Introduction

Riding an electric bike has all the freedoms of riding a normal push bike and with less effort but with increased costs and weight. A to B magazine lists a few more arguments. Some newspapers have noticed the new electric bicycle phenomenom and given it their support. Never think of a little electric power assistance as cheating versus a normal bike, instead, it lets even a beginner cyclist replace a big costly car for normal commuting. China is full of millions of electric bikes but many are really electric motorbikes which are a bit more dangerous. If you have ever lived in Thailand or Vietnam, you would have been amazed at how much more convenient a motorbike is than a car for trips around town. I have been eating dinners where the host has realised there was a missing ingredient or the beer had run out and twice nipped to a shop and back in under two minutes. This is not possible with a car because because of distances, parking and congestion which never affect a two wheeler and shop locations adjust accordingly. Cars make poor transport around cities because they are big, heavy, expensive, kill people directly and via pollution, will soon be outlawed, and need huge parking spaces where they sit doing nothing nearly all the time. Watch how efficiently bikes can cross a small intersection in Hanoi.

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Cycling Advantages

Cyclists are the happiest commuters because they suffer no congestion, no parking charges, no parking problems and get free endorphins and free healthy exercise. Bicycles are clean, cheap, healthy, sociable and efficient. Congestion and traffic lights remove any potential speed advantage of cars and motor bikes on city commutes. It is amazing how little motorists notice how much they are wasting their lives getting fat and angry inside cars stuck at traffic jams earning money to buy cars, and to pay for insurance, repairs, lost interest on their investment, taxes and also a little on non-renewable fuel. Even in the United States of America, things may be changing to help cyclists. Bicycles are the most efficient form of personal transport: both cooler and faster than walking (or running) and more efficient than any other personal vehicle (like a car) and cheaper and more flexible than any public transport because trains need expensive active rail tracks and points, stop running late at night and are crowded with sneezers all Winter. Remember that one always gets a seat on a bicycle. Some people cycle for sport or exercise and so may want showers but cycling is more efficient than walking so uses less energy and has more breeze cooling than walking so has less actual need for showering than even walkers do (especially where there are few hills and if the cyclist has enough time to slow down for a few Km before stopping).

However, bicycles are not aerodynamic and drag rises with the square of the velocity so a cyclist going 50 Km/h needs to generate around 4 times the power of one travelling at 25 Km/h. Normal bicycles will never be quick but aerodynamic ones have been pedalled over 1000 Km in 24 hours by a single rider but faired recumbents will never be as convenient as a normal bike and hills cause special problems too so very aerodynamic HPVs are not going to appeal to most people no matter how expensive petroleum becomes. Instead, there is another way to boost the bicycle to speeds higher than normal city traffic (<20 Km/h) and to keep the health and social benefits of cycling (no one can see you in a car) - just add a little electric boost motor.

Electric Bike Advantages

The main advantage of an electric bike is help on the hills and into nasty headwinds. All the other problems of cycling remain but that little bit of electric help means that many people who have not been cycling for ages are now able to start slowly getting fit again and do even less work than a normal cyclist so always arrive cool and non-sweaty regardless of all conditions. A perfect electric bike would also be able to increase the average cycling speed.

Electric Bike Technology

Across Europe all electric bikes should be the same soon because they may all be defined by the same law - even in Britain. (This law is Europe at its best creating common markets and sensible standardisation). The law says amongst other things that the bicycles must have pedals, must not provide power above 25 Km/hour and should have a continuous rated output below 250 Watts.

Motors

There is no perfect electric bike on the market yet though some are getting close. Most electric bikes fall into two groups: Crank motor or hub motor. The crank motor puts power through the gears so has the advantage of an efficient freewheel and a large even power band from steep hills up to level ground but has the disadvantage of measuring force through torque which means that power pulses from your pedals are amplified on the bike and weak riders get less help than strong ones which is plain wrong. In Britain, weak cyclists with hilly country might be better served by a direct power control lever like a twist-grip throttle but these may be illegal. Power levers don't work as well as torque sensors for other situations because adding more power needs a change in gear to maintain the same pedalling cadence so one needs to move two levers together in coordination which is no fun at all. The Nu Vinci continuously variable transmission might mitigate these problems but, in practise, it has been reported to be heavy, inefficient, and expensive so not worth considering.

