Computer Controller Question

[Rex Schimmer]

Having seen Rob's car the addition of a load cell some place on the rear axle would be difficult to impossible, there might be a chance to use a strain gauge on the real axle housing which would require some load testing to scale the gauge and then a standard type of closed loop controller can be used. It would probably require a displacement transducer on the screw actuator for stability and accuracy. Another method would be to use the surface speed differential between the front (undriven) wheels and the rear drive wheels and then close the loop around the difference to maintain traction. This control could not be very exact as you would be controlling tire spin by trying to control down force through the actuation of the wing flap, lots of uncontrolled variables and probably a pretty slow system.

You could also do a type of open loop control using calculated down force vs. speed and flap angle, Eric should be able to generate these numbers for you. You could then use this "map" of down force vs. speed and flap angle to set the flap angle for the speed you are running and the down force you require. It would require a position feed back on the actuator but it would probably be the simplest system. Similar to how present day top fuel cars set their clutch lockup. You could then increase or decrease down force using a simple off set to the down force map to "tune" the system.

Lots of avenues to go down and a pretty challenging problem.

Rex

[Jon]

Don't know the specifics of you gear ratios etc Rob.
Is it as simple as having an angle for each gear or is that too coarse?

I know this doesn't answer your question.

I wouldn't be trying to control the angle with a feedback loop, it's another variable to tune that I can't see the benignity for.

Cheers
Jon

[robfrey]

Rex, I think you hit the nail on the head in relations to the speed vs flap angle map. The positioner that we have actually has a 0-5v sensor so it is pretty easy. The FAST dash-logger has a configurable output with 16 x 16 map that we could program to give us what we need.
I'm just concerned about rule 2.Q.

[hotrod]

One other possibility would be to monitor pressure differential between the top and bottom of the air foil, and control angle to maintain a specific pressure differential (ie total down force) for each speed.

As above you would need some wind tunnel or computer modeling to figure out what down force you want at each speed and build a down force vs speed map.

Larry

[Dean Los Angeles]

If this was easy ANYBODY could do it.
In the wing was set up neutral with minimal drag and you have no wheel spin then abracadabra done.
That blown A motor makes that not probable.
Without feedback you are relying on computer simulation, and that is only going to get you so far.
I would create a speed map and adjust the angle based on speed. You need to log that speed vs wheel spin so that you can dial it in.
That does nothing for your big, fat, right foot. If you plant it hard at any speed the traction control and downforce are never going to keep up.

It's all balance, ain't it?

[robfrey]

Yes Dean,
It's all balance. The cfd will only get us so far. I have chosen 3000 lbs of downforce as a target downforce number. Maybe we only need 2000 if the salt is good? We will just have to make some runs and get some data, then we can tune the system. The idea here is to actually design and build an easily tunable system. The biggest thing to consider is the cost of spinning the tires. One good spin and there goes $1600. Ouch! We will have to sneak up on the flap tune.

[Dean Los Angeles]

Without feedback how do you calibrate cold and dry vs hot and humid?
Records are set by solving for all of the variables.

Yeah, I know, you have to start somewhere.

[John Burk]

Rob how about have the waste gate and wing flaps advance to preset points each time the transmission shifts .

[Jack Gifford]

... I'm just concerned about rule 2.Q...

Not easy for folks to stay focused on that. It will be interesting to see whether the rule ever gets changed to remove some ambiguity.

[robfrey]

John,
I only have two shifts and first one occurs at 200mph. We need to move the flap in smaller increments. This idea would probably work on a five speed.
Because of movable flap feature, we can apply full power by the end of first gear. As of right now, we plan on eliminating the boost controller and replacing it with a simple regulator to the waste gates. I can pedal it through first gear. The waste gate controller is just one more electronic component that can give us issues.

[John Burk]

Rob then how about a timer that updates the settings .

[robfrey]

A timer in LSR is a sketchy thing. I do not even like using time based boost controller on my drag car let alone LSR.
From run to run there is too many variables that determine speed vs time.
I guess it would help by starting the timer at the fist gear change.

[NathanStewart]

so have you asked the rules committee if your computer controlled aero package would be legal yet?

[bbarn]

so have you asked the rules committee if your computer controlled aero package would be legal yet?

When I posted the topic in the SCTA Rules questions section, I thought we were asking them. Is there a better/more direct path to take to get the answer?

[JustaRacer]

... I'm just concerned about rule 2.Q...

Not easy for folks to stay focused on that. It will be interesting to see whether the rule ever gets changed to remove some ambiguity.

The rule doesn't appear to be ambiguous; it just appears to be dated.  Says:  Just an engine controller and a datalogger.  However, more than one entry has run more computers.

If you break somebodies record and they protest, I can see where they would have a legit beef.  Perhaps they DID want to run digital aero controls, but didn't because of the rule.

Sounds like a rule change is right wrench to fix the problem, not a ruling.