Build an Inexpensive Electric Bicycle

An electric bicycle can easily be built by taking an existing bicycle and adding five parts: 1) a motor, 2) a linkage from the motor to a wheel or pedals, 3) batteries, 4) a throttle and 5) a motor controller (the brain that regulates how much battery power to send to the motor based on the position of the throttle). Buying parts that work together is the hardest part. Here's the cheapest solution, which is a bottom bracket driven, non-freewheeling electric bike.

Steps

  1. Find a bicycle in good working condition to modify. Make sure it is comfortable and has good brakes. Any problems the bike has when you start are going to be magnified once it has 40 pounds of electric "stuff" added to it and an extra horsepower pushing it around. It'll be harder to stop and the ride will be rougher. Full suspension department store bikes actually work well, but you'll probably want to change the low-pressure knobby tires to some higher-pressure street tires (going from 35 to 65psi makes a huge difference! This is a cheaper way to get extra range rather than buying more batteries). For this bike build, you want a bike with some space in the triangle between the rider's legs.
  2. If your bike doesn't have multiple sprockets on the cranks (the part that your legs spins), you'll need one that does. Alternatively, you can get the crank and sprockets from another bike and transplant them to the side of *your* bike that has no sprockets.
  3. Get a rear rack for the bike. This is where your batteries will go. Want some extra storage capacity? You can use U-bolts and some cheap plastic, rectangular trash cans from a place like Big Lots. Just attach them to the side of the rack using the U-bolts.
  4. Find some batteries. You need to know the voltage of your battery pack before you start buying the other parts. 24 volts and 36 volts are very common voltages for electric bikes. You can go higher but all the parts start to get more expensive and harder to find. The easiest to obtain and cheapest batteries are small gel cell lead acid batteries often used in uninterruptible power supplies (UPS). These come rated at 12 volts and 7 to 12 amp-hour capacity. Car batteries won't work! First off, if they turn over, the acid can spill out. In addition, they're built to be used hard for a few seconds, rather than lightly for a long time, and they will not last.
  5. You’re going to need at least 1 amp hour per mile on a 36 volt system and wires to hook it all together. Multiple batteries can be wired together in "series" to get a higher system voltage and in "parallel" to get a higher system amp hour rating. Mouser.com stocks 12volt, 7 amp hour batteries for around $25 usually. Get some braided copper cable to attach the batteries together. Solid core wire like Romex (used for wiring household electrical stuff) will not survive the vibration of a moving vehicle.
  6. Find a charger for your 24v or 36v battery pack. You can probably get one at the same place you get the following items... (On the other hand, for lead acid batteries, a car charger will work, but you will need to charge each battery separately).
  7. Buy a motor with a bicycle chain sprocket on the output shaft. Most motors come with no sprocket or a sprocket that only fits No. 25 or No. 35 chain (which is used on go-karts and scooters). Sticking to bicycle chain will make your life a lot easier. The Unite MY1018 is available as a 250Watt-350Watt motor on several scooter parts stores online.
  8. Buy a "brushed" controller such as the YK42 from tncscooters.com.
  9. Buy a "hall effect" throttle from the same place you get the controller. It's more likely the connectors on the throttle and controller will match if they come from the same place. If in doubt, ask the store. Sometimes you need to buy the connectors separately.
  10. Buy some connectors for your batteries that match the controller also. This is usually difficult, so the backup solution is to get some Anderson Power Pole connectors from a place like Newark.com, cut off the connector that comes with the controller, and just use the Anderson.
  11. Get some 1/8" steel metal plate or 1/4" aluminum. Aluminum is much lighter and easier to work with than steel, but it's more expensive. The dimensions will vary on your bicycle's triangle.
  12. Get three large, screw operated hose clamps that can attach to the tubes on your bicycle. The tubing size varies so you'll have to measure it. These are likely called "stainless steel plumbing clamps" at your local big box home improvement store.
  13. 1/8" single speed bicycle chain OR a grinding tool and 3/32" multi-speed bicycle chain
  14. Master link for the bike chain (1/8" or 3/32")
  15. Some small washers and possibly replacement bolts for the motor (it has 3 bolts used to secure it to a plate; if you use aluminum, they won't be long enough because the aluminum is too thick)
  16. Wait for UPS.
  17. When everything shows up, connect it together. Attach the throttle to the controller, then the motor to the controller, connect the batteries together, and then connect the batteries to the controller.
  18. Here's how to link batteries in series (they're voltages add together, let's use 12v batteries as the example here): connect a wire from the + of one battery and connect it to the - of another battery. The - from the 1st and the + from the 2nd battery are now 24v apart!
  19. Here's how to link batteries in parallel (they're capacities will add, let's use 12 volt, 7 amp hour batteries as the example here): connect the + of the 1st and second batteries together and connect the - of both batteries together. The + and - are now still 12v apart, but the combined battery has a capacity of 14 amp hours!
  20. Be careful when wiring up the batteries. Don't ever make a complete circuit with the batteries alone (there should always be two wires hanging out freely!), they will discharge quickly, melting wires, leaking, burning your fingers, and possibly starting a fire!
  21. Turn the throttle. The motor should spin. If it doesn't, recheck all the connections. Be patient, a wrong move here can be costly.
  22. After it all works, WRITE IT DOWN!!! You'll forget by the next morning.
  23. Okay, it's time to get building. The idea is to mount the MY1018 motor in the triangle formed by the bike's frame and attach a chain from the motor to a crank sprocket. Which sprocket? The choice will depend on alignment.
  24. Test things out by holding the motor in place and looping the chain around the crank sprocket and the motor. The master link is used to connect the two ends of the chain together, but only every other link can be replaced with a master link, so make sure the motor is positioned correctly. It should be snug but not tight. If it is loose or sloppy, it will tend to fall off during hard acceleration or going uphill.
  25. If it all looks good, hold the metal plate up over the triangle and the motor. Get out a sharpie and draw where you will need to cut the plate for the motor to fit and for the plate to fit on the bicycle. The motor will bolt to the plate, and the plate should touch the bicycle's frame at 3 points-- any less and it will not stay in place.
  26. Get out your reciprocating saw and start cutting. A grinder will help clean things up. A hand file is time consuming but works too, especially on aluminum.
  27. Test mount everything again. You'll probably have to go back to the grinder again a few times.
  28. If you've got that all sorted out, go and drill the holes for the motor in the plate. It's very hard to get all 3 holes just right the first time around, just try to get two right and then re-drill the 3rd hole until it lines up. You might need to get the grinder back out again.
  29. Now mount the plate and motor to the frame. Remember the three spots that touch the frame? Now you'll need to drill or cut holes at those three points so you can attach the plate to the frame using the hose clamps. A dremel with a cutting wheel works very well. A drill works too but requires making a lot of holes in a straight line.
  30. Once you have it all mounted, get your chain on around the motor and crank sprocket. Either use a chain tool to shorten the chain or cut the chain (the cheap Walmart chain tools will work for two or three uses). You can remove the damaged link with a nail, hammer, and a vise.
  31. Now you have a bicycle with a motor mounted in the frame triangle and attached to the pedals. You can no longer change gears on the front sprocket because then the two chains would collide, so adjust the shifter to prevent this from happening (or just cover it with duct tape). Once all the "mechanical" pieces are worked out, go for a test ride to make sure nothing is stuck and the chain doesn't fall off.
  32. Attach the controller either to the rack or to the tubing somewhere. Zip ties are perfect for this.
  33. Mount the throttle. The hardest part about mounting the throttle is getting the hand grips off. There's an easy way to do this. Get something thin and stiff-- an old bicycle spoke or coat hanger are perfect-- insert it between the grip and the handlebar, then pour some 50/50 water, and dish soap mixture down the coat hanger. It will work its way under the grip, you can then twist it around, and it will come off.
  34. Slide the throttle onto the handlebar. Usually, there is an allen head set screw to tighten the throttle to the handlebar. Tighten it.
  35. Attach the wires from the throttle to the controller.
  36. Attach the wires from the motor to the controller.
  37. To test things out, turn the bicycle upside down (or otherwise ensure that the wheels aren't touching the ground, even if the bicycle shakes violently). Attach the battery pack to the controller per the instructions that came with it. Twist the throttle. Does the motor spin? Does the bicycle's rear wheel spin? Let go of the throttle. Does the motor stop spinning? If you didn't secure the wheels off the ground, you might now find the bike taking off across the garage without you on board.
  38. Attach the batteries semi-permanently. You'll probably need to make some revision after riding a few times.
  39. Use zip ties to secure the wires from falling into the chain. Duct tape doesn't hold up in the sun and rain, and it leaves a gooey mess behind.
  40. Unless you are very meticulous or lucky, there will be some chain alignment problems. This is where washers come in handy. To be honest, you'll find things stretch after riding for a little bit, so you'll probably have to make adjustments after the first few rides, so don't expect to ride to a job interview on your first trip or anything else important.

