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Ebike DIY – How to make an electric bicycle: Part 1 – planning an ebike

May 2014

Introduction

This is a how-to guide for people planning to make an ebike from an existing bike and bought parts. This page is to help you plan your bike, and part 2 will tell you how to physically put it together.  
Using these instructions, you should be able to convert a bike for well under $1000.
My focus is on making “transport” bikes: bikes with a primarily personal and family transport job to do, including carrying stuff. The bikes you can use to replace a car.


I also focus on long-term economy of operation. I want your bike to be reliable and cheap to run and maintain.
This bike will use a 250w hub motor and a 36 volt lithium battery, and be more or less road legal.
I assume you have, or can develop, some skills and tools for working on bikes. If you don’t have them, then this is the time to start. Sheldonbrown.com is a great place for information about servicing bikes.
Bicycles, electric or not, are splendid machines that can bring great benefits. Remember, however, that riding always involves risk, and to take great care that your bike is in safe condition every time you ride.

How you make an ebike

Making an ebike is pretty simple. Here are the steps:

  • Choose a bike
  • Decide on your motor and battery format (e.g. front or rear motor)
  • Buy the parts
  • Add a wheel with a hub motor, replacing the bike’s front or back wheel
  • Add a battery 
  • Add a throttle (I usually use a left-hand twist-throttle, replacing the LH handlebar grip)
  • Connect hub motor, battery and throttle to the controller (usually in or on the battery box)

This document is about the first 2 steps above: choosing the bike and deciding on the format. How to put it all together is in part 2.

Choosing a bike

The best thing about making your own ebike is that you can choose a bike that suits you. Different people are different sizes and shapes, have different transport needs and are chasing different images. Start with a bike that fits you and can do what you want. This is the most important choice you make in this process.

Making your own bike also gives you control over quality. Cheap Chinese ebikes are frequently poor in quality. By “quality”, I’m not talking about position in the bike gear heirarchy arms race, I mean simply being good enough gear on a good enough frame, able to be adjusted and maintained for reliable, long-term use.

Body fit


If this bike is going to become part of your daily life, it needs to be a pleasure to use. Most importantly, it needs to fit your body.
Beware the culture of sports bikes! Most bikes on the road these days are styled and shaped for sports, either racing in the Tour de France, or leaping logs on an extreme bush trail. Your electric bike won’t be doing either of these things, so ditch the sports styles and the sports riding positions, and set your bike up for comfort on the long haul.
I like a comfortable, upright, riding position, with the handlebars a little higher than my seat (~2cm). 

I also don’t like to reach too far forwards to the bars, so I don’t ride with so much weight on my arms and wrists – a frequent source of pain and fatigue. To achieve a more upright position you can fit handlebars that sweep back (often found on “girl’s bikes”). You can also use a stem/gooseneck that brings the handlebars back, and/or a steerer tube extender that lifts the handlebars higher.
Sheldon Brown’s expansive article on frame sizing may be useful: http://sheldonbrown.com/frame-sizing.html

Frame material: steel, aluminium, carbon?

I like steel frames. They are strong, durable, repairable and easily found second hand. They very rarely break in normal use, threads rarely strip and they can be easily modified. Steel frames are a little heavier than aluminium or other modern materials, but for the electric transport bike this is hardly relevant.
Better quality steel bikes use “alloy” or “high tensile” steels, which are harder and stronger the than “mild” steel used in cheaper bikes. This means the frame needs less steel for the same strength, so it’s lighter. “Alloy” means a mixture of metals, which can be based on steel, aluminium or any other metal. So when a bike part is described as being “alloy”, it can be hard to tell if this is an aluminium or steel alloy.
Aluminium frames are becoming the norm, and may work okay. However they are fragile and can’t easily be modified or repaired. Threads strip, tubes crack, and repair is a job for a specialist tradesman, so take care.
You can usually tell at a glance if a frame is aluminium or steel by the size of the tubes and the welds. Aluminium bikes have fatter tubes and bigger weld fillets (the worst steel frames use oversize tubes to mimic aluminium bikes and are consequently very heavy).
Large welds on an aluminium frame
If you’re not sure if the frame is steel or aluminium, try a magnet on it. 
Carbon? I was only joking: I can’t imagine anyone really wanting to put 7kg of ebike gear on a bike made of carbon fibre, but I’m sure it’s been done…

Hub motor or mid-drive?


