What range would entry-level ebike commuters need/want/use?

[midwest mayhem]

I am working on a design project for a class (I'm a mechanical engineering student in an electronics design class) that involves designing a friction drive system aimed at mass production.

I'm still in the "back of the envelope" calculation stage, and was wondering about how big I should size the battery. I know how to calculate range from efficiency and battery specs, that's not the issue. I'm trying to gauge how far I should scale the pedal-assist system to be useful, desirable, and still inexpensive to an entry-level biker. Any useful studies that show bike commute or average commute habits? Also, I'm thinking I can't really do LiPo for the masses... in that case, what's the next best battery chemistry and geometry that could handle user abuse and misuse? I have experience with LiPo and LiFePO4 Headway, which are two opposite ends of the spectrum.

Also, pack voltage? Lower voltage means cheaper components in general as I understand, especially in the charger... is 22 or 36v too low?

The hoverboard batteries look to be around 160 Wh for $50-60, and their price point is ~$300 for the whole system which would be much more complex than a solid friction drive (I'm therefore looking to be under $300 for a levelized cost... )

I am going to actually build something with custom PCBs and whatnot, and based on the performance and what I think costs would be on a large-scale, maybe go for a crowdfund thing if it looks feasible (way down the road optimism here).

Any commentary appreciated!

 

[Hillhater]

Range ?
Need? .. 20 miles
Want ?.....100 miles
Use ?.....10 miles
......im not sure "entry level" ebikers actually know what they want or need ?
36 volts is a good operating voltage for low level assist without needing high amp levels.
Suggest you focus on 18650 cells and packs as they seem to be the "industry standard" for commercial Ebike packs these days.
Bulk buys of OEM 36v 10Ahr ready made packs, can be very cheap, especially if on a commercial basis.

 

[Mike Allred]

Firstly, I'm no expert, my only claim is to have built an ebike including the removable battery. My experience is that although I like biking and do plenty without electric assistance, when on my ebike I'm lazy and don't pedal at all - unless I see police. Suspect I'm not alone on that one. With a 14S7P set up (51V) I get 45 km range at 45 km/h. Maximum speed with my Mac 10t hub motor is 47 km/h and Ah current is somehwere just below 20Ah. I can increase the Ah all day long but it won't go faster unless I increase the volts. I'm now in the stage of changing the battery config. to 17S6P. That should give me 56 km/h. That's based on simple maths of 47Km/h x 17/14. Your problem is a bit different but the principle is the same. You need to look at the "Kv" of the motor to determine the volts you need. You might want to check on the web but I understand that the maximum rpm of the motor will be volts x Kv. Take at look at model aeroplane motors on a site such as Hobbyking or Progressive RC. Find a big powerful motor with a low Kv such as 130Kv (from memory). If you supply 36V, the RPM will be 130 x 36 = 4680rpm under no load. (Amps will give you the torque to compensate the load when on the road). Then you need to vary the volts to get the RPM you want based on the desired speed and wheel size. What I don't know is if your RPM target should be some margin below the no-load rpm value based on the KV. Maybe. Also bear in mind that as the cells in the battery pack drain, and also under heavy load, the yolts supplied by the battery pack will decline - you need to allow for that. Check out this site - http://lygte-info.dk/review/batteries2012/Common18650comparator.php.

Also, to save a lot of hassle, I would suggest only good "known" brand 18650 li-ion cells in a pre-built pack with a BMS. Bottle style is probably convenient and Samsung make a nice dolphin style one that everyone copies but watch out for the width. There are other good "dolphin style packs. Check the pack dimensions carefully to be sure it fits on your bike. They can be obtained almost only in 36V and 48V so you might want to choose your motor with that in mind. Lipo might set your pants on fire - that maybe ok but your house might also burn.

Mike

 

[Alan B]

It depends.

Commuters have well defined needs, but they vary from a couple of miles to 20 or more. At some point the time spent commuting becomes the limitation, and that is determined by the average speed. Pedaling is okay as long as it doesn't make the rider sweat or get too tired. At least on the way to work. On the way home the rules change.

My last job's commute was 13 miles each way with 1800 total feet of height gain. Combine that with a rider and gear weight around 200 pounds plus whatever the bike weighs. Add a few more pounds for protective gear, after the first spill, or before if smart. Even a minor spill does a lot of damage to body parts.

