GOING UNDERGROUND

The challenge was to design a method of delivering and removing a probe underground

Fibre optic cables tend to be in a similar location to other service cables. Typically, they are buried four to five feet deep and can be under any surface from desert to tarmac. For that reason, one major US long distance communications carrier wanted equipment designed to detect its own cable among the others.

To fulfil that need, Radiodetection developed a probe that could be operated by one person. While another company, Wren Engineering, was chartered with the job of developing a method of driving the probe into the ground in a controlled manner and then helping the operator to remove it.

The solution involved designing a gearbox in which a pair of weights, of different masses, rotate in opposite directions around a common axis. One travels at twice the speed of the other.

In probe driving mode, the weights are designed to reach bottom dead centre at the same time. The resultant centrifugal force is applied vertically downward, forcing the probe into the ground.

This operation is duplicated on either side of the probe which is clamped through the centre of the gearbox. To assist in the removal of the probe, a lost motion sequence is electrically instigated, re-aligning the relative positions of the weights on the axis and diverting the centrifugal force upwards.

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