I can only help you make an ebike with a hub motor. However there is another option: the “mid drive”, where the motor drives the cranks and the power goes through the bikes gears. This has significant theoretical benefits, as the motor can be kept in an efficient rpm range over a range of speeds. However there are a range of practical drawbacks: complex engineering, complex installation, increased drive-train wear, gear-changing complications, cadence limitations.
To be a road legal bicycle in Australia or Europe, an ebike can only be powered up to 25km/h – setting the top powered speed of the motor. With motor assistance, an ebike can keep you going faster than 15km/h on all but the steepest hills. Thus the normal powered speed range of an ebike is very narrow, in my experience 18 – 25km/h. In these road-riding conditions, a hub motor works really well, is very simple, cheap, reliable and doesn’t put any loads on the chain and sprocket.
If your interest is in off-road hill climbing, there are a range of mid drives available. An excellent overview is available at this link:

Wheel size

A key characteristic of a bike is the wheel size, usually described in inches. The most common sizes are 26” (mountain bikes and some commuter bikes), and 20” (BMX, kid’s and folding bikes). These sizes are my favourites.
20" wheels on a folding bike
There are real benefits to sticking with these 2 sizes, mostly because it is easy and cheap to find new and second hand parts for them. These wheels are strong because they are small, and plenty of tyre styles can easily be bought at low cost.
26" wheel bike, front motor, rear hub gears
700c wheels are increasingly popular on transport bikes, and are the norm for road/racer bikes. These wheels can be made strong, with wide sturdy rims and 36 spokes, sometimes called 28” for transport bikes, or “29ers” when used with fat, off-road tyers. However many 700c wheels are made in a more fragile style, with reduced spoke counts and narrow rims.
700c flat bar road bike, derailleur gears
16” and 24” wheels are fairly common, mostly on kids’ bikes, but have much less range of compatible tyres, rims etc..
Hub motors for electric bikes generally come in 2 speeds, suitable for 20” and 26” wheels. Externally these hubs look exactly the same, but the copper windings inside the motors are wound with more or less turns to spin at a suitable rpm for these diameters of wheel. Generally motors are made to give the bike a top speed of a little over 25km/h. If you use rims with a different diameter to the designed size of the motor, it will affect the way it works. Your bike will go faster and have less torque (pulling power) if the rim is bigger than the hub design size, or be slower and have more torque if the rim is smaller. If you put a 700c rim on a 26” motor, you should be fine (and fast), unless you do a lot of long, steep hill climbing. If you put a 24” rim on a 26” motor, you’ll go a little slow, but have improved hill-climbing power and efficiency.

Front or back hub motor?

Hub motors are made for either front wheels or back. Front motors are generally 100mm wide (“over-locknut dimension” between the outer nuts and washers) to fit normal forks. Rear motors fit in standard 130mm – 135mm rear dropouts, with the ability to adjust using washers and spacers. There are advantages and disadvantages to front and back motors and both are in common use.
Front motors are my preference in most situations. They don’t interfere with the complexity of your chain and drive system, allowing you to use whatever gearing system you prefer. They are much more easily removed for service (e.g. tyre and tube repairs) than rear motors. However front motors tend to cause wheel slip when riding up steep hills on dirt roads, when the bike and rider’s weight moves back to the rear wheel. My family and I live at the bottom of a very steep dirt road, and we have several front motor bikes, so we live with the skidding front wheels, usually by walking the bike up the steepest sections.
Rear motors require you to use derailleur gears, usually with 6 or 7 speed spin-on clusters, although some rear motors are now available with splined freewheels to take 8-speed cassettes, at higher cost. Rear motors give better traction for climbing steep slopes with slippery surfaces, such as dirt or wet roads. I use a rear motor on my Xtracycle cargo bike, partly because this makes it really effective at carting heavy loads up steep dirt roads, and partly because the BPM motors I like for cargo bikes are easier to get as rear motors.
Xtracycle cargo bike with rear BPM hub motor and derailleur gears
If you’re converting a folding bike, a front motor could be a challenge, as many folders use front wheels which are 75mm wide, with forks to match. I’ve had success bending folder’s forks outwards to fit hub motors, which then requires some adjustment of V-brakes to enable the pads to reach the rims. A rear motor avoids the need to confront the front brakes, but cuts off the option of hub gears.

