Building an Electric Bike, Part 1
Where Do You Live?
Hybrid cars are increasing in popularity. You know, they’re the ones that combine battery electric power with a petrol engine. With their on-demand high torque electric bike motors and effective regenerative braking, hybrid cars are fun to drive and incredibly economical. But for even the cheapest new hybrid you’ll need to hand over about AUD$30,000.
So maybe a amalgam car is out of the question, but what about a amalgam bike? Yes,you can add battery electric assist to a bicycle with a bit of ingenuity. It won’t rocket you up hills at an absurd clip but it will accommodate abundant advice for your annoyed legs. On flat roads, well, you can stop pedalling. And aback you arch downhill, balloon the caliper brakes – instead, adorning braking will apathetic you bottomward and at the aforementioned time, put allegation aback into the battery. That’s power that you can then access at the next hill!
Sound good? It is!
And for those of you with driving licenses that are, um, a bit tenuous, an electric bike might be the answer to your short-term mobility needs!
The Cost
The bike that you see here was electrified for initially under AUD$120. However – and it’s a big ‘however’ – that cost includes lots of bits that were scrounged for near-nothing.
Most of the drive system, comprising an electric motor, heavy duty cables and high current switches, were obtained at the shop at the local rubbish tip… so apparently amount beneath AUD$5 for the lot. The battery charging system - two 1-amp 13.5V plugpacks and dropping resistors – were also got for near-nothing. The motor abutment and array trays were fabricated from aluminium sheet, aboveboard tube and bend which was bought from a atom metal banker – say addition AUD$5. In fact, the only big buck items were the two new 12V Sealed Lead Acid batteries – these cost AUD$45 each. (But then I splurged on an ammeter and a electric bicycle computer!)
So this alternation doesn’t awning in step-by-step detail how to add electric ability to a bike application apparatus that you can buy at the bounded shop. Instead, it shows how it was done application the genitalia that I could lay my easily on at the time.
However, the acquaint – the successes and failures – are illuminating. In fact, I sure wish I’d read these articles before starting work! (And of advance if you ambition to buy aggregate new, there’s annihilation to stop you – it will aloof amount more.)
The Overall Design
The bike you see actuality is absolutely the third electric bike I accept congenital over the years. So I speak from experience when I say it’s easy to overcomplicate things, make the system too heavy, and not provide enough power.
To put things another way: an electric bike needs to use a mechanism that’s light, simple and powerful. It sounds obvious, but it’s not!
The simplest, most readily available powerful low voltage electric motor is a 12V brush-type permanent magnet motor. That’s the blazon acclimated in car windscreen wipers, amateur motors, electric hydraulic anchor boosters and electric ability steering. It’s also the type of motor most commonly used in electric scooters and cheap electric bikes.
Click for larger image
This breed of motor has several characteristics that make it useful in this application. It’s common, low cost, can act as a motor or a generator, and its ability increases rapidly with accretion ascribe voltage. So in this design we use a 12V perm mag brushed motor.
The abutting footfall is to drive the bike assiduously with the motor. Two requirements need to be met: (1), because the electric motor spins a lot faster than we want the bike wheels turning, we need to gear it down, and (2), we have to find a way of connecting the output shaft of the motor to the wheel.
Both problems can be apparent in the one footfall by application the motor to drive a baby bore roller which is brought to buck on the footstep of the tyre. Again, it’s simple, cheap and effective.
Sealed Lead Acid batteries, although heavy and without the power per kilogram of more modern battery designs like nickel metal hydride, are widely available and (again those words!) simple, bargain and effective. They’re the ones we used.
Leave a Reply