How would you make an airbrake for a car that is activated by the brake light signal ?
 

How would you make an airbrake for a car that is activated by the brake light signal ?
My first thought is using servos for large R/C planes, but how complex would that be ?

Arduino controller or similar. The third brake light can't distinguish a panic stop.

It would bleed off energy you paid money for most of the time.

Beware the level arm between your solution and the center of pressure (IOW put it at the rear like a shuttlecock).

Find the control signal for the abs system and use a mosfet to sample when it activates. Or a Throttle pot on the brake pedal set such that more pedal gives you more or less signal/voltage.

However there will be a lag time in milliseconds between activation and appropriate movement of any surface so use in a panic stop may require some janking about

Thanks guys. Great advice.
This is just a 'backburner' idea.
I think it would cost too much to just do as a hobby, but I have had the idea for quite a while now. ( years ! )
I wouldn't replace the brakes, but rather suppliment them with the airbraking.
I would just have an R/C servo that is trigger on and off by the brake light elecrical current.
In addition to braking, the flaps would also add downforce at just the right time that you need it most.

I wonder why something like this has never caught on.

Pedestrian safety laws perhaps ?

'caught on'
 

Currently, Bugatti and Koenigsegg are both using air-brakes.
We're talking 258-mph, and 310-mph cars though.
The retarding force, like any other aerodynamic force, is going to vary as the square of the velocity.
I know from observing passenger jet air-braking that, at rather high velocities, the effectiveness of spoilers and thrust-reversers kind of peters out, and they've got to introduce hydraulic braking.
I'm unsure what the breakover velocity would be on an automobile.
At Bonneville, I believe that they want drag chutes to precede friction brakes at around 175-mph, in order not to inadvertently burn the friction material off the pads and shoes.
The owner / driver of the Royal Purple streamliner told me that he shredded both parachutes on a run once, and it took eleven-miles to get the car to coast down to a safe braking speed. Floating Mountain must have looked pretty 'BIG'.

Pagani, et al, use dynamic spoilers for cornering. It doesn't require the discernment and reactrion time braking would need.
The 1955 Le Mans gave air brakes a bad name.

Quote:

https://www.wbur.org › onlyagame › 2018 › 10 › 19 › craig-breedlove-spirit-of-america-land-speed-record Craig Breedlove's Quest For The Land Speed Record | Only A Game - WBUR "He has no brakes. He's going 500 mph. He's running out of course, and he's got no way to stop." Images from Spirit of America's on-board camera during a run at Bonneville in 1964....

It was discussed and tested in this video series by the infamous Julian Edgar:
https://www.youtube.com/watch?v=oxn0RShug_I

Too long; didn't watch? While it does work, it's not really worth the effort at legal road speeds.

^^ I was going to make a similar comment.

In order for an airbrake to be effective at normal road car speeds, it would need to be massive.

Coroplast not fit for purpose.

Killing lift is one thing, but straight up drag is another entirely. I played with it with the beetle descent from '7000 on Mt. Rainier to ~'3000. It is pretty subtle to say the least at under 60 MPH.

When I first read "air brakes" I was thinking of the commercial vehicles I've driven having compressed air actuated brakes. Those definitely are not for the average driver as they need more maintenance and care (water can get in and ice up in the lines cause brake failure, for an example).

But yes, air foils that add down force would be awesome!

I remember he did do a video on this topic. I watched it back then, and forgot the conclusion.
BTW, The linked video is on another topic.
I watched the entire thing. He talks about the air brake, but he plans to test in a different video.

One more thing - why the word "infamous" ?
I think his throttle stop testing method is brilliant.

Notorious? Public opinion is fickle.

I still miss slowmover's contribution.

He got banned here as well as a few other places. He really likes to argue. Yeah, the throttle stop idea is so simple and brilliant! I definitely need to use it on my Insight when I start doing aero mods! I believe he sold his Insight, which is kind of disappointing.

I still plan to look into this.
Just to clarify, this airbrake will in no way replace, or even really help my car's wheel brakes.

I just think it is a cool idea, and would like to try it in real life.

The airbrake will be the size of the factory rear spoiler, or larger.
It would fold flat against the roof when there is no electrical signal going to the tailights.
Gravity and air drag would activate the closing.

The 12v ( ? ) signal going to the tailights when I brake would cause the servo to pull a cable on a pulley to flip it up.
A large servo for giant scale R/C planes would be used, or something similar.

So why would this not work, and how would you do it ?

- Thsnks

I'd paint a clownface on the underside, to help with tailgaters.

I might get shot.
I actually plan to have it say " AIRBRAKE" on the underside, so that people would know what it is, and not think the car was falling apart.
I still think it would come as a shock to people though, since you don't expect parts to suddenly move on a car.

Do you think the idea could work ?
I plan to call Tower hobbies and ask them about it.
The main hurdle I see right now, is the voltage.
12 volts from a car battery signal going to a signal lamp, versus what you see on an R/C plane.

I have seen some massive planes that are R/C, so I would think there are certainly some servos that would have enough torque to handle a large flap moving into 80 mph airflow.

https://i.dailymail.co.uk/1s/2020/01...8385561308.jpg
https://www.dailymail.co.uk/sciencet...ers-touch.html

Not the concept car I was thinking of but it will serve. The other one was copper colored with ccntiguous hexagons.

