Scoota Rebooted Pt.1 – The Big Makeover

September 7, 2012

The rebuilt scooter with Lyen 18-FET 4110 controller, 1500W motor, big Bopper 120/90 tyres and extended centre-stand

While I was dismantling and fixing the motor and had so much of the back end in pieces, it was a good opportunity to give the bike a proper makeover. With all the commuting I’d done in all weathers, and the amount of time it had sat outside my workplace in the pouring rain, it was getting a bit rusty round the gills, with the swing-arm, battery box and other frame parts in need of a clean-up and respray. There was also a broken bracket on the battery case where a crater in the road had jarred me hard enough to almost bring me off the bike.

Swing arm removed

Swing arm and stand removed

There was also the matter of the centre-stand. I’d recently decided to go for even bigger tyres than the 3.5″ K-62s, and decided that the 4.2″ equivalent Michelin Bopper would fit the bike, give me a more comfortable ride, and also increase the amount of distance covered per turn by an extra 8.5% compared to the K-62 tyre, which would aid top speed with a sufficiently powerful controller. However with Big Bopper tyres front and rear, the bike stands at over an inch higher, with the centre stand barely able to touch the ground.

I’d ordered a custom, 18-FET controller from Lyen, and while I was waiting for it to arrive I got to work on cleaning up the bike and giving it a respray. You can see the swing arm below looking a bit worse for wear from the weather.

Likewise the stand, but before the stand got a respray it would need some surgery to make the legs longer. To extend the stand, I decided to do a ‘cut-and-shut’ with two inch-long pieces of steel tubing. Fortunately my local metal worker had some of exactly the same gauge and diameter.

After sanding off the paint around the cuts with steel wool, I set to work on it with an arc-welder.

A bit of grinding to tidy up the welds and it’s an inch higher and ready for its respray. I also took care of the broken bracket on the battery case.

The nice, shiny, resprayed swing arm goes back on with the repaired motor.

After a respray, the back end is ready to be reassembled

This is where I finally get to put into commission my custom-made, heavy-duty torque arms. Because of the length and the longer adjuster slots, the wheel can be slid back a further inch or so keep it well clear of the battery box. Standard torque arms are especially susceptible to wearing out when people use regen, as accelerating and then decelerating under regen alternately turns the axle one way and then the other, which can lead to it gradually chewing its way through the retaining slot. Hopefully these much sturdier pieces will let me use regen with impunity. I might even double up with a couple of extra ones just to be ultra-safe…

While I was at it, I removed the plastic panels to get better access to the frame and battery box. While the battery bank was having a couple of weak cells replaced, I had resprayed the battery box with hammerite inside and out. Once everything was reassembled, the wiring was re-secured with fresh cable ties. To accommodate the larger tyre, the mudguard needed a couple of inches of the forward end trimming off as the tyre was rubbing against it. However that part of the mudguard serves little purpose as it’s below even the base of the battery box.

Sprayed and back in place, the extended stand gives the extra inch that the larger tyres need to allow the bike to be properly parked. The rear wheel therefore has about the same ground-clearance as it did before – about an inch, so that the wheel can be spun while the bike’s on its stand.

The stand – extended by an inch so it works with the bigger tyres

All reassembled and ready to go, there’s just one thing missing: The silver panels that came with the bike had been getting steadily more battered, and one finally broke. While I was buying my motor from Steavan, I also got a couple of fresh panels that he had for sale.

The best match he had for the bike were black ones, which I think look fine.

The Road Test

Once I’d got Lyen’s controller up and running, it was time to run it in, steadily increasing the rated and phase currents until I found a setting that gave me the power I needed, but without getting the controller to run dangerously hot. I eventually settled on 60/150 rated/phase, though a little less than that would probably have made no difference. It seemed that any setting at all above 55A or so made no extra difference to the power. But since I’m putting 4KW plus through a 1500W motor, this is hardly surprising – it seems that the motor just won’t draw any more than that. The next stage on the upgrade path is an even bigger hub motor. The controller, though, runs pretty cool, topping out at 60°C only after a great deal of extended thrashing.

The performance though, is fantastic. Very torquey, with phenomenal acceleration that’s more than adequate to beat most things away from traffic lights – I’ve recently noticed shocked boy racers in BMWs or Audis chasing me to try and make a point.

Though the acceleration is excellent, I didn’t end up with quite the top speed I’d hoped for. With the Lyen 12-FET controller I was getting 43-46 mph satnav. Now I’m getting 48-50mph satnav, topping out at about 52mph when the wind’s in the right direction. That’s the equivalent of about 55mph clock-speed though, and more than adequate for short hops between towns. I was hoping for a little more than this, as I thought my 120/90 tyres would leverage me a bit more speed, but different motors are wound for different types of performance and it’s just pot-luck what you end up with. I believe this one is better on acceleration because it’s wound for ‘torquey’ rather than ‘fast’. Still, I’m more than happy with the results.

With the new motor/controller combination, regen is a little harsher than it was before, and I might tweak the resistor value to make it a bit lighter. I’m also thinking of wiring a button into the regen self connector so I can switch it on and off without plugging my laptop in and changing the settings.

