Andy Meng <piclist@mit.edu> wrote:

> we have about five drivers (which I think is too many - but that's
> not my decision) and bringing them all up to the same point would
> probably be a bit difficult given their level of experience.

    Nah, just let your best driver find the right launch and shift
    RPMs, then have him tell the others.  Once they know where to
    hold the revs and when to shift, even your worst drivers should
    do fine.  I mean, GIRLS do ok on the dragstrip, so how hard can
    it be? 

    [That was a joke...] 

> ideally, we will have a pot that will allow us to adjust the amount
> of slip for different conditions such as tire temp, rain
> tires/slicks, etc. 

    That's only "ideal" if you can know exactly how those variables
    affect the optimum setting.  I'm not sure you can. 

> Tire deformation should be pretty close front to back, unless the back
> is spinning out of control (ever seen top fuel/funny car tires at
> launch?)

    Fortunately for you, your rear tires won't do that.  The
    deformation I was referring to isn't the wind-up and ballooning
    that you see with drag slicks, but the smaller changes that can
    come from weight transfer...  But with your engine's torque, I
    don't even think that'll be a big issue.  

> We have a Zexel-Torsen diff, which I understand to be limited slip,
> torque balancing (still curious about how that works...

    Torsens are really nice.  Your diff has its own web page:

        http://www.torsen.com/fsae/fsaefaqframes.htm

    but there isn't much "how it works" info there.  Try:
    
        http://www.sonic.net/garyg/zonc/TechnicalInformation
        /TorsenDifferential.html


> > I'd simplify the output side of the system by choosing to reduce
> > engine power by retarding the timing; it's fast, effective, and
> > less intrusive with fewer unwelcome side-effects than cutting
> > fuel or spark. It also requires only one output instead of the
> > four that you're planning on. 
> 
> This is the main part of the post that is getting me thinking. I
> can't think of a way to do this with the stock ECM, other than
> maybe delaying the ignition pulse generator

    That seems like a pretty good way...

> As far as one-line control, I would prefer to have a variable
> amount of effect, i.e, with control of each cylinder, so we can
> cut a different number of cylinders depending on how much we need
> to slow down the engine.

    If you have a distributor, you only need one line to control all
    four cylinders (and if not, there's probably still a single wire
    somewhere in your ignition system that pulses -- or shorts to
    ground or whatever-- for each cylinder's spark).

    Delaying that signal retards your timing.  The amount of delay
    can be adjustable, and you can choose spark-by-spark whether to
    delay the timing at all (although you'll probably find that
    there's no need to have control of each cylinder individually). 

> What are the side-effect of cutting fuel/spark you are referring
> to?  By the way, we are using an F4i engine (CBR600)

    Cutting fuel (at least on your motor, which has an injector per
    cylinder) isn't TOO bad; airflow through the induction and
    exhaust system suffers, but you don't care much about that, since
    you're trying to reduce power anyway. With injectors that are
    shared among multiple cylinders, cutting fuel is more dangerous,
    since you run the risk of loading a cylinder with a lean mixture
    that'll detonate.  On a carbureted engine, cutting fuel probably
    wouldn't be worth attempting to do. 

    Cutting the spark has the potential for bad side-effects, as
    well.  Unburnt fuel can collect in the cylinder, wash down the
    cylinder walls, and blow past the rings into the crankcase where
    it'll dilute your oil and/or build up in the form of explosive
    vapor.  Fuel that doesn't end up in the crankcase will get
    pumped into your hot exhaust system to burn there.  None of this
    makes your car go faster or last longer. 

    Of course, your motor isn't going to spend a lot of time in the
    reduced-power state -- and it doesn't have to last a long time
    anyway -- so these are mostly academic arguments... But in
    general, retarding the timing is safer and smooother than
    cutting fuel or spark. 

> > I'd simplify the input side, too.  The entire system can be made
> > ENORMOUSLY simpler if you find a way to sense slip without
> > measuring wheelspeed.  Such a way exists, but I don't want to
> > ruin the surprise for you.
> 
> I was trying to think of ways to sense slip other than wheel speed
> determination and couldn't think of any. Since we had to start the
> design, I went with it. I guess another way would be to sense
> acceleration and try to get the best acceleration (start cutting
> power after you go over an acceleration peak). It seems like it
> would be hard to know when you could stop cutting it, because the
> indication would be relative. Another poster mentioned basically
> taking the derivative of engine speed and if it was too great for
> what you knew available traction could support - you could also
> have a pot to adjust the desired maximum engine derivative. The
> problem that comes to mind with this is that it would change as you
> got into higher gears and with different loads.

    With what you've said above and in your other emails, you
    already have all the building blocks to come up with a
    slip-sensing method that doesn't require wheelspeed
    measurements... But if it doesn't come to you, just say so and
    I'll post it. 

> Another key task (far more so than traction control) this year is
> getting a solid electrical system.

    Yeah, it's funny how the high-tech stuff (like a 500kbps data
    link from each wheel, for instance) is easy and reliable, but
    what makes you lose races are the dumb low-tech mistakes like
    failing to crimp AND solder connectors, using spade lugs instead
    of rings, forgetting to make everything waterproof, letting wires
    brush against the sharp edges of holes you've punched in
    sheetmetal, etc. 

    Best of luck.

    -Andy

=== Andrew Warren -- aiw@cypress.com
=== Principal Design Engineer
=== Cypress Semiconductor Corporation
=== 
=== Opinions expressed above do not
=== necessarily represent those of
=== Cypress Semiconductor Corporation

_______________________________________________
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist