Designing a $200 ebike kit that climbs any hill

F

flyingpants

1 mW
Joined
Apr 12, 2013
Messages
17
Location
Hamilton, Ontario
Hi there. Like the title says, I'm looking to design a bike that can climb any hill. The Bafang BBS series is great, but expensive, and I like my front gears. Also, I'm always scared the chain will not shift properly, or get caught on my shoelace or something. So, no mid-drive!

A hub motor is great for pedal assist, but not for hill climbing. The Xiongda dual-speed internally-geared motor is a great concept but there have been many reports of failures. So I thought how to design my own solution.

Requirements:


  • It needs to do a 8-9km/h up most hills with no pedalling
    Hill climbing should be fairly efficient, unlike most hub motors
    It needs to do 20km/h+ on flat roads, 25+ with pedal assist
    Total system weight should be under 7-8lbs (minus battery)
    Total system cost should be ~$200 ish (minus battery)
    It will use a small 3lbs 300W battery or similar

My solution is a dual motor setup. A cheap hub motor geared to the back wheel like this: http://i.imgur.com/Xq2h8XC.png It only needs to go 8-9km uphill, nothing more. For the rest of the time, you'll be going downhill, or cruising, and can rely on another ~3.5lbs motor on the front wheel, maybe with pedal assist.

Is it worth it to bolt the motor on like that for the extra torque?
 
I've seen a number of builds like that on the forum and on youtube, most using RC motors. It looks like something that can be done, dubious as to how well it actually works....
 
Lurkin said:
I've seen a number of builds like that on the forum and on youtube, most using RC motors. It looks like something that can be done, dubious as to how well it actually works....
Click to expand...

I had the idea of using a 1-2lbs RC motor for the pedal assist, and a slightly heavier, 4-5lbs 850W peak hub motor bolted on for the hill-climb feature (would also work as a starter motor). But I'm not sure saving 1-2lbs is worth trying to use an RC motor all the time.

Maybe an in-wheel hub motor for cruise, and 2x 400W RC motors for hill-climb? I doubt RC would last under these conditions.
 
The old currie E zip motor that attaches to the rear hub was cheap, and could climb any hill.

You can still get the motor and mount plate, and the controller it needs here. http://www.thesuperkids.com/eztrelbi450w.html
 
I've read back through what you want. $200? I think you'll end up with some pretty stink compromises. If you think about your design, you will have a motor with fixed gearing (unless you somehow have a second derailleur somehow shifting your second motor chain), which is fine for one gradient, but poo for another. This is exactly why people like mid drives to start with - it has the weight and gearing advantages for going up a hill. It'll also hang off the side and be pretty ghetto...

If you want it to climb up the wall, you want gearing (for your power and for the motors) and a battery with decent discharge. more capacity and more discharge generally = more money.... Lastly, you want decent control to run it exactly the way you want to.. more control usually = more money....

Honestly, I think you would be better off increasing your budget and going with either a small hub motor or a mid drive kit that will work, together with a reasonable capacity, high discharge battery. If you want to tinker, I would go for Cyclone 3000w kit...

Alternatively, have a look at Keplers friction drive designs. Using a bike wheel as reduction gearing is a lightweight, cheap way to replicate the middrives internal operation... given you want low speed this could be a viable option.. but can you mimic his immaculate installation? 8)
 
Lurkin said:
If you think about your design, you will have a motor with fixed gearing (unless you somehow have a second derailleur somehow shifting your second motor chain), which is fine for one gradient, but poo for another. This is exactly why people like mid drives to start with - it has the weight and gearing advantages for going up a hill.
Click to expand...

You're right, the rear motor will be a fixed gear ratio. But it doesn't matter, because it will be a guaranteed 8km/h up any hill. If I understand correctly, if I max the throttle, it will even do 8km/h on a flat plane. No harm in that, at all.

The mid-drive is too heavy, expensive and I don't want to run anything through the bike derailleur. I have the money to buy one, but I'm against it on principle. I'm looking ahead to when you can buy 300Wh of cells for ~$50, we will need an equivalently cheap and light motor setup, seems like it will work fine


dogman dan said:
The old currie E zip motor that attaches to the rear hub was cheap, and could climb any hill.

You can still get the motor and mount plate, and the controller it needs here. http://www.thesuperkids.com/eztrelbi450w.html
Click to expand...

