Introduction: Electric BMX Bicycle

Picture of Electric BMX Bicycle

Step 1: Frame

Picture of Frame

The first thing to decide when making an e-bike is which frame to use. When choosing a frame, keep in mind that the size, material, and rim options. If you are going to weld mounts to it, look for frame that are steel and not aluminum. Also keep in mind that usually only 20in BMX rims and road bike rims have threads on both sides to mount an additional sprocket to. I chose a BMX frame because it it's steel, has rims I can mount to, is light weight, and compact so it can fit into a car.

Step 2: Electronics

Picture of Electronics

The next thing to consider is what electronics to use. Keep in mind price, size, speed and distance you want to travel on one charge. I was given my electronics for free so I did not have any options, but my bike has:
Motor- 500W 30A
Battery- 26Ah sealed lead acid
Speed Control- Alltrax 300A 24-48V
Throttle- Currie 0-5K ohm potentiometer thumb

Step 3: Mounting

Picture of Mounting

There is a few ways to mount electronics, you can bolt things on or weld usually. I used 1/8in thick L-bar from Ace Hardware. I measure out the batteries and welded 2 mounts that the batteries fit snugly into. I then made a similar mount for the motor with slotted holes drilled for the motor to change chain tension. Once the mounted were made, I measured and sanded the frame where they will be fitted. The final step I did was masking the frame off so I could paint over the unfinished metal components.

Step 4: Drive Train

Picture of Drive Train

This can de difficult, but with a little research, you can usually find a hub that has threads on both sides allowing for a sprocket on the left and right. Because the thread is both right hand, you need to make a key on the left side of the rim so it doesn't unscrew. I filed a small notch in the freewheel, threaded it on, and and drilled a c shape in the hub where notch sat. I then cut the solid end of the drill bit off and used it as the key as you can see it sticking out on the picture. The sprocket, chain and freewheel were all from tncscooters and cost about 30$.

Step 5: Chain Tensioner

Picture of Chain Tensioner

On this bike I had to make a chain tensioner to clear the frame. To make it, I cut the end off of an old scooter motor I found in the garage (sprocket side) and removed the 2 bearings out of the motor to side on the shaft I cut of. I peened off the cut end so the bearings wouldn't fall off, and finally secured it to the frame by using 2, 1inch hose clamps. (Make a chain out of the 2 and tighten one around the 2 bearings and the other around the frame

Step 6: Mounting Batteries

Picture of Mounting Batteries

Once the frame is welded up, you can secure the batteries a few was, I used stainless steel hose clamps (2foot long) and wrapped 3 around each battery and the mounts I made. Large heavy duty zip ties is a slightly cheaper alternative, but not quite as strong in my opinion.

Step 7: Speed Control Mount

Picture of Speed Control Mount

Because I will soon take of my overkill of a speedo, I decided to bolt on a mount instead of weld a mount on. I cut some 1x1/8in aluminum bar to the same width as the speedo and countersunk a hole in the middle for the mount screw. Then I drilled 2 holes in the top of the frame between the batteries to mount the bracket. Once it was on I bolted up the speedo.

Step 8: Wiring

Picture of Wiring

When wiring take into consideration the amp draw your project will take. For mine I used 10awg wire all around and soldered at all points. I also shrunk wrap any exposed points to eliminate and arcing that may be caused. I also wired each battery to deans plugs. That way you can unplug it when you're not using it, and it makes charging easy. I'm using a harbor freight car charger, so I wired it to plug right in and charge the 2 batteries in parallel.

Step 9: Test and Tune

Picture of Test and Tune

Once the project was done, I fine tuned the motor by cleaning the com and playing with timing to optimize power. I also aligned the chain better and played with the brakes to cope with the added weight. Finally I added a light and speed gauge to help with testing.

Step 10: Results

Picture of Results

The bike now does 29-30mph on flat ground and has a range of 13-20 miles depending on how hard you ride it.

I've never posted on here, but if you have any questions feel free to ask if it's possible.


