My DIY Electric Brompton project

[Pedalo]

This project has been brewing for a few months. I thought it was time for a bit of a write up.

My main motivation for getting a Brompton is lack of space in our house. I have a big bike (Cytronex Trek) that I've been using for the last year for getting into work and it's a terrific bike but it does get in everyone's way in the hallway. If the Electric Brompton works out well I'll probably sell the Cytronex.

The Bike
I took ages deliberating over which handle bars and which gears to choose on the Brompton. In the end I settled on an M6L-X with the gears reduced by 12%.
While I knew I could handle my commute using only 2 gears with the motor assist, I decided to choose the bike I would have chosen if motor assist wasn't available. I like to ride my bike unassisted for the majority of the time and will only use the motor if I'm feeling tired. I went for the M bars over the S bars for comfort.
Going for the lightweight Titanium option was in hindsight perhaps over extravagent - especially since in the end I'm not benefitting from the lighter forks and front hub that comes as part of that expense. And the weight saving is negligible by the time the motor is added. However I may well choose to revert the bike back to non-electric if I get super-fit. Without the motor the bike weighs about 10.5kg.

More soon with photos...

 

[Pedalo]

The Electric Conversion
I wanted to use a Tongxin motor for light weight and good freewheel properties.
The same motor is used by the Electric wheel company for their Nano kit and also by Freedom ebikes. Cytronex also use Tongxin motors.

My approach is very similar to that used by JerrySimon so my thanks go to him for his very detailed posts on this forum and for his time taken to reply to my PMs and emails regarding sourcing parts and other tips. Also thanks to Daniel Weck for his great contribution.

I did consider buying a kit from EWC or freedom but I'm a tinkerer at heart and wanted to understand how it all worked to be in a better position to swap parts out or make repairs myself - so I went down the DIY route.

I ordered most of the parts from a supplier in China. It took a very long time to arrive and there were moments when I thought the parts would never come. Looking back, I think it may have been less stressful getting a kit or parts from EWC. I've since found they are quite flexible and will for example sell a kit without a battery.

 

[Pedalo]

The motor and kit
I ordered this from Billy Lei of the Donguan Desheng company.

Here's what I got:

It consists of Tongxin motor, controller, brake lever and a thumb throttle with integrated fuel guage and switch. I actually got two of everything so I'd have spares. The postage was quite expensive but not much more for a second kit.

 

[Pedalo]

The Battery

Like Jerry, I used A123 battery cells. In my case I bought them from a supplier in Hong Kong ready made up as 6S1P.

I bought two of these and wired them in series:

They fit quite sngly into that box they were supplied in so I'll probably leave them there for now. Also included in the circuit is a 15A blade fuse. This fits neatly into one pocket of the Brompton C bag with a little space underneath which I'll probably stow away some tools or a spare inner tube.

 

[Pedalo]

The wheel

Here's the motor fitted into the wheel and the wheel fitted to the forks and the forks fitted to the bike!

I used a 1-cross lacing pattern and a Sun rim. As Jerry promised/warned it is very difficult to fit tyres to and there is now an alternative (see Jerry's thread), but I already had the rim so thought I may as well use it.

Spokes and nipples came from a supplier in Taiwan (I think the same Dan used).

In the end I decided not to use the original Titanium forks as I didn't want to put them through the required modification - and I wanted the option of reverting the bike back to non electric later. So I fitted some steel forks instead. I used a dremel to grind down the cutouts and the threaded bar technique to widen the forks. I found making use of the tabbed washers that came with the motor was a great way to stop the threaded bar springing out when doing the widening.

Swapping out the forks in the Brompton was actually quite tricky. The expander bolt hoding in the headset was well and trully jammed so it required a lot of effort with a hammer to free it. A bit of WD40 sprayed in through the underside of the forks helped.

 

[NRG]

Looks good Pedalo, do you have any contact info for Billy Lei or the Donguan Desheng company? PM me if you want, thanks.