It has to be reliable. No one wants to be late to work. Or break down on the way home.

Sometimes it is possible to charge at work, sometimes not. Depends on the situation. This affects the capacity by a factor of two.

Recreational riders have much more varied requirements, and generally a lot more range is needed, plus more climbing.

Best of luck in your project.

 

[icerider]

I ride a Bionx 350 7-8 miles a day for fun/exercise. Max assist, good strong pedal input, up and down a lot of short but steep hills, and some flat parts. Average speed 16.5 mph. At the end of that I am good and warm, but not sweaty on cool mornings. Use about 4Ah on a 41 volt battery for 20-25 Whr per mile.

If that was the first half of a daily commute I would want 10Ah or so of battery. If it really were 10Ah, I would probably baby it a little on the way home to keep DOD less than 80%.

I think 10Ah battery with a designed-in slot for a second identical 10Ah battery would be a fine starting point for an entry level commuter.

 

[LockH]

"40 percent of trips Americans take are, on average, less than 3 miles."
J. William Moore, editor-in-chief of EV World

 

[titusmc]

20 mile range has been sufficient for me. My commute is only 8 miles one-way. I would say 50 miles would be my desired range (20mph, light pedaling).

 

[dogman dan]

Assuming about 25 wh/mi, 150wh would be enough for many. That's that 3 mile one way trip.

I don't have a survey, but I do talk to people about what their ebike needs are, all day, every day. The company sells a shitload of lead batteries to people all the time, and they are happy with 6-7 mile range most of the time. But they also like it that they can go 10 miles if they need to.

I'd say 10 mile range is the minimum, and unless your cells are stellar, or your power comically low, that means 10 ah whatever the voltage you use is. Any less is going to hammer those cells hard. That's clearly been working great on the hoverboards.

My gut reaction is it would be pretty stupid to go with any less battery size than the majors are using, Bosch, etc. 400wh at least. Lots of reasons why less just becomes a problem. This may blow your whole plan out of the water, but you did say commuter. The commuter has much more demanding needs than a casual rider. He will ride in weather, and or have to deal with steep hills that will make 250w a joke. He may do 90% of the riding using 200w, but there will be days he needs at least 500-800w to get er done. He's got to get there even when the wind is crazy. He's why the company I work will no longer stock a tiny motor. They'd burn them up the day they had a headwind up that hill.

 

[LockH]

... your power comically low

Hehe... But, but, but... "entry-level ebike commuters"...

So, assumes maybe that a first-timer will NOT be riding recumbent. And ultra aerodynamic a la "velomobile"-style.
I've been assembling signs of (light-weight) plastic coroplast to make a shell body for my trike. So more aero PLUS better rain/weather protection.



My first "ebike" as a stand up kick scooter (with extra kick via motor and betteries) musta had the aero efficiency of the "broad side of a barn door". I COULD drive power consumption per km lower just by learning how to use as little power as possible. Kicking (think "pedaling") from stops, rolling up to stops (using brakes is energy lost in heat production), using gravity as much as possible... etc.

 

[midwest mayhem]

Assuming about 25 wh/mi, 150wh would be enough for many. That's that 3 mile one way trip.

I don't have a survey, but I do talk to people about what their ebike needs are, all day, every day. The company sells a shitload of lead batteries to people all the time, and they are happy with 6-7 mile range most of the time. But they also like it that they can go 10 miles if they need to.

I'd say 10 mile range is the minimum, and unless your cells are stellar, or your power comically low, that means 10 ah whatever the voltage you use is. Any less is going to hammer those cells hard. That's clearly been working great on the hoverboards.

My gut reaction is it would be pretty stupid to go with any less battery size than the majors are using, Bosch, etc. 400wh at least. Lots of reasons why less just becomes a problem. This may blow your whole plan out of the water, but you did say commuter. The commuter has much more demanding needs than a casual rider. He will ride in weather, and or have to deal with steep hills that will make 250w a joke. He may do 90% of the riding using 200w, but there will be days he needs at least 500-800w to get er done. He's got to get there even when the wind is crazy. He's why the company I work will no longer stock a tiny motor. They'd burn them up the day they had a headwind up that hill.