Gears

Gears are great. They make hills so much easier to climb, and bikes so much more pleasant to ride. Single-speed fixies might be cool for lightly-laden, childless cool cats living in flat cities, but gears make bikes much more useful and enjoyable.
On the other hand, I urge scepticism about the “more is mightier” culture of bike gears. For many cyclists, a 3-speed hub with well sized sprockets will be much more useful, reliable and economical than a 27-speed derailleur setup.
a Shimano 3-speed geared hub on a folding bike with front motor
The first thing you want from gears is the right ratios – that’s what gears are for. Most importantly, you want your lowest gear to be low enough to ride up most of the hills you usually encounter. On an ebike, your motor helps you up the hills so you don’t need the lowest gears sported by many bikes. There is also no shame in walking up the steepest hills, especially when your ebike pushes itself up the hill with its motor while you walk. Super-low gears aren’t needed on most transport ebikes. For example, my cargo bike’s lowest gear is 32t front to 24t back, on 26” wheels, and that is used on 15% plus slopes every time I ride. Most people would do fine with a lowest gear that is higher than that.
Once your lowest gear is suitable, consider your highest gear. For transport cycling, this doesn’t need to be very high. If you’re trying to win a race or want some high-adrenaline cycling, you need high gears so you can still push your bike faster while you zoom down hills. But for the rest of us, downhill riding is about coasting and having a rest, so you don’t need high gears. The fastest gear on my cargo Xtracycle is 42t front to 14t back on a 26” wheel, which spins my legs out at about 35km/h. I don’t feel a need to pedal if I’m going faster than that.
What I’m saying is that a narrow gear range is fine. Several of our ebikes have 6 or 7 derailleur gears, ranging over only 200% (fastest gear is only 2 times the slowest). 
Folding bike with rear Cute brand motor and derailleur gears
Others have 3 hub gears ranging over 186%. These bikes ride on mountainous roads very comfortably. By choosing the right chainring, we give the bikes low enough bottom gears to climb the required hills.
Don’t be a bike snob about old-fashioned spin-on clusters, as used on rear hub motors. They are cost-effective and work fine. While they have a narrower gear range than some cassettes, this is fine for most ebikes. 7 and 8 speed chains are cheap and durable (I recommend SRAM PC870), and wheels have less dish (and are consequently stronger) with lower gear counts.
Consider hub gears, as a robust, low-maintenance, easy-to-use option. 8-speed Shimano Alfines are luxurious and easy to use with a 305% gear range. 
Dahon fitted with Shimano Alfine 8speed hub, with old derailleur used to tension chain
Cheaper and simpler hub gears are also good, such as Shimano and Sturmey Archer/Sunrace 3-speeds with 186% and 177% ranges, or Sturmey Archer 5-speeds with 256% range. These hub gears have bigger jumps between gears than some derailleur gears, but this is fine if you’re not in a race.
One of the best things about hub gears is that they are so simple to use. One shifter, and not too many gears. No decisions to make about whether to change at the front or the back. No need to adjust the derailleur for alignment, and far less trouble. Having a single shifter on the right-hand of the handlebars makes it easy to put the ebike throttle on the left-hand side, without having to arrange access to another shifter.

Brakes

Like every other part of a bike, brakes are the subject of too much bicycle status anxiety. What you need is the ability to stop quickly, when you need to, and this doesn’t depend on how much you pay.
Vee brakes (I can’t see anything “V” about them) are universal, cheap, reliable and very effective when properly adjusted (all brakes need proper adjustment). In my experience, their only significant drawback is with bikes used for exceptionally long, steep, downhill slopes requiring lots of braking. In these conditions, V brakes (like any rim brake) can overheat the rim and sometimes cause tyres to overheat and pop off – a potentially disastrous event. However this is not your usual hill, so don’t think V –brakes aren’t good enough for you just because you go down some hills. Lots of downhill braking also wears out rims, especially if you ride in sand or dirt and/or carry heavy loads – I’ve worn out rims after only a few thousand km of mountain riding. However I’ve also seen rims last 10s of 1000s of km with rim brakes on moderately hilly roads.
Disc brakes are good, but for people cycling on normal terrain, they bring unnecessary complexity. I have installed disc brakes on all the bikes I use, because of my mountain cycling. They save me worn rims and remove the risk of losing a tyre to an overheated rim. But they are more difficult to service and adjust.
Recently we have installed a few Shimano roller brakes on bikes along with hub gears. These look promising. Essentially they are a long-life, low maintenance drum brake in a sealed unit which attaches to the hub (only if the hub is designed to take roller brakes). They use similar principles to back-pedal (or coaster) brakes, with greased metal to metal friction doing the work. These are worth considering if you are planning to install a geared hub and don’t have long steep hills (which would overheat these brakes).