 

[Pedalo]

Looks good Pedalo, do you have any contact info for Billy Lei or the Donguan Desheng company? PM me if you want, thanks.

There's a link to their website in this thread:
http://www.pedelecs.co.uk/forum/electric-bicycles/6289-anyone-been-touch-billy-dongguan-desheng-recently.html

If you are thinking of going down that route it would be worth asking how long it would take for them to get the motors. I think they've had trouble getting them recently. I had a wait of about 12 weeks and not much communication along the way.

 

[Pedalo]

Latch Extender

I made use of the latch extender block which was being sold on this forum and on Ebay. See here:

The mudguard stay needs a bit of reshaping to fit around the wider axle and to accomodate the slightly wider wheel.

Unfortunately, a corner off the latch extender snapped off while I was bending the mudguard stay - but it still seems to work.

 

[Pedalo]

Motor Connector

I used a sureseal mini connector for attaching the motor:

Purchased from here:
Simtek (UK) - The Competition Specialists

I quite like the connector. It's very compact and by using some waterproof heatshrink (adhesive lined), it's possible to make a connection that's completely waterproof.

Only downside is that it's very tricky getting the pins into the connector housing. There is a special tool that would do it but it's extremely expensive. A bit of care and a pair of pliers does the job. Apparently if you heat the connector slightly it makes it a bit easier.

 

[Pedalo]

Battery Charger

Very cheap rubbish bought from China on Ebay:

It seems to work but doesn't feel at all substantial. I wouldn't leave it alone while charging. I bough two. One for work and one at home.

I might look around for an alternative at some point.

 

[Pedalo]

The bike in all its glory!

Here's the (almost) finished project:

 

[Pedalo]

Handlebar controls

I've used the throttle control as supplied.

It's big and ugly so I'll probably look for an alternative. I might even work out some kind of switch arrangement with electronics to give controls similar to my Cytronex which I really like.

I decided not to fit a brake lever with cutout switch but I'll probably use a reed switch & Magnet instead.

The push switch on the front of the throttle controller does not work with the controller I have. I added a MOSFET circuit to turn it into an on/off switch. The circuit also removes the horrible spark you get when connecting the battery.

The controller and associated wiring can be seen here:

The MOSFET circuit is wrapped up in heatshrink.

Similar to Jerry's arrangement, this stuff fits in one pocket of the Brompton C bag and the Battery fits into the other. A Bulgin connector is used to connect the bag to the bike and Deans connectors are used throughout for power connections.

 

[Pedalo]

First Test ride

So I've had my first test ride and it works!

I used a turnigy power meter to keep an eye on current consumption and can see that it makes a lot of sense to ease off on the throttle when climbing steep hills because the current shoots up without proportional increase in speed.

As I already knew it makes a lot of sense to pedal up to speed before engaging the motor.

I've seen the current go as high as 15A when setting off from an almost standing start or when climbing a steep hill on full throttle (even with pedalling).

I can still get up a steep hill with 4-5 A with slower pedalling and half throttle which is far more economical on battery power.

My trip to work is about 7 miles. I'll probably recharge for the return journey to be kinder to the battery - but I think it would do my return trip on the same charge given that I'll also be putting in a lot of the work.

That's about it for now. I'll provide an update when I've decided what to do with the handlebar controls...

 

[jerrysimon]

Great to see you got there finally. The motor wait must have been really frustrating/worrying but well done for being patient.

1. Bit broke off my extender too (no worries)

2. Tyres are a bugger on those Sun rims Also I found the stock tyres rubbish and fittted Marathon Plus especially for the winter.

3. Nice to see you using the same Bulgin plug. Mine seems to be holding up well. I also fitted one to the block to stow the other end when its not in use.

4. I see a max of 15 Amps too.

5. I have the same charger at work and home. I have left them unattended (used over 8 months now) and they have been fine.

Interesting how like me you went from the Cytronex (great bike) to the EBrompton. I just love its portability, both for popping into a shop and folding it up when I get to work and putting it in my office.