What's the price point of those ~400Wh batteries and their total systems? And what's your definition of "a tiny motor?"

 

[anotherkiwi]

All of Europe ( and Japan and Australia etc.) gets by with 250 W nominative motors (up to 600 W in reality) and most systems are 36 V. We have hills, and even mountains! My commute is 38 km if I miss the train and 15 if I don't so about 100 km would be nice. That is at least a 15 Ah battery, 17 Ah would be comfortable for those days I'm tired or lazy.

Oh we don't have throttles, they are illegal so we have to pedal at least a little.

 

[spinningmagnets]

Check the link in my sig at the bottom of this post. I have some experience with friction drives.

It is a realistic goal to use 1000W, but above that you will have traction problems with the roller contact. With a round-profile tire, I had issues at 500W, and when I switched to a wide beach-cruiser tire with a relatively flat tread, I was able to go to 1000W. If you plan to sell drives to customers with skinny fixie-style single-speeds, you will likely be limited to 360W if you want happy customers.

People who never used one frequently expressed concern over accelerated tire wear and loss of drive traction when the tire got wet after running through a puddle. Tire wear was not an issue, but wet conditions definitely cause a temporary loss of roller traction. Pedal a hundred feet on dry road and the tread would dry off enough to work again. Forget about using in the rain or wet streets, regardless of the tire used.

Battery range efficiency was good. The tiny motor had high RPMs and effectively experienced what could be described as a high reduction (roller diameter compared to tire tread diameter). The "Share-Roller" kickstarter device has three battery sizes available, and if more range is needed, the stock pack is easily swapped out.

Don't even consider LiPo in a product that will be sold to the public, use 18650-cells. You could use 22V LiPo (6S) during development if a friend has RC models, allowing you to use his charger and maybe borrow a battery pack. At 24V, I was able to accelerate in an adequate manner, and easily maintain the federal speed limit of 20-MPH. It struggled on steep hills, but did not overheat. I swapped in a 36V system with the same motor and hills were easily managed after that. The higher volts allowed the drive to use lower amps on flat land, less heat in the motor/controller/battery...

If budget is not an issue, I'd say go direct to a 10S system (36V). One way to improve the roller/traction issue is to make a 2WD system, which doubles whatever traction a single wheel system has. Of course that would double the price...

I agree with dogman on starting with a 10-Ah pack. Actual miles depends on how much the rider pedals, weight of bike + rider, steepness of hills, and head-winds...

 

[midwest mayhem]

Check the link in my sig at the bottom of this post. I have some experience with friction drives.

It is a realistic goal to use 1000W, but above that you will have traction problems with the roller contact. With a round-profile tire, I had issues at 500W, and when I switched to a wide beach-cruiser tire with a relatively flat tread, I was able to go to 1000W. If you plan to sell drives to customers with skinny fixie-style single-speeds, you will likely be limited to 360W if you want happy customers.

People who never used one frequently expressed concern over accelerated tire wear and loss of drive traction when the tire got wet after running through a puddle. Tire wear was not an issue, but wet conditions definitely cause a temporary loss of roller traction. Pedal a hundred feet on dry road and the tread would dry off enough to work again. Forget about using in the rain or wet streets, regardless of the tire used.

Battery range efficiency was good. The tiny motor had high RPMs and effectively experienced what could be described as a high reduction (roller diameter compared to tire tread diameter). The "Share-Roller" kickstarter device has three battery sizes available, and if more range is needed, the stock pack is easily swapped out.

Don't even consider LiPo in a product that will be sold to the public, use 18650-cells. You could use 22V LiPo (6S) during development if a friend has RC models, allowing you to use his charger and maybe borrow a battery pack. At 24V, I was able to accelerate in an adequate manner, and easily maintain the federal speed limit of 20-MPH. It struggled on steep hills, but did not overheat. I swapped in a 36V system with the same motor and hills were easily managed after that. The higher volts allowed the drive to use lower amps on flat land, less heat in the motor/controller/battery...

If budget is not an issue, I'd say go direct to a 10S system (36V). One way to improve the roller/traction issue is to make a 2WD system, which doubles whatever traction a single wheel system has. Of course that would double the price...

I agree with dogman on starting with a 10-Ah pack. Actual miles depends on how much the rider pedals, weight of bike + rider, steepness of hills, and head-winds...

