eBMX

SOON.

I will be following this closely! I really need to stop thinking about a project like this and actually do something...

The Unboxing:

The Plan:

So, I got bit hard by the ebike bug after reading the Gizmag article on Luke Workman: http://newatlas.com/luke-workman-zero-interview-liveforphysics/42320/ I started some research and fell down the rabbit hole over at endless-sphere.com, THE ebike forum. After months of research, I've started collecting parts. I started w/ the BMX because it is what I had lying around, and also thought a 40mph BMX would be ludicrous

What we have in the above pic is a mid-2000s Giant MODEM heavy-ass all steel flatland/freestyle/BMX bike. Spread out below like presents under the tree are:

• 1500w leafbike.com hub motor laced into a 20 inch wheel. This came with switched brake levers (to engage regen braking), and a half-throttle (the outer half of the throttle side grip doesn't move. This is to prevent unwanted acceleration in case you bump against something or lean your bike against a wall. Electric bikes don't have neutral, so if you bump the throttle it'll just go...)

• Echo tool batteries. There are several battery choices to be made. Some are simple and quite cheap, but can be very dangerous (Lipo hobby/RC batteries, they can explode if mistreated), some are safer, but more complicated to build (18650 cell batteries. Similar to what TESLA uses. DIY all the way, have to buy a spot welder, nickel strips, and get to work), or some are very safe, but also expensive (aftermarket battery packs sold by reputable vendors). I went with the tool batteries for the novelty, simplicity, warranty, and the fact that I can head over to Home Depot and grab one off the shelf if mine dies, as opposed to waiting for one to arrive from China.

• Rim, hub, and massive disc brake. Its an Avid BB7 mechanical caliper which is highly regarded and a 200mm disc. And a Shimano hub w/ disc mount which I've since found out will not likely work w/ my forks But the plan is to mount the disc to the hub, mount the hub to the forks, and mount the caliper to the disc (the caliper has double adjustable pads). Then line the caliper holes up to the fork to make a mounting bracket and weld that to the fork. Viola! massive disc brake on a BMX.

• Moped tires. On the back of the BMX you'll see a fat, misshapen tire. I found out that a 20" BMX rim is actually 16" diameter and that moped tires will fit straight on to the skinny little rims with no problem. I just so happened to have an old dry rotted moped tire here to test fit. It fits! This will give me much better rubber, puncture resistance, and speed rating for my intended use of this little monstrosity.

Stay tuned...

Oh this should be good. BB7s are nice brakes. What kind of run time are you expecting per charge?

I heartily approve of your chosen method for exiting this earth. Carry on, w/ pics please

bluej wrote: I heartily approve of your chosen method for exiting this earth. Carry on, w/ pics please

this made me lol.

In reply to thatsnowinnebago:

Like everything, it will heavily depend on throttle discipline. I got two of the Echo batteries. They are 4ah each, in parallel is 8ah total. If i can draw 40A at full throttle, I'll get 12 minutes, at half throttle, 20A, I'll get 24 minutes. Hills, head or tail wind, and pedaling will all affect range pretty dramatically...

There will also be room on the bike to add a third battery for 12ah.

I'm very curious about how the balance will be since you won't be bracing your body against the acceleration by the bike seat like you do on most other e-bikes.

Insert tab A into slot B....

So simple! Especially without instructions of any kind!

No instructions, unlabeled wiring connectors, and lots of electrons.

Fire risk level: expert. You continue to impress!

(Please note, since sarcasm can be tricky on the tubes, I really do love this!)

Keep it comin', sarcasm's the only language I understand.

For added fire risk consider constructing your own battery using lithium battery cells.

Use lipo they said! The energy density! The cheap!

Yeah...

40MPH?! I can't wait to see you take it off some sweet jumps.

Holy carp! Took me a minute to check that that wasn't your bike en flambe.

Will be watching this for sure! Have always been interested in electric transport.

I'm thinking that an ebike conversion is in my future, too, so I'll be following along for sure!

Coooooooooool- this would make an awesome pitbike.

Okay, so a lot of waiting for parts and tools to show up, figure out they are the wrong parts and tools, and then more waiting for more parts and tools to arrive. Ugh.

