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…


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…

Blog History

October 23, 2010

20/07/2010 Hello Fellow Ego Scootees

31/07/2010 It’s here…!

01/08/2010 Time to start modding…

02/08/2010 Front Disc Woes

03/08/2010 At last I can see my Turn-Signals!

06/08/2010 Wire we waiting…

06/08/2010 The Joy of Sixty Volts

09/08/2010 ‘Voltage Curve’ Experiment

10/08/2010 Zap!

16/08/2010 Can’t Stand It…

22/08/2010 72V… Up and running at last (mostly)!

23/08/2010 Turning Cantonese…

27/08/2010 Battery Meter Upgrade

02/09/2010 Pow!…

08/09/2010 Bling it on…

11/09/2010 K62, no skiddoo

17/09/2010 A Tale of 34.4 Miles

04/10/2010 K62 – Times Two

09/10/2010 Not so good vibrations…

23/10/2010 What to do with a Warped Brake Disc

01/11/2010 Thunder still not struck…

20/11/2010 Thunderstruck (not-just-)72V Converter

18/01/2011 Spring is in the Air

20/02/2011 Adding a Controller Pre-charge Switch

31/03/2011 My Electric neighbour

04/04/2011 Ohmless and Angry…

10/04/2011 Fifty at Fifty Amps

19/04/2011 Shocking

24/05/2011 LED Headlight Upgrade

10/07/2011 Building a LiFePO4 Lithium Pack

14/07/2011 That’s LiFePO4…

15/08/2011 Installing a Speed Control Switch

28/08/2011 Building the “Zephyr” Circuit Board

28/08/2011 Wiring and Assembling the “Zephyr” BMS Unit

03/09/2011 Meltdown

05/09/2011 Monitoring Pack Cell Voltages

23/09/2011 End of charge Foibles

31/12/2011 What have you got on your wheels this winter?

04/04/2012 Power Hungry

07/05/2012 The Big Bopper

26/05/2012 Busted!

04/07/2012 Torque Talk

12/07/2012 Replacing a Hall Sensor

21/07/2012 Testing the Hub Motor

28/07/2012 Disassembling and Reassembling the Hub Motor

07/09/2012 Scoota Rebooted Pt.1 – The Big Makeover

06/01/2013 Scooter Rebooted Pt.2 – Controller Heatsink

04/04/2013 Charge Point Success!

07/08/2013 Speedo-Driver Problems

08/09/2013 EMC-ya-later

29/09/2013 Low Voltage Cutoff and Alarm System (Zephyr BMS)

02/10/2013 Fitting a Digital Speedometer/Odometer

14/11/2013 It’s Back! – The Fechter-Goodrum Zephyr v4.4a (‘Zenid Edition’)

12/06/2014 To PCB or not to PCB…

20/09/2014 Resistance is Futile

Scoota Pictures

August 26, 2010

The bike in the early days

Here you can see the power point I installed on out the outside wall of my place (above)

After programmable battery level monitor

The 3.5″ K-32 tyres were my first choice to replace the 3.0″ tyres that came with the bike

New shocks. The ride quality got much better after I replaced the substandard ones that came with it

Some bling to celebrate the 72V upgrade


After the 72V SLA upgrade – the underseat compartment

I replaced the headlight and sidelights with LED modules –  much brighter and more efficient

The 24s2p LiFePO4 Lithium pack build

The BMS, built from scratch with a Goodrum-Fechter board

A BMSBattery EMC-900 charger charges the pack at 9 Amps – total recharge time 2 hours 50 minutes from ‘flat’

After the LiFePO4 Lithium pack upgrade

I used three CellLogs to give me a battery pack monitor for the Lithium pack

The torque arms that came with the bike (right) were too fragile, so I designed a more sturdy, heavy-duty torque arm

Here’s the new torque-arm in situ

Switched from 3.5″ K-62 to 4.22″ equivalent ‘Big Bopper‘ tyres

Fitting the bigger tyres and adjusting the mud-guard

After respray and rebuild with 1500W motor, 16-FET controller, lengthened centre-stand legs and Big Bopper tyres

HS11 1600

I built this custom, copper heatsink to mount the controller on

P1080003 (Large)

After over 2 years faithful service, my BMSBattery EMC-900 charger finally blew up, so I upgraded to the more powerful EMC-1200 above. This is now running 13.6A, giving a full recharge in about 2 hours, as compared to the 2 hours 50 minutes needed with the old charger running at 9A