You can easily build an electric bicycle starting from a normal bicycle and adding five parts: 1) the motor, 2) a connection between the motor and a wheel or pedals, 3) batteries, 4) the accelerator and 5) a controller for the engine (the "intelligent" element that regulates the flow of energy from the batteries to the engine according to the position of the accelerator). The hardest part is getting compatible components. This article illustrates the cheapest solution, that is an electric bike in which the motor is connected to the bottom bracket of the pedal set (without the so-called "free wheel").
Steps
Step 1. Get a bike in good condition to modify
Look for a comfortable one with good brakes. Any defects on the original bike will be magnified after the addition of nearly 20kg of electric paraphernalia and with the thrust due to a lot of extra power. It will be harder to brake and drive. A bicycle equipped with suspensions, of those commonly sold in department stores, will be fine but it will be better to replace low pressure tires and tubes with others capable of withstanding greater pressure (the passage from 2, 5 to 4, 5 atmospheres will do a huge difference). In order to make the necessary changes you will need a bike with some space available in the triangle between the legs.
Step 2. The bicycle must be equipped with a gearbox, those with more gear wheels on the pedal
Alternatively, you can take the sprocket assembly from another bicycle and mount it on yours, on the side of the pedal set opposite where the sprocket is.
Step 3. Get a rear bicycle rack
It will serve as housing for the batteries. If you want more capacity you can add sturdy plastic containers, fixing them to the sides of the basket by means of U-bolts.
Step 4. Get the batteries
You must know the voltage of your battery pack before buying the other parts. The most common voltage for bicycle batteries is 24 or 36 V. You can also use higher voltages, but then the parts will tend to be more expensive and difficult to source. The easiest batteries to find, and also the cheapest, are lead-acid batteries of the type used for small uninterruptible power supplies (UPS). They usually have a voltage of 12 V and a capacity of 7 to 12 Amp hours. Car batteries are not good. First of all, if they tip over easily, acid can escape. In addition, they are designed to deliver great power for a few seconds rather than extended use, and would not last long.
Step 5. You will need a capacity of at least 0.6 Amper-hours per km in a 36 V system, and cables to connect the various parts together
The batteries can be connected to each other "in series" to increase the overall voltage and "in parallel" to increase the amp-hours, that is the capacity. You can find 12 V and 7 Ampere / hour batteries online for around € 13. Take flexible copper wire, braid type, to connect the batteries together. Semi-rigid core copper cables, sometimes used for wiring in buildings, are not suitable for withstanding the vibrations of a moving vehicle.
Step 6. Get a charger for your 24V or 36V battery pack
You can probably find it in the stores where you buy the other parts. In the case of lead / acid batteries, a common car charger could also work, but in this case it will be necessary to recharge each battery (12 V) separately.
Step 7. Buy an engine that has a sprocket suitable for a bicycle chain keyed onto the shaft
Most engines are sprocketless, or have one for size 25 or 35 chains (which are used in go-karts and mopeds). One that is already compatible with bicycle chains will make your life a lot easier.
Step 8. Purchase the controller
An example can be the YK42 model from tncscooters.com.
Step 9. Buy the throttle (better if with Hall effect technology
It is easier for the throttle and controller to be compatible if they are produced by the same manufacturer. If in doubt, ask the shopkeeper for suggestions. In some cases the connectors are sold separately.
Step 10. Purchase battery connectors, possibly which are compatible with the controller as well
It is not easy to find compatible ones, so alternatively you can buy clamps for quick connections, of the type used by radio amateurs to connect to batteries (a popular model is the Anderson Power Pole), after which cut off the connectors from the controller cables, strip the wires and use the quick clamps directly.
Step 11. Get a 3mm thick steel plate, or a 6mm aluminum plate
Aluminum is much lighter and easier to work with than steel, but it is more expensive. The dimensions depend on the size of the triangle of your bike.
Step 12. Get three large, screw-adjustable hose clamps that are sized to fit your bike's hoses
They can be found in hardware stores or in DIY stores.
Step 13. 1/8 "or 3/32" bicycle chain
Step 14. False link for the chain (1/8 "or 3/32")
Step 15. A few washers and possibly new bolts to fix the motor (motors usually have 3 bolts for fixing; if you use an aluminum plate they will probably be too short because the aluminum is thicker)
Step 16. Wait for the delivery of materials
Step 17. When you have everything, connect the various parts together
Connect the throttle to the controller, then the motor to the controller, connect the batteries together and finally connect the battery pack to the controller.
Step 18. The series connection (used to sum the battery voltages) of the batteries is done as follows:
connect a cable from the “+” pole of one battery to the “-” pole of the other. At this point, assuming that the two batteries are 12 V, the voltage between the "-" pole of the first battery and the "+" pole of the second will be 24 V.
Step 19. The parallel connection (used to add the respective capacities) is done as follows:
connect the “+” poles of the first and second battery together, and then connect the “-” poles together. Now the voltage between the "+" and "-" poles of the battery pair will always be 12 V, but the overall capacity will be doubled (for example, if each battery had a capacity of 7 Ampere / hour, now the pair connected in parallel will have capacity of 14 Amperora).
Step 20. Be very careful with the connections between batteries
Do not close a circuit comprising only the batteries, without load. The two final connections must remain open. Otherwise you run different risks: rapid battery discharge, melting of the connecting cables, leakage of liquid, burns and fire. For the same reason, be careful: never connect, even accidentally, the “+” and “-” poles of the same battery.