Wet weather

If your bike provides daily transport and you need to ride in the rain, it’s worth being prepared. Mudguards are uncool and can be troublesome, but they are great at keeping water and mud off you and your bike.

Wet weather clothing for cycling is not easy. Normal raincoats or jackets tend to leave your pants in the rain, and waterproof pants are steamy and awkward to put on and off. I use a cycling cape which forms a little tent from your handlebars around your body, and keeps all of you out of the rain:

Choosing the parts

In addition to a working bicycle, you will need:

  • A hub motor to suit your bike
  • A rim and spokes to fit the hub motor
  • A controller that suits the motor
  • A battery for the bike – probably 36 volts, 10 Amp hour, Lithium Iron Phosphate
  • A throttle to connect to the controller
  • Some connectors to join the battery to the controller
  • A box, bag or mount for the battery
  • A pannier rack to carry the battery box
  • Zipties to tie cables to the frame

In addition, I recommend:

  • A meter to measure battery current and voltage

Hub motors

Mass-produced Chinese ebike hub motors are an excellent piece of technology. Essentially they are a 3-phase, permanent magnet motor which drives your bike in one gear, i.e. the motor can’t change gears as you change speed. For legal, on-road cycling, being single-geared is not a problem, as bike motors rarely have to operate outside a narrow speed range of 15-25km/h. Compared to the alternative of driving the chainrings with a bottom bracket drive / mid-drive where the motor drives the bike through the chain, hub motors are really cheap, simple, reliable and don’t wear out the drive system.

For most bikes, I recommend Bafang 250w motors from China. Bafang motors, also branded as 8Fun or Suzhou Bafang, are low cost, adequately reliable, repairable, and strong. They use nylon planetary gears to drive the hub from a high-speed motor inside the hub (spinning faster than the wheel turns). These motors freewheel, which means that when you aren't pedalling they spin without resistance and don’t slow you down. It also means they can’t do regenerative braking (recharging the battery when you go down hills). They are used in many branded ebikes, and easily bought online from China via Greenbikekit.com (GBK) or BMSBattery.com.
Regenerative braking catches people’s imagination (it’s usually the subject of people’s first question about ebikes), but it’s not as useful on an ebike as you might first think. Some bikes use regenerative braking, and can recharge the bike battery when descending hills. This is a great idea, but a little thought shows it would contribute very little to most cyclists. Cyclists actually do very little braking in most places, and use hills to give speed rather than wear out brakes, so there is actually very little energy available to harvest. Regenerative braking requires the motor to be always engaged with the wheel (instead of freewheeling), so there is resistance anytime the motor is not pushing the bike along. So leave regen braking to electric trains and hybrid cars.
250w Bafang motors usually come in 2 speeds, to suit 26” and 20” wheels, each giving a top speed between 25 and 29km/h. The different speed hubs are mechanically identical, except for the number of turns of wire on the motor poles. 20” motors can be hard to get, but I have been able to buy them from Greenbikekit.com on special order.
Here are the usual Bafang motors and their key attributes:

SWXK

o   250w, 36v front hub motor, usually with 36 spoke holes, 2.75kg
o   A relatively light, medium-duty motor. Greatest weakness is overheating on long slow climbs, which is not a problem for most people (see my page http://bruceteakle.blogspot.com.au/p/burning-out-bafang-hub-motors.html)
o   6-bolt disc brake mounts, but it’s hard to fit most disc calipers between the disc and the hub
o   most SWXK power cables have a waterproof plug close to the hub, which makes disconnection easy for servicing (flat tyres etc.)
o   easily available for 26” (or 700c) wheel, harder to find for 20” wheel
o   easily opened for service by unscrewing the side plate with a special 4-lug spanner

Bafang SWXK front 250w motor before lacing to a rim

SWXK5

  •  A variant of the SWXK motor with more room for disc brake calipers, otherwise the same

SWXH

  • 250w, 36v rear hub motor, usually with 36 spoke holes, XXXkg
  • A relatively light, medium-duty motor. Greatest weakness is overheating on long slow climbs (not a problem for most people) (see my page at http://bruceteakle.blogspot.com.au/p/burning-out-bafang-hub-motors.html)
  • 6-bolt disc-brake mounts, with adequate space for most calipers
  •  takes 6 or 7speed spin-on clusters for derailleur gears
  • Some variants open with a difficult spin-off side plate requiring a special 3-pin spanner, some open easily with 6 screws (which can work loose)
  • Power cables emerge from a hollow axle on the sprocket side, usually without a plug, making servicing and tube repairs more difficult.

