Assisted Pedal Cycles. Converting an existing bike using the
Bafang BBS01 Mid-Drive kit
by David Knight
Click image to view enlarged in a new window.
The terms "Electrically Assisted Pedal Cycle (EAPC)", "Pedelec" and
"e-bike", can have various meanings; but the most common, and indeed
the most useful, definition is: 'A bike that provides the
with a degree of electrical assistance, but is regarded in law as a
pedal cycle.' This means that the e-bike of common usage can
ridden without registration plates, road tax, MOT certificate and
insurance (at time of writing),
and the rider does not need a driving license or a type-approved
helmet. In the UK (excluding Northern Ireland), the basic
requirements for such an exemption are that it must be possible to
propel the vehicle using pedals, the electrical assistance must stop
when the speed reaches 15.6 mph (25 km/h), and the motor power must not
exceed 250 W. In the UK also, there is a minimum age
of 14 years.
People from all walks of life seem to
like the idea
of owning an e-bike; but there is a particular attraction for those who
would like to do a lot more cycling but must realistically admit that
never going to achieve the necessary level of fitness. Such is the case
the author, who underwent an operation for a replacement aortic valve
2012, has some permanent heart muscle damage as a consequence of the
valve failure, and is separated from his local town (Ottery St Mary) by
mile (1.9 km) long
stretch with a height difference of about 90 m. Thus the road
most need to use has an
average gradient of around 1/20 (i.e., 5%). Going down to
therefore no problem, but coming back again without stopping to rest
potentially life-threatening experience. I notice also, that
perfectly able-bodied neighbours don't like cycling up the hill either,
and show a general preference for 4×4s. Access to a
4×4 (or a horse) is desirable if you want to
out of the
house every day, because the road
fast-flowing river in wet weather; but on fine days, it would be good
to get a little exercise while doing the shopping.
There are two routes to owning an
e-bike. Such a vehicle can be bought outright for the price
of a fairly good second-hand car; or for those who might question the
sense of paying thousands of UK£ for a push-bike with a
battery and a small electric motor, it is possible to convert an
existing bike. In the matter of conversions also, there are
two principal choices; that of fitting a motorised wheel, or that of
motorising the pedal-drive system; the latter being known as a
Mid-Drive or M-Drive conversion. The motorised wheel option
seems to have little to recommend it for people who live in hilly
terrain, because it lacks any method for
changing the gearing ratio. The most straightforward approach
also involves the
front wheel, and so will make the steering heavy. So it
for the fiscally prudent hill dweller with an engineering bent, the
M-Drive is the obvious solution.
The huge advantage of an M-Drive system
is that it provides electrical assistance directly to the pedals.
This means that it operates through the existing rear gear-changing
and so, in principle, can provide high torque when
configured with front and rear sprockets having suitable numbers of
Thus diverse mobility requirements can be
accommodated, but that does not necessarily mean that you will be
supplied with the right ratios at the outset. It
is also the case that an M-drive kit will require removal of the front
dérailleur, if provided, generally eliminating the small
mechanical advantage and making
electrical assistance not only available for hill climbing, but also
At this point, assuming you decide not
to break the
law (advisable, see legal info
below); the remaining
choice is that
of the Bafang 8Fun BBS01 or clones
Some initial thoughts on
gearing and choice of bike
It will be presumed here that you are thinking of converting a
reasonably modern mid-priced bike that uses a cassette-type
rear dérailleur system. This allows cogs to be
changed easily and inexpensively during maintenance and to optimise
gear ratios. Converting an expensive racing bike into an e-bike would
make no financial sense.
I own a Saracen
mountain bike with 29" wheels
. This came with an
tooth Shimano 9-speed rear dérailleur, and a triple
chainwheel with a choice of 44, 32 or 22 teeth (i.e., a 3×9
chainwheel is for going fast on good roads, and has proved to be of
little use in
the cramped streets of Ottery and the pot-holed single-track lanes
through which my house communicates. Also, it has to be said
that, since heart surgery, I haven't got the strength to make
the bike go fast in top gear; and the fitting of a mechanical aortic
valve requires that I take Warfarin to keep my blood-clotting time
between 2 and 3 times that of a normal person. I therefore
cycle extremely defensively, and generally pull to the side and stop
when I meet other vehicles in the lanes. Given the dire consequences of
falling off, I also don't go fast downhill. It follows
that I would barely notice if I didn't have the 44T chainwheel, and
this is of concern because the fitting of a Bafang BBS01 drive normally
involves discarding the front dérailleur and
fitting a single front
chainwheel of either 44, 46 or 48 teeth. That would put the
bike permanently into my top front gear or even higher; and I find it
hard to get going from standstill in 44/32 (1.375:1).
Changing to a 12-36T MtB (mountain bike) cassette would offer
with the smallest Bafang chainwheel, which is somewhat better, and of
course, the whole point is that the motor supplements the rider's
strength; but the bike essentially becomes unusable
once the battery goes flat.
As an alternative to fitting the
chainwheel, people also manufacture spider adapters that can be used to
mount non-Bafang chainwheels. These are available for bolt
diameters (BCDs) of 104, 110 and 130 mm. The problem here
is that the standard Bafang chainwheel is dished to bring the chainline
towards the body of the motor. The use of a smaller
therefore might not allow such a good chainline; introducing the
possibility of dérailleur adjustment issues and
wear. On the other hand, a 104 mm BCD spider might allow
use of a 32T chainwheel, and 32/36 would give a very acceptable bottom
ratio of 0.89:1.
A further set of alternatives is
provided by various 3rd
party manufacturers who make Bafang compatible chainwheels. Some of
these sprockets are flat, and some are dished to improve the chainline.
Exact details of the design can however be hard to
obtain from the online information.
The difficulty at this point is the
accumulation of unanswerable questions. This eventually led me to the
decision that I
would not start by experimenting on my perfectly serviceable Saracen,
I would instead get
hold of another bike to use as a test-rig. A straightforward and
modification for the Saracen however, was to fit a 12-36T rear cassette
and get a bit more mileage out of the 44T front chainwheel. This also
gave a somewhat balance-challenging bottom ratio of 22/36 = 0.61:1,
which is not particularly practical for ordinary roads, but is good
for off-road cycling on the steep tracks found in this part of the
Once I had built my first e-bike, I did
eventually get around to converting the Saracen to make a second one.
