Dirty BMX build log

[wldmki]

Hi all, first post here. Here's a few pics of a BMX I've started working on. A few years ago I had it running a 49cc pocket bike engine.
It was a fun bike, could reach 52Km/h, very loud and smelly. It was a filthy high maintenance ride.
Last year began converting a MTB to run a c80-100 outrunner, I plan on reducing it to drive the BB so I can keep most of my gears.
that's an on off project, so i figure i have this outrunner and all electrics ready, my BMX is rotting out back, just need to strap some batteries
on and bolt the motor on the back for it to go..
So here it is, I plan on this being a quick upgrade and be finished in a few weeks..

Specs:
Speedwell 80's BMX
c80-100 130 Outrunner mounted above rear wheel
160A ESC
Custom build throttle with programmable acceleration curve
(In future will add BMS function to throttle controller)
9-12S 2P Nanotech LiPo's total 12Ah
Currently using 25H pocket bike chain with 8t pinion
Exercise bike BB sprocket bolted onto rear wheel (no freewheel)
gets me to 39Km/h with 9S lipo

Now on with the build log..

1) to make a battery box and hold all the guts together

The ride with battery box mounted

Battery box material is old microwaves cut up and folded

battery layout, two batteries thick, total of 8 batteries with space for two more behind the seat pipe

Batteries will be held in place with space invader foam.

Fill it up with foam, close the two halves and let it set.
Then open it up and cut out spaces for batteries and electronics
Throttle will have temp sensor input for batteries and ESC will be mounted out of the box for cooling.

This is where its at.

BTW more photos over at my flickr page
http://www.flickr.com/photos/wldmki/sets/

 

[wldmki]

Peeled off one half of the box, foam filled nicely but still a little soft

heres some more pics:

Foam still wet and it expanded a little more than expected

decided to buy some new brakes for front and back

Close up of pocket bike pinion mounted to motor shaft.
the pinion screws into the shaft and a collar with a grub keeps it concentric

over the weekend will try to fit the batteries and speed controller.

 

[Thud]

Welcome & Very Nice project. (I love bmx bikes)
Also see some nice home anodising on the
flicker pages. Looking foward to seeing it finished.

 

[wldmki]

Thanks Thud,
some more progress this week:

This is the motor mount, had a lot of flex so added the angle down the side..

Cut out pockets for batteries

taped up and ready to go, could not resist taking it for a spin.. :wink:
The yellow board in the middle is custom throttlizer I'm building up,
It will use a hall sensor instead of a shunt for current control.
at the moment it's just a throttle.
So far running 12S 1P

And here are the results

GPS taped to the handlebar

It could go a bit faster but i won't play with the gearing until the bike is refined.

 

[nechaus]

haha cool

I like it, you should put a video up

 

[Sam-Q]

Any updates? did you make that pinion adapter yourself?

 

[Tommy L]

Nice work!

Subscribed!

Tommy L sends.....

 

[wldmki]

Any updates? did you make that pinion adapter yourself?

Yes, machined up the adaptor. The shaft is drilled and tapped so a standard pocket bike pinion screws in, and the collar is over the top.

I have been working on the throttle profile, now it has smoother control rather than popping mono's and throwing me.
Also bought a narrower motor since this one is now unobtanium and a bit long for a bike, not mounted yet.

In the process of putting the rear wheel sprocket on a freewheel so it can coast without spinning the motor.
bought a triple wall welded rim and respoked it for the new modified hub, now it runs true :wink:
Also found a suitable suspension fork on the kerb, replaced the stock springs for a pair of stronger clutch springs that happened to be the same diameter
so now the fork doesn't bottom out..

eventually when I'm happy with it I will ditch the frame and transfer everything to a healthier one and give it a coat of paint.

Progress is slow, mainly collecting dust because of other priorities.