BPM

  • See my review of the BPM
  • Heavy-duty hub motor, designed for 36v but able to handle higher voltages and currents
  • Has holes for 36 spokes, and mounts for 6-bolt brake discs with room for most calipers
  • Easily available for rear motors, also made for front motors but more difficult to source
  • Made in a range of speeds, labelled according to number of turns on motor poles (more turns = slower + higher torque). Code 12 is a good 36v cargo bike motor with max speed of 25km/h
  • Side plates open easily with 6 screws
  • Power cables emerge from a hollow axle on the sprocket side, usually without a plug, making servicing and tube repairs more difficult.
BPM rear motor, with threaded boss for spin-on cluster on RHS
All these Bafang motors can fairly easily have their nylon gears and freewheels replaced, which are the most common motor failures. Spares are easily available.
If you cycle on long steep hills, or struggle with hills for some other reason, you could consider a 2-speed hub motor. See my review of the Xiongda 2-speed motor on my page here.

Spokes

You’ll need 36 spokes of the right length to lace your hub to a rim. The easiest way to get spokes is to buy them from the same Chinese supplier you get your motor and rim from. Greenbikekit.com (GBK) sell 2.3mm spokes that are roughly the right length for most of their hub and rim combinations. It is best to calculate the spoke length yourself before ordering.
If you go with a different rim to what your Chinese suppliers provide, you will probably need to calculate spoke length and source spokes of the correct length. You will probably need to use 2mm straight-guage spokes, which fit the hub better if you use brass washers.
See my page on wheelbuilding for more information about spokes.

Rims

There are a myriad of rims available with a dazzling array of features. If you’re making a transport ebike, most of these rims don’t have much to offer you (is this theme becoming predictable?).
What you do want in a rim:

  • The right diameter (there are surprises here – see Sheldon Brown’s article at http://sheldonbrown.com/tire-sizing.html)
  •  The right number of spoke holes (nearly all hub motors use 36 spokes)
  • Strong enough – most rims are strong enough, even single wall rims are strong
  • Wide enough:

  • wider rims make tyre fitting easier as there is room between the beads for the tube and valve to move and avoid pinching the tube
  • rim brake adjustment is easier and less risky as the tyre bulges less at the sides (a touch from the brake pads can wreck a tyre in seconds)
I tend to stick with 2 types of rims: the cheap Chinese rims from ebike suppliers (for lightly loaded wheels, e.g. front hub motors, rear wheels on lighter people’s bikes), and Sun Ringle Rhyno Lite rims for heavy duty wheels. I also re-use rims in good condition from old wheels (make sure they have no kinks before you unlace them from the original wheel). I’ve never had a rim fail in normal use (although I have worn out rims with rim brakes). I suspect I could use cheap single-wall rims for every wheel and never have a problem…

Controllers

Controllers are amazing pieces of technology, considering their size, sophistication and price. Essentially a controller is an inverter, which changes the d.c. power from your battery into 3-phase a.c. power for your motor. For the motor to work, the controller needs to connect 3 key components:

  •  the battery, providing d.c. electric power
  • the throttle, giving a 0 – 5v d.c. signal from a hall sensor and a moving magnet
  • the motor, with 3-phase power wires to carry the drive power, and sometimes 5 sensor wires to signal the motor’s movement

When you twist the throttle, the controller receives a signal telling it to provide power to the motor. To work out what power the motor needs, the controller senses the movement of the motor, either through the sensor wires (5 fine wires coming from the motor), or by reading signals that come through the 3-phase power wires (the 3 heavier wires from the motor). The controller then changes the direct current from the battery into rotating 3-phase power for the motor, at a suitable frequency to match the motor speed.
I prefer sensorless controllers, which avoid the need for assembling and using the 5-pin sensor plug (another connection to go wrong and difficult removal of axle nuts and washers). Many motors require sensorless controllers, as they don’t have sensor wires. Sensorless controllers also avoid the risk of failed hall sensors in the motor, which I’ve never experienced but is discussed online occasionally. I’ve almost never had trouble from sensorless controllers, after a lot of use.
Most controllers have a handful of other wires and plugs in addition to these 3 key connections. These vary, but purposes can include:

