Sunday 29 March 2020

Off the mark drag race

I've been of the view that off the line the MX60 is no faster (indeed feels a little less snappy) than the Widewheel. I've put this down to the larger diameter wheels (just over 11" vs just under 8") it has the same diameter armature and magnet rotor, which will essentially gear it higher (because leverage right). This will assist its top speed which is unquestioned (because bigger battery Voltage and higher diameter wheels).

I did some quick runs first and found that the speed limiter kicked in on the Wide Wheel earlier than the end of the run (which was about 100 meters) confusing the issues, so I turned off speed restrictions on the Widewheel for this test.

So first some data from my GPS app:


The dip in the middle is a turn around point, which my App didn't log neatly, so lets just work with take off. To me it looks like the initial hit of the Widewheel is a little steeper. Overlaying them we can see it is perhaps a little, but its close.


But this app isn't ideal for such comparisons, so I thought (in case) I'd video it and compare side by side. This is that:


This seems to show that the Wide wheel does get that initial  kick going and leads by a nose for a short time, until the MX60 starts hauling it in. Which translates to "it feels stronger" off the mark. This is not unexpected when you consider the way electric motors deliver power and the effect of the effective lower gearing of the Widewheel (discussed above).


As you can see from this figure above the motive force of the motor is strongest when its stopped and gets to a point where it starts falling off in torque soon after take off. Of course since torque is the strength to do work and power is how quickly that work can be done, the more the RPM increases the more that power increases even though torque falls away.

Eventually however the electric motor spins fast enough that back EMF overpowers the foward voltage provided by the battery and you end up with nothing.

Conclusion

So as I've been saying in my ride dialog / blabbering, the MX60 is really a great "cross town" blaster, especially if you've got a number of nice long "bicycle paths" to reduce the stop starting. In theory you should not be riding at over 25kmh anyway, and so the Widewheel will keep up with all but the most serious Lycra Cyclists.

For those not restricted by (or not interested in obeying) such laws then the MX60 will outpace everything else around you except cars.

As I found on my recent video comparison between my Widewheel and MX60 the MX60 uses more juice than the Widewheel on the same trip as a percentage of the battery. Given how much more power that is in Watts it translates to much longer charging times and or much more powerful chargers.

I've got a 4Amp charger for the Widewheel, which nicely charges it (s 13Ah) battery up from 50% in less than 2 hours. To do the same on the 20Ah battery on the MX60 you'd need more than 6A and to be comfortable with such a flow you'd really need to be confident that the charging wires are up to task.

I personally thermally checked my Widewheel for signs of problems when I first bought that 4A charger. I'd need to do the same with the MX60.

As always more power comes with more costs (both time and money).

HTH

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