As part of my upgrade, I also built a custom heatsink for the controller. Though heat is not a particular problem at the moment, that might change if I get a 6KW hub motor or something. More about that next time…

Disassembling and Reassembling the Hub Motor

July 28, 2012

Removing the stator is quite easy, but getting the cover plate off can be a little more challenging


The hub motor – like any motor – is made up of two main parts. The first part is an axle surrounded by a fixed ring of copper coils, called the stator. The second part is a housing into which the axle seated, and where it is allowed to rotate freely. This housing, which part of the rear wheel, is surrounded by a ring of strong magnets that surrounds the ring of coils connected to the axle. The hub motors used by most (but not all) electric bikes also have three ‘hall-effect’ sensors seated in a metal ring surrounding the coils, which relay signals back to the controller.

The phases wires that provide power to the motor and the thinner, sensor wires that feed back to the controller are all housed in a thick, insulated cable that runs through a hole in axle to the inside of the stator. To get access to the workings of the motor you need to remove the stator from the rear wheel, and – if necessary remove the cover plate so that the area inside the coils can be accessed.

1) Remove the bolts securing the stator

The stator is held onto the rear-wheel housing by a ring of allen bolts. A ratchet screwdriver with a suitable attachment will make short work of these. It’s a good idea to put them in a little baggy so you don’t lose any.

The stator cover – little alan bolts secure it to the wheel

2) Remove the drum brake assembly and push out the stator

First it’s best to remove the drum brake assembly from the other side of the wheel. You can see the drum brake assembly below. Remove the nut and washer from the end of the axle and the drum brake assembly, including the cover plate, lever and brake pads should just slide off in once piece.

The next bit requires a bit of force, but is quite straightforward. Even though the bolts are off, the stator is still held in place by powerful magnets, and needs a bit of encouragement to release. To remove the stator from the wheel, find a piece of wood and rest the wheel on top of it so that the end of the axle on the underside is firmly braced against the ground. Then push down firmly on both sides of the tyre. If it seems stuck, then put your knees on the tyre and bear down with all your weight. With enough force the stator will pop out and you’ll be able to remove it from the wheel.

Here it is removed. Towards the bottom, you can see the hall sensor wires where they meet the hall effect sensors embedded around the edge of the unit.

3) Remove the stator cover-plate

This is as far as you’ll need to go in taking the motor apart if all you need to do is replace a defective hall sensor, but if you need to repair damaged wiring (like on the unit here) or even replace the phase wires for something thicker then you’ll need to also get that cover plate off the stator.

The only thing holding the plate on is the friction between it and the axles’s bearing, however it’s a very tight fit and can’t easily be removed without specialist equipment. A hub-puller of the right size, or a hydraulic press can be used to push the axle through while the plate is held firmly. In the end I went to my local university’s mechanical engineering workshop, and they popped it off with a big hydraulic press.

Once removed, you can see where the cable emerges from the axle on the other side of the plate, and where short lengths of surplus phase wire are covered in nylon and tied back.

Below you can see the ends of the phase wires once released from the cable-ties and with the bits of nylon sheath removed.  You can see where they are joined to the ends of three thick, copper cables which run lead into the banks of coils surrounding the stator. Once you have access to this part, you can make any repairs to damaged wires, or even replace the thinner phase wires that come with some hub motors with thicker grade wiring that can carry more power.

4) Reassembly

The stator cover

Though the cover plate for the stator may be quite tough to remove, it’s usually a lot easier to get back on. In my case, some gentle help using a wooden-headed mallet was enough to get the cover plate back over the bearing.

Replacing the stator

As for putting the stator assembly back into the wheel, this needs to be done with a certain amount of care, as once the stator is far enough into the rear wheel housing, the magnets will slam the stator back into place quite firmly, so MIND YOUR FINGERS!

You will also need to bear in mind that the stator needs to be properly aligned so that all the holes in the case meet up with those in the housing. If not you’ll have to remove and reseat it again until it’s properly aligned. To help with this, I poked a screwdriver through on of the holes in the case and its corresponding hole in the housing so that the stator slid into place reasonably well aligned. Once the stator was in place, I replaced the bolts, diagonally from one another and eventy spaced, tightening them up alternately to ensure that the stator went back in properly aligned.

Testing the Hub Motor

July 21, 2012

Though hub motors tend to be fairly well behaved and can run for years without problems, they do occasionally go wrong. If the bike suddenly stops working or develops problems, you often end up in a position where you need to find out if it’s the controller or the motor that’s at fault.

Many enthusiasts who’ve done a lot of tinkering with their bikes usually end up with at least one spare controller lying around, in which case it’s just a case of swapping it out to see if that fixes the problem. Most people, however, do not have spares available and may need to do some specific testing to rule out any issues with the motor.

1) Access the Phase Wires and Hall Connector

The first thing to do is to remove the seat to get access to the junction where the phase wires are connected (bottom) and the hall connector socket can be found (top left). The phase wires are the three, thick blue, green and yellow wires. The hall sensor wires are five thin wires: black, red, blue, green and yellow that run from the motor cable to a 6-way mini-connector. On some bikes the phase wires are part of a plug instead, in which case you’ll have to adapt your test accordingly. For this test you will need to detach the phase wires on the motor side from the connection block so that they are isolated from the controller. Leave the hall connector connected, though.