  • Pedal Assistance Sensor (PAS): This connects to a sensor which mounts on the chainring, and won’t let power to the motor unless you are pedalling. Essentially an electronic moral guardian required by the EU standard for ebikes. If left unplugged, the controller will go on throttle alone.
  • Cruise control: Plug 2 wires together to give cruise control. You throttle on for about 8 seconds, let the throttle go and the controller will maintain power until you give the throttle a twist or squeeze a switched brake lever (only if fitted). This is risky unless you have installed the special brake levers with switches. Some older controllers had cruise control as the default, and required cutting a loop of wire to disable cruise control.
  • Power limiting: Plug 2 wires together (similar to the cruise control wires, but different colour), and your bike loses half its power. I’m not sure what this is for, perhaps for kids, or a way of crippling an illegally over-powered custom bike?
  • Brake switches: if your bike is set up to stay powered without the throttle held on (cruise control, or “pedelec”, where the motor starts when you pedal), you can use brake levers with connections to the controller which switch off the power when you brake.   

Here's a video on how all the electrics go together:

Batteries

A shrink-wrapped, Headway cell, lithium iron phosphate battery from GBK with a 240w charger
 The battery is the key to the ebike. Ebikes are only possible because we have these energy packs which are so relatively light, compact, reliable and durable. The battery is also the most expensive part of an ebike, and the source of the most ongoing expense.
My preferences in batteries include:

  • 36 Volts: This is the standard voltage of electric bikes.
  • Lithium Iron Phosphate battery chemistry: these are the most durable and robust lithium batteries. Currently I buy shrink-wrapped 10Ah 36v packs from GBK which use Headway 38120 (38mm diameter x 120mm long cylindrical) cells, which are good quality and that bolt together, allowing easy repair (which is sometimes necessary). Their disadvantage is the need to provide a battery box or bag to carry them on the bike and protect them from weather and impact. 

Lithium batteries require a battery management system (BMS), also called PCM (protection circuit module), which controls charge and discharge. The BMS prevents overcharging, over-discharging, and balances any differences in cells which develop. 
These are the Headway cylindrical cells inside a shrink-wrapped battery, bolted together for easy repair
On top is the BMS which controls charge and discharge to protect the cells
Options:

  • Other voltages: Lower voltage (24V) is less common and requires higher currents and consequently higher stresses on wires and components. Higher voltages (48v and higher) are for fast, non-road-legal bikes.
  • Ping batteries: These are assembled from flat Lithium iron phosphate pouch cells, and soldered together, usually with 2 or 3 cells parallelled to give 10 or 15 Ah. The packs are lighter and more compact than packs using Headway cells. Cell replacement is quite challenging, requiring unsoldering large joints. Also require a battery box. Ping batteries have a good reputation on forums but I’ve had some trouble with cell failures requiring difficult resoldering (with excellent support from Ping).

A Ping battery undressed: note the flat pouch cells and the soldered joints on top

  • Bottle batteries: Weather-tight (we hope) batteries that usually fix easily onto the down tube water bottle mount – not requiring a battery box. They usually use lithium-ion cells with lower current rating, shorter cycle and calendar life and I would expect them to be challenging to repair. I’m trying one out from GBK currently, because they are a little cheaper and save a lot of cost and work with battery boxes. But I will need to find a dry safe place for the connections.
  • Other bike batteries: There are a range of other bike batteries available, some with special stands and connections. I’ve been reluctant to try these, as they tend to have limited charging and discharging currents and uncertain quality, and it’s an expensive experiment.

Throttles

Most ebikes have a throttle on the handlebars. The throttle tells the controller how much power to put into the hub motor. Some ebikes don’t have a throttle, and instead the controller puts out power when it receives a signal from a “pedal assistance sensor” (PAS) that the cranks are turning, according to a power level set by the rider, usually via buttons on the handlebars.
I much prefer throttle to pedal assistance. Sometimes I want to power along without pedalling, like a moped. Sometimes I don’t want any power. The throttle gives instant control.
The European standard for ebikes requires a PAS, apparently to discourage laziness. This means that for bikes in Australia with 250w motors, a PAS is a legal requirement.
Throttles use a “hall effect” sensor, which sends a varying current according to the position of a magnet which is moved by your hand’s rotation. These hall sensors are waterproof and very robust – I’ve never had a sensor  fail.
The main options for handlebar throttles include:

  • Half twist throttle: This is like a gripshift gear changer, using a half-fixed handgrip. This is my preference. Most of your cycling effort goes into the fixed grip on the end of the bar, and I’ve never had a half twist throttle break.