That was done
because e-biking proved to be phenomenal fun, and it turns out that
able bodied (but not particularly athletic) cyclists on ordinary bikes
can't easily keep up on hilly terrain with a heart patient on a
well-fettled electric bike. I therefore built the second bike
so that others could come cycling with me.
Apart from gearing considerations;
while changing the rear cassette on the
and thinking about the possibility of carrying-out an e-bike
conversion, I become aware of an annoying issue that might be worth
considering when selecting a bike. The Saracen has bare
in its gear shifter cables. For both shifters, a short length
Bowden-cable outer is used to get from the handlebars to a lug on the
of the top frame-tube. A bare steel cable then goes from this
point to a lug just in front of the saddle-post. Then, for
front dérailleur, a length of cable-outer is used to get
around the corner
to a lug on the down-tube to the bottom bracket. For the rear
dérailleur, a length of outer goes to another lug on the
fork, and a bare cable goes to the botton of the fork and back into an
outer for attachment to the shift mechanism (see
I had been aware of the stupidity of
arrangement for some time: it precludes attaching anything to the top
tube, and it prevents the bike from being clamped securely onto a bike
adjustment; but I hadn't thought to do anything about it. Apparently it
reduces weight, but the net advantage of losing a few short lengths
of cable-outer and then having to weld a bunch of lugs onto the frame
seems marginal. It has also been said that it might reduce
friction; but while having to cycle through puddles is practically
unheard of in sunny England, there will eventually come a point when
lubricating qualities of rust and mud will contradict that view.
For an e-bike conversion, any bare
sections will probably have to go. The front down tube is needed for
the battery pack, electrical cables run along the top tube, and
existing attachment points are used up and you'll want to create new
ones. Mercifully, the front dérailleur is removed
and that solves half the problem. For the rear dérailleur
however, you'll need to run a single-piece Bowden-cable from the rear
mechanism to the handlebars with
low curvature. You'll also need the tools and parts for making-up
Bowden cables, and the dérailleur will need to be readjusted
afterwards. None of this is difficult, but a layer of messing around
might easily be avoided if you're planning on buying a new bike
A bike for all seasons
29ers are for tall people. I
am 1.82 m tall and my son Steve is 1.98 m. Both of us can use
the Saracen in comfort, but it does not suit other members
of our family or anyone else under
about 1.75 m. One consideration when carrying out an electric
is that others will want to have a go on it; and if adopters
of the technology can popularise the idea by practical
demonstration, it promises to change attitudes towards short and
medium-range personal mobility (and make the roads safer to boot). I
keep reading articles saying that e-bikes are a form of cheating; as if
cycling only attains validity by being
exhausting and causing the practitioner to need a shower and a change
of clothes. The truth of the matter is that cycling isn't
practical for the majority of people, because you don't arrive fit to
work unless it was walking distance anyway; so cycle rides tend to be
rare, and tend to be arranged so that they end at home. Thus
most people never attain the stamina and skill required to
cycling enjoyable; and a huge barrier to uptake exists.
With the ideas outlined above beginning
to form, but not yet fully realised, my son Steve and I went to the
cycle shop from which we had bought our existing mountain
a few years earlier. I must admit, I had been thinking of getting
another 29er; but Steve made the point that none of our other family
members would be able to ride it, and it occurred to me that having
smaller wheels results in greater mechanical advantage for a
drive-train. So, after much discussion, I bought a Forme
1.0 mountain bike with 27.5" wheels; which also conforms to what I
be a basic requirement, which is that of having adjustable front
suspension and hydraulic
disk brakes. The bike had a 9-speed 11-32T Shimano Hyperglide
fitted originally; but this was swapped for a
12-36T, and the slim saddle was replaced with a
more testicle-friendly gel model for a modest extra cost. I
bought some spare parts, it being my intention not to do long
on an e-bike without a spare inner tube, spare chain and
and the tools needed to fit those things. I was also given a
couple of secondhand Shimano 32T 104 BCD steel middle chainwheels for
low-ratio experiments. The Sterndale came with a triple front
chainwheel and dérailleur, which
obviously had to be removed for the electric conversion, and it is
worth noting that the middle cog from such redundant assemblies is
another possible source of 104 BCD sprockets.
A ride on the Sterndale before starting
to work on
it confirmed that the extra mechanical advantage (18.6%) given by the
cassette and the 27.5" wheels was very noticeable in comparison to the
Saracen's original 11-32T and 29" setup.
Twist & Go
The Bafang motor has an internal freewheel ratchet mechanism in
to the freewheel hub at the rear wheel. This means that the motor can
bike while the pedals stay still, and the facility to connect a
throttle control (accelerator) is provided accordingly.
Having a hand throttle or 'Twist
& Go' facility
on an e-bike is both convenient and a considerable safety advantage. It
permits the bike to pull-away
without wobbling at busy road junctions, in crowded traffic situations,
and when there are pedestrians around. It is also
particularly useful in getting going again when you have been forced to
stop suddenly without time to change down. There is however,
a legal peculiarity in relation to this matter: which is that newly
manufactured e-bikes require Government Type Approval if they are to
have a Twist
& Go control. Conversions carried out on bikes that
have previously been used on the public roads are however exempt from
that requirement (see legal info
The upshot is that, if you intend to
fit a throttle, you must convert a bike that has been used previously.
If you were to buy a frame and build an e-bike from scratch,
thereby sidestepping the expense of discarding a perfectly good
crank-set and front dérailleur, that action would
would result in a machine that requires Type Approval. The
might seem unprovable of course, but there is always an audit trail if
someone wants to cause you legal difficulties.
Installing a Bafang
M-Drive on an existing bike
Presuming that you have a bike that you want to convert, and that you
have a Mid-Drive kit waiting to be installed; the first job is
to remove the front dérailleur (if present).
