The strawberry straddler
Tractor 1 straddles two strawberry rows on 48 inch centres, its wheels running in the alleys. The operator rides up front in a closed cab; behind the cab a 300 gallon spherical tank sits down in the bridge; a Drumlin battery box rides low in each leg; and a 48 foot aluminium boom, a nozzle every foot, covers twelve rows at a time. Fold the boom for the road, swing the casters with the slider, or hide the tank to see the frame.
The track is a number, not a machine. The same design builds this two-row straddler with a 96 inch track, or a 60 inch one that straddles a single vegetable bed — the bridge is cut to length in the shop. The crop passes under an 18 inch belly.
Why a sphere. A spray tank is rarely full. In a wide, flat tank a quarter-load of water runs to the low side on every slope and sloshes on every bump; in a sphere it pools in a small circle at the bottom and barely moves — on a 15 degree side slope about 100 mm instead of nearly half a metre. The sphere sits low, down between the bridge beams, its bottom just above the plants; its lowest point is over the alley between the two rows.
A cab, because it sprays. A closed, filtered cab keeps the operator out of the drift — the way pesticide applicators are protected on commercial sprayers. It also carries the rollover frame.
Low batteries, wide wheels. Each leg carries one battery box close to the ground, between a free caster in front and a drive wheel behind. Two motors, one per drive wheel, steer it by speed difference, so it spins at the end of a row. Full, it weighs about 2.6 tonnes and would have to lean about 53 degrees before it tipped sideways — and more than that part-full, which is where the sphere earns its keep. On firm, level ground; soft soil and a slope make it worse.
The boom is 48 feet of bolted aluminium truss — about the weight of a steel one as stiff, but it will not rust in fungicide. Twelve rows a pass, so every pass meets the last one in an alley, not in a row. A nozzle every foot, six inches either side of each row's centre, puts two over every row and two over every alley — cap the alley pair and it sprays bands, with half the water. It rides a lift, 20 to 63 inches over the ground, and folds for the road in two moves: the wings swing forward along the outside of the legs, then the outer eight and a half feet of each flips up and back over its wing — so the folded boom ends at the front of the machine. It breaks away at the tips if it meets a post. The tank fills itself from the nurse trailer through a suction port on the side — the tractor's own pump does the work.
Sweet corn, while it is young. Six short posts bolt between the legs and the bridge and lift everything above them 22 inches: 40 inches clear under the bridge, for corn to about three feet, planted to fit — 32 inch rows, three inside the track, or twin rows on the strawberry beds. The battery boxes, wheels and pump stay low. It costs stability: full, it would tip sideways at about 43 degrees instead of 53, and backward at 29 instead of 38 — so half a tank on a slope, at a walk. Tall corn at silking is still the trailer sprayer's job.
A diesel version. The same bridge, cab, tank and boom on a diesel engine and four hydraulic wheel motors, steering all four wheels — Tractor 1D.
What it does not show: strength, the rollover structure's test, the boom's own structure (48 feet wants a truss), how it rides at speed, or the tank's slosh. On the road it is about 10½ feet wide and 10½ feet long.