my first build: brompton at 30 mph

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cwah   10 GW

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my first build: brompton at 30 mph

Post by cwah » Feb 22 2012 8:20pm

Hello there,

I'm almost ready to get my Brompton at 30 mph. Here are the specs:
- 4 lipo 18.5V8AH for a total of 74V8AH
- Lyen controller
- Will receive my Conhismotor mini hub tomorrow: http://conhismotor.com/ProductShow.asp?id=76. I may get another one to see the difference and more toooorque (either a Bafang or MP3)
- Cycle analyst
- Temperature meter to check the motor and controller: http://www.amazon.co.uk/gp/product/B002 ... 00_details

The actual rear dropout width is 112 mm:
Image

I'm now thinking about extending the dropout to 135 mm so I can add any motor. The bike is steel so that's fine:
Image

I actually extend about 12 mm each side, which doesn't seem a lot.


The problem is more with the forkend that seems quite weak:
Image

I'll have to hacksaw it a bit to put the axle. And get 2 very strong torque arm otherwise I don't think it will be able to handle a 30 mph motor.


Hmm.. Just realized I can't us the axle with nuts to extend the dropout. Only the forkend may move. I think I have to extend it with muscle power..
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

cwah   10 GW

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Re: my first build: brompton at 30 mph

Post by cwah » Feb 22 2012 9:23pm

Damn, the rear dropout is super strong. Don't have enough muscle power!!

Any idea what tool I can use to extend the dropout?
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

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StudEbiker   1 MW

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Re: my first build: brompton at 30 mph

Post by StudEbiker » Feb 22 2012 10:02pm

Do you mean you are trying to widen the distance between the dropouts? You will need a large prybar. There is an instructional on the SheldonBrown site for how to properly do this. If your frame is chromoly, those dropouts look pretty beefy. A torque arm would be okay, but they don't look too frail to me.

http://sheldonbrown.com/frame-spacing.html

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joe tomten   100 W

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Re: my first build: brompton at 30 mph

Post by joe tomten » Feb 22 2012 11:35pm

The length of the rear stays is quite short - being that the brompton wheels are only 16" in diameter.

Brute force opening of the stays, with out regard to what is happening with the brake mounts might get you in trouble.

My experience in widening a bmx rear with the threaded rod approach was to also use an oxyacetelyne torch. By heat relieving the stress, & working in circles around the four rear stays, you can gently widen the rear frame. This way you have complete control over exactly where the bending takes place, and you can work slowly, while you carefully watch the shape that is being produced.

Be sure you stay well away from any brazed attachments.

On the bmx rear, after bending (heat relieving) the stays open wide enough with the threaded rod, the stays were then at quite a wide angle away from each other, like "veed out". At that point i then applied inward pressure on the outer nuts of the threaded rod and heat relieved the bottom of the stay and the dropout it is attached to to bring them back to parallel with each other.

Again check that this intersection is welded and not brazed. Do not do this if it is brazed - at that joint.

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Re: my first build: brompton at 30 mph

Post by Toango » Feb 23 2012 12:24am

cwah wrote:Damn, the rear dropout is super strong. Don't have enough muscle power!!

Any idea what tool I can use to extend the dropout?
Have you tried extending width beyond 135mm (perhaps 160mm) and leave it overnight. Next day it should spring back wider than original.

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Re: my first build: brompton at 30 mph

Post by itselectric » Feb 23 2012 1:54am

cwah wrote:Damn, the rear dropout is super strong. Don't have enough muscle power!!

Any idea what tool I can use to extend the dropout?
Use a Quick-Grip clamp. Instead push together to compress, you spread it open
spreader.jpg
spreader.jpg (37.43 KiB) Viewed 2912 times

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wesnewell   100 GW

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Re: my first build: brompton at 30 mph

Post by wesnewell » Feb 23 2012 2:57am

cwah wrote:Damn, the rear dropout is super strong. Don't have enough muscle power!!