This is the point at which most online
commentators assume that what they needed to do is universal, and some
actually recommend that you destroy parts of
the dérailleur shift
mechanism with wire cutters in order to get the chain off.
You don't need to destroy anything, but you do need to own
chain-splitting tools and Quick-Links, even if you don't require them
In some cases there will be a screw on
the chain shifter that
be taken out, enabling the mechanism to be opened-up and removed
splitting the chain. On the recently manufactured Shimano shifter on my
Sterndale however, there was a place for the screw in the pressing, but
the two parts had simply been welded together. Thus I needed
remove the chain, but I found that it had been supplied with a Quick
Link already fitted. If you read about Quick Links online,
say that they are unreliable. I asked about this at the cycle
shop, and was told that such links are perfectly reliable; and
practice of pushing chain pins back in with a chain splitter is the
greater source of breakages. To
Quick Link requires a set of special pliers. Some Quick Link
pliers can also close the link (i.e., force the rollers apart), but
this operation is also fairly easy to accomplish by assembling the link
and tugging the chain. If you part the chain using a link
extractor and then fit a Quick Link, note that the links come in
different widths (8, 9, or 10 speed) depending on the number of
sprockets on the rear dérailleur cassette.
The next operation is to remove the
It's best to do this while the cranks are still on the
bike, otherwise you will need to hold each crank in a vice and risk
A 15 mm open-ended spanner is usually required. The
side of the bike (the side opposite the chain side) has a left-hand
Removal of the cranks from low-end and
mid-price bikes requires a
special tool known as a 'crank puller'. Before buying a crank
puller, you need to take out a retaining bolt on the crank-set you
intend to detach and have a look at it. The Bafang 8Fun uses
a 'standard' old-fashioned square-taper fitting, but more modern bikes
will often have a splined crank. Shimano Octalink®
cranks (as the name implies) have an 8-lobed spline, and Isis®
have 10 lobes (and there may be others). The splined
cranks can only be removed with a standard crank puller if there is an
additional anvil piece to fit into the end of the crankshaft. I got
caught-out by this, but I have a lathe, so I was able to make an
adapter out of a piece of mild-steel bar in about 10 minutes.
The item I made is functionally identical to the Shimano
TL-FC15 (see list of tools
the end of the article).
Octalink sealed crankshaft unit with crank puller and adapter.
The top-hat shaped piece fits into the end of the crankshaft,
allowing the bolt in the crank puller to push against it.
Once the cranks have been removed, it's
time to remove the bottom bracket. This requires a special
tool with a 20-lobed spline that fits into the retaining nuts on either
side. This is the point at which you have an opportunity to
ruin the nuts, destroy the tool, skin your knuckles, and write a
venomous feedback article casting doubt on the tool-seller's parentage.
Alternatively, you might try using the thing properly.
You will notice that the tool has a
it to be turned using a wrench or spanner, as well as a socket for
a ½" ratchet wrench. There is a very good reason
has both. It is usual to see explanations of how to remove a
bottom bracket in which the commentator snaps the tool onto a ratchet
drive and (supposedly) turns the nut. That might work, or it
might not; but the second possibility is very likely. A
common comment is that the nuts can be 'fairly tight'; which is like
saying that being cornered by a pack of hungry wolves can be
inconvenient. Of course they are tight. The bike is
meant to go thousands of miles
without the bottom bracket falling apart.
Assuming that you do not own a
pneumatic impact wrench, a completely stress-free way of
loosening the nut
is to hold the tool in place using a G-clamp, with a block of wood on
the opposite side to protect the paint (see illustration below).
An open-ended spanner or wrench can then be placed on the
hexagonal part; and a sharp, but not particularly hard, tap on the
spanner with a soft mallet should free the nut. What happens
here is that the shock of tapping the wrench shatters the crystalline
structure of any rust, dirt or adhesive in the thread.
The G-clamp can then be removed, and the nut can be unscrewed
using a ratchet drive.
Holding the bottom bracket tool in place with a G-clamp
while persuading the nut to turn. The sprocket-side nut has a
left-hand thread. If the nut is very stiff, use a proper
open-ended spanner, not an adjustable.
Another reason why people destroy the
bottom bracket tool is that the nut on the sprocket side has a left-hand thread
needs to be turned clockwise to undo it.
Note incidentally that, for the Shimano
sealed crankshaft unit at least, it is convenient to remove the
nut first. That withdraws the complete crankshaft and bearing
assembly. The nut on the other side is merely a sleeve to
the shaft straight in the bottom bracket.
Once you have removed the crankshaft
the bottom bracket without wrecking anything or injuring yourself, you
are free to install the Mid-Drive motor unit. Furthermore, if the
author's experience is anything to go by, the procedure is then quite
closely related to the information given in the various versions of the
That all depends however on the bottom bracket being
"standard", which means that it must measure between 68 and 73 mm from
one side to the other. You can estimate this very
approximately by waving a ruler in its general
before the crankshaft and pedals have been removed, but it is a good
idea to confirm the measurement afterwards.
The thread around the crankshaft on the
Bafang motor unit is M33×1.5. The motor is held
bottom bracket by a hard steel M33 castellated round-nut, which is then
covered over by a splined aluminium-alloy locknut. The outer
hide the castellations of the inner one. It can be difficult
get the steel nut as tight as it needs to be to stay done up for a long
time, and so a good quality C-spanner (hook wrench) is needed in this
case. Also, the valanced
locknut has to be unscrewed if you want to check the tightness during
periodic maintenance (recommended).
Early versions of the 8Fun just had two castellated nuts,
being a less attractive but more secure arrangement.
Hard steel castellated nuts can be ordered online (on ebay for
example - try "round castle locknut"). Note that stainless
is also hard and has the added benefit of corrosion resistance.
