A question to farmers who use irrigation, (Pivots)

[Bsavulis]

I am not sure this is the proper place for this post, if not feel free to move it to the appropriate location.

I have watched many YouTube videos posted by a number of people who do larger scale farming. Many use pivots to irrigate their crops. From watching these videos, I have noticed that a "pivot" can be amazingly long. The whole assembly rotates around a central location. It appears that each segment has a set of driven wheels to move this huge beam around in a circle. Obviously, the driven wheels travel much slower closer to the center point than way out on the end of the irrigation system and that the travel speed must increase at each set of wheels by a very specific amount. My question is...How is this speed determined / set. Is there a specific tire size or gearbox at each location? The videos I have watched it seems as though the folks are using random wheels / tires that are available, and they just seem to grab a random gearbox off the shelf when needed.

BTW,
Thanks for farming.
Brian

 

[Rockbadchild]

I am no expert and do not use irrigation but here what I got from it...

The electronics (control panel) control each motor, adjusting its speed based on the gearbox ratio and its position along the pivot. To maintain a consistent rotation speed across the entire system.

Each tower typically has a pre-set gearbox ratio, and the control system (often using timers, GPS, or sensors) activates the motors in sequence to keep the alignment correct. If a tower lags behind or moves too fast, the system adjusts the motor accordingly.

The outermost tower is typically the "master" and moves at a set speed based on irrigation requirements.

 

[Halftrack]

Near each set of wheels is a flexible joint and each joint has two micro switches which activate power to the wheels. When that set of wheels falls behind, one switch will power the wheels until they catch up to the line. The speed of the system is controlled by a per cent age dial that controls the outside wheels (perimeter) so that they would operate 20%, 50% up to 100% of the time. The inside wheels (towers) wiggle to keep up with the outside tower. There is a safety that if one tower falls behind, it shuts down the entire rig.

 

[pmsmechanic]

The most common pivots use electric motors to move the towers. At each towers set of wheels there is a control box with micro switches inside. These micro switches control when the power goes to the electric motors. What appears to be continuous movement is actually a series of starts and stops.

There are also water drive pivots that use water pressure to turn the wheels. The water is controlled by valves that regulates the flow of water to the large water piston that moves the pivot through a ratcheting mechanism.

There are also hydraulic drive pivots that use oil to energize hydraulic motors to move the pivot. Again valves are used to control the flow of oil to the motors. These pivots come the closest to the ideal of continuous movement with no starts and stops but they don't hold a continuous speed as the viscosity of the oil changes as the air temperature changes resulting in incremental changes in overall speed.

The overall speed of the pivot is controlled by the last tower. There is a timer built into the control box which controls how long the last tower has power going to it. 100% means that power is flowing continuously to the last tower. the rest of the towers are controlled by their respective micro switches. The speed of hydraulic and water drive pivots is controlled by regulating the flow of oil or water to the last tower.

 

[bigtiller]

How is the water volume controlled to get an equal amount of water on both ends of the arm?

 

[Halftrack]

How is the water volume controlled to get an equal amount of water on both ends of the arm?

by the number of sprinkler heads per section of its length.

 

[MAX-24-Dean]

by the number of sprinkler heads per section of its length.

And by the nozzle sizes of the sprinklers.

 

[Joe Batt]

Destine explains the contact switches: