Electric tractor needs no operator


Electrically powered | The 400 h.p. driverless tractor goes into production next spring

FARGO, N.D. — The Spirit Autonomous Tractor uses two diesel engines to power four electric motors, which drive twin rubber tracks.

And as the name implies, it’s autonomous. There is no operator.

It’s no experimental garden tractor or small scale orchard tractor. It’s a 400 horsepower working tractor aimed at broad acreage prairie farmers who are short on manpower and want a simpler, less expensive tractor.

Electricity is a more efficient power source, and early indications are that the electric tractor can do the work of a rubber tracked 500 h.p. diesel machine.

The Spirit was designed by the Autonomous Tractor Corp. (ATC) in Fargo and the Automation Research Corp. in Minneapolis. It goes into production next spring with an expected price tag of less than $200,000 and a projected first run of 25 to 100 tractors.

“No one has rethought the ag tractor from the bottom up in probably 80 years,” said ATC chief technology officer LeRoy Anderson.

“Equipment has tried to meet the needs of farmers by incremental innovation over many decades. The result is ‘creeping elegance’ that has produced giant machines that are prohibitively expensive, inefficient, difficult to transport, complicated to operate and unserviceable except by the most highly trained mechanics.”

Terry Anderson, in charge of systems development at ATC, said diesel-electric has been working well in other industries for decades, so why aren’t farm implement manufacturers doing it.

“It lets you eliminate the initial investment and long-term maintenance of the transmission and differentials,” he said. “That saves money and simplifies the whole tractor.”

He said it also allows the use of two diesel engines that have a lower horsepower rating. Either engine can power the tractor.

“One of the things I always hated was when a tractor went bad out in the field. You’ve got to somehow drag it out of the field and back to the shop to fix it. If you couldn’t do that, then you’d be out working in the mud and snow.

“So on the Spirit, we have two 202 h.p. Isuzu four-cylinder diesels in the tractor, plus each track is driven by a front and a rear wheel motor, so you’ll never be left out in the field.”

He said either diesel can turn the Marathon genset alternator feeding a 650 volt bus. The second diesel kicks in when more power is required. It takes only one direct electric drive motor on each side to propel the tractor.

“The object is to make sure the tractor is never left stranded in the field. No matter what happens, the Spirit can get back to the shop,” he said.

“There’s a two hour replacement time for any component on this tractor. So if you have the part, you’ll be back in the field in two hours.”

All four drive motors are the same and all 14 bogie wheels and seven axles are identical, as are the two Isuzu motors. Anderson said the company wanted to keep the parts inventory as simple as possible.

Service intervals are every 500 hours and life expectancy of the tractor is expected to be 25,000 hours. There are no high-wear items on the tractor, such as clutches or transmissions.

The Spirit can also have 200 h.p. of electrical power ready out the back or up front to drive an air seeder fan, grain cart auger or mower.

The oil cooled electric motors are wrapped in an oil sleeve and the oil is pumped to the heat exchangers.

“Pull performance is better with electric motors because the system immediately senses if one track starts slipping, just like the latest traction control systems in cars and trucks,” he said.

“The control instantly reduces power on the slipping side and increases power to the side with better traction.”

Anderson said the controllers take readings and adjust power left to right 10 times per second. That’s not as often as the systems on Formula One cars, but the Spirit has a significantly slower ground speed.

The Bridgestone rubber tracks are capable of pulling 40,000 pounds of tension on either track, if that’s what the controller demands.

He said the sensitivity of the controller saves the Spirit drive system from the immediate shock damage experienced by some mechanical drive tractors.

“On the Quadtrac, for example, if you get three corners spinning all at the same time, the torque automatically transfers to the remaining corner that has traction. That, along with the fact that the drive lugs have no forgiveness, means you snap an axle on the corner with traction.

“We deliberately use standard 22.5 inch semi truck tires so we do not have total hookup. No drive lugs like the Quadtrac. They provide just enough torque so you don’t break anything. And the standard grooves let the mud and water escape instead of building up.”

Anderson said weight distribution is a perfect 50-50 front and rear. The tractor can be equipped with implements that have been commonly used in Europe for decades.

“You can have hitches, hydraulics and better yet, electric power front and rear. You can do push and pull in the same pass.

“You could put a seed drill out front and a roller at the back. Or a tillage implement out front with a seeding implement at the back. If you power your implements with electric motors, the p.t.o. and universal joint become obsolete.”

He said ATC does not put a p.t.o. at the back or front of Spirit tractors because electricity is easier, safer and more efficient.

“We’re working with a company now that produces big mowers with five cutting tables. So instead of triple splitter and double splitters, we’re building them a system with five electric motors. Just run the cables to the cutting tables and install the five motors. With the same tractor horsepower, it delivers 30 percent more power to the cutting heads compared to the gearing nightmare they have now.”

Anderson said the company’s decision to make the tractor autonomous was a response to the skilled labour shortage plaguing agriculture.

“We talked to a few hundred farmers here in the Red River Valley and asked them about their biggest implement problem. Nearly every farmer said the biggest problem was finding qualified people to drive the darned tractor without busting things up. Or, the problems they have themselves driving the tractor.

“And this problem isn’t just the Red River Valley. It’s all across North America and around the world.”

He said ATC looked at GPS early in the development of the Spirit, but decided it was not good enough for an autonomous tractor. It needed a better, more reliable navigation system.

“Thank goodness we were smart enough to realize early in the game that GPS is not as good as on-the-ground control stations.

“Other autonomous systems rely on those satellites zinging around. We rely on four Earth-bound towers, and each one has a range of (40 kilometres).”

He said that kind of range means it’s nothing at all like laser beams or other GPS systems that require the operator to relocate the tower everytime he moves from field to field. A single setup can handle just about any farm.

“In Brazil, we’re working with a farmer who has one field that’s 1.5 million acres.

“The field is (40 km) on the longest side, so we think we can handle it with just four of our transponders. There’s no more of this business of putting a station in the corner of a 160 acre field and moving it everytime you change fields.”

Anderson said the company started working on its own Area Positioning System (APS) seven years ago, which is a combination of laser and radio.

He said APS controls the Spirit in the field to within a fraction of an inch. The system is capable of controlling a number of autonomous tractors, each performing different tasks.

The Spirit will follow a farmer to the field using a manual control panel in a pickup, seeding tractor, combine or all-terrain vehicle.

When a farmer gets to the field, he parks the Spirit and does a perimeter around the outer edges, driving around tree lines, pothole and rock piles. This information is automatically logged into the Spirit controller.

Anderson said the company has built safety redundancies into the control system.

“The Spirit will not break out of those parameters until you tell it to,” he said.

“You can unplug any cable connection in there and the tractor will still remain in the field until you command it to move. Now, we’re not telling you or anyone else exactly how we accomplish that.”

Anderson said the control system was first developed and tested by the U.S. military.

The Spirit is controlled by four independent fail-safe controllers, two of which are safety controllers and two of which are positioning controllers.

Safety controllers are connected to a separate light detection and ranging (LDAR) system and a perimeter ultra-sonic sensor. The Spirit shuts down immediately if anything obstructs the tractor or indicates danger.

A separate APS unit and base station master controller talks to the LDAR to control and map the tractor’s path.

The Spirit is small compared to other tractors in the same horsepower range. Rather than the one inch thick frame rails found in most high power tractors, the Spirit is based on a steel tube lattice frame. It measures 102 inches wide, 152 inches long and nine feet high.

The tractor uses many off-the shelf components, which simplifies the production process.

The factories will be nothing like those of the major tractor manufacturers.

The first assembly run will be at the Fargo plant in March. Beyond that, Anderson said the company will build five more assembly plants in North America.

Farmers will buy directly from the factory, so there will be no dealerships.

“Service and repair is so simple that we don’t feel we really need a dealership network,” he said.

For more information, contact Terry Anderson at 605-645-7680 or 701-429-3964 or visit www.autonomoustractor.com