I actually bought a BBS01 kit with a
chainwheel, but then bought a 44T chainwheel separately as an
afterthought. Both of these sprockets came with a plastic
chainguard, the 46T version having a larger diameter than the 44T
version. Both guards however have the same hole circle
for the fastening screws, so the large one can be used with the smaller
sprocket if so desired. I first commissioned the bike with a
fitted, but later left it off on the basis that flared trousers went
out of fashion over 40 years ago. It might conceivably
the chain from jumping off on the outside on rough terrain, but it also
prevents access to the five Allen screws that
hold the chainwheel to the motor shaft, making it difficult to check
tightness or swap chainwheels. Being plastic, the chainwheel
cover is of little use as a bashguard; and a sprocket guard is in any
case not sufficient to protect the BBS01 motor because there are three
electrical cables coming out of
the bottom of that. Riding without grounding the motor housing is
unless some kind of motorschutzblech is devised. Such
a guard is available for the BBSHD, but there are no obvious
attachment points on the BBS01/02, which means that it would have to
attach to the bike frame.
Ratio tables for various
chainwheel sizes and some MtB cassettes.
given in the table below are the number of
turns of the back wheel
per turn of the pedal crank. To get the distance travelled, multiply
the ratio by πD, where D is the diameter of the back wheel.
chainwheel sizes listed are
examples of what can be fitted on a BBS01/02 M-drive conversion, 44 and
46T sizes being made by
Bafang, a 38T being available as a
Hallomotor aftermarket product, 42T being made by PreciAlps
32T and 36T being made by mounting an
intermediate front sprocket on a 104 BCD spider
adapter. Other sizes can also
be made-up using aftermarket spiders; but the larger Bafang chainwheels
dished to give the best chainline, with 42T being the smallest size
that can be
dished in this way.
Shimano HG400 12-36T 9-speed cassette.
|Front chainwheel teeth
(smallest possible dished type is 42T)
There are also 48T
and 52T chainwheels made
by Bafang, but these are intended for small-wheeled bikes, and give too
top ratio for road use with bikes having a 12-36T cassette and 27.5" or
29" wheels (and have
far too many teeth for mountain biking). A recent trend however, has
been to increase the range of ratios available from the rear cassette
with a view to eliminating the front dérailleur altogether.
Since loss of the front changer is a matter of force majeure for e-bike
builders, and front sprockets having less than 42T are flat rather than
dished, these new systems are of considerable interest.
The table below is for the Shimano
Deore XT 11-46T cassette, which has a particular advantage over more
exotic possibilities in that it can be retro-fitted to an existing
freewheel hub. Note how its use with the PreciAlps 42T
front chainwheel practically covers the entire ratio range of
the table above.
The change ftom 37T to 46T is large, but pedaling cadence is not an
important issue for
e-bikes, and it provides for hill climbing by giving an extra position
on the end of a fairly reasonable set of road ratios.
Shimano Deore XT 11-46T 11-speed cassette.
Controls and wiring
|Front chainwheel teeth
Where the installation manual is justifiably vague is in the matter of
lay-out the connecting cables and fit the controls. Bikes
have a great deal of variability, and all that can be said with
certainty is that the job must be done in such a way that cables cannot
get accidentally crushed or snagged. There are
however a few specific issues worthy of comment.
I decided to fit a right-hand twist
throttle, the same configuration as is used on motorcycles. I
found a problem however, which is that the throttle was not compatible
with the control levers for my rear dérailleur. It was
not possible to get the shift control into a good ergonomic position
relative to the hand-grip with the throttle twist-grip in between.
So, it occurred to me that, since there was no-longer a front
dérailleur, I should move the shifter to the left-hand side.
My first thought on this matter was
that it might be possible to buy a left-hand 9-speed shifter, at which
point I made the mistake of looking for information online.
According to some of the web fora, this is a huge problem for
disabled people who lack the full use of the right hand. The
general view seemed to be that the issue is insoluble, although one
suggested 'solution' was to dismantle a 3-speed shifter and get a
machine shop to create a left-handed 9-speed ratchet
mechanism for it. I began to form the view that I should
discard the right-hand throttle and get a left-hand one; but then I had
a careful look at the bike and a strange heretical thought came into my
mind: 'Er. . . ., why can't I just take the shifter off the
right handlebar and put it onto the left one?' Five minutes
work with a couple of Allen keys and I had a left-hand rear shifter.
The numbers on the indicator are upside-down, and I have to
change down with my forefinger and up with my thumb; but so what?
Getting used to the arrangement while out riding took a few
with 9-speed shifter on the left and twist throttle on the right.
The Bafang kit is supplied with a pair
of brake levers that have motor cut-off switches on them. An
however, is that the included levers are only suitable for
brakes, they are of no use if you have hydraulic actuators, and they
also cannot be used if the bike has combined brake and
gear shifters. These limitations ensure that many people do
bother to install the switches (which are in any case not
I felt however that there might be an
retaining the kill-switch functionality, and so I ordered a
Bafang BBS magnetic brake-sensor switches. These can be
retro-fitted to a wide variety
brake actuators, a small magnet being attached to the lever arm using
an adhesive pad, and the switch body being attached to the fixed part.
A problem I found when the new switches arrived however, was that my
brake actuators were not compatible with them; and while I could see
that I might be able to manufacture some sort of secondary mechanism to
make them work, I certainly wasn't going to be able just to stick them
on. Riding without
kill switches was therefore the practical solution, at least in the
Subsequent riding experience suggests
that there will be a worthwhile ergonomic improvement in having kill
switches. This is because there is a lag of several hundred
milliseconds between cessation of pedaling and the shutoff of power
assistance. It is not a serious safety issue however, because
the motor output is only 250 W, and the bike brakes can easily absorb
the small burst of surplus energy.
The setting-up procedure given in the manual is actually pretty
straightforward and does not take long. There are however two
peculiarities worthy of mention.
One necessary aspect of setting-up is
to input the bike's wheel size. It would be good if the wheel
diameter could be put in accurately, say to the nearest 0.1", but the
options are limited to standard sizes. In the case of a bike
with 27.5" wheels, it is necessary to put in "700c", but this is not
necessarily an exact definition. It is good enough, but a
little annoying if you are a lover of precision.
