Making a steerable rear axle on a agricultural implement

Hello everyone - first post in this forum. I’ve been skimming over the various posts for a while and although I probably could have pieced together quite a few of the answers I need I thought I might be able to peak some interest from the community into my project which would make this a much more rewarding experience - especially if someone else is able to benefit from it. English is not my native language so please forgive me if I don’t get the grammar correctly.

Anyway - on to the point.

What I ultimately want to achieve is to make an agricultural trailer able to turn its wheels on the rear axle left or right in an angle relative to the angle between the tractor pulling it, and the drawbar.

If for example that you imagine yourself observing tractor and implement, from a birds eye view and the tractor is driving forward turning to the right then the rear axle on the implement is turning left and vice versa.

This is easy enough as long as the tractor and implement is driving forward, but when you reverse the rear axle on the trailer will always turn the wrong way - unless they are forced to turn the correct way using hydraulic cylinders.

There is already several solutions in existence to this particular problem, ranging from a mechanical linkage running parallel to the tractors drawbar that pushes the steering linkage on the rear axle in the correct direction - to integrated solutions using solenoid valves or even PVG valves and modules. These are however OEM solutions that requires the control modules that came with the specific implement, and even though I could find a way of using them it would mean spending up towards 6000 usd on circuitry I don’t really need.

Why not just buy the implement from a licensed manufacturer I hear you ask? Well there is significant economic reasons for not doing this, but ultimately I just enjoy the challenge of making this stuff myself.

The solution I am going for is this one:

2 absolute potentiometers. Let’s call them potA and potB

potA will change it’s value as the tractor turns left or right, and is therefore a value representing the angle between tractor and implement. If we stick to 8bit values then we can assign 0 as sharpest possible left turn, 255 is sharpest possible right turn and 128 is the value we have when driving straight.

The sensors I would use provides an analog output so using A0 and A1 for reading the value of potA and potB should be possible.

potB I can attach in a position so that it measures the travel distance of the steering rod relative to the fixed part of the steering axle. Meaning there is a part of my axle that doesn’t move, and one that does. It is not an issue to attach a potentiometer between the steering rod, and the axle in a way that will get the same range of motion on potB as I can on potA.

I hope that makes sense so far?

The axle I can control with two double action hydraulic cylinders controlled by a bi-directional proportional valve with an electro hydraulic actuator attached to it.

I have several choices of actuators.

The simplest version is called an ON/OFF module normally closed. It has 3 pins. 1 to gnd , 2 is open port a, 3 is open port b.

If pin 2 gets 12 volts then oil flows through port a, if pin 3 gets 12 volts then oil flows through port b.

If neither pin 2 or 3 has 12 volts then they are both closed.

I also have the option of using a so-called medium or high module normally closed. Both of them work the same way.

Again 3 pins. 1 is gnd, 2 is supply voltage (12volts) and pin 3 is exactly 1/2 of what is on pin 2 when the actuator is in its closed position.

To open port a or b with this module then
The formular is:

Open port A= 50% of Voltage on pin 2 + (50% of Voltage on pin 2 divided by 2) = 9 volts

Open port B= 50% of Voltage on pin 2 - (50% of Voltage on pin 2 divided by 2) = 3 volts.

If pin 2 is 12 volt, then port a will open when pin 3 measures 9 volt

At 6 volts port a and b is closed

At 3 volt port b will open.

With those modules I can control the oil flow to the rear axle in either direction.

Let’s say that we connect the hydraulic cylinders to the electro controlled valve so that when port A is open then the trailer is steering to the left when looking at it from above.

As we are going straight with tractor and implement the value on potA is 128, as we start steering to the right potA value starts to increase towards 255.

As this happens I want the electro hydraulic module to open port a so that the implement starts to steer left, because I also have a potentiometer on the axle that moves as it steers (potB) I want port a on the hydraulics to stay open until potA and PotB values match each other.

Let’s say we are using an ON/OFF module to control the flow of oil to the axle. We designate pin 2 and pin 3 on the actuator as I/O 1 and 2.

The logic I’m looking for is Like this:

If potA = potB then, I/O #1 = Low, I/O #2 = low

If potA > potB then I/O #1 = High, I/O #2 = low

If potA < potB then I/O #1 = Low, I/O#2 = High

Long story short. As potA changes it’s value reading I want a hydraulic cylinder attached to another potentiometer to move in a preset direction until potB matches potA

I can make the cylinder move by getting 12 volts to either 1 pin or another pin right next to it. I can make the movement stop, by not having any voltage at all on either pin.

