Brompton M2L-X (Titanium) - Super Lightweight Pedelec Conversion

[Davanti]

... On a philosophical note, I think we sometimes get bogged down with trying to get things technically perfect to the extent that we forget why some of us embark on these projects in the first place. I must admit that I am very often guilty of this....

When one is up to one's a**e in alligators, one might be forgiven for forgetting that the original task was to drain the bloody swamp!

 

[dingrpdl]

I'd be quite concerned (ie dead certain) that one leg would bend and the other one stay the same.

Fork Spreading Symmetry

I have just begun the e-conversion on my second Brompton. To ease concerns and quash doubts about fork symmetry when spreading it using the spreader bolt method, I devised a way to check symmetry after the spread.

Here is the setup. With my Brompton set up sitting on the floor upside down, I clamped a vice to the handlebar at the centre and clamped a laser pointer to it. Then I placed a steel rule in the fork dropout slots with the 15cm mark centred between the dropouts. I adjusted to laser pointer so that it put a spot on the 15cm mark.

I then removed the ruler and spread the fork with a spreader bolt. The fork was spread from its original 74mm spacing to 90mm to accommodate the Tongxin motor width (80mm) plus some washers to centre the motor and provide motor-fork clearance. I actually had to spread it to more than 100mm to get the desired 90mm spacing when it sprang back.

I removed the spreader and placed the ruler back on the dropout slots again centering the 15cm mark between the dropouts. The laser spot shows a difference of less than 1mm from where it was before the spread.

My conclusion is that using a spreading bolt to widen the short steel forks on a Brompton a few centimetres (about 2cm in my case), you are unlikely to end up with major symmetry problems. And you can probably widen most longer steel forks (e.g. for 26-inch wheels) safely using this method.


Richard

 

[polyphasic]

Thank you very much for all the picture uploads and explanations.

I have a few decisions I have to make here about the front wheel.

1. Main question I guess is the front tire: I currently have the stock green kevlar brompton tires, according to my dealer the Brompton tire choice has improved the kevlar and puncture resistance (I believe he said the gray on the sides of the tire is the way to know if it's the newer redesigned tire) so it's a good choice for NYC metro for a fast tire. (obviously the super reliable/puncture resistant tires are the schwalbe kojaks, but so far I think that's overkill for my area). I have been considering the super fast, thin side-wall kojak tires for the front only. I know they go flat for people primarily on the rear where so much weight is unequally distributed. But then I'm thinking just keep it uniform up front since the Brompton tire is very fast rolling without much resistance. I'm told the Kojak are only to be ridden on nice streets, but I'm wondering how much it matters for the front, i.e. how much rough riding can you get away with a front kojak. Does having the motor make any difference on the wear and performance of these tires? I'm looking at how smooth the kojak is and wondering about it's grip at higher speeds, especially in wet conditions, leading me to think I should stick with the stock Brompton tire.

A video on tires from another nyc dealer (obviously they tend to sway toward the most aggressive, different than my nyc dealer, I live in the suburbs so I'm not overly concerned at this point about flats, I'm pretty confident a kojak on the rear is a flat idea for semi-rough terrain that I experience): http://www.youtube.com/watch?v=OwejmQ4v_6w

2. How do you remove stock spokes? Do I just cut the stock spokes and slide them out? Or do they unscrew? I've never removed spokes from a Brompton wheel (or any bicycle for that matter), so I have no idea what's involved. I briefly thought maybe I should buy new rim/rimtape (appears it's around $30-35US) and construct the Goldant motor from there. Not sure whether I should deconstruct a perfectly good wheel/tire setup or start from rim only.

3. Lastly, what brand/model of tools do people own to take off tires and put tires on?

 

[jerrysimon]

polyphasic,

I use Kojaks front and back for my cross city ride. Three punctures in 12 months one front, two back. I can change tires pretty quickly both front and back now. My new Brompton came with Brompton greens and I currently have them on my bike for testing. Initial comments are they are almost as light as Kojaks roll quite well but not as well. No punctures yet but its only been a couple of weeks . Kojaks are fine in the wet and many say as more rubber is on the road they hold the road better than treaded tires. The Brompton tubes are plain nasty as is the blue rim tape, replace it with velox 10mm. I much prefer the schwalbe AV4 tubes which have a threaded valve and retaining ring rather than the rubber coated Brompton one, that refuses to be pushed through the rim valve hole without a lot of wiggling. I have now tried Schwalbe standards, plus's, kojaks and the greens. Kojaks are still my preference for front and back unless you want to be certain you never get punctures (or almost certain) in which case use plus's with the associated weight penalty and slower rolling. Tool wise all you need is a set of robust tire levers. I also have a track pump which makes light work of taking the Brompton faster tires up to 90-100psi!

