about 35 km (20 miles) on a charge - assuming no wind and I pedal to start. At 35 pounds the battery is also heavy. The bike weighs in at over 90 pounds. At that weight I am afraid to think of what the ride would be like without the front suspension. It has no rear susp. so I can guess

2. I have ridden a couple of other ebikes and it seems to me that the best configuration is low weight, weight in the center (or evenly distributed front to back) and weight as low on the bike as you can. This makes it easier to handle. I rode an ebike that had a center mounted motor with a battery right behind the seat post. It wasn't that light but it handled like a bike much lighter than it really was.

I will probably sell this bike off soon and convert my beach bike as an interim project, likely with a front hub. I am going to replace the fork with a chromoly fork for added strength. I wish I could find a way to mount a drum brake outside the fork - there is not going to be any room with the motor.

I think the li-ion batteries are quite a bit cheaper here than what you guys are paying but I have to learn a bit to be able to find quality. So...am hoping to find a few more posts on this topic. Thanks for your input!

 

[xyster]

Hi pengyou, yes SLA sucks, and won't get you the range you seek unless you pack a trailer full of it. A 2500 watt-hour pack like mine gets about 100 miles per charge at 20mph on level pavement, no pedaling.

 

[cerewa]

My dream bike will take me at least 100 miles on a charge with a speed of 25-30 mph, combining the speed of the motor and my pedaling, have a built in charger, have both front and rear suspension, be about 10" longer than normal (comfortable touring bike) 2X7 speeds and weigh less than 80 pounds.

If you want anything close to 100 miles per charge, and a 80# bike, you're probably going to have to buy lithium (but not LiFePO4, they're heavier) batteries at great expense. With your desire for front and rear suspension and +10 inches length, I think you will have trouble finding any suitable bike. The Kona Ute, Surly Big Dummy, Xtracycle kit, and a couple other options are out there, none of them made with rear suspension in mind, and none of them easy to modify. You could add a suspension seatpost if you don't mind that anything attached to the back of the bike would still have no suspension.

In order to meet most of your specifications with an electric bike you'll have to be willing to pay a lot more than you'd pay for a gas powered bike. it might be even 3 to 10 times more. The cost of an electric bike would be much less, of course, if you go with a heavier battery type or choose less than 100 miles per charge of batteries or both.

If you have a limited budget or really want to stay under 80lbs, it might be more feasible for you to use a gas bike for those kinds of distances.

 

[Desertprep]

Good points. The frame I have in mind is going to be a custom mod. There is a common mountain bike sold here made of Chromoly that feels like it weighs a little over 30 pounds. I can get two used frames and have someone cut and weld two together to give me the extra 10 " I need and will only raise the weight of the bike by about 2 pounds. The 10" will give me the battery storage area/motor area but will still leave room on the rear for a passenger or cargo. The motor I am looking at weighs about 8 pounds including the necessary gearing. Not sure yet how durable it is though. The last thing I want to happen is to have my bike give away out in an agricultural area with no one around for miles and miles and miles...That gives me about 40 pounds for batteries. Even if i go over a bit I am expecting it to be a better handling bike. Yes it will be close...but that is what makes it a challenge If it were not a challenge it would be boring and not worth doing ...it also gives me room to be creative...need more speed? Hoist a sail! Why not? Has anyone ever tried?

I will keep you posted on what happens. It is pretty easy to find parts here but I have not been able to find someone able to do tig welding. Now...if any of you tig welders are coming to China on vacation....

BTW, motorcycles and scooters are not legal in most cities now in China...because they are gross polluters and because people are very reckless when they drive them. That is why I am looking into the extreme touring ebike. Imagine...150 miles a day between pedaling and electricity...recharge over night and you are ready for the next day...Bohai ocean to Turkey in 30 days? Dream...dream...that is why change is made...and now that you mention the gas powered bike, why not install a small 4 stroke gasoline engine on the bike - use the non hub motor as a generator to recharge the batteries while I am pedaling or resting? I have seen some 32cc engines that weigh about 6 pounds.

 

[Drunkskunk]

Its possable to build a geared drive that would be more efficent over a wide range than a hub motor, but in general, a hub motor is going to be the most efficent option, Especialy given what you plan to do with it.

the most important thing for you may not be the motor, but the bike you chose.

To do 100 miles at 25-30mph, you would need a big stack of batteries. With 1.75 inch tires and an upright sitting position, it takes more than 900 watts to do 30mph. your peddaling is worth around 100 watts when combined with that. Consider that at 48Volts, on Li-ion batteries, it would need atleast 60 amp hours of cells to do this.

