An ebike wouldn’t be an ebike without the electrical bits and pieces that assist in pushing bike and rider along. After all, it’s the electricity that puts the ‘E’ in ebike.
At this stage of the project Mixt-E build I have been able to source the majority of parts that would normally go into a bolt-on DIY kit. But instead of simply buying a complete off-the-shelf kit, I did it the way any unorganised person would – one piece at a time. There was reason behind this round-a-bout way of cobbling together a kit. Put simply, the specific electric motor for the build wasn’t available in any off-the-shelf kit – or at least I couldn’t find one…
However, while my erratic stockpiling of parts wasn’t the way a sensible person would have gone about it, it did give me an opportunity to gain an understanding of all the componentry that makes up the electrical system of an ebike.
Hub Motor
For project Mixt-E the intention has always been to use a hub motor. One that would comply with local transport regulations, while also fitting in with the aesthetic vision of the build.
A hub motor is an electric motor that is housed within the hub of a wheel. In this case the hub motor will be connecting to the rim of the wheel via 36 spokes. The wheel assembly is installed into the rear dropouts of the frame just like any other conventional wheel, with cabling run directly to the motor from the battery via a controller.
A hub driven ebike could work without any gears, or chain, or even pedalling for that matter. All the electrical energy is within the hub without any actual requirement to be connected to the bicycle’s drivetrain. The disadvantage however of using this style of motor is that the gearing of the bicycle drivetrain is less effective in terms of the energy transfer from pedalling to the rear wheel. This is because the electric motor is positioned after the gears inthe bicycle’s cassette in the drivetrain system. This would be equivalent to putting the motor of a car after the transmission and connecting it directly to the driveshaft. It will still turn the wheels and make the car move, but without gearing to keep the motor within its powerband, it will have to work harder and with less efficiency.
For ultimate performance, a mid-drive motor would be ideal. This style of ebike motor leverages off the bike’s gearing and can therefore utilise differing gear ratios to keep the motor within the maxium torque range.
The main reason for choosing to use a hub motor, as opposed to alternatives such as a mid-drive system, was for its integration into the finished look of the bike. Hub motors, particularly one rated at relatively low wattage, are small in physical size and can almost pass for a normal wheel hub, or even as an internally geared hub such as a Sturmey-Archer hub. While those in the know will be able to spot this hub motor for what it is from a mile away, 99% of people will not even notice that the rear hub is actually an electric motor.
From what I can (anecdotally) tell, the most popular DIY ebike motors are those manufactured by Bafang. Founded in 2003, Bafang is probably the most widely recognised of all the Chinese emobility electric motor manufacturers. Although they are based just outside of Shanghai, they have sales and service centres globally and recently have opened manufacturing plants in eastern Europe. In recent years they have been producing well over one million electric motors annually, so it’s no wonder these motors are widely used in many off-the-shelf kits and DIY ebike builds.
The motor for this build is a Bafang JS-033 Bpm, a 250W at 36V rear hub motor. This motor is perfectly suited for DIY kits and retrofits to existing frames. The JS-033 features an alloy housing, internal planetary gearing, and 36 holes making it suitable for most wheel sets.
The main reasons for choosing to use this particular motor on the project were:
- A maxium 250W to comply with local roads and traffic regulations;
- Rear hub mounted, because front wheel drive bikes – no, just no;
- 36 holes for the rims that are being used;
- Chrome/brushed aluminium finish to go with the overall look of the bike.
To find a hub motor that met all these criteria proved harder than you might think!
This motor was found from a seller on eBay Germany of all places. Luckily they had a few of these new-old-stock motors available and, after some back-and-forth via Google Translate, they agreed to ship it to the other side of the planet to here in Australia. Gute Scheiße!
Unfortunately, finding out information about this motor has been a bit difficult. While there is stacks of info out there for more recent Bafang models, because the JS-033 is an older model and no longer in production there isn’t much info for this particular hub.
I tried reaching out to Bafang to see if they could provide the specifications for the motor, but they seemed reluctant and/or unwilling to provide any technical specifications or resources about this motor…
Regardless of this, it’s a good little hub motor that will suit the project perfectly!
Battery
As with any electric vehicle, there is a battery supplying the electrical charge for the electric traction motor. Ebike’s have a relatively small capacity battery that power the bike along its way.
The most important factor to take into consideration when selecting the battery for a DIY kit is to ensure the voltage is suitable for what the electric motor is rated at. While it is possible to ‘over voltage’ a motor for the purposes of increased performance, it is not advisable for the longevity and reliability of the motor, as it puts additional energyloads (mainly heat energy from the increased current) through the copper windings of the motor. This can cause damage to or even failure of the motor.
As the motor for the project is rated for 250 watts at 36 volts, a battery rated at 36 volts needed to be sourced.
Luckily I struck gold on FB marketplace! In this case it was 36V Li-ion gold! Finding a used battery, in great condition, for a decent price, that would suit the build perfectly. Also included was the charger. This was particularly important because as you can imagine, trying to source the correct charger for the battery would have been a pain.
This battery was originally on another ebike. The seller had taken the battery off the bike prior to locking it up for the night in the garage of his inner-city apartment. The ebike was then stolen in the middle of the night, without the battery, hence why there was a battery and charger being sold separately from a bike. However as a result of his bike being pinched, it was missing the mounting hardware for attaching the battery onto the frame of the bike.
As the battery’s housing is the same as countless other DIY ebike batterys, replacement mounting hardware was easy to track down and buy. While the dull, black plastic slab that is the battery isn’t the sexiest thing to look at, there’s certainly an advantage to it being a dime-a-dozen model, with plenty of spares available if needed.