Phase wires and Hall Connector

The phase wires are the wires that provide power to the motor, magnetising sequences of coils that generate the rotational motion. The hall sensors are three little transistor-like devices embedded along the inside edge of the motor, which send information about the motor movement back to the controller.

2) Test the Phase Wires

First, with the bike on its stand (and the bike switched off), test that the rear wheel spins freely. If it doesn’t you most likely have a short between the phase wires, though this is rare. The next thing to do is to remove the phase wires from the block and short them one pair at a time (e.g: yellow/green, green/blue, blue/yellow). As you hold them shorted together, try turning the wheel again. This time, you should find resistance. If you don’t get resistance when any pair of wires is shorted, then there is a break somewhere between the phase wire and the motor.

Phase wires and hall connector, detached

3) Test the Hall Sensors

For the next test keep the phase wires disconnected but make sure that they are kept properly separated. Preferably put a bit of insulation tape on the ends to prevent mishaps. Again, keep the hall connector connected.

Next, you will need to turn the ignition on, and take voltage readings from the wires in the hall connector. Since the connector is plugged in, you will need to access it from the rear, sticking the multimeter probes into the recesses and touching the crimps holding the wires in place.

The hall sensor wires

Take voltage readings across the black wire and – in turn – the blue, green and yellow wires with the back wheel turning slowly. It’s best to get someone to help out with turning the wheel for this part, while you take readings. As the wheel turns, the signal should flip between 0V and about 4.5V, at a rate of about 23 cycles per rotation of the wheel. If you get this reading from each of the wires, then all is well, otherwise, you have a blown hall sensor and will need to open the motor to replace it.

If you have a bit of pocket money spare, and want to make life easier, you could invest in one of these very handy motor/controller tester gadgets that will do it all for you. You just plug in the hall connector, attach clips to the phase wires, and the blinky lights give you the answers straight away! The controller-tester part of the unit, however, is only compatible with controllers up to 60V, though, so it can test the motor – but not the controller –  if you have a 72V system.

Replacing a Hall Sensor

July 12, 2012

Hall effect sensors sometimes fail, but are easy enough to fix

Taking the hub motor apart and replacing a hall sensor might sound like a pretty daunting task, but it’s really not that difficult. The first thing you need to do is get hold of a suitable, replacement SS41 hall-effect sensor. One can usually be found on ebay here, or from RS components (but with a pretty steep postage price) here.

Next you remove the stator (the hub motor section of the rear wheel) from the rear wheel itself (see blog entry) so that you can get at the motor’s inner workings. This done, the hall sensors and wiring are exposed and ready to work on.

The sensors are held in little shaped grooves in the metal treads on one side of the stator’s perimeter. Now you need to identify which sensor holds the wire that you detected a fault on. Each sensor has three wires, – two of them are the 4.5V live (red) and GND (black) which serve the sensor, the third is the hall sensor wire which returns a signal to the controller based on its rotational position in the hub motor casing. The third wire for each hall sensor is yellow, green and blue respectively, as shown below.

In my case, it was the yellow wire that was showing no signal, and this one goes to the middle hall sensor on my stator.

The component itself is held in with a bit of epoxy resin and sometimes has bits of silicone sealant gummed about. The epoxy can be softened by warming it a little with the flame from a cigarette lighter.

A gentle tap with a hammer and screwdriver knocks it loose with ease.

Note how one side of the hall effect sensor has bevelled corners. This side faces outwards (on my motor, at least) and is designed so that it can only fit in its socket the right way round. This is important, as it makes it hard to accidentally reverse the wiring sequence.

Here’s the replacement sensor in situ.

You can more clearly here how it fits with the bevelled corners facing outwards.

Next it’s a simple case of soldering the new sensor in. Snip the head of the old sensor off, strip the hall sensor wires, and desolder the legs from the old one, then solder on the legs of the replacement sensor. Don’t forget to put fresh sections of heatshrink on the wires, and push them way up the wires where the soldering iron won’t prematurely shrink them. Then pull the heatshrink down into place over the soldered legs, like with their neighbours.

This done, it’s a case of fitting the sensor back into its socket. Use a little blob of epoxy resin to hold it firmly in place.

All done! Finally, carefully refit the stator to the rear wheel and test the wiring from the hall connector. If you did everything right, then you should once more have a working hub motor.

Torque Talk

July 4, 2012

The final product! – The Zenid, custom, 12mm, heavy duty torque arm made from laser-cut, 6.3mm steel (alongside the original)

I’ve taken a bit of a break from the bike in recent weeks to catch up on work and to await the delivery of some key parts for my next upgrade. I ordered a nice 18-FET version of Lyen’s controller to replace the 12-FET one I already have, and also had the current one repaired after the FET blew from the torque arm mishap.

Figuring out how to come by a suitable replacement for the rubbish torque arms that come with the hub motors turned out to be something of a journey. First I followed up a link on Endless Sphere to a guy who had custom made some torque rings that looked like they might be suitable, however they were the wrong design for the type of swing arm that the Ego and other electric scooters use.