Step 21. Rotate the throttle
The engine should start spinning. If not, check all electrical connections. Be careful, a wrong maneuver at this point can cost you dearly.
Step 22. When everything works, TAKE NOTE OF THE SCHEME
Otherwise tomorrow morning you will have already forgotten.
Step 23. Okay, now it's time to move on to the actual construction phase
The idea is to mount the motor in the triangle formed by the bike frame and mount the chain to transfer motion from the motor to one of the pedal gears. Which of these gears? The choice depends on the alignment of the parts.
Step 24. Experiment:
holding the motor still in place, fit the chain so that it goes from the motor sprocket to one of the sprocket sprockets. The false link is used to close the chain, however only one out of two of the chain links can be replaced by the false link; so make sure the motor is in the right position. The chain must be taut but not too tight. If it is too loose or badly positioned, it will tend to fall on acceleration or uphill.
Step 25. When everything looks good, place the metal plate on top of the motor and triangle
With a felt-tip pen, trace the contours of the shape where you will have to cut the plate, to obtain the place for the motor and to adapt the plate to the bicycle frame. The motor will be fixed to the plate with the bolts, and the plate will have to touch the frame of the bike in 3 points: one less and it will not stay still in its place.
Step 26. Take a jigsaw and cut the plate
A milling machine will be very useful for finishing. Alternatively, using a file will require much more work but will still be adequate, especially for aluminum.
Step 27. Make a new fitting test
You will probably have to do several touch-ups with the router.
Step 28. When finished, drill holes in the plate for mounting the motor
It is very difficult to make all three holes exactly right from the start. Don't worry, drill the first two holes and then fix the third with the drill. You may need another milling pass.
Step 29. Now secure the plate with the motor to the frame
Remember the three points touching the frame? Now you have to drill holes near these points, to pass through the hose clamps with which to fix the plate to the frame. A modeling mini drill with the appropriate wheel cutting cutter is the right tool for the purpose. You can also use a normal drill, from you will have to make several holes side by side until you get a slot to fit the clamp.
Step 30. When everything is assembled, install the chain between the motor sprocket and the pedal gear crown
Use a chain tool to shorten the chain, or cut off the excess links with pliers (however a cheap chain tool, from € 8 or so, is good for non-continuous use). Remove the cut ring with a nail, hammer and vise.
Step 31. You now have a bike with a motor mounted on the frame triangle and connected to the pedal set
You can no longer shift gears by using the front chainring, so adjust the shift to make sure this doesn't happen (or just cover it with tape). Once you have all the mechanical parts in place, take a test drive to check that nothing is stuck and that the chain does not come off.
Step 32. Attach the controller to the roof rack or somewhere on the frame
Plastic ties will do just fine for fixing.
Step 33. Install the throttle
The hardest part of mounting the throttle is removing the grips from the handlebar. Here is an easy way to do it. Get something thin and stiff (an old bicycle spoke or wire hanger is fine). Slip it between the handlebar grip and the handlebar tube, then pour a mixture of dish soap and water down the hanger. The soapy water will slip under the knob: at this point, just turn it a little and it will come off.
34 Put the throttle on the handlebar
Usually an Allen key has to be tightened for fastening.
35 Connect the cables that go from the throttle to the controller
36 Connect the cables going from the controller to the motor
37 For rehearsals, turn the bike over with the wheels in the air (or make sure that the wheels do not touch the ground, even if the bike vibrates strongly)
Connect the battery pack to the controller, following the manufacturer's assembly instructions. Operate the throttle. Does the engine run? Does the rear wheel of the bicycle turn? Release the accelerator. Does the engine stop? If you forgot to lift your bike's wheels off the ground, she's probably going around the garage by herself now.
38 Connect the batteries semi-permanently
You will probably need to make some adjustments after the first period of use.
39 Secure the connecting cables with plastic ties to prevent them from getting tangled in the chain
The adhesive tape is not resistant to sun and rain and leaves sticky traces.
40 Unless you are extremely meticulous or lucky, there will be problems with chain alignment
In this case the washers will come in handy. To be honest, you will see that after a few trips there will be some adjustments between the various parts, so you will have to do some tweaking. Don't think you can use the freshly assembled bike to go to a job interview or an important appointment.
Advice
- Sudden acceleration quickly discharges the batteries, especially when accelerating from a standstill.
- Recharge the batteries after use, and try never to let them fully discharge. They will last longer.
- It will be advisable to install a switch to turn the electrical system of your bike on and off. Use a 24V or 36V DC switch. You can also use a common household switch, but it won't last very long.
- Tensioning the chain can be a problem. You will need to tighten the hose clamps very tightly, or find some means (such as using an old derailleur) to adjust the chain tension.
- Now that there are two chains next to your legs, it also doubles the chance of your pants getting caught on them. Use rubber bands or something else to tighten your pants, or install chain guards.
Warnings
- Watch your fingers as you work on the chains. Never bring your fingers close to moving chains: they have a tendency to drag them into the gears.
- A 36V controller cannot work with a 24V battery pack, and vice versa. Make sure the voltages of the various parts are compatible.
- When testing your bike, always keep the wheels off the ground. When you disconnect the batteries, the engine may start at full speed and the bike may spin off.
- Wear protective gloves and goggles when using tools.
- The shock of 24 V or 36 V is probably not fatal except in special cases. However, if you short out a battery you can be sure of getting a good burn.