The best feature of crank drives with good torque sensors is that power adjusts automatically and without any conscious thought. Some of the electric bike kits come with complex sensor systems but still can take many seconds to start or stop power - definitely not as intuitive as the Panasonic drive. The other problems of crank motors (like Panasonic's) are that the frame needs to be customised, the clutches and freewheels are complex (heavy and customised) and the top speed specified in law is measured from the motor so pedalling cadence needs to be reduced or the motor reduces power or cuts out altogether. Also, the rear freewheel increases efficiency but means that there is no potential for regenerative braking (which is pretty limited without hills). The classic example of a well-made bike with a crank motor is the Kalkhoff Agattu. The power reduction and cut-offs for an Agattu start at only 15 Km/h in any gear and the total cut-off at 14 Km/h if you are in 1st gear so, despite the extra weight and expense, a strong normal cyclist on a flat route will be faster than an electric-assisted Kalkhoff Panasonic hub drive bike. To make the Panasonic do relatively more work, paradoxically one must pedal more slowly than usual. The Panasonic drive goes through an extra small drive wheel which is liable to wear. The Bosch system appears to be better by integrating human and electric power through a single large chainwheel. The Bosch also offers a higher power amplification of 250%. One hacked Bosch e-bike drive on YouTube shows output peaking over 600 Watts on a tough climb.

From the Kalkhoff manual:

Power assistance is not available if:
- The pedalling power is too weak
- The battery light is blinking
- when riding at more than 24 km/h in 7th gear
- when riding at more than 18 km/h in 4th gear
- when riding at more than 14 km/h in 1st gear
Graph showing Panasonic motor power reductions in top gear

A hub motor bike is directly connected to the wheel so needs gearing to reduce the high-spinning motor down to the speed of the slow spinning wheel climbing a nasty hill. This gearing can make noisy but the Tongxin motor and BionX motors are reputed to be almost silent. The Sanyo Eneloop bike has a geared hub motor with a 1 to 2 power ratio. The BionX hub motor is the classic hub motor with clever electronic controls offering high power, efficiency and regenerative braking but torque is reputed to be limited which limits hill-climbing ability which is where electric bikes should really stand out. Henshaw's electric bike book suggests that the BionX High Torque HT option is better but more like medium torque unless powering a small wheel bike. BionX kits seem to be relatively expensive. With all the custom components located in a hub, standard bike frames can be used so well-established favourites like Brompton folding bikes and normal mountain bikes can be electrified with hub motors.

2014 Motor update

Panasonic, Bosch and Yamaha are all making very high power crank motors now and Kalkhoff have introduced a second version of their own Impulse crank motor too. They are all much better for climbing because they can go over the 250 Watt limit for a short time whilst keeping to the limit on average, they fill in the torque gap better as the pedals rotate which really helps weaker cyclists, and they may try to reduce torque when changing gears which reduces the heavy wear on derailleurs and chains for non-hub geared bikes. The Yamaha allows the use of a front changer but e-bikes need fewer gears but higher ratios than normal bikes so given manufacturers are already fitting stupid 10 speed cassettes, the front changer may be doubly redundant.

Why only new crank motors when I would suggest that a doubly wound hub motor would be better for efficiency and regeneration and there would be plenty of torque if the bike had small wheels. Just look at the size of motorbike scooter wheels relative to bicycles - that should be where e-bikes are going for city use. Small wheels make a smaller lighter frame and smaller lighter wheels with more torque but the Brompton with high pressure tyres show that the efficiency penalty for small wheels may be only 5%. Tesla motors have also had the same idea and put two motors with different gear ratios into one car letting each drive on pair of wheels so at higher speeds more power is sent to the higher-geared motor and vice versa. Stromer make direct drive hub motors with enough torque for Swiss mountain climbing so it must be possible and, in 2015, Bionx has finally worked out how to create a high torque hub bicycle motor with their Bionx D series with regeneration but the price is horrific and changing spokes might not be easy.

Batteries

Many kinds of battery have enough energy and power for electric bikes but lithium chemistries are the current leaders: Lithium polymer, Lithium Iron Phosphate, and Lithium Manganese are common though the specific chemistries and constructions are merging and mixing. The cells in Tesla Motors newer cars are reputed to store over 250 Wh per Kg mass and cost under USD 200 per KWh capacity. Lithium cells can can sustain 10000 charges or more and recent scientific understanding has pushed cycle life well past 10000 charges and still with 85% of its original capacity. A car with these cells could travel many millions of miles over its life! New Silicon electrodes with new electrolyte chemistry from Sekisui Systems or Enevate should be in production soon with 3 times 2010 energy storage capacity and ORNL have made a new kind of cell using solid compounds of Lithium and Sulphur without any liquid electrolyte with 4 times the energy of current lithium ion batteries. One Japanese group with a strong pedigree called Power Japan Plus have designed a novel battery with dual carbon electrodes. More exotic Lithium metal, or Lithium Silicon, or Lithium Sulphide batteries should be available within two years. Currently, Lithium Iron Phosphate is ideal for stability over temperatures and charge cycles (> 2000) and is available now in high power (A123 offers over 60 Amps from a 2.3 Amp hour cell) or low cost (ThunderSky <400 Euros per KW-hour) chemistries . Lithium polymer needs much more care and can burst into flames with a bit of damage. Lithium Manganese is both high capacity and is more stable than older "Lithium Ion" batteries (made with just Cobolt Oxide) plus it can be recharged over 500 times if properly managed. Leydon energy recently announced a new Lithium battery chemistry that seems ideal for most uses including e-bikes. In 2013, one from solidenergy systems might be good enough for aircraft. In 2014, Oxis energy is preparing to produce lithium sulphur batteries for UK military and transport uses.