Any idea what tool I can use to extend the dropout?
I take a 2 foot 1x6, a mini sledge hammer and drive the wood in between the swing arms. I've done a couple this way. Takes about 30 seconds to reach desired width.
Need Advice? https://endless-sphere.com/forums/viewt ... =3&t=66302
Mongoose 26" Ledge 2.1 mtb bike $99, yescomusa.com 48V 1000W rear hub kit $200, Hua Tong 72V 40A controller $35, 10ah 24s lipo $217=~43mph, range=45 miles @ 20mph. 25K miles and still going strong.
Huffy Fortress 3.0 with MXUS 3000 4T motor, 24s lipo, 96V 60A controller. Total cost with extras <$700. Top speed ~50mph
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cwah   10 GW

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Re: my first build: brompton at 30 mph

Post by cwah » Feb 23 2012 4:04am

Thanks itselectric, I think I'm going to use a quick grip clamp. Going to buy it shortly.

Joe, I don't have an oxycetelyne torch and I don't think I'll have the skill to use it. Unless I can ask someone doing that I think I better use standard tools.

Studebiker and wesnewell, I think I'm going to get a quick grip clamp first as I would need to purchase either the wood or the clamp.

Thanks, clamp on the way :)
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

cwah   10 GW

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Re: my first build: brompton at 30 mph

Post by cwah » Feb 23 2012 5:36am

Found some wood bar in my flat:
Image

Maybe I can use that?
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

cwah   10 GW

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Re: my first build: brompton at 30 mph

Post by cwah » Feb 23 2012 6:15am

itselectric wrote:
cwah wrote:Damn, the rear dropout is super strong. Don't have enough muscle power!!

Any idea what tool I can use to extend the dropout?
Use a Quick-Grip clamp. Instead push together to compress, you spread it open
spreader.jpg
I checked multiple quick grip clamp, and they all have a minimum size of at least 190mm. I can't use them on my brompton because the dropout is only 110mm. Do you know where I could find a clamp that can accomodate 110mm minimum width?

Thanks
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

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dogman dan   100 GW

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Re: my first build: brompton at 30 mph

Post by dogman dan » Feb 23 2012 6:47am

A small cars jack is often used to spread a frame. Might have to heat it, if you are spreading it much. 10mm should be no problem, 5 mm per side.

cwah   10 GW

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Re: my first build: brompton at 30 mph

Post by cwah » Feb 23 2012 6:58am

Thanks Dogman. Which one do you recommend? And what tool should I use to heat my frame?

Need some help :lol:
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

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dogman dan   100 GW

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Re: my first build: brompton at 30 mph

Post by dogman dan » Feb 23 2012 7:07am

Any small car scissor jack will spread something. Whatever your buddy or neighbor has in the car.

Plumbers propane torch should heat the metal enough to bend easier, at the cost of the paint of course.

It's going to take one bend to pull the frame out, then another to bend the last few inches back paralell. To do the last bend, insert a wood block, then use a long bolt or threaded rod to bend the dropouts paralell again.

Bend as little as you can, if you can shorten the axle and have it clear the frame, do that.

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Re: my first build: brompton at 30 mph

Post by Scottyf » Feb 23 2012 10:56am

Maybe wait till you have the motor in your hand before monkeying about with the drop outs...

Butane torch you can usually get for under £10 at a local hardware store. Worst comes to worst B&Q will have one.
The car jack is about the best idea with the heat.
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cwah   10 GW

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Re: my first build: brompton at 30 mph

Post by cwah » Feb 23 2012 1:53pm

Just received my motor today:
Image

I think I'll have to extend the dropout to 135 mm in order to have a centered motor. Otherwise it's not going to work.


I'm soo impatient to have my motor fitted... Do you think I can do it with my wood bar or shall I go buy the torch and the car jack?
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

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Re: my first build: brompton at 30 mph

Post by joe tomten » Feb 23 2012 3:03pm

cwah,

Any possibility of finding a friend who has an oxy welding rig? I really doubt if mapp gas will get it hot enough to allow the steel to form to new shapes easily.

I'll still lobby for the threaded rod and hot heat approach. And i worry that the length of the stays beingso short that the generalized bending approach of the lever or jack might not produce results that you are hoping to avoid.

With the threaded rod - You can work slowly and with lots of control. And you can thus tailor the shape of the assembly so that it is not necessarily symetrical from side to side (which it looks like you will need here in order to deal with the chain line issues.). You could use those big holes just to the side of the axle dropouts, get 1/2" threaded rod, some nuts and some big bearing washers.

If it were me doing this job, i'd go ahead and lace up the wheel and have it standing by while i was doing the job so i could constantly fit and refit it, and explore all the issues that presented themselves. Chainline, brake fitting, & for 25+ mph I'd certainly want an 11t sproket on there.

Patience will be rewarded. Impatience may be punished.

