what gear size to use?

[Hugh-Jassman]

If the power of a motor does not fall off sharply until it is down to 80%, then can I calculate a gear that is close to a 20% smaller gear reduction. Or maybe I should just think about calculating the speed a bit higher than I need for the worst hill, which would be a smaller gear reduction??

I want to set the controller to not produce more than 2 “brake horse power” so I could set it a bit higher. But the police will be checking to make use I don't have more power than is allowed for a moped. This will be a Velomobile with a single stage gear reduction.

I used this calculator on the 'streamlined trike' setting. I assume that it is taking into account a two stage gear reduction loss of 15%. http://www.kreuzotter.de/english/espeed.htm

The motor I want to use produces 1500 rpm at 1500 watts [on 7% grade with 400lbs it should produce 22.2 mph]

Ie: 3”pulley on motor/12”rim pulley on drive wheel= 4:1; 1500rpm/4 =375 rpm

20” tire with a 12” rim pulley on the 20” drive wheel and 3” pulley on the motor (1:4 ratio) with 1500 rpm motor (at 1500 watts or 2 HP would give you about 22.3mph.

4”/12”= 3:1....1500rpm/3 = 500rpm = 29.73mph minus 20% = 23.78 mph? Is that close enough to keep the motor from over heating on that same 7% grade?

this is the motor:
http://www.cloudelectric.com/product-p/mo-me0909.htm

my simple wheel speed formula:
Tire diameter x 3.14 = inches of circumference x Drive tire rpm = inches per foot /12= feet per minute x 60 minutes = feet per hour /5280 ft per mile = mph.


this is the power graph:

 

[Hugh-Jassman]

I realize this is a hard question. And it maybe even be abserd to most poeple.

what do factory made modeds do, just go way over the alowed wattage?

 

[goodgnus]

If the motor can provide 6.4hp continuous at 48v I don't see how you could even get close to overheating it. That's a serious motor, weighing in at 23 pounds. Might even be overkill for what you're doing. What voltage are you planning to run?

 

[Hugh-Jassman]

well I did show the graph of the 24 volts... but really if it is better to use 48 volts I would consider it. But please tell me why I should use the higher voltage?

I got the feeling by looking at the graphs that it would produce more torque at a lower voltage. There are more graphs on the web page where the motor is sold.

so you may be able to tell that I don't really know much about this. I do realize that most people just don't even think about gears.......