Or there is the opportunity to divide input voltage and have either 1/3, 1/2 or 2/3 voltage on the same pin as it is the case with a medium or High module as they are called. 1/3 = left, 1/2 do nothing, 2/3 right

That is basically the essence of it, and making this happen on a bench-level test stand is my first milestone in this project.

I will most likely also need ways to calibrate the potentiometers in a very easy “push button type of way” in case they get misaligned in some way so that if potB is not really straight then I can just push a button an set a new center value on the go.

I would also need ways to adjust reaction time, and acceptance of inaccuracies between potA and potB to compensate for sensorlag and hydraulic fluctuations etc…

And I will most definitely need some safety features that turns everything off and let’s the axle steer freely in case a potentiometer fails while driving on the road so that it doesn’t suddenly steer in one or the other direction unintentionally.

My question is: in its essence, is this feasible project to achieve with an arduino as the hardware component controlling the voltage to the electro hydraulic actuators? Is the coding language capable of handling this at all? Or am I wasting my time trying to pursue success with this project?

I apologize for the long and elaborate post. But as you might be able to tell I have very little (almost zero) coding experience.

But that is also why I’m doing this - to learn :slight_smile:

I would love this community’s support and help/comments/opinions on this because I will most definitely need it.

Thanks in advance

TL:DR - sorry.

Even though I have not read all of the Original Post I have little doubt that an Arduino could control the system - I don't think the control system would require an enormous amount of code or require a very fast processor.

However agriculture can be a very harsh environment and I suspect a lot of the reason for the high cost of a professional solution is the use of parts that can survive in that environment.

There is a big difference between making a functional demonstration and making a robust system that can survive without attention for months and years.

You should also consider carefully whether all of the effort to design, develop and test your system will be justified by having a single working project at the end of it. Professionals expect to spread the development cost over many individual identical products.


How many axles on your theoretical trailer? How do you determine the tractor/trailer combination is NOT on a steep hillside and the driver needs to have the trailer wheels NOT make the trailer turn wide?

How do you make the trailer turn short when the combination is backing up around a corner? That case you want the tractor to turn wide.


I recall employing a haulier who had an articulated truck with steerable rear wheels on the trailer. For close-quarters manoeuvring the rear wheels could be controlled using a wired remote control operated by a man walking beside the trailer.


Here is a link to a video that shows the principle of what I’m trying to achieve:

The way the axle steers on the implement allows for tighter turns, as it it is always trying to stay behind the tractor. That is what I meant with: when the tractor turns left, the axle in the implement turns right.

I hope that clarifies the point of it all a bit.

Robin2- you make a good point with the harsh conditions, how ever it is quite possible to shield the arduino from the elements quite comfortably. Standard agricultural circuitry is not much different or of much higher quality than what I can see the arduino being made of.

You also have a good point of making a 1 of a kind system, however that won’t be the case, as I can retrofit a lot of the implements I steady have in my operational fleet with such axles and steering systems if i get it working properly.

But time will tell if it gets to that... the most valuable thing here is the experience of doing it.

I can get a proper circuit board made with the necessary components of proper quality made when the time comes for that... and then I’ll have a more or less “plug’n’play” solution working where I can update the arduino software as needed...

That’s where I see the real advantage here.

Until then - this project is in a prototype stage.

@paul - 2 axles - rear axle is steering allowing for tighter turns as you can see on the video, the front axle is just fixed. On slopes this prevents the trailer skidding downhill as it will try to steer up the hill always...

Backing it up, then because the rear axle turns the correct way the pivot point becomes the front axle in the trailer, instead of being somewhere between the two axles had they been fixed and unable to turn.

Quote: Backing it up, then because the rear axle turns the correct way the pivot point becomes the front axle in the trailer, instead of being somewhere between the two axles had they been fixed and unable to turn. unquote.

but you miss the point! The trailer wheel must begin to turn long before anything on the tractor begins to turn.


I do not see this project as a monumental hurdle.
Sensors in the front or on the steering, could signal the motors in the back.

just like a truck with tow brake, the driver could select high sensitivity or low.

even a reverse switch to allow the rear wheels to move in the same direction as the front.
(it does seem silly to call that reverse)