If you change your bike type to a recumbant with thin, highspeed, high pressure tires, you might be able to cut that battery size in half.
And if you cut back your speed requirement to 20mph, you might be able to cut that battery size in half again.

it realy becomes less about the motor, and more about the style of bike when you're looking at over all efficancy.

 

[fechter]

To go that far, you will have to supply most of the power from your legs.
Something with low drag, like a recumbent would be better than an upright bike. You will need a very comfortable seat too! My butt hurts after 10 miles on my scooter.

A small 4 stroke generator might work, but I know only one person who has tried that. It does seem to work. I have the parts for one, but never finished it.

 

[Jozzer]

...Best of all, http://www.teamhybrid.co.uk/ will have a decent stock of these in, hopefully by the end of november. Still no idea how long the gears will last, but after much abuse from several users here theres still no sign of actual wear really, ...

Not true.

http://endless-sphere.com/forums/viewtopic.php?t=2470&postdays=0&postorder=asc&start=15

At just 48V 35A it is possible to quickly wear the planetary gears with hard acceleration, this of course inst unacceptable as the motors are not rated for this power use, that said they can be made to take the increase in power.

Another thing that can happen is the free-wheel body slips on the main inner drive gear, this can be fixed simply by dropping 4 blobs of weld on to the rotor and drive gear, I did this on mine only to have the gears wear about a month later.

On my old school Puma (BMC Really) the gears have worn some and are slipping, from a dead stop if you open the throttle you go nowhere, if you go easy its fine and doesn't slip, I haven't had this motor apart nor am I too worried as I just peddle from the start and go gentle on the throttle (none of my other Pumas have done this).

This was on the old motors m8, not even from the same factory (the BMC). Many prototypes have gone around, but the later ones have suffered no such problem. there have been many revision, and for the sake of progress and a fair chance for Mark who's selling them, its important not to confuse models when giving advise!
Having said that, as I admitted, we dont really know what the lifespan really is yet.
Another important point is that most geared drive systems you could make/buy will be louder in anycase than a Puma...

 

[Jozzer]

To go that far, you will have to supply most of the power from your legs.
Something with low drag, like a recumbent would be better than an upright bike. You will need a very comfortable seat too! My butt hurts after 10 miles on my scooter.

A small 4 stroke generator might work, but I know only one person who has tried that. It does seem to work. I have the parts for one, but never finished it.

How much does that thing weigh Fetcher? I have a customer who wants a "hybrid hybrid" Electric bike, I figured gennie weight would need to be less that 10KG in order to have enough batts for his primary use, but can't find any gennies close to this weight. I wondered about making one with a 4 stroke RC motor, but they all seem mighty noisy!

 

[lazarus2405]

If you change your bike type to a recumbent with thin, highspeed, high pressure tires, you might be able to cut that battery size in half.
And if you cut back your speed requirement to 20mph, you might be able to cut that battery size in half again.

That is the best advice I can give for what you want to do. If you want that range, you'll no be able to race along. When we discuss the ranges of our bikes here, we generally specify that that speed is at 20mph, because it's really a nice compromise between battery conservation and an acceptable speed.

I think you'll find this calculator very helpful:

http://www.kreuzotter.de/english/espeed.htm

Through this you can see how different aerodynamic configurations affect your speed or power requirements. You can set either power or speed so that you can see how fast you'll go with given power, or how much power you'd need for a given speed. Then take your batterys' amphours and multiply it by volts for watthours, then divide watthours by the whatever power you're drawing to give your running time, then multiply that by whatever speed you end up with, and that will tell you your range on one charge without pedaling.

I ran some ballpark numbers, and it looks like you'll need ~1400Wh to do it. I don't know what lithiums you'll be able to get, but for comparison's sake, it'd take 17 Milwaukee 28V powertool batteries, for about $1400. It should weigh just about 40lbs, too, less if you remove the plastic cases and resolder them.

 

[Desertprep]

Thanks for the calculator! That is really helpful. Wind resistance is really critical, isn't it? I was not clear..on the section talking about bents do they have an option that is close to a tadpole? If I get a bent I think I would want a tadpole because they seem to be more stable cornering.

Has anyone seen a tandem tadpole, two people, one in front of the other?

 

[TylerDurden]

Has anyone seen a tandem tadpole, two people, one in front of the other?

http://www.greenspeed.com.au/gtt.html

 

[cerewa]

I believe a tandem tadpole is about 80 pounds without electric power or suspension. There are lightweight, low to the ground, full suspension 2 wheel recumbent bikes (which of course save a lot on wind resistance... they're a little better than recumbent trikes for that). In the USA I think one that weighs 25-30 pounds would cost $4000.

