Lamma: Larrington power dolly makes unstoppable combi

The age-old system of using a powered tractor to pull a heavy, unpowered trailer is fine in dry field conditions, but comes to grief a bit when conditions are wet.

One answer is to power the rear wheels, typically by running a pto shaft to the rear wheels or fitting hydraulic wheel motors. But this is a relatively expensive option and limits you to only one or two gears.

Richard Larrington, however, has come up with a different way of doing it. His system, which won an award at Lamma , uses the tractor’s 1,000rpm pto to power an Allison six-speed truck automatic gearbox.

The gearbox converts that to 2,000rpm, which would ordinarily give 60mph at the wheels. So a second gearbox reduces that to give a complete speed range between 0-20mph, with the hydraulic clutch connected to the tractor’s footbrake.

Two units have already been sold, says Mr Larrington, and the conversion costs about £20,000. That may sound a lot, but it means you have four powered axles and can pretty much cope with anything the weather or the ground conditions throw at you.