Introduction: Electric Bike - the HARD Way

About: I like to do electronics, metalworking, woodworking, fixing things and all sort of cool and stupid things :) I also have a YouTube channel:

I always wanted to make an e-bike.

So I built this frankenstein bike as a proof of concept.

Long story short - no ebike kits and no hub motors.

Here is a short introductory video showing how it works and how it was made:

I will further describe the fabrication process in this instructable.

Step 1: What I Wanted to Do

I wanted to build an affordable e-bike using stuff I could easily get. But without hub motors and other bolt-on kits.

Either the hub motors were not good enough or they were too expensive.

I always wanted to be able to have some gearing option so that I could set the top speed according to the type of terrain I will use the bike for. If I will be using it for hilly areas, I could reduce the gearing so I will not need to touch the pedals uphill :D At flatland I could use longer gearing for maximum top speed.

Step 2: When Life Gives You Electric Motors

My friend went to the local car junkyard and found an electric power steering motor from some small hatchback and brought it to me as a gift.

After some research online I found out that this is a 12V three phase brushless motor rated aorund 300W to 500W.

It had a weird coupling shaft, but I also managed to find the coupler for it.

But I knew that it would take a lot of work to make everything work.

But that did not stop me!

Step 3: The Controller

I wanted to have a little more power ot of the motor as I knew that automotive parts have some reserve in them.

So I decided to run it at 24V in order to get some more speed out of it.

I bought this cheap controller:

It pulled around 20A of current which is around 500W.

I also modified it with slightly better transistors to push it to 30A and tinkered with components I could get 700W of power out of it reliably. That should be enough for pedal-free cruising at 30km/h.

You dont need to use the exact same controller, I chose this one because it weas the most powerful 24V e-bike controller I could find for a cheap price.

I also bought a cheap thumb throttle, because my bikes handlebar was not convenient for twist throttle because of weird bike gear changing mechanism on handlebars and I couldn't fit twist throttle:

Step 4: The Transmission

This was the tricky part.

The motor without load had maximum rotating speed around 2700 rpm. But the the bicycle wheel rotates around 160rpm at 30km/h. So I needed to reduce the rpm by a factor of 17.

This is a lot to do in one stage - imagine using just 2 sprockets - one 10 tooth and the other would have to be 170 tooth. It would be almost half the diameter of the bicycle wheel!

So I was searching for an affordable rpm reducer. The industrial ones cost in hundreds of dollars which is too much.

So I came to a crazy idea of using a gasoline pocketbike transmission. This way I could utilize the ratio of the gearbox plus the wide range of available chain sprockets for pocketbikes. And the best thing was that it costs under 25usd!

Inside there were two metal gears, with the speed reduction factor of 4.5. Which is good.

Speed reduction of a 2 stage system can be easily calculated. You just multiply the reduction of each individual stage. Lets see how I calculated mine:

Reduction total = reduction_1 * reduction_2

The pocket bike transmission has reduction ratio of 4.5. The total reduction I wanted is 17.

So: 17/4.5 = 3.77

So, for the final gear ratio of 17 (chosen for 30km/h top speed) that left only a 3.8 reduction with external sprockets after the transmission. I managed to do that with 54 tooth sprocket at the wheel and 14 tooth sprocket at the transmission. (54/14 = 3.84)

Here I bought the sprockets:

And the chain:

Step 5: Transmission Modification

Of course I could not just bolt the transmission to the engine without modification.

First I needed to remove the clutch bell, because I dont need clutch for electric motor.

And then I needed to make a coupler for the motor shaft.

As you saw from the video, I used lathe to make a simple-ish screw on coupler

With a little of plastic in between the metal shafts, there is some wiggle room for the shafts. Because it is nearly impossible to mount two shafts exactly parallel, so the plastic gives up a little so there are no big forces present that could eventually either destroy the bearings or causde a shaft to broke off.

I also made a simple distance bushing between the motor and gearbox, to compensate for a little longer shaft. And I also used that part for mounting the assembly onto the bike.

