Electric BMX

L

littleskull99

100 W
Joined
Sep 21, 2013
Messages
113
Location
Dorset uk
Hi Folks, Been working on this project for the last few weeks. A friend of mine built the wheel as I couldn't find a cross laced 20" motor and rim. Cut down the spacers to fit 110mm dropouts. Then threw on the speedo and a back brake with some doc torque arms.

First pull away on carpet in the house nearly threw me off the back! Man these 20" wheel accelerate fast and with gobs of torque. Batts in the bag..


20140202_193245_zps12edf5d1.jpg


20140216_170755_zps4efe6f7f.jpg


20140220_103940_zps23fffb31.jpg


Thanks for looking.
Matt.
 
Nice project, but that is not a proper torque arm installation. They should be facing the other way, and be glued or welded to the frame. In their current configuration, they will give a false sense of security, but will not hold anything.
 
tsar, I hear what your saying but the bolt at the back of the torque arm goes through the dropouts and doesnt rotate at all. is there a correct way to fit a torque arm? I thought as long as the arm doesnt rotate along with axle it would be fine. il get a better pic up..
 
This is how I did it. I think the bolt through the back of the dropouts will only act as a lever to work your dropouts loose, especially if you use regen. Sure, people more experienced than me had other results, but I would rather be safe than take chances.
 
Yeah.. like what other have said, what you did there with the torque arm does nothing for you. Rotate them and bolt it on. Better to be safe than sorry.
 
TSAR,

If yours are glued on then you're going around recommending a joke of a torque arm installation as the safe way to do it. Anyone who disagrees I challenge to glue on a headtube with their DP120. There have been failures and the only reason failures haven't been widespread is due to dropouts being quite strong before the slight reinforcement of a glued on TA.

I don't like any TA solution that doesn't clamp to the axle, but at least the OP's install pushes the point failure out to a much greater radius where the forces are proportionately less making failure unlikely. That is at least until regen gets used, which exposes the weakness of all non-clamping solutions and forces frequent checking of the axle nuts. My 100mph SuperV only has one axle nut, and it's only for decoration and shin protection against ripping myself open by the sharp corners of the end of the threaded axle.
 
I am sorry for the misunderstanding: the torque arms are welded (both sides where possible) and painted. As long as the frame is steel, welding is the better choice IMHO.
As for the fine qualities of epoxies, DoctorBass is the guy to talk to (or disagree with)
I could argue about clamping vs. non-clamping, but I agree with John: clamping is better, which is probably why those bmx dropouts of mine don't have a motor in them.
 
Yeah gotta get to a welder soon to get them secured better. Its only a 1000w motor so bass arms are probably overkill. I get more axle movement fwd/bkwds from cranking on the pedals than rotation of axle. Good job im not peddling much...
 
what speed do you gett from 15s lipo?

edit: i like your post.. because i am choosing whether to make a mtb or a bmx ebike.. and there just isnt enough bmx conversiones.. i think bmx is a blast to run.. its almost like a adult toy isnt it.. if i start to convert my BMX Moongoss ill be on it everyday..
 
An electric bmx just screams for an rc motor with the small wheel size and less reduction!
Anyone have links for an rc motor bmx?
 
sobotek24 said:
what speed do you gett from 15s lipo?

edit: i like your post.. because i am choosing whether to make a mtb or a bmx ebike.. and there just isnt enough bmx conversiones.. i think bmx is a blast to run.. its almost like a adult toy isnt it.. if i start to convert my BMX Moongoss ill be on it everyday..
Click to expand...

I havent got a ca or speedo on it yet but I reckon about 25mph (il get back to ya on actual speed) could be slower but even on 12s its front wheel up and really fast to 18/19mph. I havent ridden the emtb since getting the bmx going, its too much fun!

matt.
 
you get a sense of going faster than expected being so low to the ground with small wheels and short wheelbase.. :p

http://www.youtube.com/watch?v=FJp0ynoEMvc

[youtube]FJp0ynoEMvc[/youtube]

From 2009 at 48v
http://www.youtube.com/watch?v=v7D49PyV67E

[youtube]v7D49PyV67E[/youtube]
 
wow ypedal nice vids. im thinking of going 72v (not 2wd) but may need more weight on the front end so I can ride it without going over the back. Did you try 72 rear motor only? Did you need the front motor for wheelie issues?

thanks
 
what motor do you use.. i mean is it DirectDrive or is it bafang or mac geared motor?.. nice vids ypedal.. i have to gett me one of these..
 
Yes direct drive from ebay. The.motor I got is usable on front or back I believe. I think the only difference is the spacers on the axle. for some reason you can fit the freewheel on either side, no idea why seen as you can make em spin either direction with phase/halls. I have no idea what make it is, 2nd hand but never used.
 
littleskull99 said:
tsar, I hear what your saying but the bolt at the back of the torque arm goes through the dropouts and doesnt rotate at all. is there a correct way to fit a torque arm? I thought as long as the arm doesnt rotate along with axle it would be fine. il get a better pic up..
Click to expand...

From what I understand the torque arm is used to push the twisting load away from the open "C" of the dropouts. Using a through pin in the dropout does little to move or share the twisting forces.

The torque arm needs to "become one" with the frame somehow. Looking at the pictures, the thick plate is secured by the part of the frame you are trying to strengthen. If the dropout could do the job on its own you wouldn't need the torque arm.
 
The clamping force provided by the bolt an inch away from the axle provides massive support... most bicycle frames do not have such a long slot to allow this but on a BMX you can.. for this specific install, i would not worry about it in the least with the combination of thick material on the dropout, + Docbass pucks, and the limited power of this motor..
 
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