Half-twist throttle, mounted on left, with switch and battery indicator lights. The left-hand part doesn't twist.

  • Full twist throttle: The whole handgrip twists. I don’t like these, after having a couple of them come off in my hand while riding (leaving the motor running without stopping until I could slip the handgrip back into place). The strain of your hands and arms while pushing hard can break the internal plastic parts of the twist grip. On the other hand, I have a friend who’s done 10s of 1000s of km using a full-twist with no problems…
  • Thumb throttle: These have a little paddle which can be pushed down by your thumb. While they seem the most minimalist of throttles, the paddle is fragile and you are most restricted in your hand positioning.
  • Left or right hand? Throttles can be mounted on left or right hands. Twist throttles will rotate forwards to go if they’re on the left. I always mount throttles on the left hand, almost always half-twist. This frees the right hand for doing most of the gear changing (or all of the gear changing if you’re using hub gears).

Fitting the throttle and the gear shifter (if you have a front derailleur) can take some fiddling around, and may require a change of shifters (especially if you have twist-grip shifters).  
Throttles also can include a switch, which can be used to turn the controller power on and off, and/or battery voltage lights, which give a vague indication of the battery voltage. I don’t usually use either of these, but they can be good.  

Connectors

Each of the electrical components of an ebike join together with plugs. The only connection that doesn’t usually come included with the parts is the connection from the battery to the controller.
GBK shrink-wrapped batteries come standard with Anderson-type 45A plugs. These are a common standard plug for hobbyists to use for high-current d.c. connections. These are good plugs to have in the toolbox.
The controller power plug is a 3-blade unit, with +ve, -ve and a thin wire which needs to connect to +ve to turn the controller on.
The easiest way to connect the battery to the controller is to buy a “controller power cable” from GBK. This has the right plugs to connect the controller to the battery, and also includes a wire from +ve to the controller turn-on wire. If you want to have a switch to turn the controller on, you can cut the turn-on loop and connect a switch (e.g. the switch on a throttle unit).

Battery Box

You need a way to carry your battery and protect it from weather and impact (if you drop your bike), unless you use a bottle battery or some other pre-packaged battery. You can get away with a canvas bag or some other improvisation, but a box is good. It should be strong, permanent and really waterproof.
The battery box is probably the biggest job in making your own ebike. My first few boxes were made of waterproof plywood with joints of fibreglass tape and epoxy – like a small boat. This makes a very light and strong box.
Plywood battery box, with overhang to reduce rain on the externally-mounted controller
Recently I had a set of boxes fabricated from aluminium. They were first laser cut, then folded and welded. Not suitable for a one-off box.

You need space for the battery, space for the controller and space for all the wires and plugs from the controller. If your bike works hard doing long climbs, it’s important for the controller to be able to lose heat, either with air cooling or by contact with something that air-cools (like an aluminium box). Controllers are somewhat weather-resistant, so can go outside the box, especially if they are under some sort of shelter from the rain.

Pannier racks

If you’re putting your battery in a box, it will usually go on a pannier rack at the back. My current preference is the Topeak Super Tourist DX rack. This is a strong rack, that has a bar to hang panniers below the top of the rack and is well designed to keep your panniers out of the rear wheel spokes (a very important consideration!). The lower bar for panniers is important if you carry panniers as well as a battery box, as the box obstructs the top rails.
If you aren’t already a pannier user, now is the time to give your bike luggage needs some serious thought. Panniers are a really good way to carry stuff on a bike. Keep your loads off your back, reduce the weight on your wrists, avoid sweaty shirt backs, keep the loads low and stable, and give your bike some real cargo capacity. I use Ortlieb Classic roll-top panniers, which are simple, durable, fully waterproof and attach securely to your bike.
I also like to use front panniers. These can help balance an ebike with a heavy battery at the back, especially when you’re trying to get a grip with your front hub motor going up a hill on a wet road.
Front pannier rack on 20" folding bike, with integrated steering damper. Note how top rails clear V-brake arms
 Since it’s hard to get good front pannier racks for most bikes, I fabricate my own from mild steel round bar (I’ll write a post on how sometime). 
Front pannier rack on 700c step-thru bike, with integrated steering damper
Front panniers do affect steering, but I really don’t find it a problem at all, even on rough roads and steep hills.