Yes, that sounds 100% perfect. Are you familiar with the motor? What are the power/heat limitations? Can I run it at 36/48 volts? It could really climb hills without pedalling? What was the hill climbing speed/cruising speed on a flat road? What is the weight? The website doesn't say.
 
I've never had a problem climbing hills approaching 30% grades with my 1000W dd 9.75Kv rear hub motor. even when I was runniing with the stock controller and 52V battery pack. I've seen the exact same kit for <$200 on ebay. On flats it will do 45kph on 48V.
 
wesnewell said:
I've never had a problem climbing hills approaching 30% grades with my 1000W dd 9.75Kv rear hub motor. even when I was runniing with the stock controller and 52V battery pack. I've seen the exact same kit for <$200 on ebay. On flats it will do 45kph on 48V.
Click to expand...

What is the weight of the motor? Hubs are inefficient uphill which means heat and wasted energy. Direct drive = cogging. I'm aiming at low power usage here, the bike will almost always be used in pedal-assist mode except for a hill.
 
Meanwhile, browsing round the forum, came across this: http://enggauto.en.alibaba.com/product/1927849438-221116453/electric_rickshaw_spare_parts.html

Not sure how you would mount it.. no idea of the quality... could be garbage, but at that price? hmmm.
 
dogman dan said:
The old currie E zip motor that attaches to the rear hub was cheap, and could climb any hill.

You can still get the motor and mount plate, and the controller it needs here. http://www.thesuperkids.com/eztrelbi450w.html
Click to expand...

+1 for this suggestion. These bikes show up often on craigslist. Pick one up cheap and add a front geared hub motor to it with a switch to swap between front and rear motor drive. Dump the SLA battery for a Li ion pack in the triangle. These typically came with Ananda controllers with provisions for brushless motors so you may get away with using only one controller (and controls).
 
The currie system is as close as you are going to get in the budget you are looking at. A decent RC motor that will hold up to the hill requirement is nearly half your budget, and the ESC is the other half... then you have to come up with a throttle solution to control the ESC (been done but requires a few dollars & knowhow). I'm afraid brushless tech is probably a stretch for $200... even a friction drive using the RC motors would be hard to make work here.
 
dequinox said:
The currie system is as close as you are going to get in the budget you are looking at. A decent RC motor that will hold up to the hill requirement is nearly half your budget, and the ESC is the other half... then you have to come up with a throttle solution to control the ESC (been done but requires a few dollars & knowhow). I'm afraid brushless tech is probably a stretch for $200... even a friction drive using the RC motors would be hard to make work here.
Click to expand...

Ok, so forget the RC motors for now. It's either hub+currie, or hub+crazy bolted hub. I prefer the former, but I doubt the currie can handle the 900+ watts I want for uphill.

Then it's just a question of hooking up one throttle to both controllers and praying for the best!

Will do some more research...
 
flyingpants said:
… Hubs are inefficient uphill which means heat and wasted energy. Direct drive = cogging. I'm aiming at low power usage here, the bike will almost always be used in pedal-assist mode except for a hill.
Click to expand...
Cogging is largely cancelled out anytime the controller is energized. I think the controller only draws 14W, and that's a tiny percentage if you're using any motor power.

DD hubmotors are reasonably efficient even compared to mid-drives. Hubmotors' weak point is starting from a standstill on a steep hill. Geared hubmotors are better at that if you need it, but have more complexity and failure potential.

The total amount of energy lost as heat might not be significant.
 
FWIW, nearly all suggestions are still over $200,,not including the battery.

But WES has a good point, the el cheapo 48v 1000w kits will climb just about any short hill. They will also easily get up a ten mile long hill up to 10% grade, which is damn steep and long for a paved highway. Those tend to cost more than 200 bucks, but almost always under 300.

What made me suggest the currie, is the battery to run it ( if 24v) can cost half as much as a 48v battery to run the 1000w kit.

What you need to do really, is get a reasonable budget. $500 for a half decent 48v battery with bms and charger, and $300 for the hub motor kit.

Forget that shit about the cogging, 25 watts, a mere trickle, can eliminate the cogging. 75w will eliminate the cogging and the effect of the weight of the motor and battery.

For most, 200w average cruise is very comfy, and a decent 48v 20 ah battery will last 5 hours of riding at 200w. That's enough saddle time to make most peoples ass cry for mercy.
 
dogman dan said:
What you need to do really, is get a reasonable budget. $500 for a half decent 48v battery with bms and charger, and $300 for the hub motor kit.