After enquiring with a local machine shop about the cost of custom machining some suitable parts, and doing some exploring online, I eventually decided that it would be more cost-effective to simply custom design and order my own, and sell the surplus in my shop. The wonders of the internet now mean that there are manufacturers who have pretty much automated the whole process so that you can design, explore cost options, and order whatever you want with little or no human intervention. So I duly figured out how to use some web-integrated CAD software, came up with a design for my dream torque arm, and placed my order.

The CAD design, in 3D preview mode

The only thing that wasn’t automated though, were shipping options. My manufacturer of choice was a US firm (I couldn’t find any UK company who did this, alas), and the only option was for a ridiculously expensive express UPS delivery that cost almost as much as the order itself, so I emailed them and asked if I could have it shipped by a much cheaper (and slower) USPS tracked service. The said it was fine, and told me to just add a note to the CAD drawing for the

I spent the last three weeks occasionally checking the tracking to see how the package was progressing, and it seemed to take a dog’s age to crawl across the planet from from its east-coast origin. When it finally arrived in the UK it spent nearly a full week sitting in customs before finally clearing and continuing its journey. I was none too happy to be landed with an import duty and ‘clearance charge’ of nearly £40 for the privilege of this inconvenience, but duly paid it and eventually ended up with a batch of freshly minted parts on my doorstep this morning.

The real thing, next to the original that came with the motor

Here it is, the real thing, shown next to the inferior original. They’re 62mm x 24mm, and manufactured from 6.3mm laser-cut steel, and have 12mm torque slots, with a 6mm hole for the adjuster bolt, – suitable for the 1400W/1500W motors. The torque slots are slightly wider as the 1500W motor has a 16mm axle on the cable side, as compared to the 14mm on the 1400W motor, though the slot diameter required (on mine at least) is 12mm on both. I’ve also made mine longer, with a wider adjustment slot so that the rear wheel can slide back further to accommodate larger tyres. I got a batch of them, so there’s plenty left to go in my little shop in due course.

There was a moment of panic when I put it on the axle for the 1500W motor – it’s a tight fit and needed a gentle tap with a hammer to get it over the end, but then it slid down the shaft nicely, an almost perfect fit with very little free play! Here it is next to the even worse torque arm that came with the 1500W motor (these are the ones that failed).

The bike is in bits at the moment, while I repair a bracket on the battery box, respray the swing-arm, service the battery pack and fix the wiring on  the hub motor. I’ll get round to this in due course and keep you posted.


May 26, 2012

April 30th was not a happy day for me. In addition to the torque arm failing – mangling the phase wires on my nice new motor and blowing a FET in my controller – I also got snapped by a speed trap. It was apparently one of those automated signs that tells you your speed as you approach and then says “Thank you!” or “Slow down” depending on the verdict. Whle I was taking the bike for a spin on the new motor and testing its responsiveness, I ended up wellying it rather more than I was planning to. The sign duly told me “38mph – Slow down!”, which I promptly did, but I discovered to my dismay that these signs are apparently now fitted with the same automated cameras that inhabit the more menacing gatsos.

[Edit: I’ve just been told by someone on Endless Sphere that the photo was actually taken with a Lidar gun, probably by someone sitting in a parked car nearby]

This was of course my own fault: My speedometer died the first time it went off the clock, and I’ve not got round to fixing it. The speedo/tacho cable and the front wheel assembly that drives it are fine, but clearly something behind the dash isn’t right. Fortunately, I’ve been given the option of 4-hour lecture on road safety in place of a fine and points on my license, and I’ve duly signed up for a class in a couple of weeks time.

Disassembling the hub motor

As I reported last time, the phase wires to the hub motor got a bit chewed up when the torque arm failed and the axle began to creep around in its fitting. Though the repair to the cable isn’t in principle that difficult, I knew next to nothing about hub motors and so was a bit nervous about attempting this job myself.  So at first I took it down to a motor specialist at a nearby industrial estate and asked the guy there if he could take it apart and tell me what needs doing. If it wasn’t too expensive, I figured, I’d just have it done proferssionally.

However after a week or so and two follow-up visits, it was clear that he wasn’t especially keen on actually doing anything and had just left it sitting in a corner until I lost patience and made an excuse to take it back. But in the mean time I’d been given some advice on how to get the thing apart myself, and it turned out to be a lot easier than I thought it would be to at least get the stator (the main motor assembly) out of the wheel.

Just a bit of pressure on the tyre and stator pops right out!

Once all the little alan bolts have been removed from the edge of the housing, it is just a case of resting the left-side end of the axle on a piece of wood and applying a bit of force to the tyre by pushing down firmly on it. The stator popped out with very little fuss.

Though I now had access to the inside of the unit, there was still the hub plate (right) that needed removing, and it wasn’t at all obvious what it was that was securing this to the rest of the assembly.

Again, I was unsure about how to proceed, so just thought I would drop it off at a local mechanic’s shop to see if they could tell me how to remove the plate. They said they weren’t sure just from looking at it it, but to leave it with them and they’d “take a look at it”. Unsurprisingly,  two phone calls, two visits and nearly two weeks later, it was clear that they were every bit as lazy or disorganised as the previous taker, so I made an excuse and took it back again. I’ve been given some more advice on how to get this plate off, and will give it a go when I find time.

