What config for a Brompton at 30 mph?

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cwah

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Hello there,

I'm thinking about purchasing a second hand brompton and electrify it. I'd like to reach 30mph for about 10-15 miles.

The problem is that the brompton fork size is 74mm and I'm wondering which kit would fit that? (I'd prefer a kit that cost less than $1000 shipped)

Many thanks
 
No way I would be comfortable doing 30mph on a Brompton.

It is possible though, but just because something is possible doesn't mean it's a good idea!
 
You could build one that goes 30. But you wouldn't survive a 10-15 mile trip on one except by blind luck. Bromptons are built as light as possable, and are therefor just bearly strong enough to support an average rider at moderate speeds.


But in the intrest of Cleaning the gene pool, I'll tell you the secret is an RC motor running through the chains.
 
Thanks for your answer Drunkskunk.

I'm not planning to go always at 30mph, but I'd like to be able on long straight road.

Do you know where I could find a tutorial to mount a RC motor? Most members here seem just to buy a kit. It seems to be much more difficult to mount that.

Thanks a lot
 
The narrow dropout means there aren't any kits in the US that will fit. In Europe, there were some 20X crystalyte motors that fit a folder's narrow dropouts, but it would never hit 30. and Crystalyte has discontinued that motor series.

The RC motor Idea will involve fabricating your own parts. But it is the smallest, lightest way to power a bike.
Information sources here: http://www.recumbents.com/wisil/e-bent/rc_drive/tutorial.htm
and here: http://endless-sphere.com/forums/viewforum.php?f=28

If you're realy serious about that distance and speed, forget a folding bike, especialy a superlight bike like a brompton.
 
Actually my main concern is the ability to carry it on the train.

I'd like a multimodal way of travelling, but that's still able to reach some decent speed.

If I don't mind about space/weight at all, I would just buy a 50cc scooter.

ps: I don't think with just a hub forum I'd be able to build an entire RC motor electric bike by myself. It seems that I would need some supertool to shape/cut metals?
 
cwah said:
Hello there,

I'm thinking about purchasing a second hand brompton and electrify it. I'd like to reach 30mph for about 10-15 miles.

The problem is that the brompton fork size is 74mm and I'm wondering which kit would fit that? (I'd prefer a kit that cost less than $1000 shipped)

Many thanks
Click to expand...
cwah:

NYCeWheel sell the Brompton kit, it is the only one in North America that can hit 20mph on 36v, with 74mm dropout.
http://www.nycewheels.com/brompton-electric-bicycle-motor.html

Here is the video link
http://www.youtube.com/watch?v=ChoVvbQ1_lo

It was also broadcast in Today Show's tech spot with Omar Wasow
http://www.facebook.com/video/video.php?v=10150134737348233

If you wanted get it under $1000, may be take the kit without the battery.

Ken
 
I already had previously a slow bike running at 15-20mph. It's way too frustrating and all cyclists were faster than me. Can't stand that!!

I'm really looking for something faster, otherwise I could just have a normal bike
 
cwah said:
I already had previously a slow bike running at 15-20mph. It's way too frustrating and all cyclists were faster than me. Can't stand that!!

I'm really looking for something faster, otherwise I could just have a normal bike
Click to expand...

That specific system can run at 48v, which will increase the speed around 26mph.
 
Ok, I contacted them (as well as this company: http://www.electricwheel.co.uk because I live in UK)

But I still have some doubt it can really go much faster because they only have a 250W motor.
 
Just asked them, here is the answer from NYC:
"All our systems top out at 20mph or lower. If you increase the voltage
you run the risk of burning the motor up."

So I think I'll have to go RC. But I don't know how to start :(
 
I'd like to hear more about the light weight nature of the the Brompton, and whether it would be able to handle the stresses of 30mph on smooth roads.

The {MEZEE300F High RPM front eZee hub motor only, with 144 spoke holes motor} from http://ebike.ca/store/store_motors.php can manage 30mph with enough voltage. (check out the simulator).

Heck, a 9-C 2805 can do that at probably 60v - or even a 2807 if you get the voltage at 90v on that 16" wheel.

My friend wants to do the same thing with his Brompton, so that he can pack it into his plane or on the bus and get where he wants.

The tricky bit is to retain the ability to do the whole fold up thing with the batteries, or by taking them off without a lot of fuss.

But any one who has direct experience with that bike (and it's light weight character) and the use of larger than small hub motors - we'd love to hear from you.

And about those dropouts.!!