All batteries can be damaged by improper use. Lithium batteries are very easy to damage if they get too hot, too cold, punctured, overcharged or flattened. Sometimes, they even burst into flames and burn down your house so be careful - well the old ones could but that is much less likely with the newer chemistries. So, for safety, and longevity, the electric bike needs a good charger and a careful battery management system when running. Each cell in a battery needs to be monitored as it charges and when in use. This absolutely requires independent awkward wires to each and every cell with completely reliable computers and power control electronics - unless each cell has its own internal protection circuit. Kalkhoff Lithium Manganese batteries come with a two-year warranty and seem to be very reliable in practice with very little capacity loss over 1-year. Tesla's Panasonic cells are degrading slower than expected. Lithium batteries are high cost items and are a major factor in the overall cost per distance of an electric bike so they need guarantees for safety and financial security.

Other battery chemistries

A recent cost comparison for vehicle batteries in 2015 shows how scaling and new research are more than doubling energy storage per weight. Nickel Metal Hydride(NiMh) batteries have a good reputation, are cheap and are not as fragile as Lithium batteries but they have low charging efficiency (losing about one third of the energy put-in) and cannot be discharged as quickly as poisonous Nickel Cadmium or high-power lithium chemistries. Also older (most common) NiMh batteries gradually lose their charge. After a bit of misuse many old NiMh batteries could lose most of their charge in a few weeks. Newer NiMh batteries are called "ready for use" or hybrid batteries and use a new electrical separator to reduce charge leakage. Newer NiMh batteries have names like: Hybrio, Eneloop, or Annsman MaxE but are not yet available in tagged cells for making into packs for bikes. Nickel Zinc batteries are very new and should be cheap and may be worth considering but reliability in electric bikes is not known yet. Nickel Zinc batteries are now being aimed at halving the weight of the standard 12V lead-acid batteries common in cars and should have similar costs.

Personal Favourite

So my perspective is that the Tesla Roadster car accelerates from 0 to over 120 Km/hour in less than four seconds using a single gear, with high efficiency, and carries on to around 200 Km/h but yet there is no street-legal electric bike that will go from 0 to just 25 Km/h and still significantly help on a 25% gradient - my hill. If a Tesla was 100 times the weight and 10 times faster than an e-bike, then building the e-bike might be 1000 times easier or cheaper - well maybe though I know electric moters get more efficient the larger they are ? The people who most need electric bikes are weaker folk who are not feeling very fit and anyone faced with fierce hills. Kalkhoff and Sparta bikes are tough, all-weather-capable and reliable so building the bike part is no problem. The batteries are easily good enough for any standard commute < 50 Km and well managed, they can last for 5+ years. All we need now, is a manufacturer who can produce a quiet motor and electronics that climbs hills like a goat and does not stop applying power when it gets faster than 14 Km/h. A new two gear electric motor from Xiongda appears to be the best way to handle long climbs .

I understand that the law does not say exactly how steeply the power must drop before 25Km/h, only that it must be reduced gradually and that the 250 Watts is sustained applied power after losses. If a weak cyclist dials in strong assistance, then it should be available until just over 25 Km/h so anyone can dispose of their car, save the environment and get to work quickly, safely and happily. If one includes the time spent waiting at traffic lights and trapped in congestion, average car traffic speeds in cities is already slower than normal bicycle speeds. The electric bike industry has recently asked for higher power bikes to be the new legal standard. Cycling through the steeply rolling Chiltern hills would make even 50% regeneration efficiency very welcome and save on brake and wheel wear.

