Active Rear Wing Control System. Help Needed

[Niels - Team K.a.L.M.]

hydraulics?

[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

[Peadar]

Also for those of you with an interest in cars, here's the car that the wing is been fitted to...

[daveimi]

mr giuseppe busso's best effort My dad is a race mechanic so I appreciate that engine

[overkill]

Hi Peter, I'm sorry if we are over-complicating things for you - its in our nature to come up with unique solutions and improve on whatever we are working on.

Although I can see the reason for keeping the electronics as simple as possible, using an Arduino or other micro controller (MCU) will likely be simpler than just trying to do it with relays. By having each input (buttons & switches) and each output (the actuators) monitored & controlled separately by the Arduino, you get more flexibility to fix problems and get the system working the way you intended. Even without all those accelerometers and encoders, an MCU is still the best solution.

Looking over your posts, you have eight inputs: three switches per actuator, brakes and a button. There could be one or two outputs and I would advise two so you can control each actuator separately to overcome any speed/position differences. As well as these basics, I'd recommend one or two extra outputs to give the driver some feedback - he would definitely want to know if the wing was stuck in brake mode! The system only has three states. That is a really easy situation for an MCU and would be handled by a small logic table, which we can work out for you if you are not sure about it. You mentioned safety was a big issue and an MCU can help by monitoring and reporting faults (maybe just a failure light on the dashboard).

Those actuators might not be what you expected. Looking at the specs, the 31mm/sec speed is with no load. From experience and reading other spec. sheets, the actual speed at about half it's rated load with be much slower. Have a search for higher-end actuators and you will often find graphs showing their speed VS load - its pretty disappointing sometimes! If you look at the GLA4000 actuator, it mentions a 40% speed reduction at full load and it probably has a much higher gear reduction than the GLA750s. I'd expect the GLA750s to slow down by a larger percentage under load.

Actuators usually state a duty cycle rating and its often quite low. If the wing is moving frequently, you might find the actuators overheat.

The 550 motors may not be reliable under heavy loads and they are definitely not weatherproof, so the trunk will need to be. They could also be a fire hazard as the brushes produce a lot of sparks and the open cans will allow fuel vapour in. The type of sealed motor on the GLA4000 is what you probably need. I realise the GLA4000 doesn't meet your other requirements, but that construction style and IP65 environment rating is the way to go.

After looking at the drawings and your comments, I have a couple of questions:

What part of the car are the wing supports mounted to; the trunk lid or the body?

You mentioned up to 2000N force. Is that the total on the wing or on the point where the actuators attach? This is a class 3 lever arrangement and if the 2000N is considered to be applied on the trailing edge of the wing, you will need considerably more force to elevate the wing into brake mode. I know nothing about aerodynamics, thought I'd better ask.

Are you up for some mechanical work? Would modifying an actuator to get what you want be possible?

What about the electronics work? Could you solder a few components together of do you need everything to be plug & play?

[maddox10]

Hi there,

I ment that an old school end switch/relay based setup would be large and heavy, offsetting most advantages the idea can have. One of the reasons active wing control ain't that much used.

After looking several youtube's with cars with active wing control I'm almost sure the GLA linaks will come up short.

These just don't have the grunt/speed for the demands imposed on them for an effective active wing.

Nicks remarks stay to the point. I'm curious how custom build you want to go. Building 4000Nm linaks with speeds up to 1m/sec isn't rocket science.

[overkill]

Have to agree about a custom actuator and it might not be much work. Using that GLA4000 as an example, it only has a 50 watt motor and I'd bet you a pint of Guinness that is fairly low RPM as well. By changing the motor for one with 4 or 5 times the RPM and maybe 100 to 200 Watts power, you would get the required force and speed without having to make an actuator from scratch.

Some random thoughts:

Using two actuators is probably LESS reliable than using one larger one. If a motor or gear fails, it will lock the actuator solid and the other actuator will be trying to twist the wing - either something mechanical will break of the 2nd motor will burn out quickly.

If you use an Arduino, this motor control shield might be a good match:http://tinyurl.com/bmp4lmy. It uses automotive motor control chips that have temperature & current limiting and should handle high power actuators. It will work with very little programming and has advanced features you could use at a later date.

What sort of budget are we working with - penniless student or rich sponsored/factory team?

The forces acting on the push rod and actuator are always going to be compressive, which is exactly how actuators are meant to be used. For the push rod, I'd be using a wider tube rather than a thin solid rod as it will deflect less in compression for the same weight. Add a million style points if you can use a carbon fibre tube.

[Peadar]

Have to agree about a custom actuator and it might not be much work. Using that GLA4000 as an example, it only has a 50 watt motor and I'd bet you a pint of Guinness that is fairly low RPM as well. By changing the motor for one with 4 or 5 times the RPM and maybe 100 to 200 Watts power, you would get the required force and speed without having to make an actuator from scratch.

Some random thoughts:

Using two actuators is probably LESS reliable than using one larger one. If a motor or gear fails, it will lock the actuator solid and the other actuator will be trying to twist the wing - either something mechanical will break of the 2nd motor will burn out quickly.

If you use an Arduino, this motor control shield might be a good match:http://tinyurl.com/bmp4lmy. It uses automotive motor control chips that have temperature & current limiting and should handle high power actuators. It will work with very little programming and has advanced features you could use at a later date.

What sort of budget are we working with - penniless student or rich sponsored/factory team?

The forces acting on the push rod and actuator are always going to be compressive, which is exactly how actuators are meant to be used. For the push rod, I'd be using a wider tube rather than a thin solid rod as it will deflect less in compression for the same weight. Add a million style points if you can use a carbon fibre tube.

Hi all,
Apologies for the lack of replies, I have been mad busy lately.
I received the actuators, they are very very small and light.
After considering a lot of your input (and others from various backgrounds) i have decided to make several changes to the design.

1. Use only one actuator, it seems this is a logical step for reliability and also aerodynamics. The actuator I have can handle 2300N so that will be ok on its own.
In the future i can upgrade my motor to be more powerful/quicker

2. The actuator and wing will be mounted to a subframe as such in the boot. The boot lid will play no role in suporting the wing, it will just act as a cover. The car has gone to get a role cage this week so the work will be completed then.

3. The actuator will act in the centre of the wing between the two mounts.

4. The wing has been increased in size to 1700x400mm
Here are the latest calculations after these changes...

Thats 125kg @100mph! Happy days


I'll try to keep here updated, thanks all for the input, it has been an eye opener to some aspects. I hope to be working on the mechanical construction for the next 3 weeks so I won't be focusing on the aspect at hand here. But once the wing is completed I'll have photos up for all to see and then I can concentrate on the controls aspect.

Thanks again,
Peter

[Peadar]

Also, @overkill
I am most definitely a poor student haha

[Peadar]

Hi all,
I have the wing nearly built now so its nearly time to move onto the control side as my main focus.
I have re read all of the posts here just to make sure I am up to date.
First off, I have decided to use only one of the actuators. So that will reduce some of the work load.

Assuming I am to use an Arduino or othe MCU what do I need otherwise.
The actuator I have chosen (maybe foolishly) have no feedback or limit to stop it from running beyond its maximum range. So a potentiometer or some sort of feedback is required? Is this then feed into the MCU? Just trying to get an idea of what more I will need to complete this project

As you can probably tell I am not much of an electronics head so apologies if I seem totally lost here.