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