Step 11: Resources

Bike- $40
Statru Rim- $50
Steel- $32 ace hardware
Motor- $60
Batteries- $40-60
Thumb throttle- $50
Alltrax speed control- $300

I got all the electronics from a friend. A 100A speedo is more around $40 and would still be plenty of power for such a small motor.


NickeyV (author)2017-11-26

How is the wiring done? I'm building by scratch and I need help on wiring since I'm working with those 6v battery packs from family Dollar... I'm combining 2 of them to make a stronger one. Jus to wire or connect that to an electric weed eater???

Ethan1976 (author)2017-01-22

how to make a motorcycle like throttle OR, a hybird (idk), can be used like normal and electrically, i mean. when the battery runs out, you can just ride it like a normal bike

michaelmonaghan (author)2015-04-24

Yeah you can always email me at

Velvelkjell (author)2015-04-24

Wooohoo man:) that's one NICE instructable:) thank you so so much for this you've just saved my year and probably a lot more;) I've been thinking about how to make my downhill bike into a ebike without breaking the bank :) is it possible to brainstorm and share some ideas on mail ? Best regards Kjetil

dennis.setiadiprajoko (author)2015-04-22

how to make a motorcycle like throttle OR, a hybird (idk), can be used like normal and electrically, i mean. when the battery runs out, you can just ride it like a normal bike

michaelmonaghan (author)2015-03-12

If you would like you can email at and I'll send you everything in a word document.

birdsloper (author)2015-03-12

i was looking to reference it and start building my own. Needed for transportation and it is so small as well as battery powered, I can keep it inside.

michaelmonaghan (author)2015-03-04

Doing a version 2.0

birdsloper (author)2015-03-04

What happened to the pitbike build? I know i saw it here? Maybe?

michaelmonaghan (author)2014-07-23

michaelmonaghan (author)2014-07-23

It really depends on what you want from them and your price range. The sla batteries are big and heavy, but they're also bulletproof compared to lithium which sometimes catch fire randomly (had it happen to me once) also keep in mind that a 20ah sla has less capacity than a 20ah lithium at a high discharge rate because they loose efficiently with anything over around 1amp. To make a bike feel lighter with sla batteries you should also place them as close to the front wheel as possible (that way it won't feel heavy when turning). I also made a 15hp pit bike with sla batteries and it works great as still has plenty of range.

Qrys13 (author)2014-07-22

I have an electric bike hub kit and I'm torn between lithium and agm sla for the batteries?

Wondering about your experience with sla? I'd rather do that than spen 500$+ on a lithium.

neklausk (author)2014-04-06

nice sandals man

michaelmonaghan (author)2013-10-01

I am currently working on an electric motorcycle that will be posted soon. Unlike the bike, it will have a purpose built machined out chromoly cradle frame for all the electronics. I'm still working out all the parts on AutoCad, but will start the fabrication here soon, so keep a look out for an electric dirt bike!

michaelmonaghan (author)2013-10-01

How do you post videos on here? I can do it this weekend. And yes, there are better electronic designs, but I got all the electronics for free from a friend.

Hallofo (author)2013-10-01

Awesome build! Have you had a chance to post a YouTube video of it in action?

astral_mage (author)2013-09-21

keep up the great work. also if u could post wat it cost u and or linked to where u get all yr parts as well?

padbravo (author)astral_mage2013-09-29

BTW: You write something about the motor that is AC? so, U use an inverter? or is a typo?

astral_mage (author)padbravo2013-10-01

try using a dc to dc converter of the correct range.

jwall18158 (author)2013-09-29

Just curious about something. Couldn't you use the existing sprockets and take advantage of the gears and increase your speed?

olmon (author)jwall181582013-09-30

That can be done but #1. you would need for the freewheel to be in the crank VS the rear wheel. These are available from Schwinn, (I have 2) but are not common. #2. To utilize the speeds that could be attained with more powerful motors & the multiple gear ratios, you would definitely need a bike with disc brakes AND suspension. Disc brake hubs can be purchased & your choice of rim size spoked up on them. #3 It would be necessary to run the motor through a primary chain to a jack-shaft to get the gearing in a range that would be usable and also to transfer the drive to the secondary chain to enable the use of the rear derailleur for the multiple ratios. Nothing all that hard or complicated, but still more to figure out than what has been done here.