If one lived somewhere with mountains, regeneration would make beautiful exciting rides open to everyone. Fresh air, natural fragrances and no air conditioning really opens your brain to the novel fully-awake feeling of travelling and experiencing somewhere new instead of just watching it on TV or through the windscreen. Furthermore, healthy exercise primes the Hippocampus in your brain to create new brain cells and new memories - you become more alive even though no corporation will ever pay for a TV advert to tell you this. When carefully designed, electric motors for solar cars and motor controllers can each be 98% efficient and Lithium batteries can return over 90% of their charging energy so with care and money very high efficiency is possible. I am not the natural electric bike customer but I would buy one of these all-gradients, all-legal-speeds all-weather bikes even if only to ship my friends around when the fuel protests start again. Bosch have produced a new crank motor system that seems to be more flexible than the Panasonic with higher output multiplier and bigger chainwheel.

My experiences

I have used a Curry Drive from 2005 (from helpful Tony Castles) which was excellent value but which I finally blew up (internal motor controller) when doing some extreme hill climb testing. I own a Sparta Pharos which is a wonderfully strong reliable bike but the Nickel Cadmium batteries were dying so I replaced them with A123 Lithium Iron Phosphate cells and find it can help me climb anything, even steeper than 25%, but it is not that powerful overall and it is peakier than the Panasonic crank motor in Kalkhoff bikes so each pedal turn causes two power pulses. I test rode a few newer Sparta bikes in The Netherlands and whilst they were lovely, they were not designed for hills. I tried some overpowered (500W+) hub motor converted mountain bikes which are almost into motorbike territory but probably not legal in Europe and designed for hill storming not gentle creeping. Incidentally, I initially used 8 A123 26650 cells but the Sparta Pharos low voltage cut-off was too low after I tripled the pack to 3P8S resulting in small imbalances damaging the individual A123 cells by pulling them below 2.5 volts so I dropped the pack to 7S3P. I had bought, off Ali-express, an 8S A123 battery Management System (BMS) for twice my needed current but I wasted a day trying to make it work and gave up. The A123 cells are incredibly high power (overkill) and not that high capacity relative to the latest normal Lithium Ion cells from Panasonic so, if I was doing this again, I would use them instead. If you are building a large capacity (long range, low power) pack, you should forget about spot-welding batteries together but instead look at fused clamped cells that can be popped in and out easily and safely, maybe with individual cell protection so all the balancing becomes an internal, smaller problem. I would recommend always having a BMS or indidual cell protection. In general, I would advise against bothering doing too much yourself: making an electric vehicle DIY can be endless work.

The British shop 50 Cycles let me try three Kalkhoff bikes on a 20%+ hill in Richmond, London where I found that the Panasonic controller is very clever at starting and stopping power at just the right times and fills-in power for very weak cyclists on steep hills: the 200% multiplier is ignored and, for weak cyclists, the Panasonic does nearly all the work itself as long as you keep the pedals turning. When the Kalkhoff Agattu 3-speed fell out of its power band on the steepest section of slope, I needed to get out of the saddle and do some work myself but the 8-speed never failed to do nearly all the work. If you want more exercise then, obviously, one can climb hills on less than maximum power assistance. The Kalkhoff with the Bionx high torque motor seemed even more powerful on gentler slopes but either faded a little, or fell out of its power band at the steeper top section of hill. Incidentally, never allow regeneration or power bursts on a front wheel or you will do a face-plant onto the road one day. Watch motorcyclists or a Tour de France descent to know how close to the grip limit 2 wheels can go when front-wheel grip is predictable. The BionX regeneration worked with either brake lever pulled and was good at turning power on and off but not as quickly or safely as the Panasonic does. The BionX was good at providing power until exactly 25 Km/h. The Kalkhoff Agattu 8-speed was more sophisticated, intelligent and a better hill climber than I had expected. Now I just need to try a Bosch bike ...

2014 update

I thought the Kalkhoff Xion drive bikes would finally be my perfect bike but they still lack some low end torque and seem to have been abandoned for massively expensive new bigger,better, faster Kalkhoff models. Bosch have launched three versions of their crank drive system and Kalkhoff are now selling two more that they designed with Daum so it looks like there is still trouble getting one drive that just works at a reasonable price for high torque and high efficiency at 25 Km/h. Newer crank drives try to sense when you are changing gear and reduce torque momentarily to reduce the wear on gear changers and your chain but it seems a bit tricky to get right and cannot do regeneration on hilly routes. I believe that I now know how to build my perfect hub motor system - maybe I should build it - anyone want to help me start the business ? Electric motorcycles and cars are getting much cheaper so electric bicycles are getting squeezed between cheap normal bikes and green versions of conventional transport but they actually hit the sweet spot exactly for urban transport: clean, efficient, cheap, easy-to-park, gentle exercise but not sweaty. If 80% of us will live in cities soon and even American/Yankees have passed peak car use and finally noticed the bicycle again, then the electric bike boom is about to happen now.

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Cycling Problems

To keep this balanced and fair, here are a list of the problems faced by all cyclists.



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