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

[jerrysimon]

Using the dropout retaining washers is a good idea to stop the threaded shaft jumping out.

As I said the challenge with the Ti forks, is they tend to spring back to their initial spacing more so than the equivalent steel forks.

Regards

Jerry

 

[Biker44]

Polyphasic, I spread my Brompton fork using a threaded shaft and nuts.

Richard

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

The correct way to do it is to take a scaffolding tube, drop it over the one leg, bend it out a tad and do the same to the other.

However, a plank of wood with a slot in it might be better.

 

[benjy_a]

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

The correct way to do it is to take a scaffolding tube, drop it over the one leg, bend it out a tad and do the same to the other.

However, a plank of wood with a slot in it might be better.

I used the threaded rod method and you can clearly see both legs bending as you do it. I'm sure that one probably bent a little more than the other but you can't tell. The fork legs are remarkably strong and resistant to being bent. If you were to use a bar to do this on a Brompton it would need to be very long to give you exact and sufficient control over the amount of force you were applying (unless you are superman).

I know that using a threaded rod is a common method used successfully by many to convert the Brompton.

Ben



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[polyphasic]

Thank you for the photo (worth a thousand words) and tips. I was thinking we had to spread the middle of the fork in addition to the end. Appears this is just spreading the end. It feels less daunting now.

I read that the titanium fork wants to spring back to its original shape whereas the steel fork bends with minimal spring effect. When you bend the Ti fork, how slowly do you bend it? Do you bend a little then wait a period of time? Is it better to bend it all in one go? Or just do a little bit at a time.

Polyphasic,

I spread my Brompton fork using a threaded shaft and nuts. When spreading using this method, you have to be careful that the whole threaded rod assembly does not spring out of the dropouts during the spreading operation. Otherwise it will be ejected with great force. I used the original dropout retaining washers to prevent this from happening. You can see these (in the picture below) on the inside faces of the fork securely hooked into the holes in the fork.
Richard

Oh, so the other method is a cheater bar? I was wondering whether one side would bend more than the other side.

I got a phone call this morning saying my Titanium fork that I ordered is ready to be picked up. He wasn't sure if I was able to install it on the bike myself. I'm fairly mechanical. I sorta want to do it just to have the experience. It looks pretty straight forward to do.

My question though whether it's easier to spread the fork off the bike or on the bike. I know Jerry said he had spread it on the bike. Based on that picture above, I'm thinking it likely wouldn't matter unless you were using that bar method (cheater).

I used the threaded rod method and you can clearly see both legs bending as you do it. I'm sure that one probably bent a little more than the other but you can't tell. The fork legs are remarkably strong and resistant to being bent. If you were to use a bar to do this on a Brompton it would need to be very long to give you exact and sufficient control over the amount of force you were applying (unless you are superman).

I know that using a threaded rod is a common method used successfully by many to convert the Brompton.

Ben
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One last thing, I got an email reply from Sky. Yes, the throttle option is available. Sky wrote this: "but the function should make together with pedal assistance. If you wanna add this function, pls. let me know." I assume that means we will need to still pedal or that somehow the two have to go together. I asked for clarification, so I should hear back shortly. Maybe somebody here knows what this might mean. I'm thinking it means you can do both...or maybe it's you must do both (pedal/throttle) for it to work.

 

[Biker44]

I used the threaded rod method and you can clearly see both legs bending as you do it.

Yes, you can clearly see bending within the elastic limit. However, you can also clearly see yield, and for guaranteed it will happen on one side only.

If you were to use a bar to do this on a Brompton it would need to be very long to give you exact and sufficient control over the amount of force you were applying (unless you are superman).

Scaffolding pole is long (well, OK, my favourite piece is only 5' long, but you know what I mean). The important part is that you can feel when the elastic limit has been overcome and make sure both sides get the same treatment.

I know that using a threaded rod is a common method used successfully by many to convert the Brompton.

It would be a whole lot better to bend both legs by one tad, rather than leave one leg unchanged and bend the other by two tads.

 

[benjy_a]

Fair enough but as far as I can tell my forks are still symmetrical, the bike still goes in a straight line and that's good enough for me

 

[Biker44]

Fair enough but as far as I can tell my forks are still symmetrical, the bike still goes in a straight line and that's good enough for me

You can ride with your hands off the bars?

