[Diy_efi] Traction Control System (update 2)

[Jörgen Karlsson]

It looks like the 2907 approach was a bit to simple. 

Nic wrote:

> The 2907 is designed for cruise control etc... Where you have an high
> frequency to
> convert.
> 
> For the very low frequencies you see when doing traction control it
> won't work. The
> wheels will have started spinning seriously by the time the output rises
> to the point where
> the an 8 bit ADC will start giving you a reading.
> 
> The signals from the four wheels will also differ significantly. Just
> the storage caps
> on the different 2907's will introduce a typical -10% to +20% tolerance.
> Sure you *could*
> tune it out, but how often do you want to fiddle with it?
> 
> Using 2907's will allow the wheel to break loose and start spinning
> before the controller
> reacts. Then you reduce torque somehow, and the wheel needs to shed
> momentum before gripping again.
> Your control loop has a huge delay and osscilates easily. It will work
> somewhat, but you'll be ripping
> the drivetrain apart until you have a well tuned PID. Then the
> temperature changes or the caps age and you
> start over.
> 
> If you use the sensor properly, by doing a per tooth wheel speed
> calculation, you detect the start
> of wheel spin before it has started smoking rubber. If you then back of
> torque slightly you can
> conceivably keep the wheel right at the traction limit, instead of
> swinging wildly around it.
 


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