[ausev] DIY controller?

[Chris Robison]

evehicle4me at hischopsticks.org wrote:
> Wow!  I am glad that I have google to help me understand some of this stuff!
> 
> I want to throw a curve now... it seems to me that a controller (in  
> basic form) is a huge potentiometer/relay.  Am I too far off the mark?

Sort of.  A DC motor controller is actually a lot more like a dimmer 
switch than a potentiometer. The difference is that a potentiometer (or 
rheostat or variable resistor) functions by resisting current and 
burning off the excess energy as heat. Obviously for controlling an EV 
motor, this would get extremly hot and waste lots of energy.  In 
contrast a motor controller is basically a solid state switch, that 
turns on and off rapidly (thousands of times per second), in a scheme 
called "pulse width modulation". The "duty cycle" is the ratio between 
on-time and off-time, and the higher the duty cycle, the more time the 
motor is in the "on" state, and the more current it draws. This method 
of control wastes a lot less power. (For more info, wikipedia is your 
friend: http://en.wikipedia.org/wiki/Pulse-width_modulation)


> Is it possible to find a basic controller that has the ability to  
> interface with a computer (i.e. notebook computer, not industrial chip  
> on a board with no user interface) to perform the other tasks?  I know  
> that there are programmable controllers on the market but there is a  
> part of my heart that is truly "open source" and the idea of having  
> something that the whole EV community can contribute to and improve  
> (from experience) is very appealing to me.  I know this option might  
> not save money up front but, in the long run, since motors last a long  
> time, it is possible it would save money by being more upgradeable.

There's nothing open-source in controllers intended for EV use (to my 
knowledge), but there is the "Open Source Motor Controller" for 
controlling small permag motors, for battlebots, etc:

http://tech.groups.yahoo.com/group/osmc

   --chris