In recent weeks I’ve been indundated with other work, and so for now the bike is in pieces waiting for a rebuild. The LiFePO4 pack has a couple of weak cell-pairs, and is in pieces while I get replacement cells (I have two spare, but still need another couple). The premature decline of these cells is probably due to a couple of times where I ran the bank dangerously low when I really needed to be somewhere even though I was low on juice. I never wired the LVC portion of the BMS into my throttle so it would automatically cut power to the controller if individual cells went to low. Instead I just made regular checks with my bank monitor and kept the bank regularly topped up, seldom letting it run down significantly. The times where I let it run way low would have hurt the weakest cells, and shortened their lifespan, which is one of the risks you take if you operate ‘without a net’ like I do. The cells, though, can still be put to use in non-bank related projects, but are making enough of a dent in the range to warrant replacement.

The lithium pack – two weak cell pairs need replacing

I’m also awaiting the repair to my controller, but can run just fine on one of my cheap spares until that comes back from Lyen’s little workshop.

Maintenance on the battery box, swing-arm and centre-stand

While the battery box is empty, I’ve decided that this would be a good time to sort out a broken weld on one of the brackets securing it to the frame (courtesy of a massive pothole that nearly floored me), and a split along one edge – again  from a weakened or poor weld (Chinese quality control at work). I have an arc-welder now, so I’m going to attempt this myself when I can find time.

I’m also going to take care of the centre-stand and swing arm. They’re both a bit tatty looking and rusty round the gills, so I’ll take them off and give them a respray. The stand also needs extending by about an inch to accommodate my bigger tyres, so another weld-job is in order there too.

The Big Bopper

May 7, 2012

Work in progress – fitting the “1500W” motor with its formidable new Michelin Bopper tyre

As some of you may have noticed, I’ve spent quite a bit of time these last few month trying to get hold of a hub motor that was more up to the job of handling the extra power that my performance controller can provide. The weak link in the system as it stood was those feeble phase wires on the 1400W motor that comes with the Ego Scoota. I’d trawled the internet and posted messages to forums in an attempt to find somebody who could supply me with a 2000W motor, but to no avail. Chinese vendors either simply didn’t have the motors that they were advertising, or else insisted on the deal-breaker payment method comprising of “T/T” payments, which comprises simply transferring money directly into their bank account. I never deal with anyone on that basis, as – as far as I’m concerned – it’s tantamount to handing over a paper bag of cash to a stranger in a park.

Other scooter owners, however, had reported going instead for a 1500W motor. Users like Hohi on the Electric Motoring Forum reported that even though the nominal rating of these motors was only a fraction more that the original, the phase wires that come with them are quite impressive, and that these motors were actually quite significantly more powerful. The nominal rating evidently had to be taken very much with a pinch of salt.

Hohi got his from a forum member Steavan who occasionaly buys up and breaks these bikes, so when Steavan said that he could supply me with a similar motor, I jumped at the chance, especially since he was only a reasonably short 50 mile hop away in neighbouring Leicestershire. Two weeks late and one jaunt to a scenic cottage in the countryside later, I was the proud owner of a 1500W motor that formally belonged to a Xinben Ambition. This bike had apparently only gone about about 20km from new before the Lithium battery died. It was therefore in near mint condition, with nice fresh brake pads. Though the case was stamped with “1500W 48V”, it looked identical to the one housing my ego motor, but as reported by Hohi, the thickness of the cable was worlds apart!

Wow! The phase wires on the 1500W motor shown alongside those of my existing “1400W” one

As you can see the difference is impressive. However it also made me wonder about whether the gauge of the wiring on the internal coils and the magnets inside would also be similarly improved. One clue to this, I figured, would be the difference in weights between the two motors, so when it came to changing wheels I made a point of giving them both a weigh-in. The results:

“1400W” Ego motor  – 24.2Kg

“1500W” Xinben motor – 29.4Kg

An impressive 5.2Kg extra weight. Clearly there’s a lot more to the difference between these motors than the nominal ratings suggest, so what the motor actually gets called needs to be taken very much with a pinch of salt.

Tyre options

At about the same time as my search for a better motor, I was also thinking of ways of squeezing a little more top speed out of the bike. Though the performance controllers that are available for these bikes are capable of delivering as much power as the wiring on the bike’s system is capable of handling, they are still limited by the fact that motors have a maximum RPM for a given voltage. The Lithium banks help in this respect as the 72V SLA ‘equivalent’ has a nominal voltage of 76.8V for a 24s pack, with a fully charged pack delivering as much as 84V. As I reported in my blog entries on the K-62 tyres, though, I realised that simply increasing the diameter of the tyre could be one way of upping the bike’s top speed. Bigger diameter tyres mean more distance travelled for each turn of the motor, so providing your system can deliver the power, some of that torque can be traded in for a little more top speed.

In the case of the K-62s, the difference in diameter was fairly modest. The 3.0″ rim tyres that came with the ego mean a total diameter of about 16″, while the 3.5″ K-62s up that figure to about 17″ – a modest 6.25% improvement. I had, however, heard report that 4.0″ tyres could be acquired which would up this value even more. However to my disappointment all of the 4.0″ tyres that I could find required an inner tube, which to my mind added unnecessary expense and complexity to what should be a simple swap.

Say hello to the Michelin Bopper!