 

[benjy_a]

You can ride with your hands off the bars?

Haha you try that on a Brompton with an extra 10kg on the front! One handed is the limit for me.....hence "as far as I can tell"

The bike handles surprisingly well even with the extra weight. Incidentally the threaded rod method is used by several companies supplying converted Bromptons.

 

[polyphasic]

Incidentally the threaded rod method is used by several companies supplying converted Bromptons.

What about a combination of the two? That is, threaded rod, then compensate with the bar for the side that isn't yielding as much, then back to threaded rod until you get the proper width?

But then again if you can't tell by looking at it with the threaded method, then that makes it impossible to get each fork to being close to equally spread apart.

Obviously metal bends at it's weakest link, so one side might be weaker than the other. I'm not sure how the weakest link for titanium defers from steel. I've bent steal, but never springy titanium. I wonder if this issue of unequal forks are more or less pronounced on the Ti forks.

For the bar method, I suspect you have to use something to protect the forks from getting scuffed up....do they use tape?

 

[jerrysimon]

One last thing, I got an email reply from Sky. Yes, the throttle option is available. Sky wrote this: "but the function should make together with pedal assistance. If you wanna add this function, pls. let me know." I assume that means we will need to still pedal or that somehow the two have to go together. I asked for clarification, so I should hear back shortly. Maybe somebody here knows what this might mean. I'm thinking it means you can do both...or maybe it's you must do both (pedal/throttle) for it to work.

See my previous response.

I have spoken with Sky who has confirmed a new controller which has the throttle option has been designed and will be available. Sky said that the pedelec is required because these are non hall motors but I don't see why the throttle option could not be fitted on its own. I guess the reference was because non hall motors don't really start up as well as ones fitted with halls and its better for them to be moving first.

I have actually ordered one of these new controllers with the throttle option now as well, so will report when it arrives.

Re spreading the forks I just used a block of wood which I slowly worked down the forks to spread them bit by bit. Took about three or four goes to get it until it sprung back to 80mm. I will post a pic later sorry. Several of us have used the above method with a threaded rod and it worked fine. My previous steel Brompton has over 3500 miles on it since I undertook the work. As with all these kind of modifications thinking and planning it is important, but if you want to do it sometimes you just have to get on and do it. This is what I decided in the end when I set about my Ti forks. With steel forks the worst case is you bust a set of £49 forks (very unlikely). The hurdle of getting down and attacking £275 of Ti forks is much harder, trust me.

I did scuff my steel black forks a little and of course you have to file open the dropouts a little for the larger motor main shaft so inevitability you will remove some paint. Easily fixed in my case with a little bit of Matt black Humbrol oil paint. Of course with Ti forks it does not matter as they are unpainted and don't rust.

BTW I don't think anyone in their right mind would ride a Brompton no handed either in its stock form or modified!

Regards

Jerry

 

[polyphasic]

Oh, I just reread. My apologies. I shouldn't read & respond without my coffee first. So based on your response, it appears it's a completely different controller, I really like the small size of your current controller. Did you happen to ask if the controller was significantly larger? Some of these controllers get quite large and heavy.

 

[jerrysimon]

Nope as I understand its the same new small controller but with an additional throttle option and I assume another lead coming out of it, with the associated three throttle wires. Its exactly the same price.

Me:

"I assume the new controllers are different to the ones I have for my larger Tongxin motors already ?

"

Sky:

"Dear Jerry,

The controller with throttle function is similar to the one I sent to you last time."


Regards

Jerry

 

[polyphasic]

Nope as I understand its the same new small controller but with an additional throttle option and I assume another lead coming out of it, with the associated three throttle wires. Its exactly the same price.

Regards

Jerry

Oh that's exciting. I had even contemplated the 100mm motor with the built-in controller, but since that one doesn't have throttle, this makes my decision to go with the 83mm version to be a smarter choice (for me).

Okay, I'll confess. I was thinking of being thrifty and reselling the raw steel fork. Appears they sell new for £66 ($103US), but now I'm thinking nobody probably wants to buy a new fork. So maybe I should just bend the steel fork first and leave the Ti fork neatly in a box until I'm sure this motor is the way to go. I don't see any steel forks selling on ebay.com or .co.uk, so it's probably more to gain by just starting with the steel fork first.

