ebike4healthandfitness said:
Here is a comparison I ran of a 72v GMAC 10T with 20 amp controller vs. 36v GMAC 10T with a 40 amp controller.
https://ebikes.ca/tools/simulator.html?motor=GMAC10T&mass=206&grade=6&batt=B7223_AC&axis=mph&motor_b=GMAC10T&batt_b=B3626_GA&mass_b=206&grade_b=6&bopen=true&cont_b=C40&hp_b=0&hp=0 (455 pound weight chosen to simulate two average sized americans (with clothes and shoes) on a 84 pound moped.
The 72v GMAC 10T with 20 amp controller wins (predictably) on flat ground up to around 4.5 percent grade. At 5% grade 72v with 20 amp ties with 36v with 40 amp. At 6% grade the 72v 20amp stalls (i.e. climbs at only .5 mph) but the 36v 40 amp continues to be able to climb steeper and steeper grades.
So yeah, it does appear this idea has merit if it could be made automatic/switch on the fly. (mopeds need to have automatic transmissions according to law in US and Canada (well at least in British Columbia, I haven't taken a look at the rest of Canada)).
What you want is easily implemented by a 'smart controller' where you can limit phase and battery currents independently.
This way you can have 40 (or 80 for that matter) phase amps at low speed (when your PWM is way below 100% hence *motor* voltage is way below 72v), but limit *battery* current so it does not exceed 1.5hp even at high speed using a controller/motor combo easily capable of double that.
However, using a speed limit is what this is *really* is about. When you are crawling steep uphill at 10 mph while carrying a ton of stuff and using 2+kw to do it, you are not hazard to anyone.
When blasting 50+ mph on a flat (made possible by same 2+ kw of power), a mistake can kill you and innocent bystanders to boot.
Downhill bicycles (that are cross motorcycles on a diet) can manage that, but a lot of typical bicycles are simply unsafe at those speeds. That's why there is a distinction between bicycles, mopeds and motorcycles, with each step there are stricter requirements on *mechanicals*.
Again, smarter controllers can do that (like e-bike vesc can give you 72v, 100A, but still limit your maximum speed to any number you want).