Precision spraying hits weeds only

Secret design of innovative new sprayer pushes the limits of herbicide use.

By John Muggeridge

Tales of crop circles and alien landings fill the pages of the National Enquirer, but University of Guelph engineer Ralph Brown has only managed to confuse a few local pilots with his "crop squares" in a field near Puslinch. With Guelph colleague Ken Bennett, Brown has developed a "paint-by-numbers" precision sprayer, to help save farmers chemical dollars by automatically spraying only weed patches and shutting off over weed-free ground.

Last August, pilots bound for Guelph airport did a double take while flying over a half-acre checkerboard in a clover field in Puslinch, a demonstration site to show the accuracy of the prototype precision spraying system that has been in the works at the university for three years. Brown is hoping that their checkerboard picture is worth 1,000 words - and will gain support to commercialize the system.

"We needed a way to show we could deliver precise application with sharp boundaries at a reasonable ground spraying speed," says Brown. The aerial photo (above) showed that as convincingly as any academic study. The field was plotted out with stakes beforehand, and the precision sprayer, complete with laptop computer on board, burned off a neat grid of 3 x 5m squares in the clover field by automatically applying Gramoxone herbicide at every other square, according to its position in the field. Of more use to farmers than pretty pictures, however, are promising results from two years of tests under actual farm conditions. In a 1998 site-specific test, co-ordinated by University of Guelph weed scientists Francois Tardif and Heather Goudy, the patch sprayer saved an average 26 per cent of chemical without compromising weed control or yield in a 10-acre field of no-till corn at Hartholm Farms near Woodstock. Goudy scouted the field beforehand and generated a computer weed map using a Geographic Information System (GIS), mapping broadleaf weeds and grasses on 6x6m sampling grid. Using the weed maps and positioning itself via dead reckoning (positioning using distance and velocity), the tractor-drawn sprayer then automatically applied chemical to each patch.

The sprayer can also be used to broadcast one herbicide while simultaneously spot spraying weed patches with a second herbicide. In 1999 the system was used to spray a soybean crop grown in the same 10-acre field. Treatments with the broadcast/patch-spraying combination resulted in a reduction of 50 and 59 per cent of the injected herbicide over a conventional two-chemical, tank-mix broadcast approach.

As an added benefit, by directly injecting chemical at the nozzles, the system allows farmers to use only as much chemical as needed, eliminating leftover tankmix and rinsate disposal headaches.

Brown says both farmers' pocketbooks and the environment come out winners. Weeds tend to grow in patches rather than uniformly across the field. When farmers can apply spray only where it is needed, "there are benefits to the physical environment and the economic environment on the farm," says Brown. "When you talk to farmers, most are environmentally conscious. They do what they need to do (apply herbicide) because they have to, not because they want to."

As researchers explore a systems approach to weed control, incorporating concepts such as economic weed thresholds and weed-specific herbicide rates, the precision sprayer's herbicide savings can only increase, Brown maintains.

Asked about the design of the patch sprayer, Brown says he can't divulge many details as the project is before the university's Business Development Office with a view to commercializing the technology. Nor is the actual pricetag known, as the sprayer is still a prototype. The nuts and bolts for the test sprayer came from a Guelph-based sprayer manufacturer, Precision Industries.

The sprayer's quick response to weed patches is made possible by direct chemical injection at the nozzle. Chemical is injected by a positive displacement pump into the water carrier stream at each of the six flat-fan nozzles across the 3m boom. Brown says the 3m boom is designed to be "siamesed" for a working width of 12-15m or more.

Next on the agenda for the project is replacing labour-intensive field scouting for weeds with aerial photos taken by digital cameras. Brown also plans to replace the dead reckoning system with GPS. With all the practical hurdles cleared, Brown says the question is whether site-specific spraying will be beneficial in the long term: "With the ability to locate and target weeds, we now have to decide how far we can push the limits of efficiency in herbicide use."

© copyright 1999 AgMedia Co-operative Inc..

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Cranky about improper regrinding

A machinist's "bad day" can be costly

By Keith Berglind

Crankshafts break. Car, truck, diesel or motorcycle. It's usually rare but, given enough time and stress, it's possible for any crank to fail. What we have to be careful about is not to speed up the process by improper crankshaft regrinding.

As farmers and mechanics, we have to trust specialty machine shops to do many machinist's jobs because we lack the tools or training. But the results we get aren't always good. This broken sprayer engine crankshaft (figure 1) proves it.