For most, 200w average cruise is very comfy, and a decent 48v 20 ah battery will last 5 hours of riding at 200w. That's enough saddle time to make most peoples ass cry for mercy.
Click to expand...

I have the money for a Bafang mid-drive or whatever, but that's not my goal. I'm trying to build a 35lbs hybrid super-commuter that can go up any hill, with no derailleurs at all (if desired). Transmissions are outdated, IMO.

And I want the hill-climbing to be as efficient as possible. I live right next to the Niagara Escarpment and i'll be climbing hills pretty much constantly. No extra stress or heat on the battery, controller, motor, etc. I like the Xiongda motor a lot for its uphill efficiency, but it breaks down.. If Xiongda did a redesign, I wouldn't need to worry about any of this.

As for 48V20ah, that's about 320% heavier than I'm going for. I'm going with a ~300Wh battery, hence the desire for a low power draw!
 
EIther you'll be using a small motor with a form of gearing or a large motor with none. There is no mid ground if you want to climb. A larger direct drive would avoid the need for gearing, but comes with the penalty of weight and requiring sufficient resources to feed i.e. i.e. larger batteries. This is where geared motors (which have planetary gearing inside them) or mid drives come in, using a smaller motor geared up to climb with.
 
http://www.bbc.com/news/world-asia-india-36441938
India squatters: At least 24 killed in Mathura eviction drive
"... In their view 40 litres of petrol or 60 litres of diesel should cost just 1 rupee (about 1.5 cents; one penny). ..."

The group's expectations were beyond the realm of reality.
I believe that you may be labouring with a similar expectation ... but good luck with it anyway.
 
LewTwo said:
The group's expectations were beyond the realm of reality.
I believe that you may be labouring with a similar expectation ... but good luck with it anyway.
Click to expand...

$200 for a motor and controller doesn't sound that crazy to me.


  • Small battery for pedal assist
    Downhill: no motor power required
    Flat: very little motor power required
    Uphill: lots of motor power definitely required, in the best case it just flies up the hill by itself and you can assist.
    Standstill: high torque required

Conclusion: Get a slow motor, geared for low-speed, high-torque. Internally geared hub motors are cool, but I want something that only goes 6-10mph and goes up a hill like nothing at all, I want to be able to use 48v or even 52v on it. I couldn't care less about cruising speed for this application. Does anyone know if there a motor like that?

So far I think the Currie eZip thing is the best option, just needs to be geared down by quite a bit. If there were a version that could handle 1000 watts, i'd get that and be done.
 
It will have to go through your bike gears, or a low gear on the other side of the back wheel, to get "climbs any hill" out of a low wattage, small motor.

Seems to me the BBS01 might work best for you, except the budget. I'm not sure if it will really be as light as you want, but it will be close.

Some of the other mid drives might weigh less, I'm not sure. Any of them can be run on less amps, one way or another. You will be able to climb any hill, even on very low wattage, with the motor pulling a low gear. That's how a muscle power bike does it, on 150w.

The battery can be pretty tiny, like a "40v" lawnmower battery. Or a 5 ah lipo.

An RC motor is not really off the table. It could be a simple chain or belt running to the left side of the rear wheel, and geared low as hell. Not sure how to make it freewheel, but surely it can be done.

In any case, dumbshit hub motor guys like me don't have your info. You need to read in the non hub section. Maybe even go friction drive.
 
Are you trying to design an any-bike commercial solution, or a one-of for your personal use? If a one-of for personal use, do you have fabrication skills?
 
gogo said:
Are you trying to design an any-bike commercial solution, or a one-of for your personal use? If a one-of for personal use, do you have fabrication skills?
Click to expand...

Eventually, both. Yeah I have tools, I am friends with machinists and engineers.. and I have a ton of free time :)
 
wesnewell said:
I've never had a problem climbing hills approaching 30% grades with my 1000W dd 9.75Kv rear hub motor.
Click to expand...

There are no hills like that within hundreds of miles of your location. I honestly don't think we have any segments of road that steep in the state of Texas. Unless you're climbing freeway embankments, your bike's probably never been on such a slope.
 
As usual, you don't know what you are talking about. Perhaps you just don't know how to measure slope. This might be simply enough for you to understand, but I have my doubts.
https://en.wikipedia.org/wiki/Grade_(slope)
 
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