As the purchase of this battery was semi-planned, it meant it had a length of time sitting in the workshop just chilling. The worry was that letting this battery sit for a longish period could result in loss of charge or even damage to the cells.
However, even after sitting for several weeks, the pack holds its charge with no issue. The average voltage is 38V measured at the terminals. This is an encouraging sign that the Li-ion cells that make up the pack are decent quality and are holding charge despite not being discharged/charged for a while.
Motor Controller
Consider the controller as the brains of an ebike, it controls how the electric drive behaves under certain riding conditions. It is a simple programmed computer, it takes inputs from the rider (such as throttle position, pedal speed, or brake conditions) and modulates the amperage from the battery to the motor.
For this build, the controller being used is a generic no-name Chinese model that was cheap to buy and even cheaper in its construction. Unlike the motor, which was manufactured by a recognisable and reputable company, there is no such brand recognition with this controller, it is simply called the ‘Strong Power’. Regardless of who made it, it will suit the purpose of motor control just fine.
The main reason for going with this controller is that it’s universal in its application. As the electric drive-train has been cobbled together using a bunch of different parts, having this controller as the central motor control unit will bring everything together and get everything working in coalition.
The ‘Strong Power’ features ‘3 mode’ programming (whatever that means) and is rated at 36V with various applicable current limits able to be set, with the maximum available of 20A.
One other reason for the selection was that it came with a simple display and rider interface. The display has a basic yet functional layout, with an array of buttons and EDs to indicate power assistance levels and power delivery mode of the controller. Of course, there are other, more advanced displays available with LCD screens showing information such as speed, but for this project a simple display will be more suitable.
Pulse Ring
To make the bike operate with electric assistance, there must be some form of input from the rider. The most common method of input is measuring the RPM of the pedals as they are turned by the rider. Other input methods include a twistgrip throttle, similar to a that of a motorbike, or a thumb throttle, like on a quad bike or ATV, or even a combination of the three – usually twist/thumb throttle with pedal assist.
On factory built ebike, sensors are built into the crank of the bike to pick up the speed and force being applied on the pedals. With a retrofit ebike kit, a ‘bolt-on’ pulse ring setup is used for measuring this parameter.
The pulse ring is simply a disk with magnets placed in a circular array around the perimeter. The pulse ring is attached to the crank of the bike at the bottom bracket of the frame. The pulse ring triggers a simple magnetic sensor that detects the pedals as they turn, feeding this value back to the motor controller which adjusts the current being supplied to the motor accordingly.
Unfortunately, due to my local road rules and regulations, ebikes with twist or thumb throttles are not permitted by law. As a result, the electric assist must be regulated by measuring the pedal RPM rather than by cockpit controls such as a twist throttle on the handlebars.
While it would be nice to be able to include a twist throttle, until the local government and transport authorities stop being stuck in the past a pulse ring will have to do.
If I was building this bike for myself, then I would risk it and run a twistgrip. But as it’s intended for my wife, I don’t want her getting hassled by the authorities or fined for riding an illegal bike.
Ebike Brake Levers
Well-designed ebike’s have specialised brake levers to cut out power to the motor when the brakes levers are pulled. This is a safety feature that is vital should things go horribly wrong. For example, if the motor control were to become stuck on there needs to be a simple and effective means to cut power to the motor. Ebike brake levers differ from regular bike brake levers in that there are inbuilt switching mechanisms for sending a signal to the motor controller and cutting motor power when engaged.
Yet again, these parts were an opportunistic find on ebay. While there is no branding, the suspicion is these are a factory item off another ebike that the seller must have been wrecking, hence why this pair of levers (with cut wires) was available. Visually they are almost identical to normal brake levers, the only real difference is that the ebike levers have a relatively small two core cable coming out of the brake assembly. This is connected as an input to the controller and is activated when the lever is operated.
Cut-off switches are inbuilt into the housing on each lever. There is a cover that can be removed to access the micro limit-switch embedded within the assembly. With the lid screwed in place, the switch is held in place firmly with no play.
The switches are in a normally closed state, meaning that they are fail-safe. This way if there is an issue with either of the switches or the wiring that runs from the levers to the controller, a cut or damaged cable for example, it will trigger the controller which will assume the brakes are being applied. This is a standard safety setup that is used widely in industry, where it is known as ‘safety redundancy’. It’s good to see this safety feature being implemented here also.
Looks wise, they are a simple looking lever with no real distinctive features to set them apart. They are in a natural anodized aluminium finish, with the covers over the microswitches being grey plastic to match the aluminium finish.
The challenge here will be to make these levers match the period of the bike. As they are clearly off a later model bike, to simply put them onto the handlebars wouldn’t be compatible with the overall look. At the very least, they will need to be cleaned up and possibly polished to meet the desired look that is being aimed for here.
Conclusion
This has been but a sliver of the parts being put towards the project. And no doubt there will be changes and alterations to this list as the project progresses. Rest assured, any changes that are made will be mentioned here accordingly to keep you up to speed with the latest developments.
This has been but a sliver of the parts being put towards the project. And no doubt there will be changes and alterations to this list as the project progresses. Rest assured, any changes that are made will be mentioned here accordingly to keep you up to speed with the latest developments.
As you could imagine, there is way more that goes into an ebike than simply a handful of electrical components. We haven’t even started mentioning the ‘regular’ bike bits that will be needed as part of the build – but I promise all this will come in time and will be covered fully in future posts.
For now, this pile of parts will be more than enough to get the project off to a good start. And hopefully by the end of the build we’ll all be experts in the electric conversion of bikes.
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