As I learned a little more about tyre specifications and figured out how to decode their specifications,  I realised that I did indeed have more upgrade options when it came to the tyres. Figuring this out was not helped by the fact that there appear to be two different formats, one imperial and one metric, for describing the dimensions of tyres. In the one that I was familiar with from my K-62s, the height of the tyres is given in inches, followed by the diameter of the rim and then the load rating (how much it can carry) followed by the speed rating. Hence 3.50-10 tells you in a straightforward way that the tyre height (from the outside to the inside) is 3.5″ and that it is intended for a 10″.

The other format, though, is slightly different and more complicated. Here, the width of the tyre is given in mm, followed by the profile or aspect ratio of the tyre, then the rim size. This second figure is easily confused with the height, but that it is not. The aspect ratio is the ratio of the tyre height to the width of the tyre. Hence to get the actual height of the tyre you need to multiply the width by the percentage given as the aspect ratio. So for a tyre designated 120/90, you multiply the width of 120 by 0.9 to give the height, = 108mm. Then you turn this into centimeters (=10.6cm) and divide this by 2.56 to get the height in inches, in this case 4.22″.

Armed with this knowledge, I had a look at what tyres were available for a 10″ rim. It turns out that tyre sizes as big as 130/90 are available, translating to an impressive 4.57″, however I was concerned about whether tyres of such a size would actually be able to fit on the Ego Scoota without rubbing against the mudguards or the brackets at either side that hold it in place, and – more importantly – offer enough clearance from the battery box taking into account the movements of the swing-arm that occur as the shocks compress in response to bumps in the road.

The Bopper – nice and chunky with a greatly improved 4.2″ height

After doing a bit of measuring up, and thinking about the trade off in power that would result from increased tyre height, I decided that the 130/90 was too risky. It would come perilously close to rubbing against the surrounding structures or jamming up against the battery box over a bump. In the end I settled for the 120/90 Michelin Bopper, and ordered one from I was more than happy with their service: The bopper was a substiture order for a 4.00″ K-62 that I ordered by mistake not realising it required an inner tube. Their freephone support people just told me to refuse delivery of the K-62 and they would replace it with the bopper, which they duly did.

Even next to the chunkier K-62s the difference is impressive. The diameter has now gone from the original 16″ to a nice, beefy 18.44″. That’s a 15.25% increase on the original 3.00″ tyres or an 8.5% increase over the 3.50″ K-62s. I was delighted with the result!

The Michelin Bopper (guess which!), next to the old K-62

There was only one teething problem on fitting the new wheel with its bigger tyres.The mudguard is slightly asymmetrical, and the leading edge closest the battery box was scraping against tyre slightly while under load. This turned out to be due to the fact the the forward, hidden part of the mudguard is ragged and looks like it was poorly cut by the manufacturers, however this can easily be remedied by cutting off a part of the forward section (it doesn’t need to go all the way down below the battery box anyway). For now I’ve removed the mudguard until I get round to doing this.

Time for a test run

With the motor fitted and wired up, you can see how the phase wires now look more in proportion with the thick guage counterparts running from the Lyen controller.

A test run was very reassuring. Starting at 30A, I raised the controller settings to 40A, then finally to 45A, and was impressed at the improvement in power. However, though this was a big step forward for me, this story did not have a happy ending. The higher power combined with the bigger wheel size quickly identified the newest weak link in the system – the torque arm that secures the axle to the frame and stops it rotating.

The torque arm and axle assembly (this one from the old motor)

… and from above, showing the flattened section of thread used to hold the axle in place

A few miles into my otherwise delightful test run, the controller began sputtering and eventually died. Examiningthe rear wheel it became evident that something was very wrong. The axle had worn away the slot in the torque arm that was supposed to hold it in place, and begun to rotate. The cable to the motor had been slowly wrapping its way round the axle, until the edges of the hole where it enters the motor chewed into the wires, shorting the controller and making a fair old mess of things. 😦

Noooo! – My nice new motor cable gets mangled up as the torque arm fails

Other people, it turns out have had a similar problem, and a couple of owners have had more solid replacements custom made to replace the existing one. So for now, it’s back to the old motor and my stock controller until I can fix the cable and get the controller repaired.

The adventure continues…

Power Hungry…

April 4, 2012

Wanted – 2000W 10″ hub motor with drum brake

I’ve been away from the blog for a while, and some of you might have been wondering if I’ve just run out of things to do to the bike. I’m happy to report that that isn’t the case by any means. I’ve been painfully aware that I still have one weak link in the system of an otherwise great bike: Despite upgrading to a vastly improved LiFePO4 Lithium pack and the Lyen 12-FET 4110 controller which can delivery as much power as heat dissipation will allow, I’m still stuck with the piddling little 1400W hub motor that originally came with the bike.

Amazingly it seems perfectly content with the 3.6KW that it’s being fed by the Lithium pack/controller system, which delivers 80V at a rate of 45A in its current configuration (I dropped it from 50A when I switched from the lower voltage SLA bank). Though I’d like to ramp it up to 60 amps, the phase wires start to get troublingly hot if I run it at anything over the existing current. This is essentially the bottleneck in the system, now; though motors can take a remarkable amount of punishment and cheerfully operate way beyond their nominal specifications, the narrower gauge wires will run hotter and less efficiently, and there will come a point where the phase wires will just melt (as detailed by to an unfortunate owner on the Electric Motoring Forum).