A wonderfully cryptic item in the
advanced setup menu is "Level amount setting". This sets the number of
increments that are available on the handlebar control when selecting
the pedal-assistance level. The choice is from 2 to 9, with a
factory default of 3. On one web forum, I saw a thread discussing the
discovery of 'secret extra power levels', and how the performance is
enhanced by going up from the default of 3 to the full 9. The
only trouble is that there are no extra power levels. It's
just a setting for the interval size. Three levels is a good choice,
and it certainly beats the tedium of having to press the (+) button
eight times to get to full power.
The e-bike battery
To power the bike, I bought a TLH 36V 15.6 Ah
Li-ion battery with charger. This came without
or instructions; but its operation seemed to be fairly
There is an LED status indicator that lights at the press of
button if the charger is plugged in and switched on, or if the battery
is switched on. A mounting plate and connector fits onto the
bike-frame down-tube, the
battery unit slides on to it and is locked into place using a
supplied key. An immediate issue I had with the Sterndale
frame however, is that there was only enough room for the battery on
the front down tube, and the battery-plate bolt holes were too high-up
to mate with the bottle holder attachment points. The work-around was
mount the battery upside-down. I also found that the heads of
M5 Allen screws that came with the bike were too proud to allow the
battery to slide onto the plate; and the solution was to
replace then with A4 stainless hex-head M5×12 screws
The mounting plate system allows the
battery to be
taken away for charging or
storage, but there is no obvious reason why it cannot also be charged
in situ. I feel however that, given the high energy-density involved,
charging should be done in an
outbuilding, or somewhere with a smoke alarm, and certainly not in a
building where people sleep. The battery charger gets quite warm
in use, so is best placed on a wire trivet, or a luggage
rack, or otherwise
suspended so that air can flow over it. Charging the battery
half to full takes about 3 hours; and the charger is small enough to
take with you if you are going somewhere with mains electricity.
Once charging is complete, the LED on the charger changes
red to green and the charger cools down (i.e., the charging current is
My battery installation, unfortunately,
developed a major problem after a few days riding. This was
to do with the
electrical connection between the battery housing and the
mounting plate. Four flat pins on the plate mate with
the pack. I noticed during the installation that the four
were chromium plated. This is one of the worst conceivable
plating materials for a low voltage connector, because chromium has a
habit of forming a tough non-conducting oxide layer on exposure to
air. Still, the connectors were doubled-up, two for (+) and two
for (-), and so I put my initial doubts aside and presumed that the
arrangement must be OK in practice. Using the battery upside
however, it transpires that the connector is not quite as fully
inserted as it would be with the assistance of gravity. The
situation might also arise if the battery were to be mounted
horizontally. This no doubt contributed to the problem that
emerged, for which the symptoms were: random loss of power, and random
down of the system. It was
initially difficult to identify the cause, and the misbehaviour grew
and soon made the bike unusable. Eventually I worked-out what
happening by running the bike on a bike-stand and measuring the supply
voltage at the input to the motor unit. Random shut-down was
caused by large fluctuations in the on-load voltage, and the fault
reproduced by rattling the battery pack up and down on its mounting
plate. Careful inspection then showed that one of the
been getting hot and had started to melt the surrounding plastic. Also,
the connections are doubled-up, this indicates that its
partner was barely working at all.
Mounting plate and battery pack,
with signs of connector overheating.
I might at that point have decided to demand a
replacement battery, but that would not have solved the problem of
having to use it upside down. Also, I do not think that the
connector is fit for purpose, even if it is used the right way up.
I therefore decided to forfeit the warranty and solve the
by modifying the battery pack. I did that by installing a
female XT60 connector, which, as the name implies, is rated for 60
A. XT60s have gold-plated solid copper pins and receptacles
with a high contact area, and so have extremely low resistance.
Note that carrying out modifications to a vehicle battery
pack carries a risk of fire or explosion, and is therefore a job for a
competent electrical technician (please also see my Disclaimer
Battery pack with XT60
wired across the existing connector.
A small circuit board can be purchased
for the XT60, enabling both the male or female types to be used as
bulkhead connectors. To prevent accidental short-circuits,
connectors on battery
packs must, of course, be female; so I fitted a board to a female
connector and mounted it on the battery case.
In doing that, I made a couple of pilot holes in the bottom
battery pack, and fashioned an XT60-shaped hole in the ABS using a
modeling knife and some small round and square rough-cut files.
When mounting the connector, I placed a couple of spacers on
the retaining screws, to minimise the protrusion, and sealed the
connector body into the hole I had made using architectural silicone.
I wired the XT60 directly across the existing connector,
thereby retaining the normal functionality (for what it's worth), and
also siliconed around the original connector to improve the
Finally, on reassembly, to minimise water ingress as far as
possible, I taped the join between the upper and lower parts of the ABS
housing. Note that it is possible to buy silicone rubber caps for female XT60
. These will exclude dirt and help to prevent
short-circuits in the event that the battery is stored or used on a
with the standard connector.
Having opened the battery pack, I had
an opportunity to make observations that would not otherwise have been
possible. I noticed that the On-Off switch is not capable of
handling the current required by the Bafang motor, and this function is
instead accomplished by using the switch to turn on a
transistor. Presumably, the cost of a small switch and a MOSFET is less
than that of a high-current switch. A somewhat worrying
feature however, is that plugging-in the charger also switches-on the
battery output, which is how the press-button battery-level indicator
comes to work either
when the battery is on, or
when the charger is in. This means that charging the battery while it
is installed on the bike has the effect of turning it on. The
bike, of course, does not wake-up unless the handlebar power button is
but it means that the the motor will not go to sleep straight away if
the charger is plugged-in before the battery is turned off.
Whether this is a serious issue is moot, but it is not ideal.
"Off" should mean "Off".
The appalling chromium connector
seriously coloured my initial impressions of riding the
bike. I came to the (very-pessimistic) conclusion that the
makes a rather feeble contribution to the rider's efforts, and while it
did (initially) enable me to get up the hill from Ottery without
stopping, I still had to do quite a lot of work. I also noted
that, while the twist throttle could start the bike from standstill on
level ground, it could not do so on a 5% gradient. The effect
of fitting the XT60 connector, and thereby discovering the actual
the motor, was consequently astonishing.
