Tandem-drive by roller
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• By using a roller between the tyres of a single-drive tandem-axle bogie, Neville Truck Equipment Ltd., Kirby-in-Ashfield, Notts., has devised a system of temporary conversion to double-drive. One of the first examples of the system has been fitted by North Derbyshire Engineering Ltd. to its rubber-sprung bogie.
A 9in. diameter roller, coated with aluminium-oxide grit in epoxy resin, hangs from a steel arm between the wheels of a tandem bogie. The roller is larger than the minimum space between the tyres and hangs below the wheels' centre line. The pendant arm which carries the roller is connected at the top to a bell-crank lever with an air-pressure diaphragm acting on it. When the air-pressure chamber is energized, it lifts the roller against the tyres and so allows the drive from one axle to be transmitted to its partner.
An operator near Norwich, Wilfred Foulger Ltd., has a prototype roller drive fitted to a six-wheeled Commer Maxiload with a Norde tandem rear bogie. Mr. Foulger is attracted by the cheapness compared with double drive ("at least £350 cheaper-) and the fact that there is less drag on normal hard-road work. His vehicles have to drive into fields to collect harvested crops and some extra traction is often welcome under such conditions. The roller drive will
cope with ordinary mud, he says, but slimy lime-sludge does give rise to slip. Traction-effort tests on the roller-drive six-wheeler have shown a per cent increase in tractive effort in a forward direction, and a 16 per cent improvement in reverse. These tests were done on dry ground. Better adhesion from the trailing axle was possible forwards than backwards because of the self-wrapping action of the wheels on the roller when driving forwards.