Add automatic control to my SUV's air-lift system

@davee 

Whilst the tiny trailer is unnoticeable most of the time, the caravan, at about 75% of the mass of the towing car, is fine in normal use, but can be truly terrifying if at say 60 mph, it starts to be 'upset' by something like side-wind, snaking, or a slight 'bump/scrape' from another vehicle.

That is due to the wrong weight distribution. NEVER have the trailer rear end heavy; the hitch should bear at least 10% to 15% of the trailer GVWR or GVW if overloaded. Typically, that is up to 1,500 lbs pushing down on the hitch, but more commonly, 1,000 lbs. Make sure the hitch, drawbar, and ball are rated accordingly; I usually like to go with at least 10,000 to 15,000 lbs for the hitch, drawbar and ball as I like to be 3x to 5x over spec since the life of my family plus unknown strangers depend on it. You will need to visit a garage to get the ball torqued onto the draw bar.

Not only are you 100% correct about the insurance and police attitude regarding an unauthorized home made addition to the vehicle (read your insurance fine print) but now that it has been pointed out to you here on the forum, the charge goes from simple negligence, to criminal negligence and if lives were lost I think you know where you will be sleeping for the next few years.

Hi Ron @zander,

  The (very rough) towing fraction I referred to (mass of trailer/mass of towing vehicle) e.g. for a small caravan/car, 75% could be 0.75 tonne/1.0 tonne.

  The vertical noseweight ... i.e. downward force at the towing ball is tiny in comparison to the trailer mass .. somewhere in the 100-150 lbf, or maybe 60 kgf range, and can be checked with ordinary bathroom scales. As a weakling, I could just about lift the hitch onto the ball, although using the jockey wheel was much easier!

How this compares to your trailers I am not clear, but the raw numbers you quote are scary.

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As for legal liability, I am neither recommending nor dissuading people from building and using their own equipment. That is their responsibility, according to their laws, customs, ability etc.

I was merely pointing out that a system that was powered whilst driving enabled the possibility of an unplanned glitch or fault of some type could have unfortunate consequences, that would not be possible if there was no power. That in no way eliminates an infinite number of other possible faults and problems.

Best wishes, and remember it is your responsibility to stay safe, Dave

@davee When I had a bumper tow, the tongue wt was 1,000lbs and I could not manhandle it but our trailers all come with a jackable wheel that folds out of the way. The trailer itself was just under 10,000 lbs I think as the laws in my region did not allow more than 10,000. Even my 7'x16' utility cargo trailer with two 3,500lb axles would need a 1,000lb hitch system (7,000 x 0.15)

My current 42 ft fifth wheel has a hitch weight of about 4,000 lbs since the formula for that type is 20 to 25% of GVWR and the GVWR is 16,000 lbs. Yes, I drove a 7 ton truck pulling an 8ton trailer and it towed up and down hills like a breeze due to intelligent cruise control and intelligent auto engine braking. I crossed the Rockies plus all the other hills several times, driving with both feet on the floor. 

If your hitch weight was only 150 lbs, then the trailer could only weigh 1,000 lbs (15% x 1000). My first bumper pull was 10,000 (10 times more than yours), so I needed a 1,500 lb capable hitch receiver, drawbar, and ball. This was towed by a barely capable Ford F150 full size truck. Due to the options on the truck when I got it weighed I found I only had a few pounds of remaining payload. Even my huge F450 dually diesel was slightly overloaded as was the trailer on the first trip until we got rid of some stuff.

BTW, doing 60mph with those kinds of loads is insane but I see lots of Americans doing it all the time. My cruise was set to 50mph/80Km/h.

The liability comments were not meant for you.

Hi Ron @zander,

  As I suspected, we are talking about things on totally different scales .. yours must be a lorry trailer, whilst a (UK) caravan is towable by a 'normal' car, albeit typically in the medium to larger size range, not a Mini. The caravan body itself, is typically around 10-15 ft long, although some are longer, with another 3-ish feet for the A-frame at the front for the hitch.  It is probably 20 years since I last used one, but I am reasonably confident about the numbers. 60 mph is the dual carriageway/motorway limit for most car/caravan combinations. 70 mph is the highest limit for any vehicle. Remember, the UK has lots of narrow, twisty, hilly roads, and only a limited number of motorways and dual carriageways to link the cities, which can eat some of the miles, but are usually the last place you would want as a final destination, so vehicles of the size you mention would be impracticable for most purposes, as they would probably often get stuck 30 or more miles from the destination.

Interesting to compare lifestyles!

