Flywheel/Encoder patterns

[Todd Knighton]

kleenair at ix.netcom.com wrote:
> 
> Thanks Todd, that is a very good point.
> 
> The way I was looking at the problem was that I have a maximum window of
> 720 degrees to fire the injector.  By using the 180 teeth with rising and
> falling edges, I can control my duty cycle in 0.13 % increments (1/720),
> and I thought this would be satisfactory.  But I can see your point about
> low load AND low RPM conditions posing a problem.  I think I'll be OK on
> my current project, but I'll keep that in mind for the next application.
> 

	Yes, going sequential will definately help out that problem, the stuff
I was referring to was group fire and fired every TDC.
	The only other problem I can see is unless your running a very fast
clock, you'll run out of interrupt time at high rpm.  The Porsche's with
129 teeth have a practical limit between 8000 and 8500 rpm's where with
more teeth that will drop to 5733-6091 rpm's.  But again we were using
an 8051 with a 6mhz clock, but doubling the clock rate you could
effectively have a 10,000 rpm setup.
	Something to look for further down the road.  Porsche's setup also had
a map that corrected for timing vs rpm, I'd assume this would be because
of interrupt latency.  You'll have a similar problem to deal with,
should be easy enough to correct though.
	Be careful that your interrupts are extremely short, otherwise your
program will just stay there and never do any code work.  Your registers
will have to be saved, or just make sure you deal with a different set
all together.  You'll also have to watch out for variable loading. 
After your calc's are done, you'll want to load your variables into the
ones you'll use in your interrupts, if you don't cancel all the
interrupts, you can be half done and load in some very strange values. 
Either cancel your interrupts, or set a check bit to make sure your not
doing that.

Todd Knighton
Protomotive Engineering