Electric Assist Bicycles for the Uninitiated – by Matt Shearer

Matt Shearer loves to cycle, and has been riding with BARBUG for some time.  Matt has a wonderful collection of bikes including a Pedersen.

Living  in an extremely hilly area, Matt decided that if he were to continue cycling a little assistance on the hills would be necessary. He  converted one of his many bikes to electric assist. One never being enough, and always looking to improve design, he has now built a  few.

This article aims to answer questions people put to him when they see him peddling effortlessly up a hill that would have the fittest cyclist working hard.

When I ride my electrically assisted bicycles I am often asked to explain how they work, what alternatives exist in the market, where is and what is the battery, can it generate power going down hill etc. I know my verbal explanations never do the field justice so I have written the following to bring some order to the chaos of my verbal explanations. I hope my explanatory classificatory description is useful especially for those who wish to ask further questions (of EA bike and kit retailers).

Electrically Assisted (EA) bicycles can first be divided into two groups. There are the purposely built EA bicycles where the bike, the EA motor, its control box, its throttle and battery are sold as one unit such as Powercycle, Kalkhoff, Wisper and Alien.
They seem to feature frames that omit a top tube ie they are step-through frames.

Then there are EA bicycles where the bike owner or a bike shop installs an EA kit into a bike frame the cyclist already possesses. The kit usually comprises an EA motor, a control box and a throttle device such as a ‘throttle’ or a pedelec sensor. It is this group that I will mainly describe but they parallel the complete EA bikes almost exactly.

Location of the EA motors:

The EA motors I am writing about are the modern generation brushless motors that are now used in most EA installations. The major exception is the Heinzmann range which are brushed motors. The motor can be located on the bike in one of three places. They can be within the front hub and driving the front wheel, within the back hub and driving the rear wheel or adjacent to and driving the bottom crank or chain and then driving the back wheel. The rider can assist the motor or not as he/she pleases although with a pedelec control he/she must pedal to get motor assistance.The mass of most EA motors is just over 2.0kg.

Each location and assist method has its advantages and disadvantages. A front wheel location is the simplest installation. The hub in this location is unobtrusive, it tends to be quiet in operation and from my experience can propel a rider who is not pedalling between 20 and 30 kilometre/hour on flat terrain with a 200 or 250watt motor. It is subject to about 2% wheel spin but this is not actually ever notice by a rider. Some motors are geared to provide assistance to the hill climber eg Tongxin in the Nano Brompton and others eg Bafang, seem to have a stronger focus on maximum speed. These motor like most EA motors require internal gearing because the motor spins at a much faster rate than the wheel it is driving.

In the rear hub location of an EA motor the rider is provided with assistance with or without the bikes gears which are located on the outside of the hub. By implication the gears are of the deraillier type. These motors eg Crysallite, look to be a little larger in diameter than those in the front hub and seemed to be a little less refined. Expect non pedalling top speed to be about the same as those installed in the front hub.

The third location is EA motors are those driving the bottom crank or chain and these show the greatest variety of locations and types. The motors can be bolted on the down tube, on the seat tube or the chain stay. One very efficient motor (Stokemonkey) is located between the seat tube and the chainstay on extended frame bikes. Another design (Gruber) has the motor driving the crank via a bevel gear from its location inside the seat tube.

Whatever the bottom crank location these motors either drive the crank directly through an additional sprocket and small chain or they drive the chain directly through a sprocket connected to the motor with no small chain required. All these motors have the advantage of using the bikes gears, either hub or deraillier, which should gear the motor to a lower wheel speed and so be more efficient on hills. And give an even higher top speed on the flat.

In reality the difference between the variable gear assisted bikes (crank and rear hub located motors) and front hub EA bikes is not so marked. It all depends on the gearing of the front hub. Is the front hub configured for hills as in the nanoBrompton or for the flat as in the eZee kits?  Does the front hub equipped rider want to climb hills or get home faster on flat terrain.

Back Hub


The Throttle:

Regardless of the motors location the actual assistance offered by the motors has to be selected by the rider. This demand selection can be by a throttle usually mounted on the handlebars adjacent to the hand grip. They are of two types: either a thumb throttle or a twist throttle. The alternative is a combination of an ON/OFF switch and a pedelec sensor usually located on or near the crank. This pedelec sensor notes when you are pedalling and offers only provides assistance in that circumstance. Another very simple control system also used is a simple ON/OFF switch where power level is predetermined and you either have it or not. Perhaps this is over simple!

Throttle and Power Level


The Control Box:

Added to both of the ‘demand’ selectors is a Control Box which matches your demand for power, the current rotary speed of the EA motor and its power supply. With all the thinking these units do they can get warm and should be in a location where they can be cooled. In size they are about the size of a box of 50 cigarettes.  They are connected to the ‘throttle’, the motor and battery by electric cables.The voltage of the control box is matched to that of the motor and the battery.

The control box is usually located with the battery in the same bag or box but sometimes they are separately located on the handlebars (nanoBrompton) or even near the motor with the crankdrive systems but always remember the control box is fragile. The mass of the throttle and control box together is 0.4kg.

The Battery:

With the EA motor, Control Box and ‘throttle’ is a battery to power the system. The first EA bikes used lead-acid batteries which are used to power a car’s starter motor. These batteries are fairly heavy and have a relatively poor capacity of power. Then came Nickel metal hydride batteries which were a quantum leap forward with much lower mass and much greater capacity. Now there are Lithium based batteries often with the addition of another element.

