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.
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 Oponeo.co.uk. 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…