How to run a DC motor on electric bicycle, without an expensive controller?

I hate to buy an expensive $400 controller that will control the speed of my electric bicycle DC motor. Is there any way I can avoid it? I want to feed the motor a variable DC voltage from a battery.

ac-dc8 years ago
Your options are run the bike at full speed constantly, or build your own (design it yourself or seek a premade design), or buy a used controller off an electric vehicle enthusiast website or ebay. As for designing your own controller I will give you a hint. You can do it cheaply by using parallel pass transistors (enough that they will handle peak current the motor draws), the amount of current they pass will depend on the base bias current you supply, which would be determined by your manual input as a driver to a control which turns a potentiometer, decreasing it's resistance to cause more base bias current which increases current (by raising voltage to a resistive motor) to the motor. That's an overly simple way of putting it, you still need an enclosure, heatsinking, enclosure cooling, to ruggedize and fuse it so it's less dangerous if it rains or you crash or it overheats or any other number of mishaps. If you wreck and the controller gets busted shorting batteries capable of dozens of amps or more, the result may not be pretty, or inexpensive to repair.
ac-dc ac-dc8 years ago
I should add, my design hint was the lossier method, but the easier one. More efficient would be to use a switch mode controller where you vary the pulse width, but to someone who has not built anything like that before, it is going to be as time and cost effective to buy something ready built, a used product.
omnibot8 years ago
The old way of doing this before everything was digital was relay's. Feed the relay with a PWM (take one of the 555 kinds on this site).