Power meters

It really helps to have access to some sort of metering on an ebike, even if you don't always use it. The main use of a meter is to measure how much energy you use for your trips, compared to your battery capacity. This requires a special sort of meter, which can measure Amp-hours (Ah) flowing through the meter as your bike uses power from the battery.
Measurements other than Ah can be useful, especially when things go wrong. For example, if your bike won’t go, you will want to see the battery voltage.
There are a few ebike meters to choose from:

  • The Cycle Analyst (CA): this is the top in ebike meters, for the ebike nerd or numbers person. The CA takes a range of measurements and integrates them into very useful data, from Amp-Hours to Watt-hours per kilometer, trip distance and total lifetime distance cycled. I keep one of these on one of my bikes, and use it to check batteries for condition and capacity.
  • Remote-control watt-meters: there are a few of these self-contained units available from a range of suppliers, at a range of prices. They are made for the remote-control model market, and are used by hobbyists to test battery-powered remote-control gear. Options include:

o   Generic “Watt Meter”, in an aluminium case. I’m buying these from ebay currently, as they are low cost and ebay provides buyer protection. The display has no back light, but this is not a problem.
Generic Watt Meter from ebay
o   Turnigy 130A Watt Meter and Power Analyzer, from Hobby King. I’ve used a few of these which have been mostly good. However the last 4 I bought failed very quickly, and I was disappointed with Hobby King’s service.
o   “Watt’s Up” and other similar meters. I haven’t tried these, but they are well reviewed online.
All these Remote control watt-meters are very similar. They have 4 readings on the face, showing Volts, Amps and Watts continuously, and the 4th reading rotates between several readings, including Amp-hours. This means you need to wait for the reading to rotate to Ah to find how much energy you’ve used.
They also lose their data and reset as soon as they are unplugged from the battery. This is a problem if your battery switches off (usually from low-voltage cutout, but sometimes from a failure), because you can’t find out how many Ah the battery takes to cutout unless you are checking frequently (not convenient with these meters).
Once you have measured the Ah use of your normal trips, you can plan when you need to recharge and a meter is not so important. However it can be useful to keep one in your pannier in case of a problem.

Conclusion

I hope all these words help you to plan your ebike project. Part 2 will explain how to put it together.



3 comments:

  1. Hub motors for electric bikes generally come in 2 speeds, suitable for 20” and 26” wheels. Externally these hubs look exactly the same, but the ... electricbikewheel.blogspot.com

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  2. Hi Bruce,web info on headway 38120,s is varied. I was looking at using a 36v pack with screws for ease of maintenance. Would you still recommend them for a Xiongda?
    If so, could you supply a link as I'm a little confused about things like C rate, number of cells and if a bms is required.Also any info on balance charging and a link to equipment required and info on battery maintenance howto as I'm new to all this and a step by step procedure would be greatly appreciated

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    1. Hello Rob,
      I've bought Headway packs from both BMSBattery and Greenbikekit, with good outcomes. These are supplied with BMS, output plug and charging plug. Compatible chargers are also available from the same suppliers.
      I've had occasional problems, once from a bad BMS which killed one cell and then killed the replacement. Overall they've been reliable and easy to repair when I've had problems.
      Headway 38120 cells are Lithium Iron Phosphate chemistry, which creates a lower voltage per cell than other Lithium chemistries. Thus a 36V pack needs 12 cells in series (other lithium chemistries only need 10 cells). These cells can deliver big currents, but the BMS needs to be able to handle the current too.
      The standard BMS on a Headway pack from Greenbikekit is good as it can deliver 20A continuous current. This is fine for any 250w motor (these draw up to 15A on a standard controller) or even a BPM with a Con91 controller (which draws up to 18A). The purpose of the BMS is to protect the cells from too-low discharge, to protect the cells from too-high charge, and to balance the cells to avoid the gradual change in state of charge due to slight cell differences.
      Most of my batteries are this one:
      http://www.greenbikekit.com/lithium-battery/lifepo4/36v-10ah-headway-38120s-battery-pack.html
      It comes with a BMS, charge plug, discharge plug and shrink-wrap skin.
      I mostly use the 240w chargers:
      http://www.greenbikekit.com/battery-charger/240w-lithium-ion-battery-charger.html
      These supply about 5A charge which helps me to recharge quickly during a day of multiple trips. The 120w chargers are also good, and may increase battery life due to less heat if you have plenty of time to charge. I'm shy of the bigger chargers (like 360w) as they may stress the BMS and are expensive (I'd rather spend the money on 2 smaller chargers so I have a backup unit).
      I hope this helps!

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