Although the following calculation
conjecture, we can easily get a rough idea of just how deleterious the
original connector was. If the Bafang BBS01 were to have a
peak power consumption of 250 W at 36 V, it would require a current
of 6.9 A. In reality however, if it is to deliver
W to the road, it needs a somewhat greater input than that,
probably approaching 300 W. This means that we should expect
typical peak current of about 8.3 A, or say 8 A in round numbers.
Hence, in the state of maximum demand, the motor looks something like a
36/8 = 4.5 Ω resistance.
Now, if the connector were to have a
resistance in the region
of 1 - 2 Ω, then at times of peak power demand, it would be
expected to cause a voltage drop of between about 6.5 and 11 V.
Instead of a nominal 8×36 = 288 W input to the
motor, we would have
= 193 W and (36-11)2
= 139 W.
Approximately halving the motor power would indeed result in
performance, and the reduced voltage is likely to cause the controller
to assume the battery to be
dead and switch off.
When I built my second e-bike, I bought
model of battery again but fitted an XT60 connector immediately.
Bike performance with
(44T with 12-36T cassette).
The gearing configuration I adopted initially for road use was a 44T
front chainwheel with a 12-36T 9-speed rear cassette. This
turned out to be a perfectly acceptable combination for the type of
and country cycling I do, giving speeds in the range of 6 to 20 mph in
gears 3 - 7, the ability to reach 25 - 30 mph in gear 9, and the
ability to pull away on the hand throttle on uphill gradients a little
in excess of 10% in gear 1.
Bafang dished chainwheel gives a chainline exactly parallel to the
frame-line in gear 5, which is ideal. Dérailleur changes are
smooth, provided that the pedal or motor force is slackened-off, just
as in normal cycling; and there seems to be no need for the gear-change
sensing system provided with some of the more exotic versions of the
In order to understand the effect of
assistance, it is useful to be aware that a normal cyclist (i.e.,
someone who is not an athlete) can produce an output of 100 - 200 Watts
for fairly long periods, and an output of 400 - 500 W in short bursts
for going up hills or hard acceleration. An additional 250 W
the electric motor therefore makes climbing hills seem like traveling
on the flat. In my case, having limited cardiac output, I can
happily produce the 100 - 200 W needed for prolonged periods of level
cycling, but the 400 -
500 W needed for steep hills is beyond me. Add the 250 W from
BBS01, and I get 450 W, which means that typical road hills no longer
present a problem. If I pedal moderately hard, I find I can
up the 5% (average) hill from Ottery to my house at around 11 mph in
gears 3 - 5, without any need to take a rest. I also found
could get up the hill on the throttle, without any pedaling at all, at
around 6 mph in gear 1. It is of course tedious to go
slowly, but it does give me the reassurance that I can still make it
home even when I am completely exhausted. Incidentally, the
that it is fun to pedal within the physical capabilities of the rider
makes using the e-bike into an excellent form of exercise.
The way in which the motor unit
to the rider is initially somewhat strange, but getting used to it is
not difficult. As set-up for use on British roads
(assistance stops at 15.6 mph), motor output is at its greatest when
rider pedals slowly, and decreases progressively as the speed climbs
towards the assistance limit. This gives the curious effect
assistance can be increased by changing up when going uphill. The
provision of a freewheel ratchet in the motor unit also permits what I
'faux pedaling', which is where the act of turning the pedals too
slowly to lock the ratchet and propel the bike, causes the motor to
propel the bike instead. This gives onlookers the false impression that
you are doing some work, even though you are actually getting a
completely free ride.
I have so far not managed to exhaust
the battery before recharging it;
but with moderate pedaling, I would estimate the range to be in the
region of 40 to 60 miles.
Low ratio gearing
(32T with 12-36T cassette).
For my first hill-climbing and off-road cycling experiments, I fitted a
intermediate front sprocket to a 104 mm BCD spider adapter from
RisunMotor (also avalable from Hallomotor and ConhisMotor).
Strictly, the spider was designed for chainwheels
34T and greater, but being made from hard stainless steel, it was
possible to grind it down (using an ordinary workshop tool grinder)
until it just cleared the chain on a
After-market spiders with 104 mm BCD are available for the
Here, a Shimano 32T intermediate front sprocket is
attached to a Hallomotor stainless steel spider adapter. A
spacer of about
mm is required to prevent the
chainwheel bolts from rubbing on the motor housing. The
spacer is easily made
from a piece of 20 SWG aluminium sheet (starting by laying the spider
on top and marking the holes with a scriber).
Here a 32T Shimano sprocket is mounted on an aluminium
104BCD spider. As is the case with the steel spider, this one
is intended for sprockets of 34T and larger, and so requires some
filing to make it clear the chain (do not try to shape aluminium using
workshop grinder). A 0.9 mm
spacer is required between the hub and the spider, as for the steel
The 32T front sprocket fitted to a bike
with a 12-36 cassette gives a lowest
32/36 = 0.89 turns of the back wheel per turn of the crank.
very roughly the same as changing down by a further two gears relative
to the ratios available with the 44T front sprocket. It gives
bike with 27.5" wheels the ability to pull-away uphill on the throttle
on a 17% gradient
The disadvantage of the small front
that it lacks the dish-shape of the standard Bafang sprocket and so
gives the best chain-line in gears 7 and 8. The Shimano
however have a tooth profile and shifting ramps that permit
them to be used
with a fairly severe degree of misalignment, and this allows the lowest
ratio to be used reasonaly successfully. One downside is
that the chain tends to climb down the cassette if the bike is wheeled
backwards in gears 1 or 2. That situation is usually
however, because gear 3 is about the same as the lowest required road
ratio. Fortunately, the additional freewheel hub in the Bafang motor
prevents chain climb-down on backpedaling. Critical setting of the
low-limit (L) and back-tension (B)
dérailleur adjustments is necessary to avoid clicking
and grumbling when climbing very steep gradients, and the drive sounds
noisy under high loads. Fairly rapid wear is to be expected during
This chainwheel is somewhat too small
for use on the roads.
downhill, it is difficult to pedal fast enough to catch-up with it,
even in gear 9; so freewheeling is the order of the day. Going uphill,
there is not much cause to use the lower ratios on ordinary roads, but
the bike in this configuration is nevertheless serviceable if somewhat
(42T with 12-36T cassette).
