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 32 foot boom covers eight rows at a time. Fold the boom for the road, swing the casters, 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 2.45 tonnes and would have to lean about 54 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 folds its wings forward along the outside of the legs for the road, and 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.
What it does not show: strength, the rollover structure's test, how the boom rides at speed, or the tank's slosh. On the road it is about 10½ feet wide.