Best wishes, Dave

@davee Yes, very different. Most cars over here are now unibody construction so can't tow any kind of trailer, it has to be a truck or wannabe truck like a full sized Jeep because you need a frame to attach the hitch to.

I never heard of a lorry trailer. A 10 to 15 ft trailer is about the size of my old cargo trailer, not at all suitable for living in. Here are some pictures showing the 15ft cargo trailer, and the old bumper pull 21 ft trailer with the F450 truck that weighs 14,000 lbs and can pull up to 40,000 lbs with an appropriate hitch.

The first 2 are the old cargo trailer used to store and transport some of our household goods. It is about 10 ft high, 8 ft wide and 15 ft long plus the 3 ft hitch. The axels are rated for 3,500lbs each. No normal car can pull that, it would need to be a full size with frame.

The next two are of our first travel trailer, it was about 21 ft long. I don't remember the weight, but it would be about the same as the cargo trailer, so definitely needs a properly equipped truck.

Next post will be of the 5th wheel, a 16,000 lb 42 ft long trailer that is typical for North America.

@davee Here is the trailer we lived in for 6 years. It is 42 ft long, weighs 8 tons has a washer and dryer plus a residential (110VAC) refrigerator. It has 2 slide-outs of the super size variety, so the width goes from 8ft to about 12 ft.

Got the idea now?

@davee In our case over here in the colonies, moving 30 tons down the highway at 60+mph isn't a problem, it's stopping it!

Hi @zander,

 Some interesting pictures indeed. Thank you for sharing. The contrast in scale of roads, space etc. is huge.

Even with my 'small' caravan, I have been down many roads with the border hedges rubbing both sides of the caravan at the same time (as well as the sides of the car). 

  For the UK 'lightweight' (a ton plus or minus a bit) caravans, accelerating to 60 mph (& more if you are so inclined, which I wasn't)  isn't a problem with a larger family car ... and stopping in a straight line isn't usually too bad as the caravan overrun brakes do a reasonable job when driven smoothly ... the fun bit is when the caravan thinks it is a pendulum or gets pushed sideways by a side wind, etc. 

The term 'tail wagging the dog" is quite appropriate!

And when that happens, applying the brakes is often the worst choice of 'remedy' possible!

Best wishes,

Dave

@davee A world of difference for sure. The size of the roads is definitely a major factor, thank the stars for google earth.

Posted by: @zander

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@iwannastout True, nothing can increase the load capacity, but airbags can keep the vehicle level and make the ride smoother. Keep in mind that the difference between dry weight and fully loaded includes passengers, fuel, water, and basically everything added to the SUV and trailer since they left the factory.

Yeah I get that, but thanks for restating it for those that might not be aware.

Posted by: @zander

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Double-check your tow capacity (that is a marketing term) by looking at the stickers on the driver-side door post. I think it's the yellow sticker, and it is unique per vehicle. It will tell you what your vehicle is rated for; it will never be more than 6500 and can be quite a bit less.

Okay, I double-checked mine (door sticker) and it is rated at 6001 lbs.  Yes, that is different than the glossy brochure 🙄.  I have no clue why it was listed at 6001 rather than 6000?!?  What the heck does that extra 1 pound make anyway?  lol 

Posted by: @zander

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EDIT: I forgot what I wanted to mention, there are devices today to measure actual load on the hitch. I am fairly sure that is what is called a load cell, so you might expand your project to use two of those that is calibrated to determine what your hitch weight and tow weight really is.

Yeah, I have seen those on Amazon, but I don't have one.  Not sure how they will work with a load distributing hitch.  I guess you would do your measurements without the load bars engaged.

Posted by: @zander

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I assume you have LT tires on the SUV, so maybe adding a temperature sensor as you likely already have TPMS.

Yep I do, and they only see occasional use, when I am either running errands or pulling my RV.

Posted by: @inst-tech

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@iwannastout, Hi, and welcome to the forum!

Thanks!  Sorry it took me a while to respond, I guess I have been pretty busy these days.

Posted by: @inst-tech

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I was just looking at your proposed project of controlling air bladder bags using MCU ( micro-controller units) and some hardware. Looks interesting from a controls stand point, so I thought I'd jump in and give you some suggestions on how to proceed.

First of all, the solenoid valve you may want to use will require two of them, as you can only use one if it's a 3-way, normally closed, and it would have to be energized all the time in normal operation. See the drawing I have provided below where I use (2) n/c 2-way solenoids at 5 V, 2 watts. However, you can use what ever suits you, and just modify the drawing for 12 v solenoids if you wish. This is in no way recommending any model or manufacture of parts mentioned in the drawing.. it is simply a layout of how you could go about it. If you need more info.. just reply back with my handle @Inst-Tech, and I, or others, will try to help you get your project going.