A narrow-wide chainring is a very clever thing; and once you realise
what it is, it is difficult not to want one. Since bike chains
have alternating inner and outer links, and must have the same
number of each (provided that there are no half-links); a chainwheel
can have alternating wide and narrow
teeth, provided that it has an even number of them. This gives a
dramatic increase in the strength of the sprocket for a given material
type, allowing hard aluminium alloys to out-perform steel. This profile
cannot be used for the cogs on dérallieur assemblies, because
must go onto the sprocket in a particular way; but it is still
possible to re-fit a chain in the dark, because it won't go on unless
is properly aligned.
Strength is also not the only
advantage. The chain fits securely on the
narrow-wide structure, and this reduces the side-to side movements
that cause noise and wear and can sometimes trigger the chain to jump
when going over rough ground. Hence, the narrow-wide profile is
becoming increasingly common on the front chainwheel of
high-performance 1×n drivetrains.
When fitting a narrow-wide chainwheel, note that while there should be
no half-links in a system having a tension arm, it is important to be sure that there aren't any.
| The skirt
of the PreciAlps chainwheel is deeper than that of the ones supplied by
Bafang, and I when I bolted it directly on to the motor on the
Sterndale I found that
the teeth rubbed on the bike frame. To overcome that problem, I
included one of the 0.9 mm spacers that I had made previously, as can
be seen by careful inspection of the photograph above. It would be
useful if manufacturers would recognise the importance of having such shims available when building an e-bike.
It would also be possible to place
shims of about 33.5 mm internal diameter between the motor body and the
bottom bracket, but while that might be useful in compensating for
variations in bottom bracket width (68 mm vs. 73 mm), it is easiest by
shim the chainwheel provided that the thickness does not exceed about 3
mm (shear forces on the bolts must not be too great).
Relative to the smallest dished Bafang
(44T), the 42T PreciAlps gives a 4.8% increase in mechanical advantage.
This makes it noticeably easier to get up steep hills, without
sigificantly compromising top speed. What was most noticeable however,
was the smoothness and lack of noise from the drivetrain (particularly
in comparison to the non-dished 32T front chainwheel that I had just
>> more to follow.
Electric bikes, 2016 UK legal
EAPCs in the UK (excluding Northern Ireland) are limited to a maximum
assisted speed of 15.6 mph (25
km/h), a maximum motor power of 250 W, and must have pedals that can be
used for propulsion. The bike can go faster than 25 km/h, but
only under power provided by the rider. Failure to comply
with these rules causes the bike to be classified as a motorcycle;
which requires registration, an MOT certificate, tax, insurance, an
approved helmet and a
license. Non compliance is therefore a serious offence and
can lead to a heavy fine and a general driving ban. In the
event that some idiot knocks you off your bike, it might also
compromise your ability to claim compensation.
& Go - self conversion type approval exemption
The DFT rules state that an EAPC with a Twist & Go facility,
i.e., the ability to move under electrical power at speeds up to 15.6
mph without pedaling, requires type approval. The reason for
the requirement is that the motor does not necessarily cut off when the
rider stops pedaling. This seems to cause a problem for
people who want to convert existing bikes, but the link above relates
to a clarification. The DFT recognises that Twist &
Go is an important improvement for people with limited physical
abilities, and the Type Approval requirement is strictly directed at
manufacturers. If an existing bike that has already been used
as a pedal cycle on public roads is converted for electrical assist,
the fitting of a
Twist & Go control does not constitute an offence.
Future legal changes
There are pressures within the EC to require e-bike users to have
party insurance. There will no doubt be much wrangling over this issue
in the months and years to come; but to the author's mind this is not
an entirely bad idea provided that the costs to the rider reflect the
actual risks. UK rules might also diverge from EC rules at some point
Note that an M-Drive kit does not usually include a battery; the latter
because there are choices of capacity. The Bafang BBS01 and
clones are sold with a thumb throttle, usually said to be for off-road
use only, but see the Twist & Go type approval exemption info
above. There are also ½-twist throttles available for those
who are used to riding a motorcycle. Some motorcycle
have an adjustable friction pad, to allow hand signals with power on,
but an e-bike throttle should spring-back when released.
sales UK - Bafang BBS01 Conversion kit with 44T chainwheel
MAF Scooters - Bafang BBS01 with 46T chainwheel
Classified on the website under > Parts > Electric Motors.
Bikes - Panda M-Drive 36 V 250 W kit
clone, 48T chainwheel).
Whoosh Bikes - Bafang BBS01 with
Bikes - Bafang BBS01 with 46T chainwheel
Pedalease - TLH 36 V 15,6 Ah
Li-ion battery packs.
Good source of information as well as parts. Good
advice on how to use the BBS01
BBS01 Kit, product manuals, Bafang
BBS brake sensor
, spider adapters allowing the
use of non-Bafang chainrings (see Bafang/8Fun spares).
France. Mid drive parts and accessories, lightweight
spiders for the BBS01/02. 42T is
the smallest possible chainring size that allows the optimum chainline
(i.e., a dished chainwheel). PreciAlps chainwheels use the excellent
alternating narrow-wide tooth profile.
Note that chainwheels for
the BBSHD (1 kW) M-drive do
the BBS01/02. The sprockets look similar
in photographs, but the ones for the high-power drive are smaller and
have a smaller BCD for the 5 mounting holes.
(Shanghai). Spider adapter, etc.
The perfect solution for adding extra accessories (smartphone / GPS
holder, action camera, headlight) once the e-bike conversion has used
up all of the handlebar space.