What was your final weight for the bike on its own i.e. just motor and throttle ?

Regards

Jerry

 

[Pedalo]

I don't have great weighing scales but it looks like it's about 13kg as predicted.

I'm surprised what you say about the stock tyres. They are the green kevlar ones and they look the part - but I'll see how it goes and I'll swap them for marathon plus if I'm getting punctures.

your idea of using an extra bulgin connector for stowing the cable is genius. I may well do the same.

 

[jerrysimon]

Maybe I have just been really unlucky with the two stock tyres I had. My favourites this summer are Kojaks, super light and super fast. They also have kevlar strip so provide reasonable puncture protection. I have been using them on my old Moulton MK3. Now I have a Bromtpon rim laced up with a Tongxin, I may try them on my EBrompton as at least I know I will be able to do road side repairs. Would save about 0.5-0.75 kg over the Plus.

Another pic of the stow plug. You can get them in Maplin. Screw through the center into the luggage block and super glue. You have to cut all the back of the pins off flush first. Just make sure you dribble some super glue into the back of the pins before you cut them down at the back, or the bits left in the socket will fall out. Oh and make sure you let the super glue dry before you test the plug in it

Regards

Jerry

 

[daniel.weck]

Superb !
Congratulations, enjoy the many rides to come !!

 

[Pedalo]

I've been using the Brompton again this week. I'm still not happy with the control layout but I'm working on it.

I've plugged in a Turnigy power meter over the last couple of days to monitor power out of the battery when riding and power in when charging.

Odd that I seem to be taking more power out than I'm putting in!

For example yesterday morning I took 27Wh out but the charger only pushed 17Wh back in.
Yesterday evening I took 54Wh out but the charger only pushed 45Wh back in.
This morning I took 28Wh out but the charger only pushed 23Wh back in.

Does anyone have any idea what could be happening here? I was expecting to get less power out than I put in! Perhaps I have magic batteries - or perhaps they'll just fail to deliver anything someday soon...

I should probably try to run the batteries down to exhaustion to give me a true picture of what they are capable of but I believe it makes sense to treat A123 cells gently for the first few charge/discharge cycles.

 

[TheWarden]

If you are thinking of going down that route it would be worth asking how long it would take for them to get the motors. I think they've had trouble getting them recently. I had a wait of about 12 weeks and not much communication along the way.

Can I ask how much you paid for the two sets of motors and how much the postage cost? Did you have to pay duty on this end too? I am also interested in doing the same thing but lacing them into a 700cc wheel.

I have a Bafang 36v/250W atm but I would prefer to have something more akin to the Cytronex in terms of stealth, weight, noise and freewheel. And from what I've read the Tongxin can't be beat atm. The Cute 85 motor is nice and small but the noise and freewheel don't seem so great:

YouTube - Kanal von monimi1

 

[daniel.weck]

I have a Bafang 36v/250W atm but I would prefer to have something more akin to the Cytronex in terms of stealth, weight, noise and freewheel. And from what I've read the Tongxin can't be beat atm.

Been there
I keep my 8-Fun / Suzhou Bafang wheel because of its superior performance (i.e. torque and speed) and robustness / reliability ... if need be, I can just swap the Tongxin wheel (it's literally a straight swap, controller/battery/controls are all the same).
The Tongxin is a little gem. I'd like to have a version more suited to my 16" rim size (I have the 195rpm instead of 260rpm...you do the maths...), because the 25km/h cut-off threshold happens at 18km/h, which kind of interrupts my cycling flow, so to speak The 260rpm version would be nice.

The Cute 85 motor is nice and small but the noise and freewheel don't seem so great:

Well, a hub motor with internal reduction gear that fits in such a small package is bound to present drawbacks, the most glaring of which probably being the increased noise due to the thin casing. The new 8-Fun motors are noticeably more silent due to the thicker gear ring, which provides some kind of sound insulation against the noise created by gear friction.

Cheers, Dan