Engineering Design by RFA Minnesota Engineering

Featured Article: Feeding the Combines

Most clients seek RFA’s engineering help with a part of a machine or a phase of a project. The draper header for the John Deere STS Combine was different. In a situation unique for both parties, John Deere Harvester Works in East Moline, IL, asked RFA to begin at ground zero and create an entire draper header. Beginning in September 1996, RFA engineers concepted, designed, redesigned and helped build and test three generations of prototypes, following the project all the way through to production in 1999.

"A number of design consulting firms were considered," said Deere’s Project Manager. "RFA’s technical expertise, professionalism and experience with other Deere units were major factors in partnering with RFA."

John Deere STS Combine with 36ft. Draper Header

Work on three versions of the draper header (25, 30 and 36 ft. widths) included the design of the frame structures, suspension system, mechanical drive system (including drive shaft and gear box), towing system, draper belt conveying system and hydraulic drive system. Deere, meanwhile, was designing a new combine, as well as new reels and a new cutting system for headers.

When the project started, RFA did all the design work, but as the job progressed, Deere’s staff grew to five people, all working on different aspects of the project – engineering, purchasing, manufacturing site selection, organization of production facilities.

"Until well into the last generation, we were dealing almost exclusively with new design work, design changes or modifications with Deere reviewing our work," said RFA’s Project Engineer. "Then in the end, as we became involved in various manufacturing and tooling decisions, we were interfacing with a number of other suppliers as well."

The draper header is primarily used to harvest small grains, such as wheat, oats, barley, rice and canola. The word "draper" refers to the conveyor belt that brings cut material to the center of the header platform, where it is fed into the combine. When first invented, drapers were made of canvas with riveted wood slats. During use, the canvas would pick up moisture and the drapers had to be unbuckled, dried out, re-installed and re-tensioned after each use. Modern drapers, made of rubber-clad polyester weave with molded ribs, require much less maintenance.

There are several advantages to using drapers instead of augers to harvest small grains. Drapers improve material flow, preventing what is called "slug feeding," a build-up that enters the combine all at once and does not get threshed properly. Besides more uniform feeding, drapers can feed material faster than augers and can be built wider, increasing the cutting swath.

In the early 1990’s, Deere had the capability to build larger and larger combines, but didn’t have a header big enough to feed them. The combines were "header limited" in that the maximum width for an auger head was 30 ft. "The 36 ft. draper was made for that purpose – to feed the appetite of the big combines," said RFA’s Project Engineer. "In a dense crop, a combine with a 30 ft. auger header could run 3 to 3_ mph, forward speed being limited by how fast the auger header could move that amount of material. By contrast, the 36 ft. draper header cuts 6 ft. more crop and allows the combine to travel up to 4_ mph, an invaluable asset to the farmer at harvest time."

Power input for the header comes from the feeder house on the combine. After passing through a drive shaft and then the gear box designed by RFA, it powers the header’s hydraulics and mechanical drives, including the reciprocating knife or sickle bar. In use, a pickup reel lifts grain into the cutter bar, then onto the drapers. The two side belts bring the grain in from each side to the middle, where a center belt conveys it to the combine. There a rotating auger with fingerlike protrusions propels the grain into the feeder house.

Design work began with the gear box. First, RFA engineers built a chain box with changeable sprockets which allowed them to experiment with gear ratios. This was used on the first year’s prototypes. Once they had determined the best ratios, they designed a gear box, focusing on the most efficient use of space and the most efficient way to transmit the horsepower. This box, originally built in the United States and used on later prototypes, is currently built at John Deere Iberica, S.A., a subsidiary in Madrid, Spain.

One of the biggest design challenges, according to a Design Engineer at RFA, was the problem of keeping the frames straight on the wider 30 ft. and 36 ft. headers. Designers had to calculate the exact "prebow" for the frame when it was in the weld fixture so that the finished product would be straight. "That was a big challenge and it didn’t happen overnight," said the Designer. "Using Pro/ENGINEER, we modeled the frame straight and then added a table for the calculations, but a lot still depended on field tests. As we went through different generations of builds, we took measurements and learned from experience. That’s how we ended up with the final numbers for our prebow." In addition to Pro/E, the engineers used ANSYS to assist in the calculations.

RFA created a number of unique features for the draper header, one of which is an unusual suspension system. Pivoting gauge wheels, located near the ends of the header, allow it to roll over uneven terrain while keeping the sickle bar as close to the ground as possible. Instead of the usual suspension springs, RFA chose to use air bags on the gauge wheels. The air system, unique to John Deere, provides improved suspension and flotation, and is well received by customers.

Also unique is the entirely self-contained transport system designed by RFA. Most headers must be loaded onto a trailer, but the Deere machine has an integral transport system designed into the platform. A swing arm lifts up and underneath the platform for storage when the combine is in the field. For travel, the operator swings the arm back down, removes the dual-purpose gauge wheels from the ends of the header platform, remounts them on the swing arm, extends a telescoping tongue from its storage space and hitches up to the towing vehicle. Combine and header can be rolling down the road to the next field in a matter of minutes.

Obviously, communication was critical on such a large project. According to Deere, "An extremely close working relationship with the RFA team made this project a success. It would not have been possible without constant communication." Early in the project RFA engineers traveled to Moline for a meeting every two weeks, "to make sure we were headed down the right path." They also wanted to get Deere’s input and decisions. "Some suggestions came from their end, some from our end. Some worked, some didn’t. There was a whole circle of feedback – information from field tests, customer comments, etc.," said the RFA Design Engineer.

Schedule adherence became a challenge as spring approached with prototyping targeted for April and May. "Late design changes further compressed the design completion windows," according to the Deere Engineer. "Through overtime, additional staffing and superhuman effort, prototype builds were completed with minimal schedule slippage." RFA engineers assisted with the builds and traveled to several of the many field test sites. Trying to get in as many hours and as many different crop exposures as possible, Deere conducted tests all over North America – in the Midwest grain belt, in California, in the rice paddies of Louisiana – as well as in Australia.

"From my perspective, this was a super project to work on, with great people to work with," said the RFA Design Engineer. "I was impressed with the leadership at Deere. And there were good people on our end, too, that got things done when they needed to be done. To start on a project at ground zero and follow it all the way through each phase to production was invaluable experience for me. And it was fun because of the people who were involved."

Deere introduced the new header along with the new STS Combine in August 1999. The summer of 2000 was the first full season of usage in North America, followed by the Australian harvest beginning in November 2000.