I think I am going to go with one solenoid valve, and a "T" going into the valve, with one side going to the tire pump (which will have a "check valve" between the pump and the "T"), and the other end of the "T" plumbed into  the air bags.  Then I should only need 2 relays, one for the solenoid (to lower the pressure in the system), and the other to the tire pump (to increase the pressure).  Both will be setup in a NC (Normally Closed) configuration.  Also, so I don't have to energize a relay all the time.

I think I am leaning towards NOT doing a control panel on the dash.  I think a simple smartphone app should be sufficient for how often I plan on using this.  Otherwise, I would have to run a bunch of wires from the dash to the back of my SUV where the pump and sensor will be located.

@iwannastout The 6001 comes from the scale that they use to weigh the vehicle as it leaves the factory. Those load sensors would measure the actual weight on the hitch. It would be interesting to do a before and after with the load equalizer bars to see how much weight was removed from the hitch and redistributed to the front tires and trailer axles.

Posted by: @zander

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@inst-tech @iwannastout I wish I knew about those small solenoids. The one I used for my main water was much bigger (3/4") and used much more power. I only had one, and it was designed to shut off the water when there was no power. RVs are notorious for failed toilet fill valves that then flood the RV (an RV toilet has no overflow) The only caution I have, and it's so obvious I apologize for mentioning it, is that you will need to either add more relay contacts and/or hardware safety switches OR do it in software, make sure your software is fail-safe, in other words, have the setup code set all devices to the 'safe' position, you don't want both valves open at the same time. Use esp_restart(); for any errors.

Yes, the valves are gas valves so work with air or water.

Thanks, I don't anticipate needing a lot of fail-safes in my design, probably going to go with a single solenoid valve that will be used to decrease air pressure in the system.  If it fails "closed", then I can always manually lower the pressure with the Schrader valve.  If it fails "open", then I won't have any benefit from the airbags.  It will just be like towing without them inflated.

Posted by: @davee

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Hi @iwannastout,

 You already have some great advice from others who are familiar with the type of vehicle you are discussing, which I am not, so this is just a single observation, which might not even be relevant.

From your description, it looks like your system is only used for a short time, in advance of a journey, as part of the preparation. If that is the case, then perhaps you could reduce some of the safety concerns by having a master power switch to your automated system, which would only be closed for the short time needed in the preparation phase.

The rationale being a concern that a voltage spike or other unexpected event might trigger the system to start doing something, not necessarily the right thing, whilst you are driving it, or maybe when it is parked unattended. Having a master power switch effectively limits the time when it can activate to periods when you will be alert and able to take any appropriate action, probably including opening the same switch, which obviously needs to suitably placed for easy and safe access.

You would probably have naturally included such a provision, in which case, I hope you don't mind me emphasising it. One of the problems when considering safety is that it is difficult to spot every possible way something can fail. Many possible tragedies can be contained to minor inconveniences, if the design assumes that even the 'very unlikely' failures mode will occur (sooner or later), and provision to accommodate that failure is included.

Best wishes with your project, Dave

Yeah... it's not critical either way.  I just like the 'feel' of having the airbags inflated when I am towing my RV.  My SUV came equipped from the factory with load leveling airbags, rather than coil springs.  Which I had replaced with new coil springs and heavy-duty shocks shortly after owning the SUV for about 2 years (and it was used when I bought it).  I recall having some issues with the system and decided to replace the airbags with coil springs, rather than spend the extra $$$$ to fix it.  Then I added the Air-lift 1000 system, so I can stiffen up the rear suspension when I am towing my RV.

Posted by: @zander

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@iwannastout The 6001 comes from the scale that they use to weigh the vehicle as it leaves the factory. Those load sensors would measure the actual weight on the hitch. It would be interesting to do a before and after with the load equalizer bars to see how much weight was removed from the hitch and redistributed to the front tires and trailer axles.

True, and it depends on how much tension you have in the weight distribution system when engaged.  I did watch some YouTube videos on how to fine-tune the system.  Some have you measuring the distance from the ground to the apex of the front wheel wells before and after engaging the system.  Then you adjust so it is back to about the same height when engaged.  But I have normally just used the "is my RV and SUV level when loaded and hooked up".  Yeah I know, not very technical, but it works for me.  And I believe the other method was to use a ball-weight measuring device, which I don't have.