Combine on Point

September 8, 2010 06:25 AM

To keep your combine on target, you can choose between GPS-based auto-steering that tells you where the corn row should be and mechanical row-feeling systems that tell you where it actually is.

A GPS-based system makes it easy to find the correct row after turning on the end or after crossing a waterway, especially when corn is down. A mechanical system keeps you on the row after you find it because, even though you planted with auto-steer, the planter may have moved a bit because of implement draft, or you may have steered manually for a while after losing contact with a satellite.

Greg Ruestman and his father, Arlen, who farm near Wenona, Ill., wanted the best of both systems—RTK GPS-based auto-guidance for turning, along with perfect row tracking. They got their wish when Greg combined TrueSight row guidance sensors with their Trimble RTK auto-guidance system. Greg received $500 for winning the technology category of Farm Journal’s “I Built the Best” contest.

“With our auto-steer monitor, I can bump the combine left or right if I get off the row a bit,” Greg explains.

“But on some fields, it seemed like that was all I was doing—bumping the row all the time.”

Correcting trim adds to fatigue, which already is high enough during harvest season, Greg figures. And, while varying slightly from dead center may not cost a lot of yield, the Ruestmans hate to leave even a single ear in the field.

The system uses row sensors to send commands to a control box in the combine cab, which relays them to the GPS antenna. The antenna moves left or right to steer the combine onto the row.

Control box. Greg’s friend Jeff Kennel, who operates Kennel Industries in Wenona, made the control box by modifying a conversion kit for a John Deere Dial-A-Matic header height control. “We used the Dial-A-Matic control because it had the brain work we needed for filtering,” Greg explains. “The sensor moves really fast, bouncing off the cornstalks. If there’s no filter between the row-feeling sensor and the antenna, the antenna will just wiggle back and forth.”

A knob on the control box lets the operator center the antenna. It must be set with a screwdriver to avoid accidentally changing the setting. Other knobs adjust the sensitivity of the row sensor, center the sensor on the row and dial in the header height at which the row feeler and antenna sensor engage.

The control box lets the operator make corrections to the row sensor. “I may adjust the system if corn is goosenecked badly,” Greg says. “But usually I don’t need to touch it.”

An electric actuator controls the side-to-side movement of the GPS antenna. A red light on the control box tells the operator when the GPS antenna is moving, shifting the combine left or right on the row.

“Initially, we had problems with overcorrecting,” Greg says. “The antenna moved too far, too fast, causing the combine to weave. We fixed that by using pulse modulation to slow down the speed of the actuator on the antenna.”

All of the pivots on the antenna are sandwiched with rubber grommets to eliminate vibration.

The antenna is tied into the feeder house position sensor, which returns it to the center position when the operator lifts the header at the end of the row. That puts the RTK auto-guidance back in charge to find the correct row for the next pass through the field.

Components for the system cost about $1,000.

Low Bridge—Everybody Down!

The modifications to Greg Ruestman’s GPS antenna mount don’t end with side-to-side movement. He also modified it to move 18" up and down, as a safety feature when entering sheds or underpasses.

An adventure with a previous combine, in which Ruestman scraped the bin extension on an underpass, alerted him to clearance issues. His current combine came with hydraulic bin extension closers, but the RTK GPS receiver antenna extended 18" above the cab. Ruestman added an up-and-down pivot point, operated by an electronic actuator, to the antenna mount. He tied the actuator in with the bin extension closer, so they operate simultaneously. Initially, the actuator operated too fast, so he used electrical relays to slow it down.

The two actuators, up/down and sideways, make for a busy antenna but a less stressful experience for the combine driver.


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