2. How do you remove stock spokes? Do I just cut the stock spokes and slide them out? Or do they unscrew? I've never removed spokes from a Brompton wheel (or any bicycle for that matter), so I have no idea what's involved. I briefly thought maybe I should buy new rim/rimtape (appears it's around $30-35US) and construct the Goldant motor from there. Not sure whether I should deconstruct a perfectly good wheel/tire setup or start from rim only.

These questions you are asking indicate to me you should be taking your motor to someone else to build into a wheel rim for you, or at the VERY least do some serious reading up of wheel building BEFORE even attempting to do it. It is not rocket science and most people should be able to build a wheel, providing they do some background reading, take their time and approach it in a methodical way. Maybe check my Brompton wheel building thread out first which has some links to good source material and documents my first ever wheel build.

With the Goldant motor drilled with 28 holes you can use a stock Brompton rim, (buy a new one and keep the original wheel as you may want to fit is back later), a big plus IMHO over the SunCR18 rims which although much better made, make for difficult fitting of tires with its very shallow well. With the Goldant lower powered motor the stock rims will suffice anyway.


Regards

Jerry

 

[Biker44]

Fork Spreading Symmetry I have just begun the e-conversion on my second Brompton. To ease concerns and quash doubts about fork symmetry when spreading it using the spreader bolt method, I devised a way to check symmetry after the spread. ... My conclusion is that using a spreading bolt to widen the short steel forks on a Brompton a few centimetres (about 2cm in my case), you are unlikely to end up with major symmetry problems. And you can probably widen most longer steel forks (e.g. for 26-inch wheels) safely using this method. Richard

I'm the Jeremiah who warned everyone against this method, so I stand corrected.

I imagine what's happening in this case is that the steel in the critical spot is still in a softened condition from heating and bending (or slow-cooled after welding?). It's neither been quenched nor work-hardened.

When one leg bends first (as its bound to do) it work-hardens in the critical zone and the other leg becomes the weaker of the two. Up to a certain fairly small limit, dingrpdl has proved that the two legs will yield equally.

The good news is that the modified forks is stronger than it was before. Well, I say that, in a shunt you want the forks to bend, not the frame. But I don't think that's a major concern on a Brompton, or indeed on any cycle!

I was going to issue a word of caution, older Bromptons may have work-hardened in this region. The very good results obtained in this case by dingrpdl were achieved on a brand-new machine (judging by the pictures?) I think you'd get equally good results on a used machine, but can't be sure.

Similarly, longer forks need to bend less - the results should be equally good, but again one cannot be sure.

Oh, yeah, and my dig about such a modified cycle not being rideable hands-off was just that, a dig

 

[Biker44]

I have been considering the super fast, thin side-wall kojak tires for the front only. I know they go flat for people primarily on the rear where so much weight is unequally distributed.

There is a reason that most punctures are in the back wheel - a nail etc lies flat on the road, is kicked up by the front wheel and run over by the back. Motorcycles suffer this effect a lot, it may be less of a feature on bicycles. It could be a "power delivery" thing, but I think not.

 

[polyphasic]

Tool wise all you need is a set of robust tire levers. I also have a track pump which makes light work of taking the Brompton faster tires up to 90-100psi!

Check my Brompton wheel building thread out first which has some links to good source material and documents my first ever wheel build.

Jerry, you are my leader to the eBrompton free world! JK Yes, I'm totally new to bicycle repair/modifications. Read/ask questions to ad nauseam is the way to satisfy the soul of a DIYer. So I purchased a roll of velox 10mm tape and a couple of schwalbe AV4 tubes direct from the manufacturer. I'll just sell my stock front wheel/tire and start from scratch on a Brompton oem rim with a racing slick on it.

There seems to be a plethora of styles of tire levers to choose from and buying a track pump seems even more confusing, but I'm sure any old track pump/lever will do the job. Read read read...thanks again.

 

[jerrysimon]

There seems to be a plethora of styles of tire levers to choose from and buying a track pump seems even more confusing, but I'm sure any old track pump/lever will do the job. Read read read...thanks again.

As I said just a robust set of tire levers. Only a few pounds and better than the cheap thin ones you get included in a puncture repair kit. I tend to carry a spare tube with me which makes for quick roadside repairs and then fix the puncture in the comfort of my work shop.

Track pump wise I would recommend one with a pressure gauge. I own and am very pleased with the Topeak Joe Blow (might be called sport or something now). I little more expensive but has a lovely smooth action. Again that all sounds wrong lol

Regards

Jerry

 

[Pedalo]

+1 on the JoeBlow! Excellent pump.

