# The electric BMX conversion ( the build blog )



## voyager (18 Sep 2015)

Hi Folks 

The e-BMX has been on the road for about 10 days now and I am starting to tidy it up and do a lot more testing to it -

Basically an off road bike - built to explore an old hamlet high on the south downs that was used as a training ground in the second world war and demolished by Canadian tanks .

It started its new life with me a rather rusty beast that was in need od a lot of TLC and a few bits , The stem was rusted solid in the front forks and after a liberal dose of a 120mm grindette the forks gave up and were removed .
New ( for the bike ) suspension forks and flatter bars with a longer extension were fitted and the seat pin is due to be extended and have a set put in it for a better riding position .

The fun bit came next with another n"ew to the bike " set of wheels , The front one a standard BMX and the rear was a 24voly Currie e-hub extracted from a 16" rim and fitted into a 20" rim ( this unit was originally fitted to the original 20/20 e-trike and was currently redundant since the q100 upgrades for the trikes.
A car trolley jack soon stretched the rear end to fit the 2" wider hub that would soon propel this little beast along .
Currently equipped with a road tyre rather than the chucky off road tyres to reduce road noise and the feel of riding a two wheeled tractor !

A standard vee brake is fitted to the front and the rear wheel has a standard Currie band brake fitted that works well , The gearing is a standard 42-16 T setup as generally fitted to a BMX and gives about a 50" gear 
New brake cables were fitted to the new kill brake levers and the refurbished business ends of the brakes .
The simplicity of a single gear means there is only a thumb throttle and brake levers to play with on the bars 

a 36 volt LifePO4 battery supplies the power to the 24v hub motor that was originally designed to give 15mph at 24v on a 16" wheel - 

The maths are simple 
In theory 
20/16 x 15 x 36/24 give a possible top speed approaching 27mph and torque is improved by a tad under 40%
On the road with a 250/350 controller with kill switches on the brakes and a thumb throttle , its just like a standard BMX to ride but a lot heavier at 54lbs it is a "lump" to carry . 
On the flat in derestricted mode about 22mph is possible and there is more than enough torque to pull away from a standing start .

The local youths and a couple of friends that have tried it have come back with a huge smile on their faces and have all expressed a wish to own one ! or fallen in love with it 

It is as I have quoted before "a marmil eater " if used on the road (  ) but it has been built with a specific purpose in mind , then it will probably be stripped and used in another project ( unless it has a value to someone else ) 


The controller I have used is a 250/350 watt 36/48v controller and you can probably imagine the power if the battery was increased to 48v with a theoretical top speed of 36mph and a possible range of 15miles on a 10 ah battery - but then it becomes more of a TOOL than a toy.

The use of panniers and a rack helps to disguise the battery and hub motor and makes it look like an overloaded BMX tourer .
The original lipo battery proved a little to heavy for the bag behind the seat and with a 6 mile range proved the concept but it needed a better range








The 5ah lipo was fitted in the triangle bag and the controller was cable tied to the seat tube




The rack hides most of the batter and takes the eyes away from the hub motor 

Other photos will follow when I get some free time ( when we are not playing on it )

all we need is some  so I can find this flattened hamlet in the south downs 




Postcard issued pre WWII .before it was evacuated and used as a training ground for Canadian troops .
My interest in the site is that my grandfather was born in the hamlet about 135 years ago .

regards emma


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## Lonestar (18 Sep 2015)

Hope you got good brakes for it.


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## Phaeton (18 Sep 2015)

We were in the village/town of Crickhowell earlier in the year, as you come away from the river there's quite a steep hill, a mamil struggling to get up it, when 2 old biddies on electric bikes went sailing past pedaling away with ease. It was quite a funny moment.


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## voyager (18 Sep 2015)

Lonestar said:


> Hope you got good brakes for it.



The brakes are adequate , its more the tyres I am worried about , 20 mph plus on two 20" wheels in damp weather will worry me . 


regards emma


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## voyager (21 Sep 2015)

After a further weekend of roadie scalping and mamil munching as well as a little more tidying up . The battery end caps that were missing have been remade and a little cosmetic work to a couple of rust patches on the cranks and the fork crown . The addition of a charging socket allows it to be charges without the fuss of connecting a pair of leads precariously to the battery.. Its as finished as it will every be , I have cut and welded up an extended and racked back seat pin destine to be fitted when I replace the top clip on the rack mount , but that will be a when and if job.
.
More of the local natives had ridden it and have come back with a huge grin on their face . 
Here is a photo of Ken coming back after a scalping session up the hill another unimpressed ridden of roadie to the list 

On the road it looks more like a shopper than a bmx but the frame I hope will put up with more abuse than the e-shopper that Ken is currently using 








regards emma


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