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e-bike  Lighting & Electrics
Improving e-bike ergonomics and safety by adding standard motorcycle lighting equipment and other electrics.

Brake switches
Commercially produced e-bikes are required to have motor kill switches, which operate when the brake levers are pulled. For those who build their own e-bikes however, this functionality is optional, and also sometimes difficult to implement. The Bafang BBS01 and 02 mid-drive kits, for example, are supplied with replacement brake levers that have switches; but those levers only work with cable-operated brakes. For those who have hydraulic brakes, there are magnetically-operated switches that can be bought separately; but the parts attach to the brake levers using adhesive pads, and many levers have no flat surfaces on which to stick things.  Also, the resulting open magnetic circuit has a large compass-safe distance (>0.5 m), which precludes mounting a compass on the handlebars. Finally, there are hydraulic brake systems designed for the e-bike market, with switches built-into the levers (such as the Tektro Auriga E-comp); but having to replace the brakes on an existing bike is expensive and requires considerable work, and the switches are also usually magnetic.   
     Given the difficulties, the lazy solution to the kill switch problem is simply not to use them. They are designed to be open-circuit until the brake is applied, and so it is not necessary to plug them in to the motor wiring harness. There are then however, many situations in which it takes the motor controller several tenths of a second to realise that power output should cease; and in those instances, the unwanted energy must be dissipated in the brakes. This effect is not necessarily serious, but it does imply a degradation of stopping distance, unnecessary brake-pad wear, and a small extra drain on the battery.
     As stated in the parent article, the author has two e-bikes; one based on a Forme Sterndale with 27.5" wheels, and the other based on a Saracen 29". Both of these have hydraulic brakes, with levers that lack anywhere to put stick-on magnetic switches. It was my firm intention however to fit switches somehow; not only for the motor-kill function, but because, apart from legislative inertia, it is hard to think of a reason for excusing e-bikes from having brake lights.
     The Saracen 29 has Tektro  Auriga brakes that have an M4 reach adjustment screw on the brake lever. It can also be observed that some Tektro levers, such as the Orion SL and Auriga Pro, have a reach adjustment screw with a large knurled head; which suggests that a longer screw might be used without interfering with the rider's natural hand position. I therefore fitted longer screws with locknuts, the point being that the protruding part might be then used for attachment of some kind of linkage, and rode the bike like that for a while to see if there was any ergonomic downside. I found that I was completely unaware of the non-standard screws, and so started to consider how I might make use of them.
     My first thought was to try to fit spring-loaded or pull-operated switches to the brake lever bodies. There is however nowhere obvious to attach anything; except perhaps for a tapered region next to the hydraulic hose connection, and a simple clamp attached at that point is unlikely to grip reliably. It goes without saying of course, that after a long career in engineering, I have a strong aversion to sticky pads (perhaps they have improved, but all of the ones I have ever used fell off after a year or so). It seemed therefore, that I would need to develop complicated mouldings to fit around the brake-lever bodies and give mounting points for waterproof micro switches, and that I would probably need to disconnect the hydraulic hoses in the process of fitting them. In such circumstances, it is best to wait and see if a simpler idea comes along.
     This work took place at a time when I had already ridden for many miles without kill switches. This meant that I was unaware of how much benefit they might give in practice; and while I definitely wanted them, my principal interest was in upgrading the e-bike electrics to be like that of a conventional motorbike. It had therefore been my intention to add a waterproof ABS box of 160 × 45 × 56 mm beneath the handlebars, orientated so as to allow the mounting of traffic indicators compliant with the statutory minimum separation of 240 mm. I mounted the box on an aluminium bracket attached to the handlebar stem by means of extended clamp bolts and spacers. I also put a 30° bend in the bracket, to make the front of the box vertical relative to the road. It was while doing this work that I realised that by positioning the indicator stems to be as far forward as possible, there was enough room behind them to allow the fitting of motorcycle rear brake-light switches. These are simple spring-loaded mechanical pull-switches, mounted by means of an M12 plastic nut, and supplied with a pull-spring that can be bent to fit a wide variety of bikes.
     I must confess that, had I come up with this solution in the absence of any intention to fit indicators, it would have seemed complicated and inelegant and I would probably not have implemented it. With the indicator box present however, it became immediately straightforward, robust and cheap. The arrangement is shown below, with the lid of the box removed to show the switches inside. This, incidentally, is the original test configuration, with the switches in parallel connected directly to one of the Bafang kill-switch ports (the brake light circuit has yet to fitted). The kill function is activated by shorting the blue and black wires in the Higo Mini B3 cable (which was taken from one of the Bafang-supplied brake switches). The red wire (Hall sensor B+ 5V) is not used, but must be insulated.

