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Trailer Brake Controller — Parallax Forums

Trailer Brake Controller

bigirvbigirv Posts: 37
edited 2013-04-01 02:05 in General Discussion
Has anyone attempted to use either the propeller or basic stamp to create a trailer brake controller like the ones installed in trucks? I am looking for some insight on the best way to go about this using an accelerometer to determine what percentage of stoping power is being used in the vehicle and applying that to the trailer. Any help would be apreciated.

Comments

  • kwinnkwinn Posts: 8,697
    edited 2013-03-30 11:09
    First, a warning. Having brakes on a trailer can be dangerous if they are not properly controlled. If the wheels lock up the trailer may jacknife or sway enough to cause the tow vehicle to loose control.

    The ideal trailer braking system should brake the trailer at the same rate as the tow vehicle, and avoid trailer wheel lockup.

    The braking rate can be controlled by measuring the force applied by the trailer to the hitch ball or fifth wheel, and using that to control the braking force.

    Wheel lockup can be controlled by measuring and comparing the RPM of the two wheels and the rate of change of the RPM. A sudden drop in the RPM of one or both wheels indicates lockup. A single wheel lockup is more dangerous than both wheels locking up.

    Google "ABS brakes" and read some of the results for more details.
  • PropNut1960PropNut1960 Posts: 23
    edited 2013-03-30 12:01
    I agree with the above, not really a good idea to try and re-invent the wheel on this.
  • pedwardpedward Posts: 1,642
    edited 2013-03-30 17:17
    Prop trailer brake controller = 2x the cost of a commercial controller + liability = too expensive

    FWIW, the simplest controllers are basically a pendulum design with adjustable spring tension. The don't use pendulums anymore, but rather a more reliable design that can be mounted at angles other than level.

    Many don't use any accelerometer feedback, it's just a timer and variable output, the brakes are applied over a ramped time to the maximum amount commanded, rather dumb really.

    As for driving with a trailer and locking up the brakes, the only way a trailer jackknifes is if the trailer is going faster than the towing vehicle, think about it. Now, the trailer losing all yaw control can cause the vehicle towing it to "wag the dog" and lose yaw control too.

    In general, the trailer brakes applying first is good for stability, I have 2 trailers and have towed several with heavy loads, and having the trailer lead the vehicle takes the slack out of the system and helps to maintain yaw control because the weight isn't instantly transferred to the tongue.
  • xanaduxanadu Posts: 3,347
    edited 2013-03-30 17:38
    Sounds like you'd need a Propeller. I'm not going to beat the 'don't do it' issue to death. I will offer up some advice though. Start with a smaller project... Like reading and logging the accelerometer data. Reading the vehicles brake light sensor and making an LED light up. Using a Propeller pin to output higher voltages. Implementing some type of fail safe(s). You could even add anti-lock sensors (not tied into brakes) to the trailer and test them out. There's a ton of stuff you can do without actually controlling the brakes, or creating a potentially hazardous situation.
  • kwinnkwinn Posts: 8,697
    edited 2013-03-30 19:42
    @pedward,

    Re: "As for driving with a trailer and locking up the brakes, the only way a trailer jackknifes is if the trailer is going faster than the towing vehicle, think about it."

    Not quite. The static coefficient of friction is higher than the dynamic coefficient of friction. Tires on wheels that are turning have more traction than those that are locked up and sliding on the pavement. This means the tow vehicle can decelerate faster than the trailer, and that can result in jacknifing.
  • Duane C. JohnsonDuane C. Johnson Posts: 955
    edited 2013-03-30 19:48
    Hi bigirv;

    I don't begin to know what Parallax would say, but...

    This project could be considered "Life Rated", not to the extent of a heart pacemaker, but serious business nonetheless.

    Many companies won't even sell things to you without a negotiated contract. It's in the fine print.

    Duane J
  • Duane C. JohnsonDuane C. Johnson Posts: 955
    edited 2013-03-30 19:55
    Hi kwinn;

    Very correct.

    In addition there can be considerable weight transfer which results in unloading the front tires which now have less steering ability. This can happen even with a properly operating system.

