Project Q bike

[john]

Hi Flecc,
I read your q-bike project on your web site and some of this thread, but one thing puzzles me:
You said that you wanted to make a street legal bike and so didn't go for a kit. But I think I read that your q-bike motor helps up to ~18mph. To be legal the motor needs to be rated at 200W (or 250W) continuous (whatever that means) and cut out at 15 mph.

Cheers, John

[flecc]

Hi John

I didn't in any way alter the motor drive side of the Quando for performance purposes, or change it's gearing to raise it's speed.

There's lots of manufacturer interpretations of the 15 mph limit, and the most common is not to actually limit the speed but to gear the motor so that it attains approximately 15 mph on the supply voltage, electric motor speeds being controlled by that.

This can be interpreted as having 15 mph at the freshly charged voltage, gradually slowing as the battery charge reduces, or 15 mph at the battery's lowest voltage, meaning it goes faster when the battery is freshly charged. eZee use this second interpretation on their models, and the market is roughly split along those lines, lower powered motors geared for the lower interpretation, higher powered ones the other way.

The Quando was originally designed with a nominal 36 volt NiMh battery, which has a peak of around 39 volts which drops the moment it's put under load, and with that the bike did about 17 mph on the flat when freshly charged. Later the Li-ion battery was introduced to all models, and that happens to correspond to 37 volts nominal, with a peak of over 41 volts which doesn't drop so fast under light load. Therefore the bike does about 18 mph or a little more with a battery freshly charged, though as the content is used up, it too drops to 15 mph eventually.

In saying I wanted my bike to be road legal, I meant as supplied legally to the market, as distinct from using the usual performance route of a motor deliberately designed or changed to break the law.

In fact few hub motor bikes actually have a specific speed limiter cutting the power at 15 mph, and it could be said that there are hardly any that actually comply strictly with the law. That states that the power should phase down well before 15 mph, normally from around 12/13 mph, gradually subsiding to zero at 25 kph (15.5 mph).

The only bikes that do that completely at present are those using the Panasonic standard crank motor unit, even those ones with the higher power option not observing the law strictly.
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