Since it has a steel fork, and you only need 25mm (1") more space to fit the 100mm hub in there, wouldn't it be possible to use the "threaded rod and oxy-acetylene controlled spreading procedure" to increase the fork spacing? A number of us have successfully employed this trick on our old-school bmx rear dropouts to get the requisite 135mm spacing.
 
Not sure if I did my math right, but if I reach 30 mph (50kph) on an Ezee 20" I need 90V:
Ezee_speed.jpg

http://ebike.ca/simulator/

For that, I'll consume around 30 Wh/km


Here is a comparison to a RC motor (friction drive):
eBike%252520-%252520Economy%252520vs%252520Speed.PNG

https://sites.google.com/site/commuterbooster/performance

I'll consume around 15 Wh/km

So maybe I'm wrong somewhere, in that case please tell me, but it seems that RC motors are around 2 times more efficient than bike motors?
 
They are lighter, indeed. Run higher rpms from the start, so less inefficiency at low speeds.

But once you are going, i seriously doubt the differences in efficiency are 2X.

I use between 13 and 30 watt hrs/mile depending on which (hub motor equipped) bike i ride and the speed i go.

I personally don't have the expertise to integrate an rc system onto a brompton. Much less a reliable one.

You will need to possess some significant mechanical and engineering fortitude for that.
 
It's possible. But using alot of volts to get the rpm you need.
You'd need high voltage but very low amps. At 96v you need a large controller or least but one and current limit alot.

You'd struggle to peddle past 20mph though unless you legs can keep a up with a huge cadence.
Surely 20mph is plenty quick enough on a bromton.
 
If you are concerned about portability & weight, you will need to undeerstand the implications of your speed expectations.
As you have seen ( and we all know ) 30mph will need 1kW+ of motor power and even more battery power ( eff loss's).
Assuming you dont want to kill your batteries with 100% DOD, then you will need about 1kW hr of battery to reach your 15mile target safely.
Even assuming you are prepared to run Lipo, that will be 10kg ( & $600 ) of battery alone, and more if you chose some other chemistry.
 
I am sorry, you are all missing a very important point here. You can always spec out a faster motor, Crystlayte HS, 9C, eZee, whatever that are out there. And the key word is "Brompton".

Brompton doesn't use standard parts. When it come to folding bike such as Dahon, Brompton, BikeFriday, etc.. the configuration compare to a regular bike are differ.

Brompton use 74mm dropout, and 7.5mm axle, nor of other motors will fit. If you want to use hub motor, there are two hub motors in the world in production that will fit, which is:

- Nono motor (too SLOWWWW, this a 180w motor)
- Crystalyte 209 motor

There are two other manufacturers that are making motor that will fit, but no in production:

- ultraMotor which recently file for bankruptcy
- can remember the name at the moment (from india)

You can always hack the bike by change out the front fork replace with 100mm dropout, install the RC motor to make a mid drive system, but the minute you do this, it is no longer a folding bike or a Brompton bike, it become a bit of Frankenstein. You might as well to do this on another cheaper bike that are more suitable this kind of modification, such as Citizen bike:

http://www.citizenbike.com/
 
Then maybe it's a matter of how far frankenstein it goes.

A new front fork widened and ground for the bigger axle. &

Put the 11t cluster on the back, be happy with a ~25 mph top speed (which is really quite sufficient for a short wheelbase bike).

And go light weight with the battery - aiming for about 10 miles of range at 60-72 volts.

Then you are not totally compromising the lightweight character of the Brompton.

But I agree w/ itelect.

If you are going to go heavy, then buy a cheaper 20" folder and make life easier (fatter tires for one). At that point the assets of the Brompton are no longer assets.

a Kepler drive system would be cool, but i couldn't see how it could work out.
 
I would go for the Brompton kit without the batteries, then run it with 48v Lipo. That must be very close to your budget and target speed.

I agree that riding 30 Mph on a Brompton is somewhat crazy.
 
MadRhino, I asked NYC seller and they said I may burnt the motor if I increase the voltage. And I won't really have much speed increase.

Maybe I'm just going to purchase a 20" bike and wait for the commuter booster to be ready..
 
Finally I contacted crystalite europe for the 209 motor. They said it could have a speed close to 30 mph with a 48V25A controller. (What battery should I have to do 15 miles with this controller?)

But they'll have a new 209 motor in january only:
http://www.crystalyte-europe.com/product.php?productid=16137

Seller said it will be a new design... Anyone has an idea about the specs of the new motor? What would be the main changes (except for the design)?
 
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