    Duane J
  • pedwardpedward Posts: 1,642
    edited 2013-03-30 20:41
    It's true that skidding tires have less traction than tires that are rolling, however the basic physics of weight and polar moments will dictate that the trailer can't pass the tow vehicle unless the tow vehicle is going slower in the same direction.

    The trouble people get into is the tail wagging the dog because loss of yaw control on the trailer can result in the loss of yaw control of the towing vehicle and the whole rig spins around with the heavy portion of the pendulum taking them for a ride. This is the classic inverted pendulum problem that you face with robots and devices like the Segway.

    Something to consider--actuating the trailer brakes only is a valid way of inducing stability into the equation, just think of the pendulum.
  • Phil Pilgrim (PhiPi)Phil Pilgrim (PhiPi) Posts: 23,514
    edited 2013-03-30 20:45
    What's wrong with hydraulic surge brakes? They're both simple and reliable. You guys are overthinking this, methinks.

    -Phil
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-03-30 22:42
    Vehicle accidents are reputed to have killed more people than all the wars in history. You might have less legal downside with something attached to a working firearm. We seem to have a lot of people developing firearms in the US and prospering.

    Why not go after the mosquito, it kill just about more people than anything else that is an identifiable problem.

    I do admit that understanding the geometry and design of such a device is a worthwhile study project. It is just a legal minefield.
  • Mike4421Mike4421 Posts: 131
    edited 2013-03-31 08:36
    Brakes are a serious business, you can get good info if you read a CDL license manual, a good starting point can be Arizona's CDL manual, online DMV for a copy
  • icepuckicepuck Posts: 466
    edited 2013-03-31 18:18
    Back in the early nineties I tried experimenting with ABS for electric trailer brakes using an i386ex board. The problem I ran into is how do you anticipate failures and how is the system going to behave during a failure and/or malfunction.

    Last semester I had a class on air brakes. It's now a federal law that all semi's and trailers have ABS. And on top of that OEM's are now working on ATC(automatic traction control) integrating that into the ABS systems, which have to communicate(via can bus) with the engines ECU . Both trailer and truck ABS systems communicate via the power wire that powers the trailers ABS controller something like what x10 did for AC. ATM I don't remember what is called.

    So if you don't mind dealing with all the laws and regulations that go along with such an endeavor then go for it. Kept in mind that the end user
    can get sue happy when something malfunctions and some one gets injured.
    -dan
  • kwinnkwinn Posts: 8,697
    edited 2013-03-31 23:51
    icepuck wrote: »
    .......... It's now a federal law that all semi's and trailers have ABS. And on top of that OEM's are now working on ATC(automatic traction control) integrating that into the ABS systems, which have to communicate(via can bus) with the engines ECU . ..........
    -dan

    Oh, joy, let's see what happens. I am trying to get up an icy hill and 3/4ths of the way up I hit an icy patch with one wheel. The wheel spins, the ATC applies the brake to that wheel and reduces the RPM to idle, and my car looses all forward momentum. Now I have to back all the way down the hill to take another try at getting up or just give up and go away.

    This is not a hypothetical scenario. It has happened to me several times, and makes me curse the idiots that came up with the idea. I had far less trouble getting around in a car with a clutch and standard transmission than I have had with any vehicle with "traction control'.
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-04-01 02:05
    I am not a big fan of 'smart' operator interfaces, or the beauracracies that mandate that we must adopt such. Fail-safe systems are actually very scary... ever since we created the A-bomb.

    California has a license board for just repairing brakes. I did my own brakes on all my cars for about 30 years and saved huge amounts of money, but I never got certified. The guy that taught me how to properly repair brakes never graduated from high school, and could barely read -- buy he knew automotive mechanics which he learned hands-on and orally from his father.

    On other fronts, I did see an article that mentions that automobile deaths are actually on a steady decline in the USA (why is this so? new systems, or less drunk drivers?) and in a few years the USA can proudly claim that firearms are causing more deaths per year than vehicles.

    That's progress? You need to take a look at the curves and projections to sort it all out. But, it is all rather weird.

    http://www.usatoday.com/story/news/nation/2013/01/09/guns-traffic-deaths-rates/1784595/

    Conclusions? Get your own California Brake Card and you can pick up some extra cash by DIYing your own and doing friend's brakes.
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