However, as I understand it 40 or 50 pounds of lithium-ion batteries will be good enough for your distance requirement if, as suggested, you travel at about 20mph and contribute pedal power. If a gas bike is not an option, and you're basically trying to make an electric bike that is cheaper than a new car, then I suppose 50 pounds of lithium batteries won't seem so ridiculously expensive to you.

Suspension bikes are a couple pounds heavier than comparable non-suspension bikes. If you're going to be traveling on pavement you might do better with no suspension or front suspension only... but it does depend on whether you go 20mph or 35mph, and if it's really poor quality pavement then suspension is worthwhile either way.

Gravel roads, or paved roads that are almost as bumpy as gravel, will reduce your range a lot.

If you're going to go with a custom-made frame, it might work well to weld most of a full suspension bike's frame on to the back of a non-suspension frame. Is that what you were thinking of doing? It would give you about 10 inches of space that is cushioned by the suspension (hopefully able to carry a person and/or batteries+cargo). of course, the part of the bike behind the suspension pivot would still be difficult to use for cargo-carrying.

 

[Desertprep]

Cool...lots of room to put batteries behind the head cyclist

 

[Geebee]

Regarding the air drag, have you considered a velomobile?
The quest in the calculator is a particularly clean design, but if you go with a bottom bracket drive and a velomobile in theory a 220w motor will give you a 30 mph speed on the flat, so a 1 kw battery pack will exceed your requirements with NO pedaling.
I have just installed a Tongxin 160 w hub in my velo as a bottom bracket drive, it makes a slight hum and you can hear the chain running so I would not class it as noisy.
I will not be able to test propely for a week or so due to injuring my back at work, but I think that I maybe able to join the 30 mph club with a bit of gear fiddling if I feel the urge.
It has already shown itself to be 50% quicker up a 20~25% hill than the standard geared hub mounted in the back wheel.
Good luck and let us know how you get on with whatever you decide to build.

 

[Desertprep]

I just googled some pics of velomobiles...really cool! Can they be made out of kevlar or other carbon fibers? It seems like you still use a metal frame with one of these. Is it possible to integrate the frame into the body - unibody - or would that be too complicated?

Thanks for all of your comments. I am beginning to get a good idea of what I need. The bent does seem to be more useful, especially something like the tadpole, maybe stretched a bit to accommodate one non pedaling passenger or cargo. I am a bit worried though about a low profile vehicle on the roads that I want to travel...lots of debris, small and big rocks, etc. I saw a tadpole that had 5" ground clearance...that is about as low as I would go in this area.

How do you make the shells for the velo's? Can you begin by making a light frame, covering it with styrofoam so that you get the right shape and then layering it with your desired material? I am already getting some cool ideas for a shape...

 

[Geebee]

Cheap light weight method.
http://velomobilebuild.fotopic.net/
There are alot of options, google and http://www.bentrideronline.com goto forum and velomobile thread, or direct link http://www.bentrideronline.com/messageboard/forumdisplay.php?f=15
Have fun.

 

[Desertprep]

Woah! I can easily get carried away with this stuff...soon end up designing my own 4 place pedal car with electric assist and a full carbon fiber body...what a blast! How much does a typical velo body weigh?

 

[Geebee]

They vary dramaticaly average is probaly 30~35 kg's? complete ready to ride.
My shell and frame weigh between 3~4 kg's (closer to 3), trikes vary from 12 kg upward.
My all up weight was 20kg's (17 kg trike) before the electrics, motor weighs ~2kgs and my batteries are SLA's at the moment.

I would love some of the commercial ones but they are way out of my price league and weigh to much unless assisted as I live in the foothills of a mountain.

 

[cerewa]

it's possible to build a unibody velomobile. A guy in germany had a website (the site might still exist but I can't find it now) about the 2-wheel fully enclosed unibody bike he built. I'm pretty sure it was a kevlar fiber/carbon fiber mix. The guy that built it said his job was aerodynamics engineer at BMW, I think, and he used his home-made unibody bike to get there.

 

[Desertprep]

Have you seen any plans for a unibody? Sounds good...probably a little lighter than a frame with a covering, probably a little stronger and more weather proof.

 

[cerewa]

yeah, the unibody construction can be pretty lightweight. I had never considered that it might be more weatherproof, but if done properly I'm sure it would be extremely strong.

I don't think any plans exist and there may be only one bike in existence that was built that way. If you really put your mind to it you may be able to design your own.