Eliminating faults makes the ultimate post driver
By Andy Collings
JUST when you thought all post driving was about was dropping a big weight on top of a post from a great height along comes a design so radical that conventional builds look like contenders for the museum.
Stuart Hooper and his co-designer Michael Stanley believe they have created the ultimate machine, one relatively light, yet powerful, and sufficiently compact to be transported in a pick-up.
Eighteen months in the making, the Supadrive post driver is the result of assessing the faults of existing machines and applying thought and technology to solve them.
"Most post drivers are inherently unstable," says Mr Hooper, who runs his contract fencing operation from Rumbush Farm near Solihull. "When they are not in use they have to be tied up against something to stop them falling over; very dangerous. They also need a really heavy weight to work well and, more often than not they are designed to be attached to a tractors three-point linkage, which makes awkward places hard to reach."
The Supadrive can be attached to the end of a tractor loader, a backhoe loader or any other mechanical protrusion if there is a suitable hydraulic supply – 25 litres/min at 2000psi. "It just needs a sub frame assembly to connect the two," says Mr Hooper.
So, what is so different about the Hooper design? Ater all, there is still an impressive lump of heavy metal where you would expect it to be.
Well, first, posts are not just pounded in to the ground by weight alone, the Supadrive has a hydraulic system which exerts a pressure of up to 6t on to the top of the post before any vertical violence commences.
And even when the machines 110kg block starts to thump, all is not as straightforward as first appears. Raised and lowered by a small ram – and yes, it is powered in both directions – the weight is attached to the end of a ram-like canister, the action of which can be likened to that of a pogo stick.
For here is the real secret of the machine. The vertical raise and lower arm enters the canister and terminates as a flat disc about half way down its length. There is a spring above it and a spring below it so there is no positive connection to the weight. In action, as the weight is pushed down, the bottom spring is compressed and when it is raised the top spring is compressed. The next cycle sees the top spring expanding to accelerate the weights downward travel and the bottom spring compressed, which speeds the lift from the post.
"It all sounds very complicated but, put simply, the weight uses the stored energy from its lift to exert extra force on the way down. This means we can use a much lighter weight and create the same force," says Mr Hooper. "The post is always under load from the secondary system and this prevents any weight bounce."
Four levers are required to operate the driver. One activates the weight – pulling it starts a continuous up and down movement (no need to pull and push the lever), a second sets the operating height of the metal cap which rests on the post top, and exerts the 6t, and the other two angle the unit fore and aft, and side to side.
Posts up to 3m (10ft) can be handled and, depending on terrain, most post sizes can be persuaded to lower themselves into the ground. Operation can be either directly in front of the tractor or, if required to the side, as the whole unit can be pivoted through 90í. Should a post be placed in the wrong place, the machines weight exerter can be reversed to pull it back out.
"Apart from its mechanical prowess, one of the main advantages of the Supadrive is its low transport height," says Mr Hooper. "Overhead wires and branches pose no problems. And when moving sites, the 600kg machine can be placed in the back of a pick-up."
Initially Mr Hooper intends to market his Supadrive directly but has plans to place it with dealers. Price? – £5300, he says. *
Supadrive in action. The ram-like cylinder just above the weight contains the spring system which accelerates the weight down on to the post.
Stuart Hooper: "The Supadrive is a totally new approach to post driving."