Another thing to keep in mind is that most states limit the legal top speed of motorized bicycles to about 20MPH. Above that speed it may be considered (legally) a motorcycle & come under all the licensing & equipment rules that pertain to motorcycles.

Gelfling6 (author)2013-09-30

An alternative mount, I used to have a mini gas powered conversion engine (AKA Happy-Times, looked like a miniature motor cycle engine, 2-Cycle, and highly DANGEROUS! (manual clutch, pop-start, not to D.E.E.P. compliance standards)) that mounted to the wheel sprocket that was held through the spokes with a pair of neoprene rings and a split ring. The center of the main sprocket, fit snug against the center hub.

jtechian (author)2013-09-29

Nice work. One thing you should consider, Brakes. With the speed and weight increase, You might consider retrofitting some disc brake to this rather then the caliber ones. Also I would consider putting the batteries on a saddle rack behind the seat with the motor. Or distribute them front and back for balance. Keep at it, you are doing great.

criggie (author)jtechian2013-09-29

BTW "caliper" unless you're talking about bullets or ebook software.

jtechian (author)criggie2013-09-29

Yes sir officer !
It was understood what was meant.

criggie (author)jtechian2013-09-29

-grin- I tried fitting my two 9AH batteries to the bottom part of the frame, just above the crank... it was a mountain bike so I used the drink bottle mountings and this kept the battery about as low as possible on the bike.

Downside was the motor was 250W which is the legal maximum here, and it barely pulled itself forward empty, let alone with a rider on board.

Its now a project for another day.

jtechian (author)criggie2013-09-29

Were the batteries wired in series or parallel? As it sounds maybe you feed 12 volt to the 24 volt input.

criggie (author)jtechian2013-09-30

Nope - I had 25.5V at the leads from the batteries to the controller. And the controller says "minimum voltage 20.5V"

So I wired a 24V DC power adaoter straight to the battery input leads and it was still useless, generating about 4-5 KG of pull at the wheel rim, measured with a spring balance and the wheel in the air.

I think 250W is just too little, or my motor or controller is naffed.

jtechian (author)criggie2013-09-30

You said 24 volt adapter? Why did you put this in line, as the motor controller would be fine without it. Also did you use heavy enough wire from your battery to controller? This sounds from what you said about no power from the motor, it is not getting enough amperage from them batteries. Have you tried also a different set of batteries to test? Perhaps as a static test use 2 car batteries to temporarily test it. You should not need any kind of voltage limiter (adapter) for this, and even if you did have a limiter, it would have to pass 50 amp to work proper. I have a couple E-scooters with 250 watt motors and they pull my 200 pounds around fine :) Hope you get yours working.

kmpres (author)2013-09-29

Great job for a first attempt! I'm sure you'll find many ways of improving the design as you ride the bike and further the research. Others have noted the problem with the brakes and position of the batteries. I would add that the sharp corners of your angle-irons should be ground down as you don't want to ram a knee or other body part into them in a minor (or major) road mishap. Also, there is a way to really streamline the design with no batteries on the center bar, a much smaller speed controller, and almost invisible motor. For a motor and speed controller combo you could use a variety of devices normally used for model airplanes. They are very rugged, very strong for their size, can withstand 180 amps or more in bursts, and the speed controllers are only about 2"x4"x1" in size. The motors are only slightly larger than that. Total weight is maybe five pounds. Brushless motors give the best power to weight ratio and weigh far less than the big one you have behind the seat. Use a "servo tester" for the throttle (designs for building your own are online and very simple to make). If you use lithium batteries you can save lots of weight, get just as much range and power, and are so small they'll fit in a pouch under the seat instead of in the way of your knees up front. The only disadvantage is the cost. FYI: Some online e-bikes now have the motor built into the hub, either front or rear, and some people have installed motors in both wheels. Again, great job, and I hope you improve your design!