Lithium based batteries are the current state of the art for an EA rider. They provide the most useable power for the least mass but not for the least cost and the manufacturers of batteries (mainly in China) now seem to have the reliability

problems under control. Nickel metal hydride batteries of the same voltage are cheaper.

Other things being equal whatever the type of the battery it is going to weigh at least twice the weight of the rest of the kit so the mass of the battery can be fairly critical. In general the aim on a bike is to keep things as light as possible.

The capacity of the battery you will require (expressed as Amp/hours or Watt/hours where Amp/hrs X Voltage =Watt/hrs) will depend on the planned use of the EA bike and how much a pessimist the rider is. If one just wants to ride to and from the local shops –say 10km or 5 miles then a low capacity battery as used in rechargeable power tools may be sufficient. If one is considering touring then you may want the largest capacity battery you can afford and the bike can comfortably carry –say 500Watt /hrs for a 36volt battery. The mass of this battery is 3.7kg but with less watt/hrs weight can be reduced.

Always remember the motor is rated for a certain voltage, say 36v, and that determines the voltage of the battery. It is possible to ‘overvolt’ some motors with a battery of higher voltage than the rating of the motor and that will definitely give motor cycle riders a surprise but such an installation will encounter severe motor reliability problems.

Location of the battery:

The problem of where to put the battery on a conventional bike frame or folder has been ‘solved’ in six ways. The nanoBrompton and Bromptom Freedom put the battery in a bag suspended from the head tube but it could put in any rack or bag suspended from the handlebars or sitting on a front rack. A second location is hanging from the top tube in the inner triangle of the top tube, seat tube and down tube. A third location which is used by most commercial EA bikes is in a slot parallel to and behind the down tube. A fourth location is on or on the side of a rear rack. A fifth location is hanging from the back of the seat and lastly the battery can be placed in a pack on the riders back.

The battery is relatively heavy and a relatively fragile object so I would not recommend locations where Newtons First Law of Motion could be demonstrated. Keep the mass as low as possible on the bike and keep it very firmly attached to the bike.

Battery Pack with Ignition Key


The Complications:

I have not covered the regenerative EA motors ( BioneX and Panasonic) for three reasons. Firstly they are not really that efficient in reclaiming power as one cycles down hills. Secondly bike do not need the type of regenerative braking that these systems provide (and certainly heavy trains need) and lastly I believe these systems overcomplicate the electronics. Always follow the KISS principle in engineering.

Battery voltage is another challenge to the installer. While 36v now seems to be the industry standard and that is the voltage I have chosen 12v, 24v and 48v batteries can be purchased and  different systems utilize them all. Remember however that the motor, controller and throttle should be matched to the voltage of the battery. While it is possible to say ‘overvolt’ a 36v motor with a 48v battery and achieve 80k/hr it is not recommended for a number of obvious reasons.

Gears on an EA bike: With an EA motor doing some of the work for you on hills and with its maximum speed limitations (with a front hub motor) I have found my hub gears almost redundant. Except on the steepest hill I seldom use their assistance. On the Bromptom I feel its two ratio derailler is not used as the hub remains in the direct or second gear of the hub most of the time. On my Surly the Rohlof hub usually remain in the 11th or direct gear and never seem to drop below the 8th gear in to the lower ratios even on the steepest climbs. On my Speedwell (a 1960s Australian frame) which has a seven ratio Sram hub gear with the 4th gear as the direct gear I have yet to used the 2nd gear since I have installed the EA kit. Wind resistance, the limited top speed of the EA motors and my sensitive nature and fear of what will happen if I fall off at speed precludes me using the gears above the direct drive ratios. EA motors on bikes greatly reduce if not almost eliminate the need to change gear ratios as you ride.

The alternatives:

A nanoBrompton (the hill climber) has a 200watt Tongxin motor, the battery (36Volt) resides in a front carrier bag and the control box is suspended between the handlebars. The distance that one can expect to ride with the nanoBrompton seems to be about 50miles but that does not mean that if you do not pedal and expect the motor to do all the work you will ride for 50 miles. The key word is ASSIST. The maximum (no pedalling) speed on flat roads one can expect from the nanoBrompton is about 20k/hr

A 250 Watt Bafang motor installed in the front wheel in my Surly frame will drive the bike at a minimum 25k/hr (non pedalling on flat roads). This combination has almost the same hill climbing capacity to the Tongxin but it is obviously noisier and the motor is larger and heavier. The Bafang motor has the advantage in that a disc can be bolted on the side of the motor for the utilization of a disc brake. With a 36v, 14amp/hr battery (500watt/hr) trips of over 50miles seem feasible. Certainly there seems to be some power left at 50miles of mixed riding.

With preassembled commercial EA bikes eg Power Cycle, Kalkhoff range the decisions as to the type of equipment have already been made. Just pick an EA bike that suits your need/aspirations and your pocket. If you are constructing an EA bike utilizing a frame you love (steel for me) then the field is open to many variables: motor location,  method of power selection, battery capacity and battery location.

So for an add on EV kit we have three motor locations, three realistic battery locations, two control systems (throttle or pedelec), three types of batteries (lead acid, nickel metal hydride and lithium)  excluding at least four possible battery voltages.

This allows fifty four different combinations to achieve EA cycling happiness.To insure future happiness chose an EV retailer whom you can really trust. Some internet retailers promise much, take your money then deliver nothing. This technology is new and of variable reliability. You need a retailer who will back up his product in the future.

About BargoSal

Keen cyclist, my aim is to get bums on seats, work with council to improve cycling infrastructure and driver awareness. I am also a website designer.
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