 

[amigafan2003]

Crazy work Jerry. I love your new bike

Too sad you don't like torque or higher speed

I've got one of these motors on order and I'm going to runi it at 63v/650watts/25mph

Current Tongxin Nano has over 3000miles with the same setup - just fancy playing with something new (and lighter)

 

[slaw]

Jerry, what is a maximum speed of Your Brompton with Tongxin-Goldant motor on flat road ?

best regards
slaw

 

[cwah]

I've got one of these motors on order and I'm going to runi it at 63v/650watts/25mph

Current Tongxin Nano has over 3000miles with the same setup - just fancy playing with something new (and lighter)

Have you successfully overvolted this mini motor since? Please run at 20+ mph and 10 degree slope without peddaling

i'm more than interested.

 

[jerrysimon]

With a 36v battery on my 20" Swift this motor is still helping on the flat when I reach around 18mph-19mph. This is using the stock controller and pedelec only function.

Personally I find that more than fast enough. For me ideal assistance where I feel safe (around pedestrians) and in control is around 15-16mph. In a 16" wheel with stock controller it assists to about 16-17mph.

I have just tried this motor in a Dahon and am about to post some build pics.

Jerry

 

[cwah]

With a 36v battery on my 20" Swift this motor is still helping on the flat when I reach around 18mph-19mph. This is using the stock controller and pedelec only function.

Personally I find that more than fast enough. For me ideal assistance where I feel safe (around pedestrians) and in control is around 15-16mph. In a 16" wheel with stock controller it assists to about 16-17mph.

I have just tried this motor in a Dahon and am about to post some build pics.

Jerry

That seems better than I expected. But again it depends on how you're peddaling

I'm thinking of having a super lightweight vehicle to travel in a multi-modal way.

Could either be a brompton with the goldant / cute 85 or even a small electric skateboard that would take less space and weight only 7-8kg

 

[jerrysimon]

cwah I pedal assist almost all the time except perhaps when I coast round a corner and am feeling lazy. Of course with pedelec you stop pedaling the motor stops assisting as well

I am inclined to say I still prefer thumb throttle over pedelec though pedelec is a kind of fit and forget option though as I said you always have to be pedaling to get power. Perhaps thumb with cruise control though, I still don't like the idea that if you are in cruise and crash the wheel will continue to spin unless you blip the throttle or engage a cutout brake, assuming you have one fitted!

The Cute 85 is more like the original Tongxin "Nano". The Goldant is a whole level smaller, lighter and less powerful.

Jerry

 

[piotrmacheta]

Just for info, I have the 260rpm Goldant with built in controller fitted to a 700c wheel on my race bike and on the flat with some pedalling gets you to about 24mph. Apart from the mad dash to 20mph when you start pedalling and the slight 2 to 3 seconds delay when you stop pedalling, it's a great system. Very free running and quiet.
I decided to buy a Birdy instead of a Brompton and the 80mm one with external controller fits lovely into the forks with some spacers. Not finished this yet but looks like it will be perfect for this bike. In the 18" wheel I would expect about 15 or 16 mph based on above experience.

 

[piotrmacheta]

PS I like the skateboard idea but are they legal?

 

[cwah]

With something like this:
Boosted Boards - Motorized Longboards- World's Lightest Electric Vehicle

Everyone is going to think its a normal skateboard. Therefore, for the same reason to my brompton, its legal

 

[hech]

Aha a new orange micro-nano hub motor on every quarter. Does it have bluetooth steering as well perhaps? Cwah, I fear that you are a dangerous radical that must be stopped at all costs! That skateboard is a WMD!

 

[jerrysimon]

Just for info, I have the 260rpm Goldant with built in controller fitted to a 700c wheel on my race bike and on the flat with some pedaling gets you to about 24mph. Apart from the mad dash to 20mph when you start pedaling and the slight 2 to 3 seconds delay when you stop pedaling, it's a great system. Very free running and quiet.
I decided to buy a Birdy instead of a Brompton and the 80mm one with external controller fits lovely into the forks with some spacers. Not finished this yet but looks like it will be perfect for this bike. In the 18" wheel I would expect about 15 or 16 mph based on above experience.

Thanks for the update piotrmacheta. I prefer to fit a cutout brake to prevent the delay in the motor stopping when I stop pedaling. I also have an on off switch to bring the pedelec in when I want assistance.

Look forward to seeing a write up/some pics of your Birdy conversion. I am also in the middle of a conversion of a Dahon Uno using a Goldant motor. Like you said needs a couple of spacers to get it centered in the forks, but the motor all but drops in to the Dahon forks. You will probably get a little more than 15/16 mph (17/18 mph) on your Birdy given its nearer 19/20mph in a 20" wheel.

Jerry