CENTRE PIVOTS: four-wheel drive or not?

THEUNS DREYER, MANAGING DIRECTOR, SENTER 360

Have you ever had the frustration of your centre pivot getting stuck in a waterlogged field or sinking too deep into wheel furrows?

If you have high clay content in your soil and have sensitive crops that tend to be irrigated on a more regular basis, permanent or multi-seasonal crops such as sugar cane, along with certain pastures, tend to be prone to this problem as well. A familiar experience you will all know too well.

The first problem is that the centre pivot wheel tracks become too deep towards the end of a planting or crop season. Then the gearboxes start ploughing into the ground, eventually stopping the wheels from taking the weight of the machine.

As a result, the wheels simply start spinning. Problem number two is caused by waterlogged areas in the irrigation field resulting in the centre pivot getting stuck every time it travels over the same path.

Here, the first solution is to cover the tracks by hand labour with soil, plant material, gravel or stones. This however may have to be repeated several times as it is seldom a permanent solution. It can also become a problem when working the fields for the follow-up crop.

The second solution may be to use a purpose-made implement drawn by your tractor, unfortunately damaging the crop and creating further technical issues as well as the cost of extra fuel. This will also have to be repeated during the season.

Thirdly a centre pivot drawn implement can cover the wheel tracks with every rotation on an ongoing basis solving the problem. The only existing patent for this is the FurrowBuster (a product of Senter 360). The second and third option will solve deep wheel tracks, but not if there are specific areas retaining excessive water.

Although more expensive at first glance, an alternative way of solving these wheel track problems as well as the problem of “getting stuck” on a regular basis, would be opting for a four-wheel drive system for the centre pivot.

Instead of the usual two, four wheels are fitted to specially made drive units on the centre pivot towers. Each wheel has its own gearbox and is therefore driven by drive shafts connecting all the gearboxes to the same drive motor. The advantages of such a system is that by doubling the amount of tyres per drive unit, the tyre contact area of the centre pivot drive unit will double as well.

The effect of this is that the weight carried by each tyre will reduce the load of the pivot by half. This has the same effect than halving the weight of the centre pivot tower. It has the added advantage that each individual gearbox has less tower weight to cope with and actually lasts much longer than those on a two-wheel driven tower.

It is important not to double the width of the tyre by fitting two tyres to the same gearbox, as the effect is not the same. Doing this will firstly kill the gearbox as it is not designed for this type of load stress as well as missing the advantages of lining up the wheels. The main advantages here, apart from the larger tyre area, are that wheels are fixed to a strengthened ridget drive tube.

With all wheels directly driven, one wheel might be in a muddy spot without traction, while the other three wheels are still pushing or pulling it through.

Tests have shown and proven that this system is the most successful way of solving traction and wheel track problems on permanent or long-term cropping fields that get waterlogged on a regular basis. Where only one or two towers of a multi-tower centre pivot is prone to getting stuck, only those towers can be fitted with this system. Although this is a standard factory option with Senter 360, units can be fitted to most brands of centre pivots.

The worst field test was actually done on an eight tower Zimmatic centre pivot, retrofitted with these drive units. The specific centre pivot has 8" towers being extremely heavy, running on high clay soils with carrots planted for the testing season. This machine was the owner’s biggest nightmare. In the past he had six workers permanently employed to daily cover tracks and dig out towers that got stuck.

After fitting the new drive units, the deepest part of the worst wheel track by the end of the season was only 200 mm. No incident of the centre pivot getting stuck during the season was reported. We have since converted two other machines for the same client with orders for doing more machines on an on-going basis. The system is well-affordable and conversions can be done without changing existing infrastructure.

It is well-suited to flat land areas with high clay content and/or fields prone to waterlogging or having isolated areas of waterlogging. It is however less suitable for very uneven or heavily contoured fields where an articulated four-wheel drive unit would be more suitable.

This option is not only more expensive than the ridged four-wheel base beam, but loses some of the unique advantages of the ridged four-wheel drive system. Because of the configuration of an articulated four-wheel drive system, an additional drive motor will be required, doubling the power requirements of the centre pivot as well as the power supply cable to the centre pivot.

For more details, contact Theuns Dreyer at (018) 469-1331, 082 564 5955 or visit our website at www.senter360.co.za.