Computer Controller Question

[manta22]

Strictly speaking, a servomechanism is not a computer.

BTW, the first high wing that Jim Hall used on his Chaparral Can-Am car was mechanically linked to the rear uprights; it changed its angle of attack as the ride height changed.

Regards, Neil  Tucson, AZ

[JustaRacer]

I would imagine that most the people who drive today rely on several computers for safety.  If your car is newer than 1989, you have safety computers.

Today's cars can have up to a dozen (or more?) interconnected computers that all have some safety features to them.  None of our family cars have fewer than 8.

Some have computer controlled downforce and suspensions.  More than you think BTW, not just racecars, some are just family cars. 

Why did the auto MFR's do this?  Same reason they put in electric starter motors and windshields.  Safety.

Best way to survive an accident is to NOT CRASH.  No amount of post-crash safety equipment in the world can protect you from a crash. 

It just depends on how you define safety.  Is safety surviving a crash?  Or is safety the whole package?

[bbarn]

Just to try and keep this thread on track. We are looking to use a computer to maintain the flap angle on the wing of the car. There is a computer program that will evaluate the speed of the vehicle and set the flap to a pre-determined angle. The intent is to keep the down force at a constant through the entire run.

There are alternative manual methods of performing this same function, but the simple question remains, can a computer be used in the streamliner class to move aero devices? We aren't looking to circumvent an existing rule or make a new one, we are just trying to identify the boundaries.

[Moxnix]

You might check with Nivek R&D, best via email, to see if he has a program that might do what you like.  He's doing some aviation things and builds the Zeus modules for some types of racing.

[jdincau]

Can we use a computer to control the flap on our streamliner (NACA 66 Special - A/BGS) to adjust down force or must it be a manual process? Specifically we are looking for an interpretation of rule 2.Q.

Chief Car Inspector       Steve Davies   flyingkiwi97@aol.com            (714) 671-9454

Car Technical Co-Chair  Lee Kennedy   Lee.Kennedy@AVMetrics.net   (805) 522-8134

[manta22]

Maybe I wasn't specific enough in my last post about servomechanisms-- it is not necessary to use a computer to adjust a wing so that it provides a constant downforce. Here's how to avoid using any computer at all:

1. Sense the position of a rear upright in relation to a fixed point on the chassis; this change in length will be proportional to the rear spring compression-- which is a function of downforce.

2. Amplify the difference between that sensor output and an output from a voltage reference.

3. Apply the amplified difference voltage to a power amplifier capable of driving a DC motor or linear actuator connected to the wing.

4. The feedback from the sensor will drive the motor to adjust the angle of attack so it will keep the ride height constant-- providing the feedback is negative. If it isn't, just reverse the two wires to the DC motor.

5. The ride height can be adjusted to be the same as the static ride height (no downforce) at speed, lower ride height (downforce), or higher ride height (lift) by setting the reference voltage.

6. Use enough gain in the amplifier so that the loop error is small but not so much gain that it is unstable (oscillates). This is a simple feedback control system but it can be made a bit more complicated by adding integrators and differentiators to form a "PID" loop.

7. At rest or at low speed, with the reference set for downforce the wing will be at maximum angle of attack because the servo is trying to get downforce without any air passing over the wing. As speed increases the wing will assume whatever angle it takes to generate the downforce that you've asked for.

Voila! ...no computer. Now whether this would be legal is another matter.

Regards, Neil  Tucson, AZ 

[robfrey]

Neil,
That's very ingenious but we have no rear suspension.
It would be very complicated  to add suspension to our current design.

[robfrey]

I can understand why this would not be legal in the lower production car derived classes but the "special construction" Streamliner and Lakester class is the place where innovation is encouraged. With today's computer availability, I don't understand why this rule applies to the Special Construction category.
We do not need the rule to be changed for our mechanism to be successful but I'm trying to make the driving job as easy as possible.
If the rule cannot be changed, we will use a the dash logger to tell us when to reduce flap angle via indicator light. As speed increases, an indicator light will be activated on the dash and I will press and hold a button on the left side of the steering wheel until it goes out. I will need to repeat this several times during a pass.

[Dean Los Angeles]

Modify the wing mounting to incorporate a load cell. That will give you a direct reading of force.

[manta22]

Dean's suggestion would also give you the sensor feedback to the servo.

Regards, Neil  Tucson, AZ

[robfrey]

Again, great idea but there is no good place to put the load cell as the wing is integral with the body. We would love to gather data on just how much load wing is generating. We will have to rely on the cfd. Fortunately, this is something that cfd does well.

[johnneilson]

Rob,

what mechanism is being used to move the flap?

could you sense loading on the flap itself and then change attitude?

The issue I see is the wording in the rule book, it specifies no computer control other than engine.
By definition, a computer is any device that reacts with a input or series of inputs to control something.
Many ways to skin this cat, especially with todays small PLC controllers.

[robfrey]

We will be using a dc linear actuator to move the flap.
We could monitor the load on the flap but it will not be very linear to total loading on wing. I have also thought about ways to spring the flap in the up position and let the air try to flatten it out at high speeds. The more I have learned about airplane controls, the more I understand why this won't work very well.

[Dean Los Angeles]

Traction control was illegal in the past. It was made legal because so many racers were using it and
SCTA had no way of even determining if you had one.

I think that you should head in the direction you would like to go and call it good.

Ok, if the load cell on the wing won't work, then move it to the axle attach points. At some point you transition from composite to metal and can read the load. Real load feed back with CFD beats CFD computations alone any day. 

[SPARKY]

Dean ---is this the same guy who took issue with the water tank vent system spilling water in to the slip stream   --lol