This crankshaft, from a VW air-cooled Spray Coupe engine, was reground in an Ontario machine shop and it ran only a few hours before breaking. Typical of many farm repairs, this overhaul was done in the fall but not put to work until the next June. By the time it failed there was no hope of getting the machine shop to accept responsibility.

The problem, as I see it, is the way the crank journals were ground with a very sharp fillet radius. The rod journals were ground to .040" undersize because of damage to the rear rod bearing. The journal beside the break shows no sign of discoloration, so there was no earlier trauma in that area. Some black and blue crankshafts should never be rebuilt, but that was not the case here.

I didn't have an original crankshaft to compare the corner radius with the reground, broken crank, but it was obvious that whoever ground this shaft used a grinding stone with a very sharp corner. This fracture started along a line so sharp and perfect you would think it was drawn with a glass cutter. And, cracks always start in sharp corners.

Let me explain that. Breaks in steel are very similar to cracks in a car windshield, where a stone spot makes a few short cracks, often so short you can't see them. But they are stress-risers: sharp points where a long crack can start.

This crankshaft failed the same way. The rod journal corner (fillet radius) was too sharp. As soon as the engine was put to hard work, the crack took off and spread through the body of the crank until it finally broke in half.

How to avoid problems
Obviously, dealing with a good machine shop would be your first step. But, even then, a staff member might have a bad day and you're heading for trouble. Warranty doesn't mean much when your truck or sprayer dies in a rush season.

I would suggest you express your concerns to the machinist when you take the job in for regrinding. The shop may have a set of radius gauges, and they could check your original fillet radius while you watch. Now you have something to compare after the crank is ground. And, if the machinist knows you're going to be checking, I'm sure your job will be done correctly.

You can check the fillet radius yourself first, using a set of drill bits, before taking the crank to the machinist. Try one size at a time, holding the drill bit in the corner of the crank journal. When you find the bit that fits in the original shape, record that drill size. The original fillet radius will be one-half the diameter of that drill bit.

When the crank comes back from the machinist, use the same drill bit to check the new fillet radius. If it doesn't look right, it probably isn't. If so, take it back and discuss the problem with the machinist. There are some non-original shapes that are perfectly acceptable, but you need to know if yours is good or bad.

The first machinist job I ever had was grinding crankshafts. And my foreman was only interested in how many cranks we ground each day, not the shape of a fillet radius. It takes time to put a proper radius on the stone, after the stone is trued up with a diamond. And there are different radius specifications for different engines.

Read all metal breaks
It's important to know why something breaks. With practice you can learn to "read" most types on metal breakage. Look for the point of impact or stress where a crack first started, often long before it broke. There's always a reason. And, there's no sense in just repeating the error and waiting for the new part to fail. Learn to spot stress-riser problems.
Keith Berglind is a licensed heavy-duty mechanic

© copyright 1999 AgMedia Co-operative Inc..

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Small things prevent grief

Some good ideas cost very little

By Ralph Winfield

The Bag Spike
How many times have you chased seed bags across the field? Or looked in vain for a stone or lump of soil to hold them down?
About five years ago I made a bag spike. (See the illustration.) Basically it is an old car tire rim supporting a piece of one-half inch pipe, about four feet long. The pipe is topped with a new diamond harrow tooth.
Everything is welded together. The tooth must be reasonably sharp so it will readily penetrate the bag(s). The spike will hold about 150 bags. When not in use the sharp tooth is covered with an old glove. And, yes, we use bulk seed as extensively as possible, but the spike still gets a lot of use each year. It has already paid for itself many times in frustration reduction.

The Drill Shaft Monitor
How often have you wondered whether or not a shaft was turning? None of us likes to mis-plant or goof when fertilizing. It gives the neighbours something to talk about all summer!

Most of us have electronic monitors on our planters. They are really "peace of mind" devices. However, in some applications we don't need expensive "peace of mind" monitors.

After a drive chain jumped off the sprocket on a new drill, I devised a very simple monitoring system. Note the fluorescent green plastic tie straps on each of the two drill shafts. They can be seen from the tractor seat. Depending on shaft speed, you can use two or four straps at each location. The cost is minimal and the peace of mind is great.

Neither shaft has stopped since we started to monitor them. However, I must admit to realigning the drive sprockets by shimming before installing the tie straps.
Agricultural Engineer Ralph Winfield farms at Belmont in Elgin County.

© copyright 1999 AgMedia Co-operative Inc..

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