To make it, I used the CNC router, but I could just as well cut it out by hand with a saw.

Step 6: Mounting Sprocket to Rear Wheel

That was also a bit tricky to do, since my bike was an old junk I had in elementary school 15 years ago and it does not have disc brakes.

So I needed to make a mount for the sprocket from scratch.

I made 2 plastic pieces with my lathe that hugged and sandwiched the spokes in between. I overengineered this a little and tried to catch the angle of the spokes on the plastic bits.

The inner one was then cut in half with a saw in order to get it to the inner side of the wheel and then I bolted everything together. IT works like a charm. The sprocket is dead centered.

Step 7: Making the Motor Mounts

As you could expect, the motor had to be mounted somewhere.

Initialy I wanted to put in above the pedals for optimum weight distribution, but the motor with the transmission was too wide and it would interfere with pedaling.

So I mounted it above the rear wheel. I constructed the frame to go around the wheel and mount itself on the wheel shaft. I think it came out quite good.

It was a lot of welding and grinding with my basic stick welder.

Step 8: The Chain Tensioner

The dificult bit was to make a some sort of chain tensioner which would lift the whole bracket a little bit higher in order to apply the tension on the chain.

A little bit of welding and grinding, this came out quite nice. It is basically a threaded rod which lifts the whole thing with two nuts.

Step 9: The Battery

I designed a simple stainless steel battery box which would hold pouch cells that I managed to salvage from an old electric scooter. The batteries were still good enough for a lower powered bike. I just had to cut the PCB to smaller size in order to use it for my bike.

I went to 24V, 6 lithium cells in series, 3 in parallel, giving me a little bit above 20Ah of capacity, which is plenty for over 40 kilometer range.

I designed the box in 3D software and got it cut on a laser. The box has a combination layout D-SUB connector with two power pins for main power lines and a bunch of smaller signal lines used for accessing all cell voltages for balancing with a regular hobby RC charger.

I also included the automatic 50A fuse used for car HiFi systems for safety. It also has a litle swithc lever which is great to use for disconnecting everything when not using the bike.

Step 10: Making the Battery Mounts

Not much to say. again a bunch of welding :) I wanted to mount the battery between the handlebars and the seat. That was the only available place to put it.

I also bolted the controller on the side of the frame.

Step 11: Final Details

I assembled the motor, mounted the chain and I figured that it would be very dangerous to put the finger between the chain and the sprocket during driving,

So I 3D printed a simple cover to keep my fingers safe.

Step 12: The Finished Bike

Behold the magnificant electric bike!

It came out quite interesting. What do you think? Not bad for a frankenstein build :)

Step 13: The Charger

I wanted to charge the bike with a good and cheap hobby RC charger:

(affiliate link - you pay the same price, I get a small percentage for the future projects. You don't need to use it if you don't want to)

But these chargers are supposed to be powered from 12V, so I needed a power supply to convert from the mains voltage.

Luckily I had an old one laying around for years (it is used and got it for free) and it was a pleasure to use it. 15V and 400W was more than enough.

I used XT150 connectors for high power connections for charger and wiring around the bike:

Step 14: Making the Charger Enclosure

Again saving money and getting rid of stuff collecting dust on the shelf :)

I had an old telephone central which was obsolete, but the enclosure is very nice. And my power supply and charger fit inside very nicely.

I used my little CNC router to route the opening for hobby charger (see it in the video). Also drilled two holes for the fans and the enclosure was done!

Step 15: Additional Electric Upgrades

I added the power meter and analyzer. It shows the voltage, current and power used by motor and it keeps track of how many Ah have been discharged from the battery while driving, so I know approximately how much juice I still have in the battery. Very nice thing to have.

I also added the voltage checker in order to see all 6 battery cell voltages (affiliate link):

With that I would notice if any of the cells starts to die. The voltage on it would get lower than on the other cells. This way I would not overdischarge the cell and I could replace it when needed.

With that my instructable is complete. Hope you learned something new and I encourage you to build your own version of the electric bike, the HARD way!

And check my other instructables and other video projects on my youtube channel!


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