A wide span tractor designed for vegetable production

Hans Henrik Pedersen is completing a PhD at Aarhus University in Denmark. He was a key speaker at LandWISE 2013: “New Ideas”. Hans told delegates about his work investigating a wide-span tractor as an option for cropping farmers.

Vegetable farmers, who adopt CTF, face serious challenges at harvest because very few harvesters are designed to match CTF systems. The soil structure is severely damaged when heavy harvest machines run over the well structured growing beds. A few farmers have modified harvesters, but to our knowledge only one CTF vegetable farmer has succeeded in matching harvest machines for all his crops.

As CTF farmers are still a minority the limited demand means that machinery manufacturers do not yet perceive a need. Also 3 m track width, as used by most CTF vegetable farmers, is a challenge as mass produced harvest machines need to meet road regulations in different countries.

In a Danish project partly funded by the Danish Business Innovation Fund a 9.6 m prototype wide span tractor has been developed. It will be tested by a commercial farmer (Jens Kjeldahl, Samsø) who will grow onions on 9.6 m wide beds spanned by the tractor. ASA-Lift A/S has designed and built the wide span tractor. Besides cultivation, drilling and plant care operations, the tractor will be used as a bunker harvester for onions and possibly for other crops. At harvest, the machine will unload at the field edges, thereby avoiding tractors and trailers in the field.

ASALiftGantry First presentation of the ASA-Lift WS-9600 tractor, summer 2012. Photo: Brdr. Kjeldahl

A wide span tractor solves two main challenges facing the traditional tractor:

  • Restrictions in width (e.g. due to road regulations) are solved by changing the direction of travel between field work and road transport. The machine is wide in the field and long when transported on roads but only 2.55 m wide.
  • Weight of the tractor can be reduced as implements can be mounted within the span of the tractor. The forces from the implements are transferred directly to the tractor as opposed to traditional mounting systems, where the tractor needs weight to pull the implement. Also, in conventional implement designs, a strong, heavy and often complex structure is needed to transfer the forces through the tractor hitch, as well as to fold the implement for transport.

Earlier work on wide span tractor designs e.g. as described by Chamen et al. (1994), unfortunately did not lead to commercial production.

A key point in design of any technology is to ensure that the development process is targeted to the priorities of potential customers. As part of my PhD. Studies I have performed a Quality Function Deployment (QFD) to derive user-requirements and design parameters.

Twenty eight farmers and farm managers in Europe and Australia have been interviewed about their priorities for the design of a new growing concept based on wide span machines. The majority of those interviewed were CTF farmers. The farmers were asked to score 28 specific requirements on a scale from 0 to 4.

The 10 requirements with the highest priority were: (average scores are given in parentheses)

  • Automatic accurate steering of the carrier (3.9)
  • Reducing soil compaction (3.8)
  • Durability of the machine (3.4)
  • Overview of the entire machine from the operator’s seat (3.4)
  • Total costs per hour (3.3)
  • Clear view and manoeuvrability to avoid damage (3.3)
  • Semi-automatic control for increased productivity and ease of operation for the driver (3.3)
  • Comfort of the driver (3.3)
  • Automatic accurate steering of mounted implements (3.3)
  • Capability to carry heavy loads in the field (3.2)

A next step involved technical experts suggesting technical solutions (Design Parameters) to accommodate the priorities set by the farmers. The results of this QFD analysis can be used by any manufacturer who wishes to develop wide span machines.

Tractors as we know them today were very successful in replacing horses. Since they were introduced in the 1920s, rubber tyres and four-wheel drive have been established, along with other features, but basically the design has not changed. However, the power output has increased more than 10 fold and the weight of tractors has increased by a similar factor. The load of agricultural machines is challenging the productivity of soils. We believe it is time for a change to the traditional tractor and that the wide span alternative can be designed to suit the needs of modern agriculture while significantly improving production efficiency.

Reference:  Chamen, W. C. T., Dowler, D., Leede, P. R., and Longstaff, D. J. (1994). Design, Operation and Performance of a Gantry System: Experience in Arable Cropping. Journal of Agricultural Engineering Research 59, 45-60.

Look also at the CTF-Europe website for more from Hans Pedersen, Tim Chamen and colleagues



3 thoughts on “A wide span tractor designed for vegetable production”

  1. Good to talk with you (briefly) at the LandWISE conference in NZ. I had to leave very quickly Wednesday at lunch time to catch my plane so I’m sorry we could not talk further.

    Hans and Tim
    The widespan tractor was the major “ah ha” moment for me at the conference so I’m keen to hear more about this, especially if anyone is going to take it to production.