Tips

  • Hard acceleration will use up the batteries the fastest, especially from a dead stop.
  • Charge your batteries after riding, and try to avoid wearing them down all the way when possible. They'll last a lot longer.
  • You'll want an on/off switch for your bike eventually. You will need a 24v or 36v DC switch. Household light switches will also work, but will not last very long.
  • Having two chains by your legs just makes it twice as likely that the bicycle will eat your pant leg. Use rubber bands or straps to secure your pant leg, or install chain guards.
  • Chain tensioning can be a problem. You need either to crank the hose clamps down hard or use something to tension the chain such as an old derailleur.

Warnings

  • A 36v controller won't run off 24v batteries and vice versa, so make sure the voltage rating on your components matches.
  • Wear gloves and safety goggles when working with power tools.
  • 24 volts or 36 volts probably won't kill you unless it touches an open wound. However, if you ever short out a battery it can certainly burn your fingers.
  • Always test the bicycle with the wheels off the ground. Sometimes when you connect the battery the motor will go full on and the bicycle can take off across the room.
  • Watch your fingers when working with chains. Never bring your hands near moving chains; they have a tendency to pull your fingers into the machinery.

Things You'll Need

  • Sharpie
  • ruler
  • sawzall
  • chain tool
  • grinder (optional, but very nice)
  • drill
  • wrench
  • pliers
  • soldering iron
  • duct tape

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