The e-Bike craze, get into it!

I have a regular rant and rave to bemoan the lack of an indigenous electric vehicle industry in this country every now and then but it seems there are plenty of folk working on EVs here, some even use them each and every day.

However, these aren't slick, carbon-fibre creations that go head-to-head on our arterials and motorways with regular sedans and hatchbacks. These are the e-bike builders and riders.

Over the past few months I've "bumped into" a surprising number of people who are cobbling together their own electric bicycles either just for fun, or as a viable way to actually save some money.

Perhaps it's time to do some brainstorming and see just what can be done by people with a few clues and a penchant for an electrified ride.

The good news is that just about everything you need to build an e-bike can be had online for a surprisingly small amount of money.

The bad news is that you're only allowed a pittance (200W) of power before you run into the hurdles of licensing and warrant-of-fitness requirements. It also wouldn't surprise me if you'd have to pay road-user tax as well, since electricity doesn't have such a tax already built into it like petrol does.

So let's look at the basics...

Obviously you're going to need an electric motor of some kind. The 200W limit means you'll only need a tiny motor -- unless you want to build a really practical e-bike and say "sod the rules" by fitting something a little bigger.

How small is "tiny"? How much bigger is "bigger"?

Well you might be stunned by the efficiency of modern brushless electric motors with rare-earth magnets. Take this unit for example. It will deliver just over the 200W legal limit for unlicensed e-bikes yet it weighs a mere 85g and is only 28mm in diameter.

Of course if you want some real "get up and go" power then there are units like this one that will deliver a stunning 6.5KW of power (that's almost 9 horsepower!).

Of course the most important component will be the batteries chosen to power whatever electric motor you choose and this is where things can get a little spendy.

The cheapest option would have to be the low-cost 12V 7AH sealed lead acid (SLA) batteries we've all seen used in alarms, UPSes and other applications. There's usually a steady stream of these batteries going for a song on TradeMe as a result of them being swapped out long before they're dead, simply as part of regular maintenance schedules. Most of these still have plenty of life in them and the last lot I bought cost just $10 each.

Next up you could go for a big block of NiMH cells such as these. However, creating a suitably sized battery pack from those cells would be a major soldering exercise and NiMH are "so last century" as a technology that they're probably not the best choice.

If they're good enough for Tesla Motors then these might be good enough for your e-bike but again, you'll need a few soldered up into a nice battery.

If you don't mind the risk of fire then lithium polymer (LiPo) packs are small, light and very energy-dense, as well as being available in a huge range of shapes, sizes and capacities

Perhaps the best battery technology however, is LiFePO4 but unfortunately, they're still a little spendy, even when you buy them from China, and some of the cheaper cells are not that good, to be honest.

Of course once you've got your motor and your battery, you're going to need some way of connecting the two so as to properly control the power delivered. Brushless motors can't just be hooked up to a battery -- that's because they're actually a multiphase AC motor. To make them work requires a bit of electronics called a brushless electronic speed controller (ESC).

Fortunately these are also an "off the shelf" item but prices vary immensely, depending on quality and current-handling capabilities. Generally speaking it's worth buying the biggest and best you can afford - the really cheap ones are often over-rated and not so reliable.

Unfortunately, an ESC needs to be fed a control signal which tells it how much power to deliver to the motor. This can be done by hooking up a servo tester and using the knob as a throttle. No doubt most people will arrange some kind of linkage from a twist-grip throttle to the little potentiometer.

Of course there remains the issue of transferring the rotary motion of the motor's shaft to the wheels of the bike but this is something that any "good kiwi bloke" can work out for himself. I've seen solutions as simple as just having the motor shaft rub on the bike's tire to a clever arrangement involving a sprocket, extra chain and sprag clutch.

One thing's for sure -- the internet is a mine of valuable information from folks that have already "been there, done that".

So, if you're keen to get an electrified ride, there's the info you need to get kick-started.

But remember -- you must write "190W" with a marker-pen on the motor of your choice so that if you're stopped by the cops, your bike will still qualify as a power-assisted bicycle and not a moped or motorcycle.

Is anyone inspired to build their own e-bike?

How many Aardvark readers have already built one? Care to share your experiences?

Who's ferreted out some interesting e-bike sites or video?

- AAP

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