How to Build A 35mph Electric Bike on the Cheap

Here at Fabricate, we like moving fast. We also like quick hacks that people can afford. So when we found that we could retrofit a standard road bicycle with a 1kW motor for $750 (compared to thousands for a standard electric bicycle conversion kit), we were sold!

The DIY Electric Bike Conversion Kit:

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As with most large purchases, this is one you'll want to do online - we found a very affordable electric bike kit that get you a 40V 1kW hub motor, controller, LCD display, throttle, and weatherproof rear bag. The wheel even has an inner tube, so you simply have to add some air and the wheel is ready to go!

The other expensive item was a battery to drive the motor; we went with a 20Ah 48V battery that only cost $400 and came with its own charger. It's massive, heavy, and doesn't have any kind of wire connector at the end of the leads, so a little soldering and a leftover connector pulled from spare parts were required to get it mated with the power connector on the controller. That being said, it's cheap, and has a lot of capacity. You could also try running your bike with 4 LiPo batteries in series for $140, but you'll only get 3Ah of capacity.

 

Installing Your Electric Bike Kit:

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Installation is fairly simple if you know what you're doing... but we were still learning when we attempted the kit for the first time. The instructions provided with the kit didn't actually match the parts we received, so we had to guess a few steps. We removed the front wheel, bolted the hub motor in place, attached the display and throttle and ran all the wires to the back of the bike where the rear bag was Velcro'd into place.

A quick test while suspending the front of the bike read a speed of over 40mph! Unfortunately we didn't secure the front wheel well enough... it slipped off slightly, juked, and damaged the internal hall effect sensors that track the motor's rotation. After another week's wait and one replacement wheel later, we were good to go - it was time to take it on the road!

 

Impressions:

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We did a quick test outside in a parking lot to get a feel for the handling. Let me tell you - people stop to look at this thing. During our parking lot test we had several people ask about the motor and how it worked, and we were only testing at around 10mph!

We took it to a circular bike track nearby so we could safely test it at higher speeds. Without any pedaling we managed to hit a reliable top speed of 32mph - and on a bicycle, this is wind-whippingly, eyes-dryingly fast. It was actually hard to lean into turns due to the gyroscopic forces on the wheel!

If you'll be taking this on the streets, you'll want to have good brakes - disc brakes are preferable, but if you're upgrading an old bike (like we did), you'll want to check with your local bike shop to brakes capable of handling the extra weight and speed.



Conclusion:

We set out looking for a powered way to get around without breaking the bank, and we succeeded - for half the cost of an entry level motorcycle and without the cost of gas, licensing*, and insurance, we now have a street legal bike that'll get us from A to B with minimal effort. 

Feel free to comment below if you have any questions!

 

*A note on licensing (thank you to Aidan Garnier for pointing this out): different localities have different regulations when it comes to electric bikes / motorcycles. Make sure to call your local DMV before taking it out on the streets! Fortunately, the kit does come with the technology to work with the two most common rules - a maximum speed limit, and controlling your speed via peddling (Peddle Assist) instead of with a throttle.