I have looked through your thread extensively! Along with Kepler's and others before starting this project. I bit the bullet yesterday and bought a 6s 10ah lipo for testing, just to get a feel for this type of setup. And yes I would like it to be able to engage effectively with skinnier tires - thanks for giving me realistic wattage ranges for different conditions, that's very helpful.

I'm not trying to make a system that performs excellently in all conditions - rather, a cheap, slick, attractive system that works in average conditions for most bikes and allows newbies to get the "EV grin." I would hope that this kit/add-on would leave people wanting to invest in a hub motor or mid drive setup.

Thanks all for the great discussion so far.

 

[LockH]

G'Luck. Re "friction drive"? I wanna experiment with bike chain bonded/welded/etc to side of wheel rim rather than rub the tire itself. Currently have rim brake, so need to convert to disk. T.B.A.

(EDIT: PS. Trike currently chain free, with pedal levers directly bolted to ends of wheel axle. Hehe)

 

[dogman dan]

Comicly low power, to an American, would be the EU standard type stuff. 250-350w. If you ran a 1000w setup from a tiny battery ( 150wh) with average quality 18650's, you'll be pushing it too hard. But you could run 200w from that size I'm sure.


The motors that fry when a big fat American rides them up mountains are the 350w geared type motors. They work fine for folks under 150 pounds, but in the US market, that's not very many people. Mid drive can work at low power, but only if the rider chooses the right gear.

Definitely no RC lithium cobalt batteries for entry level commuters. Too risky.

 

[e-beach]

I'm not trying to make a system that performs excellently in all conditions - rather, a cheap, slick, attractive system that works in average conditions for most bikes and allows newbies to get the "EV grin." I would hope that this kit/add-on would leave people wanting to invest in a hub motor or mid drive setup.
........

Hummmm entry-level......Do you mean kids? People with no money? People who are curious? Have you taken a good look at who your customers might be and specifics on height / weight / what normal activities might be? Who is your "Core Customer Base?"

I have sold all my ice vehicles, so for my needs my bike must go at least 20 miles for those days where I get caught off-guard and need to extend my ride farther then I had planned. Where I live things are spread-out all over the city so I need range. With the city riding conditions around here I can only average 12mph due to stop lights / signs ect.

If you are thinking a first product for a start-up company consider this.....a build that could get a college student 10 miles at about 15mph with the option of an "extender" battery pack that could be purchased separately. Perhaps one mounting system that could be used for different sized motors so a system could be upgraded with little effort. Up-gradability is always a way to get people on board.

 

[midwest mayhem]

The motors that fry when a big fat American rides them up mountains are the 350w geared type motors.

we have a lot of those type in my part of the country, just no mountains...

If you are thinking a first product for a start-up company consider this.....a build that could get a college student 10 miles at about 15mph with the option of an "extender" battery pack that could be purchased separately. Perhaps one mounting system that could be used for different sized motors so a system could be upgraded with little effort. Up-gradability is always a way to get people on board.

Thinking of something along the lines of this. The option to upgrade would likely add cost, but maybe not too much if done cleverly.

 

[JayCee]

Bulk buys of OEM 36v 10Ahr ready made packs, can be very cheap, especially if on a commercial basis.

I would agree with this as a good starting point (36V, 10Ahr).

 

[Alan B]

I favor a more modular approach. If the battery pack could use snap-in 5-7AH sections and go up to 20AH that would give versatility and low cost entry. Maintenance would also be easier. Each section could be 10S2P 18650 cells and the dealer could have a machine that would plug into a PC and analyze/charge/discharge a few of those sections simultaneously to see what problems they had if any. The battery frame would have circuitry to combine the sections and communicate with their individual BMS's. Working in concert the BMS circuitry of each section could be simplified, the power switching could be in the frame.

 

[midwest mayhem]

I favor a more modular approach.

I do too, but modularity usually involves a higher upfront cost. I like the idea of the option to upgrade to a bigger battery though, as it could draw more people in to an initially lower price.

Bulk buys of OEM 36v 10Ahr ready made packs, can be very cheap, especially if on a commercial basis.

I would agree with this as a good starting point (36V, 10Ahr).

A quick search on Alibaba verified this, lots of options to choose from (which ones are legit who knows).