Brake switch - Saracen

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Brake switch -Saracen detail

     The supplied pull-springs are simply bent around the extended reach adjustment screws on the brake levers and adjusted until the switch is slightly pulled-out (but not yet closed) with the lever at rest. Motor cut-off then occurs before the brake pads are engaged. The ends of the springs are formed into loops using brass inserts taken from a small electrical connecting block. This ensures that there are no sharp wire-ends for fingers to find accidentally in the dark. The original M3 zinc-plated steel grubs screws of the connector block have been replaced with stainless A4 Allen-socket screws to prevent corrosion. The loops formed are just large enough to permit the springs to be removed without using tools.
     I first tested the arrangement using a bike stand, and noted that while the shut-off of motor power was immediate on pulling a brake lever, there was a delay of about 1 second before power was restored after the lever was released. I wondered if this might noticeably reduce bike acceleration after braking, but the effect was not apparent while cycling on ordinary roads. The reason for that is probably that I did the workshop test while holding the throttle open, whereas the throttle is allowed to spring-back during normal braking. Hence there is always a delay in getting going again in practical situations, and the electronic delay is naturally obscured.
     What was really noticeable about the implementation of the motor-kill function however, was the effect on braking in response to the actions of other road users. Without kill switches, there is always a heart-in-mouth moment when suddenly required to brake while travelling at speed. This, of course, is because the brakes are inefficient until the motor output ceases. You can get-used to this, and after a while might not even be consciously aware of it; but it is very noticeable when the transient sensation of impending disaster is taken away. There is also a general improvement in the responsiveness of the braking system, and this gives a greatly increased feeling of confidence in riding the bike. I quickly came to regard kill switches as essential when using public roads, and I realise that I might have avoided considerable stress had I fitted them from the outset.
     I am however not convinced of the benefit of kill switches when riding off road. In that case, the speed is anyway very low, and the brakes can be used to give a subtle modulation of the motor output that cannot be achieved otherwise. The motor controller requires information from the back wheel Hall sensor in order calculate the rider's power requirement, and this necessarily involves an average delay of half a wheel rotation. The throttle only has about 4 power levels, and so its action is simply too crude. Controlling the motor by loading it with the brake until the system catches-up provides the solution, but not if pulling the lever causes the motor to shut down for a whole second. In my first foray onto a rough surface, I lost balance and nearly fell-off at about 2 mph because of this; and I would say that the off-road capability was badly compromised. The short term solution, of course, is to unplug the motor-kill connector; but ultimately the system used on a mountain bike needs an easily accessible switch and a warning light (the latter to remind the rider to restore the kill function when going back onto the public roads).





Engineering improvements

100 Amp safety isolation keyswitch.
 Analog 50 V meter with damping. On front console - actual battery voltage.
 Brake light and kill-switch circuit - diode operates tail light as additional brake light in daytime, transistor pulls-down the kill line. Switch to allow kill function to be disabled off-road + red warning light.
 Side stand motor kill function and red warning light. Side stands are hideously dangerous. No power until the stand is up. Can use the switch from a bafang brake lever.
 36 V 10 W LED headlights and tail light. Choice of Dip + Main on full, or alternate Dip / Main to conserve batt.
 Day running light (DRL) - often a good idea to use bike lights in the daytime, particularly in winter.
 British pedestrians and motorists are angered by the use of a horn. - Fit a bell. Use the m/c horn button as a headlight flasher.
 12 V switch mode converter, cigar socket, 12 V LED m/c flashers.
Removable handles, either side of console, to allow bike to be turned upside-down for puncture repair.

UK Road Vehicles Lighting Regulations 1989. 1796 schedule 7. Original (as made), unrevised.
Dist. between front indicators is 240 mm or greater.
Dist. between rear indicators is 180 mm or greater.
Regs are not clear on how this distance is to be measured - it probably meant 'bulb to bulb' in 1989. At least 240 mm between middles of  front indicatior lenses should therefore be OK (also, ≤ 250 W e-bikes don't have to pass MOT, but compliance is advisable).

Higo Mini-B series connectors. IP66 in-line with 1 m cable attached. Panel mount versions also available.


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DWK 29th Dec. 2018