Good luck.

cwah   10 GW

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Re: my first build: brompton at 30 mph

Post by cwah » Feb 23 2012 3:28pm

I definitely agree with you Joe. But I don't have a friend with oxy welding rig. And I don't know if there are workshop in london able to do that.

My solution for now is to use butane torch and car scissor jack. It's steel so it should be ok.

I've seen some butane torch at 1300C. It's quite hot. How hot should that be to bent the metal?
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

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Re: my first build: brompton at 30 mph

Post by joe tomten » Feb 23 2012 3:43pm

Image

1300 Farenheight is all you need for heat relief.

Do the threaded rod for more control over the bending process.

cwah   10 GW

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Re: my first build: brompton at 30 mph

Post by cwah » Feb 23 2012 4:20pm

Can I use this one?
http://www.ebay.co.uk/itm/Jet-2000-C-Bu ... 500wt_1413

It says 2000C but seems to be a bit small for the job
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

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Re: my first build: brompton at 30 mph

Post by Ykick » Feb 23 2012 4:39pm

cwah wrote:Can I use this one?
http://www.ebay.co.uk/itm/Jet-2000-C-Bu ... 500wt_1413

It says 2000C but seems to be a bit small for the job
Ridiculous... You need hands on help for this!
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cwah   10 GW

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Re: my first build: brompton at 30 mph

Post by cwah » Feb 23 2012 4:50pm

Ykick, can you provide a link to a butane torch that worth it but is still cheap? I'll only use it once.
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

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Re: my first build: brompton at 30 mph

Post by Ykick » Feb 23 2012 5:27pm

cwah wrote:Ykick, can you provide a link to a butane torch that worth it but is still cheap? I'll only use it once.
You don't need a torch any more than you need that spreader contraption from your pics. You need to find somebody with a torch who knows how to use it and who's willing to let you watch and learn how to work metal.

I've found small auto and muffler shops to be approachable with my eBike metal work needs. Much more receptive and genuinely interested than most LBS. That's my advice, do with it what you will...
Talent must not be wasted.... Those who have talent must hug it, embrace it, nurture it and share it lest it be taken away from you as fast as it was loaned to you.

- Frank Sinatra

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Re: my first build: brompton at 30 mph

Post by d8veh » Feb 23 2012 5:39pm

Cwah. This is a tricky job. You need the frame to bend evenly on both sides and in the right places. If I were you, I'd get the wheel built, and then take the frame and the wheel to a local fabrication company. Explain to them that you want the dropouts parallel, wide enough to fit the motor, and the rim central by applying heat. They'll know how to do it. Look in your yellow pages, Thomson directory or internet search to find local fabrication companies. There's always loads of them. They should charge about £30 to £50. If you're really lucky, they'll do it for a drink. Car bodywork repair shops should be able to do it as well.

cwah   10 GW

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Re: my first build: brompton at 30 mph

Post by cwah » Feb 23 2012 5:55pm

What is a local fabrication company?

I've seen this site as you told me: http://www.thomsonlocal.com/BusinessFin ... &2Box=true
Not sure if the results are relevant?

Or I can go to any car repair shop?


For 30-50£ it's a perfectly good price. If the price range is around that it's much better to ask them for help.
Help me find my stolen electric brompton: http://bit.ly/1a0vbBC and Bosch Sinus B3 http://bit.ly/1eV0WQz

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Re: my first build: brompton at 30 mph

Post by wesnewell » Feb 24 2012 3:37am

cwah wrote:I'm soo impatient to have my motor fitted... Do you think I can do it with my wood bar or shall I go buy the torch and the car jack?
Well, I've done 3 bikes using wood. Don't see why someone else couldn't do it too. Only takes a minute or two. It will spring back some, so you probably want to go to at least 150mm before knocking the wood out.
Need Advice? https://endless-sphere.com/forums/viewt ... =3&t=66302
Mongoose 26" Ledge 2.1 mtb bike $99, yescomusa.com 48V 1000W rear hub kit $200, Hua Tong 72V 40A controller $35, 10ah 24s lipo $217=~43mph, range=45 miles @ 20mph. 25K miles and still going strong.
Huffy Fortress 3.0 with MXUS 3000 4T motor, 24s lipo, 96V 60A controller. Total cost with extras <$700. Top speed ~50mph
My videos https://www.youtube.com/channel/UC0KW4U ... _G2wQhptMg

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