Hi, this is an excellent idea however, I think it would be best fit with 2 side airfoils as well. I was considering engineering one for my 2015 Fit.

I think the proper way of doing it would be to have a voltage in split off of the brake light activation (not to be confused with running lights) to an arduino that has 2 limit switches.
In scenario A: The brake pedal is not applied, the servo has a feedback from the lower limit switch telling the Arduino that it is in normal position, no voltage is applied to signal in (from brake light).
Scenario B: Brake pedal is depressed, signal goes to Arduino unit, sending a signal to the servo(s), tilting your air foil, then hits another limit switch to stop sending voltage so as to not burn or break anything on the servo itself.
Scenario C: Brake pedal is released, and Arduino senses this, which switch is activated, and sends a power to reverse motor for airfoil down position, creating a loop so to speak in a programming sense.

The hardest part would be the programming IMO. AI may be able to do it but I'd definitely be interested in how this came about. I will say personally that I don't think just a rear spoiler would be enough. Ideally there would also be 2 side airfoils that pop out as well, perhaps in doors, or near the rear of the car, only popping out enough to make a difference without causing a danger to cars around, but should give you enough area to displace a second spoilers worth of volume, thus increasing drag. Additionally side airfoils could be eventually mapped in the framework of the vehicle to help with cornering and what not, but that's more for racing applications and you get into more finite engineering at that point.

An accelerometer to sense the force of the braking, something the brake light is ignorant of.

Or even really old school: an offset weight on a shaft that's free to rotate and activate a switching device in porportion to rotation. Brake controllers had this back in the '70s

Down side is it activates sometimes during non braking decel, but adding brake light requirements would tend to solve that.

The accelerometer is already integrated to the SBC.

If the air brake adds any DF component when actuated, and if it's triggered by a brake application signal, I would think a gradual release control signal would be best for vehicle control and to maintain stability and driver confidence. I would think stopping in the wet say at speed DF would be certainly helpful if balanced well, but by simply letting off the brakes as one might do when turning, the sudden loss of DF would be a disadvantage and a bit scary.

Unless there's a cornering method I am not aware of then releasing brakes should mean you're slow enough for going around the corner unassisted: dry ,wet or icy.

Otherwise properly designed drag devices should be set to ensure the pointy end strays forward.

I suspect your knowledge and concept of a "traction Circle" is limited then?

"The traction circle is a visual mathematical way of illustrating how much grip a particular car/tire has on the road, and how it can be used. It’s a simple way of visualizing how acceleration, braking, and turning affect how much grip your tires have, and the relationship between each of these."

Best to read up on it and get back to us.

Naw kinda useless on a 4ton truck towing a 5th wheel in snow.

[Drifting] 'Do I mean nothing to you?'

Could be a correlation between sticky and whatever is going on during drifting but i betcha thats hard to quantify or even predict accurate

If you cannot develop any useful DF, any sought induced drag will also likely have a similar result, all which has little to do with the issue I noted of suddenly losing any DF under braking when triggered only by vehicle brake application.

Decipher please.

And I got to watch that cartoon for free.:D

Thanks everyone for the replies.
Lots of great ideas, but I really wanted to go cheap and simple on this one.
I spoke with a guy at the hobby store. He liked the idea, but said that it would strip the gears when the flap would go down ( air and gravity force ) if I were to use a large R/C servo.
I may still persue the idea in the future. Just to get an idea of how it all might work, I'm thinking of just using a cable and doing it by hand.
This of coarse would just be to test what kind of force is needed to raise the flap.
I'm guessing a considerable amount, since a large plate sized flap moving up into 80 mph air is going to have quite a bit of force.
I want to have it be automated using the electrical signal, since doing it by hand and applying normal brakes would be very cumbersome and dangerous.

One more thing to keep in mind: Should the roof be reinforced to handle additional force at the point of mounting the air brake?

Excellent tip !
I planned to have the pivot point right at the area that the hatch opens, but it would be attached to my coroplast Kammback / boattail.
I hadn't thought of the added pressure.
Btw, the airbrake "speedbrake" would be coroplast, but with aluminum bracing.
I actually like that this is is a challenge to think out.
It's on the back burner though after other things are sorted out.

Back in he WW2 days, on the heavy bombers with massive control surfaces there was a thing called an anti servo tab which one moves instead of move the control surface.

Fuller maintained that being a contrarian can change the World.

https://external-content.duckduckgo....1fc&ipo=images
https://external-content.duckduckgo.com/iu/?.....&ipo=images

As long as you never have to back up.

In my experiences, no it don't work that way. Not that you will be backing up at speed.

Thanks ! I'll look that up.

I was looking at my car's roof.
Along the rear edge, there are several large dents that were created when some kids stole the car and resorted to smashing the car to get my Kammback to come off.
I don't want to drill into the car, BUT this area is already battle damaged, so I'm considering adding a hinge connected to the roof sheetmetal ( sealed with caulking at any rivet points )
As a bonus, the airbrake would make a good transition strip to the start of the new Kammback/boattail.