Now that I've got everything I need, back to work. Again, so simple!

(L to R: Hub motor clamped in vice, Echo battery connected w/ 8awg silicone wire to a Sunwin motor controller, e-throttle down in front, switched brake levers up top, and my auto-panning camera mount[kitchen timer] top right)

Got it all connected up after a little of this:

via GIPHY

Most of the connectors didn't match up for the components to attach to the controller. So I ordered a Molex variety kit to get things sorted. Also picked up this sweet crimper:

...which allowed me to make really nice, professional looking crimps on these tiny Molex fittings. Are they Molex "mini" or "micro"? I don't know. I was using the 1.6 cimps:

Finally everything was connected! Time for a test. First, you plug in the two wires labeled "Self Study". The motor is controlled by hall effect sensors that determine the direction of travel. If you apply voltage and the motor spins in the wrong direction, just unplug the "Self Study" wires and then plug them in again. Then the motor should turn in the correct direction. I plugged everything in, attached the "ignition wire" and:

A video posted by @problemaddict on Nov 26, 2016 at 12:27pm PST

Motor spinny!!! (Hopefully you can see that with/without an Instagram acct)

However, then I attached the throttle, twisted, and got nothing I spent way too much time testing all the wires, connections, and the throttle mechanism itself to no avail. It finally dawned on me that this controller has different voltage settings. Mine was set at 72v, but I was using a 52v battery. The voltage was below the Low Voltage Cutoff of the controller. To get to a lower voltage you have to open up the contrller and bust out your soldering iron again.

You can see the little blob of solder next to the "72v". You can also make out pads for 84v and 60v. To get to 48v, you de-solder all the pads. Thusly:

I first tried to pop the blob off with a razor blade. I don't know what metal contacted what, but I heard a pop and saw spark. The controller wasn't connected to any power source, so I must have discharged one of the capacitors. I checked the board over and noticed one of my "shunts" had blown off!

KT-3 is supposed to look like KT-1 and KT-2. A shunt allows the controller to know how much amperage is being used by the shunt's resistance. A common mod is to wrap copper around the shunts to reduce resistance, tricking the controller to releasing more precious amps (= more power!!!). Kinda like a bleed valve on a turbo motor... I thought I must have fried my controller, but I finally got everything hooked up and twisted the throttle and the motor jumped into action. It responded normally to throttle inputs. Its just clamped in a vice that isn't even bolted down, so i just tested the throttle lightly a couple times to make sure it worked and left it at that. I'm guessing the blown shunt will have reduced the amperage this controller puts out by a third. We'll see. I can easily solder in some wire in its place. This controller is supposedly capable of over 4000w, and my motor is conservatively rated at 1500w, so I'm happy to creep up on max power one mod at a time.

Next up, I have to do some welding on the frame to fit the motor. The axles have 10mm flats while the dropouts on the frame are 14mm.

I got some steel from McMaster.com and hopefully I can weld it in there straight and have some nice, beefy 10mm dropouts. Stay tuned....

In reply to problemaddict:

Nice!

I haz the electro-stiffy. Vehy nice!

This looks shockingly fun

Check your local bike shop for some axles spacers. Its a common item that 3/8"=10mm to 14mm. All of the old bmx bikes used the smaller axle size. Modern bmx uses 14mm, with a lot of the axles being hollow. Sorry you gotta cut and paste, I cant link for E36... http://planetbmx.com/shop/neptune-3/8-to-14mm-axle-adaptors.html

Good luck and love the project!
Paul

In reply to paulmpetrun:

Here you go. http://planetbmx.com/shop/neptune-3/8-to-14mm-axle-adaptors.html

I've got those spacers for the front, but they won't work on the rear. The axle has to be pinched in the flats of the dropouts to prevent the axle from spinning. Since the hub is the motor, the axle needs to remain stationary. If the axle spins, not only do you lose forward momentum, but you rip all the wires out of your hub motor! No bueno...

This option exists for $30/pair shipped:

http://yubabikes.com/cargobikestore/axle-adapters-rear-motors

But I've got $5 worth of steel plate and need to practice my welding anyway. If I fail, I can buy these adapters...