Buying a Battery
If you are going to motorize your cargo bike you should read about batteries. If you buy one that is too small you will not get your money back. Hub motors need a larger battery pack than mid-drives because it will take more power to climb hills with cargo than a motor with a large gear reduction; like planetary gears.
One day after hooking up my Cycle-Analyst meter, I was climbing a short hill with firewood in my trailer [two large arm loads] and I forgot to shift down to my lowest gear of 20 to 1 ratio from my high gear of 11 to 1; the high gear used about 1400 watts from the battery, and the low gear used only about 600w at the same speed. And the high gear made the motor hot. A higher battery voltage would help because less amps are needed to do the same job, and amps create heat; I should have gotten a 60 volt instead of 52 volts.
Choosing a Motor
Electric motors like to spin fast to help keep them cool. Using a large gear reduction for hill climbing will help it spin faster. Creating a more efficient situation for the motor.
There is a myth going around that claims that “gears” waste energy. Hub motors are the worst energy waters there are. If you live on flat land they are ok, but Hub motors are notorious for wasting energy as heat and they have a hard time getting rid of the excessive heat created by wasting energy.
Hub motors are used for solar race cars where they have to drive as fast as possible depending on the solar power they are receiving. Cargo bikes are not racing machines if you are driving your bike faster than 15mph on flat land, you are wasting energy. “Stop-and-go” driving and hill climbing needs gear reductions to convert “Kinetic Energy” into “Torque Thrust”. Of course this uses some energy, but it is not a waste or a loss!
Driving around in too high or too low of a gear will waste energy, that is why Mid-Drive kits are so popular; you can use most of the bicycle's pedal powered gears. Hub motors are stuck in the highest gear. You can buy geared hub motors, but most of them have only one gear. And you can build a direct drive hub motor to climb steep hills, but you can't change it at will to cruise on flat land for a better milage. Only mid-drive can do both! If you have proof that this is wrong please show it to me! I will post it on this blog and on facebook.
If you want to build a vehicle that can handle steep hills with 600lbs total combined weight, and still cruise economically on flat land, you are going to need a some kind of two or three speed gear box. I have been using only two or three gears because electric motors have a wider range of useable power than gasoline motors or human legs.
1 comment:
Thanks for this info, details and fine tuning. We need to popularize all of this!
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