Eternal_Tristan (author)2013-09-29

Can haz video?
I want to see it go!

michaelmonaghan (author)2013-09-29

There are 23Ah batteries (compared to my 26Ah that are almost half as wide. I'll be using these in my 15hp electric pit bike I'm making right now.

15hp motor? You mean 1.5 right? If your right @ 15hp, what motor is it? That's close to 10,000 watts and your batteries aren't gett'in it. ;)

pecefrogg (author)2013-09-29

Wicked cool instructable. Nice work dude, and thank you for sharing. Like someone else mentioned, I was crying for a video of this in action at the end. If you get the chance to post one, you'd make some of us nerds happy. Thanks again. Way cool.

criggie (author)2013-09-29

Can you add some video? Specifically, taking off from stopped without peddling, on a flat surface.

michaelmonaghan (author)2013-09-29

The batteries are not it the way of your knees at all, but because they are so wide you toes will hit while pedaling if your feet aren't in the right place. Lithium would be the way to go, but cost about 4x as much per amp hour.

michaelmonaghan (author)2013-09-29

The brakes are a bit weak, but they are sufficient enough to lock up if you squeeze hard enough (even the front). I do like the idea of disc brakes way more, but would have to weld caliper brackets and spoke a new hub.

michaelmonaghan (author)2013-09-29

The reason I mounted the batteries near the front is for balance. Just like on a motorcoss bike where 70-75% of the weight is on the front. It help it turn in faster and keeps the front wheel planted a bit more.

TSJWang (author)2013-09-29

I want to make this so badly.
Everyone in China has these. Q_Q

nothoro (author)2013-09-29

This is cool, Im diggin it :)

danny3xd (author)2013-09-29

Well done Micheal! Really cool.

Jtechian makes a great point. You really want good brakes, front and rear.

There is a product called a "ragjoint" that is used to attach a sprocket to the left side of a bicycle wheel. Or some specialty adapters so you can use any style of wheel or bike.

Again, uber cool and thanks for posting

Zaphod Beetlebrox (author)2013-09-29

Would it be possible to use li-ion batteries rather than lead acid, so that you're knees would have space?

srsys (author)Zaphod Beetlebrox2013-09-29

Checkout laserhacker's miniboost pack. The caps and lithium polymer are expensive and the specific caps he uses may not be available but it's an option.

jorge171085 (author)2013-09-29

patetic bike

bremus (author)2013-09-29

I'm glad you added that line about not needing a 300A controller. I'm pretty sure a you don't even need 100A. Something like 30-50A should do.

TedRobotBuilder (author)2013-09-29

Nice! But aren't the batteries right where you knees need to be? O.o

michaelmonaghan (author)2013-09-24

And what's not easily removed?

astral_mage was responding to/expanding on your comment about zip-ties.

{A tip on answering questions/comments; there's a 'Reply' button at the top-right of each one. If you use that, the person gets notified of your response, and can respond back in the same way, if necessary.

Make sure, however, that any response to this is done via the Reply button on my comment, NOT the one at the top-right of your own...

So, astral_mage could have told you about their comment on zip-ties, rather than potentially being left thinking you were ignoring them. And a similar thing could be said for the other replies you've made.

Also, if you look throught the published Instructable, you will see that peoples' comments are repeated where they originally posted them - which is how I know astral_mage was commenting on.}

michaelmonaghan (author)2013-09-26

Yes, I'll look up the part # of what I put on it. And thank, I didn't see that mistake before!

michaelmonaghan (author)2013-09-26

Yes I do need to put a roll cage around the batteries, the bike has fallen on then twice already. But I'm just starting on designing a 15hp electric pit bike right now, so the bike will have to wait.

About This Instructable




Bio: I'm a recent college graduate in the fiend of mechanical engineering that is is still in search of employment. In my free time I ... More »
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