 

[benjy_a]

Oh that's exciting. I had even contemplated the 100mm motor with the built-in controller, but since that one doesn't have throttle, this makes my decision to go with the 83mm version to be a smarter choice (for me).

Okay, I'll confess. I was thinking of being thrifty and reselling the raw steel fork. Appears they sell new for £66 ($103US), but now I'm thinking nobody probably wants to buy a new fork. So maybe I should just bend the steel fork first and leave the Ti fork neatly in a box until I'm sure this motor is the way to go. I don't see any steel forks selling on ebay.com or .co.uk, so it's probably more to gain by just starting with the steel fork first.

If you have both sets of forks I would definitely say use the steel ones as guinea pigs...they are only £49 in the UK anyway...better to experiment and get things exactly as you want them before attacking the expensive forks!

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[dingrpdl]

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

In my case, the forks spread symmetrically as far as the eyeball can tell. But I suppose if accurate measurements were made, there would be some degree of assymetry.

As to whether I can ride with no hands on the bars... well I could not do it before the mod. And that certainly isn't going to change after the mod!

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. However, somewhere between spending a lot of time getting things perfect and doing a quick 'hack job', there is a happy compromise. In the end, my Brompton handles no differently from its unmodified version, the fork looks symmetrical to the eye and the added wiring does not get in the way of the folding. And I can get on with enjoying the use of the bicycle and using the motor to tackle those hills in my area.

Richard

 

[jerrysimon]

Ok Pictures as promised.

Firstly how I did my original steel forks in 2009.

Shown initially with stock spacing. I used the threaded bolt method but the one shown in this thread earlier using the stock unit fall out dropout washers, is better as my setup had a tendency for the threaded shaft to move and pop out when you opened it out undoing the nuts.

Although they only need to be spread to 83mm you have to spread them further as they spring back

Finally at the correct spacing.

 

[jerrysimon]

On the Ti forks I used a different more "industrial" method

Note the little spacer at the bottom/near the top head of the forks under the wood block which I slipped in after spreading them to hold the forks apart when I then removed the block of wood. It requires quite a bit of brute force to spread the forks with the block of wood. Once removed the spacer keeps them apart enough to fit the motor. I did this a few times removing and refitting the wheel with the motor in it before it eventually settled at the correct spacing, though its still quite tight. Probably easier to do with the motor before you lace it.

I found opening up the dropouts to 10mm for the flats on the motor shaft harder, going through a few bits on my dremel to remove the required Ti material.

It may look a little rough on the edges but the picture is a macro shot. Having already done it before with the steel forks, I was more careful this time not touching or enlarging the hole for the anti dropout/turn washers but using the stock Brompton ones rather than the one supplied with the Tongxin motor.

Finally note this is just to show you how I did it and if you choose to do it yourself using either method shown, then you are obviously responsible for any subsequent failure. As I said the steel forks have been running fine for about 30 months and 3500 miles. The Ti forks are fine up to now (fingers crossed).

I know of people who have spread the Steel and the Ti forks so they come back to rest at 100mm wide.

Regards

Jerry

 

[Biker44]

For the bar method, I suspect you have to use something to protect the forks from getting scuffed up....do they use tape?

The bar method is approved for straightening all sorts of things (pedals, handlebars etc etc) - if it's a painted item the best thing is a piece of wood, which may be held in place with tape.

My question about the Brompton riding in a straight line no-handed was tongue in cheek but the principle is important.

 

[piotrmacheta]

Last week I decided to buy 2 kits, one for the scooter with an external controller with throttle option and another with the built-in controller. Thanks Jerry for your help. Sky was indeed really helpful and easy to deal with but do make sure that you agree the motor spec in writing just to be sure you get the right spec. I'm going to put the built-in controller version onto my race bike and as it's such a light system it should still ride OK normally. I hope I can figure out what all the wires are for! Sky said that he/she would let me know when the production was ready so I'm not sure when I'll get them but I'm sure it will be a few weeks yet.

 

[jerrysimon]

No problem I love documenting my projects on here. Looking forward to hearing about yours.

The kit I ordered took about three weeks to build/complete if I recall, but on the plus side shipping was VERY fast about 2 days. I probably got lucky

As I have said before dealing with these suppliers often requires a lot of patience and you are right to get all the specs correct and detailed before placing the order.

Regards

Jerry