Active Rear Wing Control System. Help Needed

[Peadar]

Wow, genuinely amazed at the response to this. Thanks to everyone for the replies and input. Plenty of interesting ideas floating around there.

To put things in context, this project is already far beyond what is needed for this thesis and although it sounds counterintuitive I need to try and keep the electronic controls as simple as possible. Reason been the course I am completing is mechanical engineering so too much focus cannot be placed on the electronics alone. In regards to having progressive control there's no real need for it. As under braking the wing needs to move as quickly as possible. And then back to high downforce once the braking is finished. Also, hydraulics cannot be used as its a safety issue. The forces involved at the high downforce levels will be about 1500 newtons. As for when the wing moves to air brake mode, as the wing is in stall this needs to be calculated via a wind tunnel test although I would expect more that 2000N.

http://www.gimsonrobotics.co.uk/GLA-..._actuator.html
Here's the actuators been used, as said in the description they can move at up to 30mm/second. Although thats is far from quick the problem is overcome by having the link to the rod right next to the pivot point. So with a very short extension the wing can change angle quite severely.

One simple idea i had was to use two limit switches which would be activated by a pin mounted on the lower part of the connecting rod beneath the boot lid.

So when the button on the wheel is pushed the wing is activated to move in the positive direction as such and moves upwards until it reaches the upper limit switch at which point it stops.
Then when the brake pedal is pushed, maybe just through the brake lights a current could be taken to activate the actuators to move in the negative direction, once they reach the required air brake angle and trip the limit switch then the actuators stop again.
However this still leaves the problem of how to set a home position for when neither an input from the button or brake lights are received.

If you use an Arduino or something similar, you might be able to use accelerometers to automate the wing; one sensor could detect sideways motion to move between positions A & B. a second sensor could detect deceleration to move to position C. The nice thing about that is you could get proportional control with little driver input needed.

As mentioned above there's no real need for proportional control with this system as it basically can be said there is just positionA, B or C. Pick one! haha. Although there could be a system with proportional movement it would be far more complicated than what I'm at.

Another thought; with two actuators it would be quite easy for them to get further & further out of sync if one of them ran just a bit slower than the other, leading to damage or lock-up. If you use an Arduino, you can use one limit switch to set a home position and a rotary encoder on each actuator to make sure they are in sync and get full proportional control, which seems like a good idea for braking.
I couldn't find the actuators on Google, do you have a link for them?

Only this morning I was questioning my choice to use two actuators, it is a problem. But the two are needed as the forces using the airbrake could be upwards of 2000N so there needs to be an element of factors of safety. Surely if there are limit switches though set in the same physical position then they would stay in check?

As a pure mechanical guy I can construct a relay-switch based setup, but I fear it will fill the trunk.
No, the arduino sounds like the best bet. And Nicks comment are spot on.
To get perfect sync, use 2 encoders , or even good quality potmeters that measure the axle position of the wing-pivots.
If the idea of measuring acceleration in 2 dimensions is workable, you can even have the wing, if it's flexible enough, torque to have more or less downforce at each side. You could even go further, and do the same with the front spoiler.

What do you mean by it would'nt fit the trunk?
To be honest the wing is very much over engineered for safety reasons so there will be little or no twist.
Once I am done this years college I'll be moving onto the rest of the aero bits on the car, it really is endless the amount you can do but its incredibly interesting. Bits will include a front splitter, new cooling system, flat floor and a diffuser. So plenty of work to be done, in the future

I was thinking about an encoder on the wing itself but the what if the actuator on the far side ran at a different rate? It would still twist the wing and you'd never know. With just one actuator it would be fine.
I wonder if an actuator will move fast enough to position the wing in race conditions? The heavy duty actuators I have seen are pretty slow and race conditions change very quickly. They would be the simplest off-the-shelf parts to use but if they don't deliver, they aren't worth anything.
Another place to look for parts might be in the CNC world. A servo motor and an ACME threaded rod or ball screw would move much faster and servo motors usually have an encoder built in. Looking back at Peter's original description, the system already uses pushrods up to the wing, so I would look at a nut up on the wing with a short length of screw and then a rotation shaft down the the trunk. More effort to make, but fewer moving parts, probably lighter and it could move the wing much faster.
Another limitation is the 12V supply; no over-volting anything to get more speed or torque.

As said above they actuators used can move at 30mm/sec under load. To optimise the speed the connecting point on the wing will be located very close to the pivot point.
Although its not ideal it will do the job.

Encoders all the way only way to be sure on the sync of the motors,all other option wouldn't have fine enought control to have the wing perfectly square . Also you can then have the wing linked to the Speedo so it adjust continuesly with the vehicles speed

Severaly people have mentioned the gradual control before it raises some other issues as I like the idea of having an always home position as it acts as a safety as the wing always returns to the high downforce mode, giving optimum control unless another input is recieved form the push button or brake lights

hydraulics?

As said above, hydraulics were ruled out as they raise a safety issue