    The key thing for me was the headland turning ability.
    I’ve been working in organic veg/crop production for 20+ years and have been getting more uncomfortable with the increasing headlands that are being left as machine size increases. In NZ I’m working with growers that are operating 6 meter wide bout widths for all crops – onions, carrots, wheat, etc.,. This is big(ish) machinery so the total tractor + implement length can be over ten meters, and even when using RTK GPS autosteer, even with tractor + implement steering, we often end up with headlands (from the fence to the start of the useable crop row of 10 to 15 meters. As we often pass through a crop 2-6 times for interrow hoeing, the wheel traffic on the headlands means that the non-organic practice of growing a bout or two of crop along the headlands is not worth while as the crop never performs under the wheel damage and associated compaction.

    The only solution I had come up with to date was to revert to mid-mounting equipment under tool carrier tractors – an idea that was very unappealing now that RTK GPS autosteer has solved the accurate steering issue, avoiding all the complex and expensive mid-mounting issues.

    The widespan tractor appears to solve this whole problem with its headland turning ability as all four wheels follow the same single circle turning track at the headland, which also allows the widespan to do a single headland bout. Also as the widespan can repeatedly and accurately use the same headland turning tracks, it means that CTF can successfully operate on the headlands as well relieving the compaction associated with two wheel steer tractors. This means what are currently waste headland space can now be used for successful crop production.

    If the widespan can give a 33% increase in field plant populations due to reduction of wheeling numbers, then if I can add another 30 meters of row length, as I can farm up to the fence line, then I reckon that could mean 40 – 50 % increase in plant populations overall, i.e., getting close to doubling the crop per ha of land over standard beds with headlands.

    That is a VERY big improvement! Especially as much of the rest of the land and production costs will be similar (except water volume and fertilisers). My gut feelings for the cost savings would be that the return on investment would be sufficient to make the high price of changing from standard tractors to a widespan look pretty good.
    I’m therefore very enthusiastic about the idea. I also have a couple of questions.

    Are ASA lift or any other manufactures looking at going into production? It strikes me that it would be right up ASA lift’s street, in terms of the machine design, and also give them a unique intro into tractor sales.

    What is the potential for adding RTK GSP implement steering to the system? With interrow hoeing the +- 2 cm accuracy achieved by tractor autosteer is not good enough. As this variation is due to the physical limits of steering several tonnes of steel on pneumatic tyres, rather than GPS limits, having the implement GPS steered as well, which, as it weighs less than the tractor and can use metal steering wheels, means it is possible to get down to millimetre level accuracy. My gut feeling is that the widespan would still have this +- 2 cm limit, due to its weight and use of pneumatic tyres (which are essential for the four wheel circle steering) and even when it is using crab steering driving down the row (which has the advantage of maintaining perfect orthogonality to the crop row for maximum accuracy).

    From a basic engineering perspective, it would be simple enough to put a side shift on the implement hitch(s) on the widespan, but I wonder if the sideways thrust forces would produce too much side thrust on the tractor wheels so producing a feedback effect between tractor steering and implement steering resulting in them constantly trying to correct for each other’s movement.

    Do you think this could be an issue?

  2. Many thanks Charles for your carefully considered thoughts about wide span which were “music to my ears”! Ever since the early 1980s I’ve been convinced of the enormous potential provided by a wide span system of operation. You, I believe, are one of the few farmers to have had that “eureka” moment in recognising the flexibility and improved efficiency that wide span can bring.

    My aim over the past ten years has been to introduce farmers to the reality of non-trafficked soils in the hope that they will then wish to see a more efficient and practical way of providing it in the field! It’s perfectly feasible for example to get tracked areas down to around 7%, i.e., 93% of the soil will never be run on again! And, with this low trafficked area, we could perhaps afford to “engineer” the traffic lanes to provide year-round access and for some operations to proceed with little or no soil contact. For those that do, we can provide extremely precise control that minimises the potential for soil damage.

    Wide span gives us a blank sheet from which to start again and to bring true precision to farming operations. Speaking of which, and I’m sure Hans Henrik will reply on this one, it is of course perfectly feasible to introduce RTK implement steer over and above vehicle steer. I doubt that side shift would have a destabilising effect if it is managed correctly. Soil resistance is likely to be modest and speed of correction would not likely need to be great.

    It may also be the case that we use technology other than satellite based corrections for this type of work, perhaps a row relative system. Satellite corrections know nothing about the crop so would be quite happy wiping it out as not!
    I think ASA-Lift have done a superb and innovative engineering job on their vehicle which could well provide the basis of a mass production machine. The concept of spanning frame and end units being individually engineered gives the machine flexibility in size both from a spanning point of view and from a power perspective.

    A chemicals application unit might be the only dedicated guise for the machine because it is required for nearly 12 months of the year and just think of the superb stability offered by a 9.6 m (or similar) track gauge!

    This year’s field trials in Denmark will be interesting and is something I hope to see in person.

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