Don't forget to have
a look on ebay
There's plenty there, including batteries, Bafang-fitting
spider adapters, bashguards, cassettes, twist
throttles, brake sensors, bike tools (and lots of other stuff you
want). Note however that it may be cheaper to buy expensive
items directly from the supplier.
Soanes Cycles, Colyton, Devon
Long established Devon bike shop with a reputation for good
deals and good service. The author's preferred local cycle
shop, not an e-bike supplier.
Information and review
Manuals are available from most of the conversion kit suppliers (see
above). Some are better than others. Read them.
ebike - Installing the Bafang 8Fun BBS01
Dave Atkinson - Installing the Panda M-Drive
Dave Atkinson - Panda M-Drive kit
The reviewer lives in Bath, and needs to climb Lansdown Hill every day
to get home from his office. He finds that the supplied 48T
chainwheel far too big when used with his 11-28 cassette and suggests
that the ideal chainwheel size for his bike
would be in the 34 - 42T range. It depends on the rear
ratios and the wheel diameter of course, but commentators seem to agree
that 48T gives
self-powered top speeds that you just don't need (~ 50 km/h / 31 mph),
and this should be traded for torque at the bottom end.
UK (the CTC), Richard Hallett - Panda M-Drive kit
Discussion of powered wheel and friction drive options, plus
review of the Panda M-Drive and its installation process.
some derailing problems due to poor chain line. Also finds
give too high a top gear (with an 11T rear), and suggests that 45T
would be better (note
that Bafang makes a 44T chainwheel for the 8Fun). You can
get up a 1/10 hill fairly easily with the 48T front sprocket, but the
manage very steep hills will be improved with a smaller one.
- Charging Lithium Ion batteries.
Singletrack World: Shinano Deore
XT 11-46T 11-speed casette
Modern bikes are moving to a single front chainwheel configuration as
rear dérailleur capabilities improve. Although even
wider-range options exist, the Shimano 11-46T Deore XT can be
retro-fitted to an existing freewheel hub. It gives a fairly
evenly-spaced 11-37T 10-speed gear set, with a big jump to 46T to
handle extremely steep climbs. Changing into the big bottom gear is
smooth due to well-designed shift ramps.
happy to do the installation yourself, chances are you'll already have
many general workshop tools at your disposal (i.e., socket
spanners, adjustable wrench, copper or plastic mallet, G-clamp, bench
grinder, Allen keys,
screwdrivers, easing oil, Loctite blue, cable ties, etc.).
You'll probably also have a set of tyre levers. In
case, the following additional tools will provide the capability to do
general bike servicing. You probably won't need all of them for an
M-drive conversion; but if you're going to
start comprehensively dismantling bikes and messing around with
sprocket ratios, it's best to be equipped for
The items are not expensive, and you
can get most of them on ebay (if you search for
these items online, put "bike" into the search term). Note
that some of the
tools shown below are for the amateur market, and will not
industrial use; but they should do the job if applied correctly and not
subjected to excessive force.
chain wrench (sprocket wrench with hook wrench and
The spline wrench fits the Bafang outer aluminium
bottom bracket nut. The chain wrench is used for holding the rear
sprocket cassette still while undoing the retaining nut.
19 - 51mm size is required for the Bafang
bracket castle nut. A cheap multi-purpose wrench is not
good enough for the job.
puller (for removing pedals).
The basic tool is
used for square taper spindles. Shimano Octalink
(8 spline) and Isis (10 spline) crank arms
require an additional anvil piece that fits into the end of the shaft
||Octalink / Isis adapter.
For removing splined cranks when using a puller
designed for square taper cranks.
Left: magnetic type, snaps onto the end of the puller; Right:
bracket disassembly tool (20 spline). The
chainwheel side bottom bracket retainer nut has a left-hand thread.
To loosen the nut, hold the tool in place with a G-clamp,
with a piece of wood to protect the paint on the other side of the
bracket. A sharp (but not particularly hard) tap on the
wrench with a soft mallet should get the nut turning.
Used for adjusting the end-play of tapered axle
Used for detaching the cassette hub (Shimano / SRAM
Needed if you want to replace worn cogs or change the rear
dérailleur ratios. The
outer nut fits into a 24mm or 15/16" socket wrench.
||Chain rivet extractor.
Needed for removing the front dérailleur
fitted. Also a general necessity in any bike toolkit.
Convenient for rejoining chains, and more reliable
practice of pushing pins back in. Make sure you get the right
width for your rear cassette (8, 9, 10, 11 speed, etc.).
||Quick link pliers.
Some quick-link pliers can only open the link
(i.e., pull the
rollers together). You might as well get one that can also
close it (i.e., pull rollers apart), although a sharp tug on the chain
works just as well.
||Chainring nut wrench
For tightening the fasteners that attach the
front chainring to the
spider. This one (Shimano TL-FC21) also has a crank cap
and 9 and 10 mm wrenches.
||T-handled chainring nut wrench.
Allows more torque than the flat peg spanner, but
can only be used when the chainwheel is off the bike.
wrench / spoke key (for 10 - 15 gauge spoke nipples).
needed for M-Drive conversion, but used for general wheel tuning.
||Bike stand (30
Once you have fitted the Bafang display to the
handlebars, you can no longer turn the bike upside down for servicing.
A stand is also convenient for making electrical measurements
setting up the dérailleur (etc.). A 30 kg rated
had for about £25.
A measure of the gradient on which the bike can pull
away under its own power is extremely useful when experimenting with
sprocket ratios. This Sun
bike inclinometer consists of steel ball
in a curved tube filled with viscous liquid, and has scales in gradient
% and degrees. - Simple but effective.
Parts needed for Shimano
Deore 11-speed 11-46T conversion
All parts must be Dyna-sys II pull-ratio compatible.
Shimano XT CS-M8000 11-46T 11-speed cassette.
Shimano XT RD-M8000 11-speeed dérailleur, Shadow RD+ shift,
SGS (long cage).
Shimano XT SL-M8000 11-speed RH bar mount
shifter with visual display.
Shimano HG-X11 MtB 11-speed chain
Quick Link 11-sp