In recent months I’ve therefore been shopping around for something that packs a bit more power. Hub motors come in a range of sizes and powers, from feeble, 300W affairs to help people cycle up hills, right the way up to 6KW beasts that you could make a drag racer out of.  Disappointingly though, it’s proven less than easy to get hold of the 2000W motors that now come as standard with many of the recent electric scooters. Typically they only become available when someone is breaking a 60V UK Eco scooter or something else equiped with the better grade motors, and this is how most of the e-biker community seem to get hold of theirs.

Even though the internet seems to be choc-a-bloc with adverts and illustrations like the one above, mainly from Chinese vendors and Alibaba-type wholesalers, actually finding someone who will sell one is a different matter entirely. I wasted the best part of a month negotiating with a “Robert” from a website that claimed to order motors custom-built direct from the factory. The guy went to the trouble of setting up a Paypal account to take my order, and duly took $400 from me for my order for a 2000W 10″ hub motor with drum-brake. I’d asked for it to be wired for high RPM (‘fast’ rather than ‘high-power’), as I have all the power I need but wanted more top speed.

…unless you want to actually buy something

Two weeks later I was wondering where he’d got to and why I hadn’t heard from him or received any information about shipping. I duly contacted him, only to be told – without explanation – that he wouldn’t be able to get one after all. He duly refunded my money but I was hopping mad that the idiot would put us both through this ridiculous charade via what turned out to be a baseless, vapourware website. If you see the logo above, accompanied by an exciting looking catalogue of electric bike parts, then steer well clear…

I’ve had an equal lack of luck with the Alibaba and DHGate traders. Search results throw up reams of traders claiming to deal in these motors, but enquiries so far have just amounted to “sorry we don’t actually sell them, we just pretend to”. Presumably it’s so that they can get my email address and send me spam about batteries for the rest of my life.

So for now I’m keeping my ear to the ground about any bikes that are being broken for parts or even sold whole. If one comes up that’s not to far away I can hopefully land myself with a suitable replacement to the existing motor.

16-FET Controller Upgrade

Once that’s been taken care of, there’s the next and final option regarding controller upgrades, which is to move from the 12-FET controller that I have at the moment to a 16-FET equivalent. More FETs mean I can pull more power, and with a suitable motor get me a better top speed. There’s also the option of moving from a 3.50 tyre ‘thickness’ to a 4.0, which will increase the diameter of the tyre from 17″ to 18″ translating some of the power into higher (about 6%, theoretically) top speed. If I could find a vendor who can sell me a hub motor to order, I could even move from a 10″ to a 12″ diameter hub to get the top speed up even more. The rear wheel arch seems to have more than enough clearance to accommodate an extra inch of radius above the axle, and even if it doesn’t I could just change the rear shocks for slightly longer ones.

I’ll keep you posted as my quest for a better motor goes on…

What have you got on your wheels this winter?

December 31, 2011

Remember: The most important part of the bike is where it touches the ground

This is the time of year for festive cheer, family reunions, Christmas dinner and lots of chocolates. However it is also the time of year where bikers of every denomination can suddenly find themselves tumbling painfully along the surface of an oily, wet or icy road with various broken pieces of motorcycle in their wake.

Regular as clockwork at this time of year, posts appear on the Electric Motoring Forum or Endless Sphere relating tales of woe about being unexpectedly turfed off their bikes when it suddenly fails to stay upright. Manhole covers, potholes, road muck and wet and icy driving conditions make things especially treacherous for bikers, and riders of electric scooters are especially prone to this. The weight of a typical SLA bank (32Kg for a 48V bank, 48Kg for a 72V bank) puts a greater stress on the braking components and has a habit of quickly identifying the weakest link in this system.

That weakest link is invariably the tyres that come with the bike. To keep prices rock bottom, a new Ego Scoota or other electric moped will come furnished with the cheapest, poorest quality tyres that Chinese manufacturers can knock out. Invariably these turn out to be the culprit in most spills: Though they seem deceptively steady in good weather conditions, they have a habit of brutally betraying you at the first sign of trouble. As followers of this blog may remember, I was fortunate enough to stay upright through two slides: After a front slide I replaced the front tyre, but a rear slide shortly afterwards made it clear to me that the tyres that come with the bike are just not fit for purpose. With Continental K-62s both front and rear, the handling was worlds apart.

My Scoota with its chunkier K-62s front and rear

So please, please folks: If you plan to ride through the winter, consider switching to some better tyres. – If you’re riding on what came with the bike, your odds of coming off are that much higher.

Stay safe, and a Happy New Year!

End-of-charge Foibles…

September 23, 2011

Though I’m glad just to have an excellent charge control system for a great little scooter, I’ve been struggling to get the BMS end of charge (EOC) system to reliably switch off when the bank has finished charging. The ideal charge voltage for my system is theoretically 86.4V, which gives the exact 3.6V threshold per cell. In actual reality though, I’ve had to do quite a bit of fine-tuning of both the charger voltage and the EOC adjuster to get it to the point where it would reliably switch off once the cells were near enough ‘full’.

