I´m not sure if i´m straying too far off-topic but i Intend to use it as a "Trailbike" ;-)

Anyway..

Building an E-BMX seems like a neat Winters project so

any advice on how to build one is welcome.

Available parts, sofar.

An old BMX 20"

24 V 350W Brushed DC Motor With a 25A Controller in good condition.

90 T sprocket, front is 11 T #25 Chain(Same as on the small OSET´s).

2* 12V 9Ah SLA batteries(Same casing as the normal 7.2 Ah´s).

Thats great... do it, and have some fun.

First thing you need to do is know what the rpm of your motor is , you cant really progress until you know this.

next step is to work out what you want the top speed you would like ( be rellistic :-) ) it also may not be achievable with the motor you have.

SLA's are ok for initial testing but look for a better/lighter chemistry battery ( will improve performance ).

Believe a top speed at about 10 mph/15 km/h should do it and with the 2750 rpm motor ive got

I am looking at approx 20 mph on a 20" wheel( in theory) but like you suggested i also think it may be undermotorised.

Adding a battery to make it 36 Volts.. Im not sure this lowbudget motor has enough emf to produce more work

Than perhaps a bit more exess heat out of it.

So im looking for a reduction stage from 2:1, perhaps i can use a twin chain setup allowing also a more generous

Range of motor mounting positions(Bad English, sorry im Swedish).

Believe a top speed at about 10 mph/15 km/h should do it and with the 2750 rpm motor ive got

I am looking at approx 20 mph on a 20" wheel( in theory) but like you suggested i also think it may be undermotorised.

Adding a battery to make it 36 Volts.. Im not sure this lowbudget motor has enough emf to produce more work

Than perhaps a bit more exess heat out of it.

So im looking for a reduction stage from 2:1, perhaps i can use a twin chain setup allowing also a more generous

Range of motor mounting positions(Bad English, sorry im Swedish).

I think it will be fine on 36v , thats still only around 4200rpm so its still not to excessive ( unless its really is a very very poorly designed motor ) I think you will be a little disappointed with only 25A if it is geared for around 20mph that still only 900W peak, may be a little more but depends on controller.. the thing to do is try it and if the motor get to hot then gear it for a slower speed.

Edit:

if you go for 36v then I think you will need a 12.5:1 reduction and if you run 24v then around a 8:1 reduction .. so the 2:1 is way out.. the 11t front and 90 rear will be about right on 24v on a 20" wheel ( 8.18:1 )

Edited September 20, 201411 yr by gwhy

Sorry, i meant a 2:1 recuction before the 11/90 gearing ( or perhaps after would be the best to reduce the dia of the rear sprocket).

Im grateful for all input and the 36v is probably smarter, powerwise.the sla's are just initial, will go to lipo if it turns out fun:-).

Think ill also try to put a bikecomputer on our oset 20 to get a feel for if 10 mph is too slow or not.

(research on two wheels is always fun).

Also, one idea is that it could work for my kids if. It doesnt pull my 75 kgs well it will do better with 30 perhaps.

Sorry, i meant a 2:1 recuction before the 11/90 gearing ( or perhaps after would be the best to reduce the dia of the rear sprocket).

Im grateful for all input and the 36v is probably smarter, powerwise.the sla's are just initial, will go to lipo if it turns out fun:-).

Think ill also try to put a bikecomputer on our oset 20 to get a feel for if 10 mph is too slow or not.

(research on two wheels is always fun).

Also, one idea is that it could work for my kids if. It doesnt pull my 75 kgs well it will do better with 30 perhaps.

the easiest way would be to try and put a bigger sprocket on the rear , you would need around 120t for a 36v system. thats assuming that you could source a 120t and that it will fit

or you can try to source a 8 or 9t for the front

Unfortunately my boys took the BMX ..so I went scrapheap-challenge in my own garage to find som junk to put

together into some kind of bike and its coming together slowly.

Will try to post pics as it proceeds.

Anyone knows how to get the pic from my ipad in here btw?

It appears difficult to post pics from ipad so i put it in as a profile pic for now.

Its a 24" frame with Ducatiinspired tubing, sorry for the lousy pic.

Still needs a rear frame for the seatpost which i think i will simply build as a

Bolt on additive to get it flexible in terms of angles(and the fact that my welding

Sucks and i may have to redo it two or three times to get it sorted;-).

Still the same drivetrain so it will likely be a 24" slowrider..

It doesnt matter if it doesnt turn out great, it has still been fun building it.

you need to work out how to post pics !.. wish i can see it more clearly but looks good so far

A few pics of progress attached, hope they are possible to view.

The idea is to use what you have at hand and build something.

However, paint needs to be bought brand new since it´s difficult to recycle...

Edited February 6, 201511 yr by gudah

looking good...

Caught the flu wich stalled progress but spray paint fumes are considered medicin IMO so i gave it a shot.

I hope the flu goes away as the paint dries out for the next couple of days.

Some pics meanwhile:

(Orange is the new black)

A battery cover from an old car boot protective cover...

ASAP, As simple as possible instrumentation..

Folding foot pegs made from a old bicycle rack.

Sadly, the Top Gun Fork had to go since it couldn´t house a discbreak, a shame as it looked a bit

more motorcycle style and stopped the steerer from rotating freely:-(

it looks like the above fork can use a disk brake calliper .. the front wheel is the wrong way round. But its coming along nicely .. What motor are you planning to use, is it the same one you were going to use for a bmx ?

Sorry, it was a bad pic, the black part looking like a caliper mount is actually some text on the cartonbox in the background.

Yup, same cheap motor for initial test, could be switched for a 24" electric bicycle wheel if one turns up at a reasonable price.

(I deliberately chose the standard width of a front fork in the rear swing to be able to do that).

Or, perhaps the one referred to below but that needs a new controller as the 25 A one won´t do.

Does anybody have any experience from this 36 V 1000W motor from electricscooterparts.com?

I ask because it looks like it´s the same housing that the 750W OSET and could perhaps work as a upgrade

for my 42 kg boy on his OSET(A 16" upgraded with 20" wheels).

Anyone who has tested it?

Done, it was slow as suspected..

It will sit in our garage and wait for a bigger motor.

Meanwhile it will be used as a e-scooter round the block here at home.

I branded it "24" ("24-inch, 24 Volts, 24 workhours and 24 beers while building;-)

Some pics: