ASSINIBOIA, Sask. – Dwayne Woolhouse originally cut weeds on his organic farm with a swather.
“We tried it both ways,” the Assinboia farmer said. “If we had the canvases on, we ended up with a row down the field that would kill the crop out. With the canvases off, (the weeds) piled on the table and never got that clean.”
He also didn’t like how clean the swather knife cut the weeds.
“It was like pruning the crop. You prune tomatoes to make them grow. To me, cutting the weeds clean was the wrong way to do it.”
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He wanted to break the plants off.
“There’s a better chance of the plant dying or not coming back as fast. With wild oats, they’ll take longer to recover and they don’t have as much chance to set seed.”
While using a gas-powered trimmer to clean up grass on the edge of a sidewalk, Woolhouse started to wonder if the concept might work in his lentil fields.
“To start with, I took a weed whipper and I knew what speed that it ran. Then I increased the diameter because they’ve only got about a 14-inch swing. I figured out what speed they were going around on the outside and figured that out on 36 inches,” he said.
His first attempt was to install the motor on the front-end loader bucket and spin it to see what rpms were needed to break weeds.
Woolhouse built his first field-scale weed whacker in the late 1990s, using a 550 CIL swather. He removed the swather table and replaced it with a boom made from square steel tubing from the frame of a pull-type swather. The cutting blades were mechanically driven with a gearbox, belts and no hydraulics.
“When we built the first one, about 22 feet, we tried a blade that had aircraft cable, but that didn’t work. Then we tried bits of chainsaw chain. That would cut down anything, but it kinked up. We bought every kind of small chain we could find and tried them. Then we ended up going with a straight blade.”
Woolhouse used cold steel blades that were ground slightly on the cutting face but were still dull so they would smash and shred rather than cut.
“We ran that for about three years, then switched to a hydraulic one. The second one we made bigger, up to 42 feet. We made it hinged so it could fold up when we went on the road, and we built it so we could tilt it with the hydraulic drive system.”
This version uses five hydraulic motors mounted along the boom, each driving three separate blades using belts and pulleys. Each blade is about 36 inches long, with a bit of overlap, so the boom cuts a 42-foot swath.
A one-inch shaft from the pulleys drives each blade. Woolhouse added two bearings on each shaft: one at the top and one at the bottom. He said the hydraulic motors are similar to those found on air seeder fans.
To deliver the oil flow to the hydraulic motors on the boom, Woolhouse uses a large hydraulic motor from a Crop Hawk header, built by Rock-o-matic.
The company had built a few draper headers before declaring bankruptcy. Woolhouse picked up one of the headers, and the hydraulic motor, from the bankruptcy sale.
“To drive the pump, it’s a pto drive from the front of the swather that normally drives the header. We had to increase the size of the gearbox and the pto drive, which was too light from the swather. We also added an extra belt to drive the pto. The shaft isn’t any thicker but the universal joints are bigger.”
A gearbox from a Brandt auger fit under the housing at the back of the swather. There was also an extra pulley off the engine, so Woolhouse was able to add an extra belt to help drive the pto.
Two 25-gallon tanks mounted on top of the swather act as hydraulic oil reservoirs, with a radiator and fan to cool the oil.
Woolhouse said talking to an engineer who knew about hydraulics saved him from making major mistakes when designing the system.
“The tanks have to be higher than the pump on that particular pump. The reason it needs that much of a reservoir is so all the bubbles come back out of the oil. A hydraulic engineer will tell you all that.”
On version two of the weed whacker, Woolhouse redesigned the boom so it would tilt from front to back.
“On the first one, it couldn’t tilt. As you’d bring it up, the front end of the blades come up and the back ends go down. You want it, when you’re cutting, so the front is slightly lower than the back. It’s easier to spin and does a better job cutting. That’s why it tilts.”
The angle of the blade can be changed when necessary because the boom hangs on a lever system that pivots in the centre.
The boom is also hinged, so the machine can be put in transport. A wheel at the end of the boom helps it track over hills and obstacles.
“It’s touching the ground, but it doesn’t have much weight on it. It won’t even show in the crop.”
Woolhouse said the setup is designed so he can remove the weed whacker and install the swather header. The modifications don’t affect how the swather operates.
The weed whacker generally runs at eight to 10 km-h in lighter weed populations, but has to slow down when the weeds get thicker.
“(We use it) mostly in lentils, but I did use it in some durum this year that had some wild oats in it, to clip them off. You could use it in other crops, as long as you can set the height high enough.”
The original unit operated for three years and the current 42-foot model has also been in the field for three years. Now, Woolhouse is planning a third version.
“The new one is going to be built on a combine, with more horsepower, more hydraulics, at least 60 feet wide. I would like to build in a system like for combine headers, to keep it level.”
He said the new unit will also have more height so that it works in different crops. He is also considering better quality steel in the blades so they won’t bend as easily. He would like more spring in the blades to reduce damage if they hit the ground.
“I’m not sure if I’ll run two blades off each motor or stick with three. It depends how much hydraulic flow I have,” he said.
“It works well, but the biggest problem right now is the swather is not strong enough to handle it. It’s worked good enough for three years that I’m not afraid to use the same ideas. Just add more horsepower and more oil.”