The charger voltage setting needs some fine-tuning

How it should work

In principle, it works like this. The charging voltage is delivered to the master terminals of the full pack, whereupon all the cells will start to charge. However some cells charge faster than others, and so a system is needed to make sure each individual cell stops charging once it reaches its 3.6V limit (in the case of LiFePO4) . This limit is the level to which it’s deemed safe to charge the cells without adversely effecting their lifespan, and is called the high-voltage cutoff (HVC) .

The HVC system comes into play towards the end of the charge cycle, usually in the last 10-20 minutes depending on how badly depleted or out of balance the cells are. When a cell reachs its HVC, a series of shunts divert excess voltage to some large resistors on the back of the board. which simply burns off the excess energy as heat. A series of orange LEDs – one for each cell – gradually come on one by one, indicating which cells are fully charged.

The shunt resistors, here mounted on the back of the board

As all the cells reach this limit, the pack draws draw less and less current from the charger, until the end-of-charge (EOC) cut-off point is reached. This cut-off point is based the setting on a 1K variable resistor (‘pot’) which is turned one way or the other to determine the lower current threshold at which it will cut off. Once the current drops below this point – around 1.0 amp in my case – the BMS shuts off and the orange main indicator light turns to green.

However sometimes I was finding that – whatever the EOC setting – it would not shut off at all. The shunts would just “run away”, continuing to draw a low current, but gradually heating up the whole unit until the case was uncomfortably hot. I found that this was particularly prone to happen when the BMS was in ‘pulse mode’.

“Pulse Mode”

In addition to this steady constant current (CC) charge mode, there is also another system that acts as backup mode to deal with any cells that are badly out of balance. This can happen if the bank has been deeply discharged and is left almost drained, or if there are one or more ‘weak cells’. However, this mode can also be triggered – in my experience – by having the charger voltage set too high.

In this mode, imbalances between cell voltage circuits shunts cause them to become ‘flooded’, and they cannot maintain their threshold HVC. This allows cells to potentially become over charged as the shunts collapse. One impressive feature of the Goodrum-Fechter “Zephyr” is its ability to cope with even very badly imbalanced cell combinations. If the shunts become flooded, then the unit goes into a cycle mode, where it switches itself on and off in pulses. These pulses allow the shunts to operate briefly and give lower voltage cells the chance to catch up, but then switch off just the point where the shunts can no longer maintain their HVC point. This cycling is visible as the orange LEDs brightening then dimming as the current is drawn in bursts. A video of the BMS in pulse mode can be seen here.

The cell circuit LEDs in ‘pulse mode’

Voltage threshold

Eventually I discovered that even though my charger voltage was set at the right level theoretically, it was causing problems for the EOC. In the calibration test the LEDs are best set so they are only just visibly lit. When my charger was running ‘live’, though, the LEDs seemed brighter and the case was getting hot when the shunts were on for any prolonged period of time.

So I decided to drop the voltage a little on the charger, dialing it down to 85.8V. This dealt with the problem of the case overheating, though with the voltage lower you couldn’t always see all the LEDs lit at the end of a charge. Nonetheless, it was clear from my range tests and monitoring off the cells that the bank was ending up fully charged and – once settled – nicely balanced.

However I wasn’t the only one having EOC problems: Richard Fechter had heard other complaints about pulse mode failing to trigger the EOC, and had done some more testing. He soon came up with a diagnosis as to what was the trouble was, and detailed a a fix for the EOC/pulse mode problem. Apparently smaller cells at higher charge rates were getting the pulse mode out of whack, and an extra diode needed to be added to make sure it could properly check the EOC between pulses.

Q3 times two

Since I had to take it apart to solder in the extra diode, this was a good opportunity to fit the second Q3 FET in the empty space under the other one. This extra FET is not included in the BOM (parts list), but is an optional extra for people who want to buy bigger chargers to take full advantage of the LiFePO4 cells’ phenomenal potential for fast charge rates. With an extra Q3 on board, the Zephyr should be able to take up to 20A, meaning that I could upgrade my 10A charger to a 15A or 20A one later on.

The charge control circuit (left), leaves space for an extra Q3 MOSFET

The position of the diode is marked in white on the picture above. Richard Fechter’s diagram deals shows it marked on a slightly different version of the board, but the locations is essentially the same.  The diode needs to go from the base (middle pin) of Q2 to the gate (top pin) of the main FET Q3. The cathode (the end with the black band) goes to Q2.

I elected to mount the diode on the underside of the board. Initially I goofed up and connected it the source of Q3 (the leg at the top in the photo below) and not the gate, but Richard Fechter pointed this out and I fixed it by moving it across to the rail serving the gate of Q3 (shown bottom in picture). Oops!  The other end of the diode just went to the bottom of the middle pin of Q2.

The LED between the gate of Q2 (top) and the rail for the gate of Q3

It’ll be some time before I know for sure that this works, as I’ll have to have run a few more charge cycles before I can see get an idea of whether it’s all better now. Between this fix, the slight voltage dial-down and slowly adjusting the EOC so it’ll trigger earlier, I hope to finally have this licked and have an arrangement that will charge fully, switch itself off when done, and won’t get too hot when the shunts are all on.

Below you can see the new Q3 FET, which should enable the board to handle charges of up to 20 amps.

The second Q3, opening the way for higher charge rates

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